View Full Version : Team Update #18
http://usfirst.org/uploadedFiles/Robotics_Programs/FRC/Game_and_Season__Info/2011_Assets/Team_Updates/Team%20Update%2018.pdf
It's a real game-changer...
Minibot scoring will be automated from here on out, and watch out for the bolts on the bottom target.
Tyler Hicks
15-03-2011, 20:05
Can you imagine how this will effect the Finals on Einstein? You know there are going to be minibots that are almost equal speed...
no!!! thanks FIRST that you make it clear i like updates and seeing this from what you learned in previous week but cant this wait till championship
Not a fan. Witnessed MANY minibot climbs this weekend at San Diego that most certainly imparted 3-4 N of force yet were not auto triggered. It's going to suck when the field fails to work correctly and teams lose points they should have earned.
Vikesrock
15-03-2011, 20:18
I saw far too many missed triggers (at least they appeared to be) on webcast this past weekend to be comfortable with this update going into our event this week.
Not a fan. Witnessed MANY minibot climbs this weekend at San Diego that most certainly imparted 3-4 N of force yet were not auto triggered. It's going to suck when the field fails to work correctly and teams lose points they should have earned.
I agree, Cory. More than once a 1 second minibot with significant momentum failed to trigger. Is it possible that the triggers still need too much contact time to register? BTW, we had a great time partnering with you guys and 3704!
Eagleeyedan
15-03-2011, 20:40
Not a fan. Witnessed MANY minibot climbs this weekend at San Diego that most certainly imparted 3-4 N of force yet were not auto triggered. It's going to suck when the field fails to work correctly and teams lose points they should have earned.
When that happened at the WI regional, the refs manually triggered it.
AdamHeard
15-03-2011, 20:43
I agree, Cory. More than once a 1 second minibot with significant momentum failed to trigger. Is it possible that the triggers still need too much contact time to register? BTW, we had a great time partnering with you guys and 3704!
Not a fan as well, we ran our minibot at around 2 seconds at san diego and it impacted with well over 2 newtons of force. It would certainly hurt to get hit by it.
We've since increased the speed a lot, more along the lines of 254, and the impact is pretty violent.
alectronic
15-03-2011, 20:52
Is it possible that the triggers still need too much contact time to register? BTW, we had a great time partnering with you guys and 3704!
The triggers are designed with multiple sensors, and the FMS only looks for 1 of those to be triggered for any amount of time. Thus making the minimal amount of force still trip the tower. The towers have been tested and proved to be much more accurate since week 1, so I think this should be a non-issue now at week 3.
The triggers are designed with multiple sensors, and the FMS only looks for 1 of those to be triggered for any amount of time. Thus making the minimal amount of force still trip the tower. The towers have been tested and proved to be much more accurate since week 1, so I think this should be a non-issue now at week 3.
Someone in another thread on Chief commented that the towers are now looking for a triggered sensor for a certain amount of time to be sure it wasn't just a jostle from a robot.
Whatever the circuitry I am 100% confident that there were multiple (greater than 10) instances at San Diego where minibots compressed the platform upwards into the sensors without the tower actually triggering.
Someone in another thread on Chief commented that the towers are now looking for a triggered sensor for a certain amount of time to be sure it wasn't just a jostle from a robot.
Whatever the circuitry I am 100% confident that there were multiple (greater than 10) instances at San Diego where minibots compressed the platform upwards into the sensors without the tower actually triggering.
Seconded!
Daniel_LaFleur
15-03-2011, 21:09
Someone in another thread on Chief commented that the towers are now looking for a triggered sensor for a certain amount of time to be sure it wasn't just a jostle from a robot.
Whatever the circuitry I am 100% confident that there were multiple (greater than 10) instances at San Diego where minibots compressed the platform upwards into the sensors without the tower actually triggering.
Do you have proof that enough force was exerted? or is this just your 'gut feeling'?
Someone in another thread on Chief commented that the towers are now looking for a triggered sensor for a certain amount of time to be sure it wasn't just a jostle from a robot.
Whatever the circuitry I am 100% confident that there were multiple (greater than 10) instances at San Diego where minibots compressed the platform upwards into the sensors without the tower actually triggering.
Do you know what thread that was? I'm curious about how that would work without limit switches.
The sensitivity of the towers now is highly dependent on how the field crew that implemented the fix did it. Really, what the minibots are doing now are pushing the bottom plate up about a quarter of an inch. However, that distance may vary depending on how meticulously the field crew assembled the plates. I was told to get up on the ladder on Saturday morning and adjust the distance a little bit more and make sure that the distances were equal, but it was only by an eighth of an inch by so. FIRST's solution works, as long as the instructions are followed to the T.
Do you have proof that enough force was exerted? or is this just your 'gut feeling'?
I could do the math for a 2.5 lb object moving 10 ft/s hitting that plate and you'd see it's more than 3-4 N, but if the plate is being violently slammed into the top plate such that you can hear it from the stands, I'd say it's a pretty safe bet they were triggered. Additionally we have 4 official towers and I can confirm that every single time ours goes up the pole it depresses the limit switches, but twice this weekend it did not show the tower as triggered at San Diego.
It seems pretty clear there are still problems with the field and I don't just say this because the tower failed to trigger with our minibot. It was a very common occurrence.
pfreivald
15-03-2011, 21:19
Assuming a .5 kg minibot can climb 10 feet (about 3 m) in 2 seconds, and that the plate depresses at most 2 cm (0.02 m), this means that its average (not top) speed is about 1.5 m/s and:
Using the work-energy theorem,
W = KE
F*d = .5(m)v^2
F = .5 (m)(v^2)/d
F = [.5 (.5 kg) (1.5 m/s)^2]/.02 m
F = 28 N
...is (actually less than) the average force needed to stop said minibot (because 1.5 m/s is the average speed, and not the top speed). If the compression distance is less, the average force will be higher. If the minibot is faster than 2 s, then the average force will be higher. If the minibot is more massive than 0.5 kg, then the average force will be higher...
...which means that, if the towers are doing their jobs properly, no one with what I would consider a "competitive" minibot has anything to worry about -- and if they DO NOT trigger the towers, then we have direct evidence that the specifications given (2-4 N of force to trigger) are simply wrong.
I'm quite tired, and didn't put much thought into this. Anyone want to poke holes in my analysis?
Al Skierkiewicz
15-03-2011, 21:21
The only issue in Wisconsin that I am aware of occurred when a minibot just touched the plate but did not move it. The Head Ref did a valiant effort to make the determination and double and triple check the rules. At first it was called a climb but was eventually called as a non contact when they removed the minibot and the plate did not move.
I could do the math for a 2.5 lb object moving 10 ft/s hitting that plate and you'd see it's more than 3-4 N, but if the plate is being violently slammed into the top plate such that you can hear it from the stands, I'd say it's a pretty safe bet they were triggered. Additionally we have 4 official towers and I can confirm that every single time ours goes up the pole it depresses the limit switches, but twice this weekend it did not show the tower as triggered at San Diego.
It seems pretty clear there are still problems with the field and I don't just say this because the tower failed to trigger with our minibot. It was a very common occurrence.
And the naked king had beautiful clothing..."Week 2 results indicated that this change was successful."
Daniel_LaFleur
15-03-2011, 21:24
I could do the math for a 2.5 lb object moving 10 ft/s hitting that plate and you'd see it's more than 3-4 N, but if the plate is being violently slammed into the top plate such that you can hear it from the stands, I'd say it's a pretty safe bet they were triggered. Additionally we have 4 official towers and I can confirm that every single time ours goes up the pole it depresses the limit switches, but twice this weekend it did not show the tower as triggered at San Diego.
It seems pretty clear there are still problems with the field and I don't just say this because the tower failed to trigger with our minibot. It was a very common occurrence.
The reason I ask is because one must takes into account that some (in some cases a lot) of that force is deflected and not transferred towards moving the plate. Many of the minibots strike the plate such that they change orientation rather than push the plate.
Hence my question if you knew that the force was being applied (and applied properly) or if it was just a 'gut feeling'. Sound of the impact does not equate into actual applied force.
Nathan Streeter
15-03-2011, 21:25
Do you have proof that enough force was exerted? or is this just your 'gut feeling'?
Although I wasn't there, I am certain he has more than a "gut feeling" of assurance that more than 3-4 newtons were applied... HS level physics state that:
mass*velocity(change) = Force*time
Our minibot weighs 2.3 pounds --> ~1 kg
Our minibot travels up the pole in about 1.3 seconds --> ~2 m/s
By just saying that the minibot stops (although ours certainly is repelled backwards, too!) you get a change in velocity of ~2 m/s.
If the minibot is being slowed by the tower for less than half a second (I can't imagine one taking that long... most stop suddenly!), then the Force is greater than 4 Newtons.
(1kg*2m/s) / .5s = 4 N
I certainly hope that refs are allowed to add judgment to obvious false negatives!
I certainly hope that refs are allowed to add judgment to obvious false negatives!
If your minibot hits the plate and triggers: Score
If your minibot hits and doesn't trigger: no score even if visually witnessed by refs.
If the tower is bumped and triggered by a robot: no score/score corrected
I was a ref in Pittsburgh when this rules was changed/reinforced.
One of the biggest issues I see with this whole thing is that most teams don't have ready access to a real tower. They'll just have to hope that their minibot triggers it. They can't really be proactive about a solution despite the warning in the update. I predict that despite this update, there will be almost just as many tower failures next week as in the past two.*
*Provided the towers are not fixed. Fingers crossed!
AdamHeard
15-03-2011, 21:36
If your minibot hits the plate and triggers: Score
If your minibot hits and doesn't trigger: no score even if visually witnessed by refs.
If the tower is bumped and triggered by a robot: no score/score corrected.
What is your basis for this statement?
MagiChau
15-03-2011, 21:37
What is your basis for this statement?
Team Update 18 and listed in the manual from a team updated around 15 or 16 because of how at week zero events robots acidentally triggered the plates.
What is your basis for this statement?
Instance 1: common knowledge
Instance 3: been proven by previous events
Instance 2: proven by Update 18
GaryVoshol
15-03-2011, 21:57
Note the second paragraph of the Update. If you hit the trigger plate directly on a bolt, it will not register. Fix your Minibot so it hits inside the bolt-pattern circle.
It should work - it did work in the vast majority of instances in Week 2. If it doesn't work, the ref and FTA can determine if the trigger is working properly.
BrendanB
15-03-2011, 22:05
It says, "we will be relying on the automated scoring of the minibots". Does this mean that there will be no referee calls at all?
alectronic
15-03-2011, 22:16
It says, "we will be relying on the automated scoring of the minibots". Does this mean that there will be no referee calls at all?
Or at the very least, less than previous weeks. Technically, the manual does say that if the plate does not trigger it, it goes not count.
Being at both a Week 1 event (Kettering) and a Week 2 event (Waterford) I can agree the changes had a night and day difference. At Kettering, hardly any of the towers registered. The slower minibots that creeped up the pole would generally register, but teams such as 27, 33, 67, and 2337's minibots would register rarely, if at all. But in Week 2, comparatively faster and slower minibots were triggering the towers with no issue at all (the only tower-related issue I saw was lights not coming on at all, but it still registered with the FMS).
The update definitely keeps a layer of uncertainty with "What if there's an error on Einstein?", but the changes seem to be working so far. That worry can be revived if we continue to see errors into weeks 3 or 4, but for now, awesome solution. From what I've seen, it works like a charm.
coldfusion1279
15-03-2011, 22:31
The rules stated minibots need to exert 2-4 N of force to register. Teams should have designed their minibots to exert at a minimum 4 N force.
All this update is saying is if teams have not designed their minibot to this spec, they will not trigger the tower in week 3, and if they have, the minibot will trigger the tower.
Perhaps FIRST has figured out a way to make the towers accurately sensitive to 2-4 N force. If after week 3, your minibot registered half the time and didn't register the other half, AND you have physically measured the force with which it hits the top plate to be >4N, then there is a case to be made.
As for right now, they are just rectifying a lapse in the rules that has been bypassed (in good faith and fairness) by the referees in weeks 1 and 2 for what they thought to be a field error.
All we can do is play by the rules.
Last Note: I don't think the vertical force problem is as simple as some of you are making it out to be. Remember 2 years ago in lunacy, there were hundreds of posts about how "it won't matter how many wheels are touching the floor because frictional force is not area dependent." In fact, it certainly was area dependent because of surface roughness- a fact that many teams overlooked. I remember team 2753 (a rookie) realized they had better traction with more wheels despite the simple physics, and made it all the way to Einstein because they had better acceleration and speed than anyone else.
In the minibot case, there are motors which stop turning when the light switch is triggered, there is rolling friction, some other parts dragging on the pole, the light switches absorb some of the force in being depressed, etc. All of these things could add up to a difference maker. And no, I have not attempted to calculate it either, but that's why if you think something is fishy about the system, you need to physically measure the force out on the practice field.
A rare 2 cents from my short arms and deep pockets...
I can see this rule being needed as we approach the Championship and many teams will have minibots, but I'd love to see the computer's results only being used when it's too close to call.
Assuming they can get the sensors to work properly this is a great change. However, from experience with Breakaway's automated scoring system, there will be many bugs which will cause teams to lose matches.
The field techs and refs have there work cut out...
wireties
15-03-2011, 22:52
Our minibot is not particularly fast but is getting better. During Week 1 at Alamo, it tripped the sensor every time. But at the next event it will be lighter and faster (a design which we built before we shipped but had no time to test due to weather-related delays). After some complaints on Thursday, the few teams with really light and fast minibots got the referees to manually judge the minibot race. It seemed fair to us, those light minibots are great machines.
I want to point out a common engineering practice. If my company had to build a minibot that triggered the sensor EVERY time in order to get PAID, we would build something with a 2:1 margin for error - something that would under nominal conditions exert 8N of force.
And I think that minibots reversing direction too quickly may play a bigger role that we think. We may add a spring in the lever that depresses the switch in our newer design.
pfreivald
15-03-2011, 22:57
And I think that minibots reversing direction too quickly may play a bigger role that we think.
That's a great point. Our minibot just turns off when it hits the top. (And usually comes back down because of the impact with the plate -- meaning that the plate is providing the impulse to reverse the momentum). If some teams are actually reversing their wheel direction before the impact is finished, this could have a dramatic effect on the overall force (and the maximum force) with which they are hitting the plate.
"Week 2 results indicated that this change was successful."
Hmmm. Like many others who have commented, our 1.2 sec. minibot smacked the target with a substantial impact in Week 2 (my calculations say in excess of 100 N), and yet did not result in a trigger light a couple of times. Clearly with all the antecdotal evidence there is still a phenomenon occuring which can miss an impact of adequate force. Any mechanical action has both a time and force component, and perhaps the rules should have specified both. Like any control system the field system has a controller with a finite scan rate, and any control system is capable of missing a signal if it is short enough. I am a little nervous about a statement that essentially says "we have determined the system is now perfect" if that means no provision will ever be made for correcting a result when it is clearly wrong. I'm grateful we are not playing again until Week 6 to give some time for this issue to get sorted out. Let's hope no Week 3 teams experience any problems which effect their results.
2 observations:
1.) Design the mini-bot so that it can't hit the bolt first. Honestly, I think the bolt pattern was the cause of most of the times it didn't trigger at Pittsburgh. We personally checked every single contact point on the towers before each day and they all triggered with minimal force.
2.) Make sure there is a delay between when you hit the top and when you start reversing the wheels.
I think this is a necessary rule for the Championships. Mini bot races are very soon going to get too close to call and we need to perfect the tower designs and also for the teams to perfect their mini-bot designs so they do not hit the bolts and provide the necessary amount of force. I think thats the only path to reliable calls at the championships.
pfreivald
15-03-2011, 23:14
Forgive my tired brain, but is the bolt pattern in the field drawings?
2.) Make sure there is a delay between when you hit the top and when you start reversing the wheels.
I think this is a necessary rule for the Championships. Mini bot races are very soon going to get too close to call and we need to perfect the tower designs and also for the teams to perfect their mini-bot designs so they do not hit the bolts and provide the necessary amount of force. I think thats the only path to reliable calls at the championships.
Where in the rules does it say that you have to provide a given impulse? All it says is 4 newtons, not 4 newtons for 2 seconds, half a second, etc.
Teams made their minibots to FIRST's rules. They should fix their (still) not fully functional system, or put measures in place to ensure that minibots conforming to their published rules actually get scored.
Instead they just say "our system is perfect, so if you don't trigger it, even if you blast the darn plate off the top of the pole entirely, you still don't get the points". If the system is proven to have any flaws then FIRST ought to recognize that it is possible for mistakes to be made.
Anyone seriously arguing whether a 2.5 lb minibot going 6-10 ft/s will impart 4 N of force or not is just being a FIRST apologist. This is simple physics and some efficiency losses due to friction, etc aren't going to change much.
Perhaps we should take some video of our official competition towers being repeatedly triggered by our minibot to silence the doubters?
BrendanB
15-03-2011, 23:23
Where in the rules does it say that you have to provide a given impulse? All it says is 4 newtons, not 4 newtons for 2 seconds, half a second, etc.
Teams made their minibots to FIRST's rules. They should fix their (still) not fully functional system, or put measures in place to ensure that minibots conforming to their published rules actually get scored.
Instead they just say "our system is perfect, so if you don't trigger it, even if you blast the darn plate off the top of the pole entirely, you still don't get the points". If the system is proven to have any flaws then FIRST ought to recognize that it is possible for mistakes to be made.
Anyone seriously arguing whether a 2.5 lb minibot going 6-10 ft/s will impart 4 N of force or not is just being a FIRST apologist. This is simple physics and some efficiency losses due to friction, etc aren't going to change much.
Perhaps we should take some video of our official competition towers being repeatedly triggered by our minibot to silence the doubters?
I agree! With all the minibot rules the time to change how the race is drawn and towers triggered is not week 3! I would expect FIRST to do the opposite and put refs in place of the electronic or at least watch.
Grrrr.
Anyone want to poke holes in my analysis?
One obvious omission is that you did not account for the mass of the plate. The plate must be violently accelerated in the short amount of contact time it has with the minibot in order to move it enough to trip the sensor(s).
How much does a 12" diameter 0.25" thick polycarbonate plate weigh? My quick calculation says it's more than 4 Newtons (please check my math). So obviously 4 Newtons is not enough force to move the plate at all, let alone violently accelerate it. So where did the 2-4 Newton number in the manual come from?
The specification of what exactly is required of the minibot in order to trip the sensors is inadequate to allow accurate analysis. What exactly is being sensed? Proximity? Rate of change? Dwell time? Some combination? Does anyone know?
I am not apologizing for FIRST, I am just advocating pragmatism from the teams. The bolt pattern was definitely not obvious and I don't remember seeing it anywhere in the official rules. They are in the official field drawings in sections 37, 38 and 69 of the Game Field Elements but I know most teams (including my own) don't check those.
Believe me I sympathize with any team who's bot successfully climbs the pole but doesn't get the points for it. I know that it must be immensely frustrating. I want to eliminate that from ever happening. Thats why I think that with a few small minibot modifications, this will become simply a non-issue and the tower results will match everyones expectations.
I know there were cases where the minibots reached the top of the tower but it didn't trigger. I am just being honest and did not see any of those cases where it was completely obvious that the bolt was not hit and that it delivered enough force and still did not trigger.
Where in the rules does it say that you have to provide a given impulse? All it says is 4 newtons, not 4 newtons for 2 seconds, half a second, etc.
Teams made their minibots to FIRST's rules. They should fix their (still) not fully functional system, or put measures in place to ensure that minibots conforming to their published rules actually get scored.
Instead they just say "our system is perfect, so if you don't trigger it, even if you blast the darn plate off the top of the pole entirely, you still don't get the points". If the system is proven to have any flaws then FIRST ought to recognize that it is possible for mistakes to be made.
Anyone seriously arguing whether a 2.5 lb minibot going 6-10 ft/s will impart 4 N of force or not is just being a FIRST apologist. This is simple physics and some efficiency losses due to friction, etc aren't going to change much.
Perhaps we should take some video of our official competition towers being repeatedly triggered by our minibot to silence the doubters?
Dave Flowerday
15-03-2011, 23:41
Where in the rules does it say that you have to provide a given impulse? All it says is 4 newtons, not 4 newtons for 2 seconds, half a second, etc.
Teams made their minibots to FIRST's rules. They should fix their (still) not fully functional system, or put measures in place to ensure that minibots conforming to their published rules actually get scored.
Cory, I agree with what you're saying. However, I've heard that, due the false triggering seen early on in week 1, the field hardware now looks to see that the towers remain triggered for 75 milliseconds before a hit is registered. I can imagine that really fast minibots hit so hard that they bounce away and aren't making contact for 75ms.
What's annoying is that this means that the rules have changed, as you suggested. The de-facto rule now appears to be 4 newtons for 75 milliseconds.
The de-facto rule now appears to be 4 newtons for 75 milliseconds.
Please see my earlier post (http://www.chiefdelphi.com/forums/showpost.php?p=1040466&postcount=39) about "4 Newtons".
MrForbes
15-03-2011, 23:48
my math agrees with yours. And I know the off switch on our minibot takes much less force than that to actuate.
Interesting.....the rules have been that the tower sensor must be triggered for it to count. Just because teams got away without triggering the first week or two, doesn't mean the rule doesn't apply.
I wonder how many slow heavy minibots will win races now?
Assuming the minibot stays on the pole after impact, the trick is to make the cut-off switches either slow (not a quick flip) or require more than 4N of force to push. Either will increase contact time with the top plate. Squishy surgical tubing comes to mind.
Design is iterative, right?
coldfusion1279
16-03-2011, 00:22
Anyone seriously arguing whether a 2.5 lb minibot going 6-10 ft/s will impart 4 N of force or not is just being a FIRST apologist. This is simple physics and some efficiency losses due to friction, etc aren't going to change much.
I would appreciate a more explicit mathematical write up as to why you are so convinced.
Most importantly, I want you to account for the drift in the motors due to momentum after the limit switch shuts down the motors at the top of the pole. Do you know, for a fact, the robot has enough speed/momentum to continue to carry itself upwards despite non-powered motors and gravity contributing to rapid deceleration? As pointed out in this thread, the non-powered motors might even stop the robot on a dime...
(For the record, I think there should be enough force too, but I think is not good enough in engineering, and FIRST hasn't given me good enough reason not to trust them)
AlexD744
16-03-2011, 00:28
I don't know about the towers at other regionals, but at Florida, for our 3 lb/1.6 second minibot, the tower triggered every time. Granted we didn't get our minibot and deployment working until our last qualifier, so it only had 4 goes at it, but it triggered it four out of four times. And for the most part, the towers there were registering minibots, both slow and fast.
However, being on the drive team leaves me with little time to watch matches, so I am not sure if every other team had this success rate, feel free to correct me if you minibot experienced a false negative at Florida.
I am not apologizing for FIRST, I am just advocating pragmatism from the teams. The bolt pattern was definitely not obvious and I don't remember seeing it anywhere in the official rules. They are in the official field drawings in sections 37, 38 and 69 of the Game Field Elements but I know most teams (including my own) don't check those.
Believe me I sympathize with any team who's bot successfully climbs the pole but doesn't get the points for it. I know that it must be immensely frustrating. I want to eliminate that from ever happening. Thats why I think that with a few small minibot modifications, this will become simply a non-issue and the tower results will match everyones expectations.
I know there were cases where the minibots reached the top of the tower but it didn't trigger. I am just being honest and did not see any of those cases where it was completely obvious that the bolt was not hit and that it delivered enough force and still did not trigger.
I have tried several times this evening to access the tower diagrams and get timed out waiting for the download...does anyone have a stored image of the top plates and the bolt pattern they can share?
MrForbes
16-03-2011, 00:30
This is what it's all about:
TRIGGERED – the act of pushing the bottom disk of the TARGET so that the sensors are tripped and a signal is sent to the Field Management System (FMS). When a TARGET is TRIGGERED, the MINIBOT RACE on that TOWER is complete.
You gotta TRIGGER the TARGET. If your minibot doesn't TRIGGER the TARGET reliably, you might need to redesign your minibot.
The description of the ARENA suggests that it will take a minimum force of 2-4 Newtons to TRIGGER the TARGET.
I have tried several times this evening to access the tower diagrams and get timed out waiting for the download...does anyone have a stored image of the top plates and the bolt pattern they can share?
I don't want to attach/upload/etc the full field elements document, but I took a screenshot of the drawing of the bottom plate, which is where it seems that the bolts are an issue. Page 69 of the 2011 Game Field Elements_RevA, if you manage to download it and view it yourself.
Edit: You can see the bolts in some of Dan Ernst's pictures: http://www.flickr.com/photos/danielernst/5526043179/in/set-72157626138552781/, http://www.flickr.com/photos/danielernst/5526709398/in/set-72157626138552781/, http://www.flickr.com/photos/danielernst/5526872042/in/set-72157626138552781/
s_forbes
16-03-2011, 01:58
Simple solution: remove off switch, replace components as needed. :)
How much does a 12" diameter 0.25" thick polycarbonate plate weigh? My quick calculation says it's more than 4 Newtons (please check my math). So obviously 4 Newtons is not enough force to move the plate at all, let alone violently accelerate it. So where did the 2-4 Newton number in the manual come from?
This is an interesting point that never crossed my mind. Quick math suggests about 4-5 newtons of force just to cancel out weight of polycarb plate. Someone should bring a scale to one of this weeks competitions and see how much force is actually needed to trigger the plate (ignoring impulse). Might lead to some exciting discussions with the refs!
This week is going to be fun.
MrForbes
16-03-2011, 02:12
The rules don't say you need to hit the plate with 4 N force to win the race. They say you need to trigger the tower.
Isn't that the way it's been all along?
Someone should bring a scale to one of this weeks competitions and see how much force is actually needed to trigger the plate (ignoring impulse).
Good luck. Ever try asking to measure the overpass height in 08 to confirm it was within the tolerance listed?
The rules don't say you need to hit the plate with 4 N force to win the race. They say you need to trigger the tower.
Isn't that the way it's been all along?
And to trigger the tower you need to hit it with 4N of force. Your argument seems sort of circular? If you hit it with 4N of force and it doesn't trigger, then FIRST failed to implement their triggering solution correctly.
Tristan Lall
16-03-2011, 02:17
You gotta TRIGGER the TARGET. If your minibot doesn't TRIGGER the TARGET reliably, you might need to redesign your minibot.
The description of the ARENA suggests that it will take a minimum force of 2-4 Newtons to TRIGGER the TARGET.Exactly: by definition, if the sensors aren't tripped, you haven't triggered it, and are entitled to zero points. It doesn't matter how hard you hit it.
Fundamentally, the problem is that the rules define scoring in terms of a process that is hard to directly observe (were the switches actually tripped, or did it hang up on the bolts?), and which is inherently impractical to error-proof (did the sensors get tripped because a robot shook the tower, or because a minibot ascended it properly?).
When the refs were scoring it manually, there was really no way for them to systematically and conclusively distinguish false positives, false negatives, true positives or true negatives. They were just guessing. (And the timing aspect being based on triggering, and not mere contact made it all the more impractical to observe from floor level.)
I think this update makes the best of a game design choice that was, in retrospect, not so good. An alternative might have been a rule change, to change the criteria for triggering, but I can certainly see that that introduces other problems. I can only hope that FIRST did some testing and established that the best balance of true and false outcomes is achieved through the changes they've implemented.
MrForbes
16-03-2011, 02:31
And to trigger the tower you need to hit it with 4N of force. Your argument seems sort of circular? If you hit it with 4N of force and it doesn't trigger, then FIRST failed to implement their triggering solution correctly.
My argument isn't circular. You're hung up on the 4N number. The game rules don't mention it. The ARENA description does, but it does not say that it's an upper limit. It suggests it's a lower limit.
You've been in FIRST long enough to know that the ARENA doesn't always behave the way the manual suggests that it might.
I guess we'll find out in a few days how our minibot does. I expect we'll probably have to play with the off switch, if we can get it to deploy legally. Should be interesting.
sanddrag
16-03-2011, 02:50
So, do you really need to hit it for 75 milliseconds!? That seems like an awfully long time. And what about issues such as switch bounce. Is that dealt with?
Chris is me
16-03-2011, 02:54
The ARENA description does, but it does not say that it's an upper limit. It suggests it's a lower limit.
I think you're reading it wrong. I read it as "the minimum force is 4n" as in "any force 4n or above will trigger".
I think first saying "lalala our sensors are perfect" and ignoring teams is just stupid myself.
WizenedEE
16-03-2011, 02:55
Well, switch bounce wouldn't matter, because you can't score twice on the same tower. Switch bounce just makes it look like there was a bunch of hits when there was actually only one.
Tristan Lall
16-03-2011, 03:10
I think you're reading it wrong. I read it as "the minimum force is 4n" as in "any force 4n or above will trigger".The manual says that "[a] minimum contact force of approximately 2-4 Newtons, depending on contact location, is required to ensure the contact sensors in the TARGET trip reliably."
I don't read that as a definition; to me, that looks like an observation for the benefit of the teams. If it were a definition, it would be the worst definition in the world. (Approximately? A range of force? Depending on contact location? And how do you quantify "reliably"?)
Chris Hibner
16-03-2011, 07:20
My argument isn't circular. You're hung up on the 4N number. The game rules don't mention it. The ARENA description does, but it does not say that it's an upper limit. It suggests it's a lower limit.
Here's my issue: if they only specify a minimum, then how to you guarantee you trigger the sensor? If my minibot applies 1000 N and it doesn't trigger in a match, then that is perfectly acceptable field behavior by the definition in the rules as you interpret it (however ludicrous that is).
As an engineer, I expect specifications that are guarantees of proper performance - not a specification of "below X it's guaranteed to not work, and above X may or may not work but we're not really sure". With no specification of "above XX N the tower WILL trigger" how do we design minibots?
Can't the silly force triggers be replaced with light sensors or proximity switches? Those won't be fooled by robots bumping into the bases, won't have different properties depending on where you hit the plate, and won't bind on the pole like I've seen the plate do.
Josh Fritsch
16-03-2011, 07:25
Easy way to know if your minibot will be ok? Have a FIRST certified tower during minibot inspection with a force gauge on it. Then you can have a document from an inspector stating that your minibot meets the minimum required force needed to trigger the target. So if it doesnt happen on the field you have some sort of justification for the refs.
This would eliminate everyone on here saying "show me the calculations to prove it!" or "you didnt account for this drag force or weight of the plate!" etc...
Vikesrock
16-03-2011, 07:33
My argument isn't circular. You're hung up on the 4N number. The game rules don't mention it. The ARENA description does, but it does not say that it's an upper limit. It suggests it's a lower limit.
I guess we were all hoping that the 4N spec was an attempt to provide a specification that teams could test or at least calculate and know where they stood.
Even if you build a competition tower exactly according to the Game Drawings you cannot test TRIGGERING at home because you don't have the FMS setup. That's not an engineering challenge, it's a lottery.
Tristan Lall
16-03-2011, 07:37
Can't the silly force triggers be replaced with light sensors or proximity switches?That's exactly what I was thinking, but unfortunately it's too late now. Teams have already designed minibots with the pressure plate as a constraint, and played that way for two weeks.
If I'd designed the thing, I probably would have used a series of three or more sensors at the desired level, and used some logic to have them "vote". When a majority say you've reached a discrete position, you'd score. (And it would fail gracefully if it didn't work: a human could still judge the position visually, rather than have to estimate whether a switch was or was not tripped.)
Here's my issue: if they only specify a minimum, then how to you guarantee you trigger the sensor?According to the logic embodied in the rules, you can't.
Al Skierkiewicz
16-03-2011, 07:39
Guys,
Lets not get crazy. The towers work. There is no complicated issues here. If your minibot can climb the pipe in under five seconds it will trigger the top. If it struggles to get up, then the plate may be able to push back with enough force to stop the minibot and not trigger. I saw more than one minibot over the weekend climb the tower with the drive wheels spinning faster than the climb rate. If the minibot made it to the top, only one was not able to trigger the tower in ten seconds. That one was spinning the tire on the pipe at the top. It was simply a matter of equalized forces. The plate did not move.
pfreivald
16-03-2011, 07:40
Good call on the math, Ether.
A lesson I seem to have to re-learn every single season is that every measurement FIRST gives is nominal, whether it's said to be nominal or not.
Brandon Holley
16-03-2011, 08:56
Guys,
Lets not get crazy. The towers work. There is no complicated issues here. If your minibot can climb the pipe in under five seconds it will trigger the top.
Al-
What your describing is in complete contradiction with some other long time FIRST vets. I've taken both yours and their advice many times, so I'm at a sort of impasse. We haven't competed yet (this week at Bayou we will) but I'm moderately concerned our minibot may not trigger the tower every single time based on its similarity to minibots these other veterans have. While I don't doubt that most minibots will trigger the tower, how can we make sure the towers are triggered EVERY time?
-Brando
Al Skierkiewicz
16-03-2011, 08:59
Brandon,
Have faith. Participants, FTAs and Refs are not going to allow teams to miss out should there be field issues. If there is reasonable doubt, I am sure the staff will take action and/or resort to manual scoring. There are contingency plans. We know how hard you work to get to the point of competition.
Brandon Holley
16-03-2011, 09:05
Brandon,
Have faith. Participants, FTAs and Refs are not going to allow teams to miss out should there be field issues. If there is reasonable doubt, I am sure the staff will take action and/or resort to manual scoring. There are contingency plans. We know how hard you work to get to the point of competition.
Thanks Al.
-Brando
Tetraman
16-03-2011, 09:34
Brandon,
Have faith. Participants, FTAs and Refs are not going to allow teams to miss out should there be field issues. If there is reasonable doubt, I am sure the staff will take action and/or resort to manual scoring. There are contingency plans. We know how hard you work to get to the point of competition.
Yes.
If an issue ends up complicating a regional, the head ref and FTA has the right to make the call and go to scoring the races manually. In fact, I'm sure many head refs will ask for the refereeing volunteers to take mental notes as to the finishes, so if a problem arises mid-match, that match's scores will still end up counting.
MrForbes
16-03-2011, 09:36
re: the force required to move the plate, vs. it's weight. If your minibot must lift the entire plate evenly, then it might take more than 4N to trigger the tower. If your robot contacts the plate on one side, then it only needs to lift that side of the plate. The plate should still rest on the two bolt heads on the other side of the pole. The force required to trigger the FMS should be significantly less than the full weight of the plate.
So Ether's math seems correct, but his lack of a free body diagram might lead one to an erroneous conclusion.
Interesting how so many people get upset about a game challenge that is not quite what they anticipated.
I guess a description of the new tower triggering mechanism would be useful for some here who did not get to see it at a week 2 regional. There are NO force sensors up there. There are simply 3 metal contact points that act as simple switches (note, this is as of week 2. week 1 had 3 limit switches). As long as 1 of those contact points is hit for enough time for FMS to read the signal it will trigger. The setup itself is dead simple.
One problem is that any changes made to the tower need to be so cheap, simple, and easy to assemble that FIRST can ship it to all the regionals and they can put put together by the field staff there. I think FIRST did a reasonable job with those constraints in mind. I would love for the bolts to not be there at all because I still think thats the cause of most robots that reach the top and don't trigger. Maybe the bolts could be reversed so that they are anchored to the bottom plate? (this would increase the effective mass of the bottom plate, so more force would be required to push it up)
Regardless, these are the current constraints of the system and I think with a few small mini bot modifications you will be able to trigger that setup every time. And if it still doesn't, then you have a better case for there being a major flaw in the triggering mechanism.
I believe that FIRST and the teams need to work on getting the automated triggering to work with very very high reliability. I believe the reason for that becomes clear if you examine the following case. For this case, lets make 2 assumptions. First, that teams and FIRST do not continue to refine the triggering. Second, that we allow the refs to manually override the triggering results.
With those assumptions, lets say we are in the final match of Archimedes deciding who will go to Einstein. All 4 minibots go up and all hit the trigger with imperceptible differences in arrival time. However, 1 minibot does not trigger. Now what do you do? A precedent was set in previous matches that the refs can make a judgement call based on what it looked like. Even if in that case the minibot was not as close of a call, but you know that will not stop the team from flooding the field with shaky video footage and their first hand accounts to try and show when it hit. I think these 2 assumptions lead to a messy future.
Now, if teams and FIRST work to refine the automated triggering mechanism then we will probably never even have this problem to deal with. And even if there are a very very small number of cases where it seems like it should have legitimately triggered but did not, then at least there is a consistent precedent of not counting it unless the robot triggers the sensors and the playing field will still remain even for all teams.
MrForbes
16-03-2011, 09:53
And even if there are a very very small number of cases where it seems like it should have legitimately triggered but did not, then at least there is a consistent precedent of not counting it unless the robot triggers the sensors and the playing field will still remain even for all teams.
Yes...playing by the rules that have been there since the beginning.
Tom Bottiglieri
16-03-2011, 10:09
Yes...playing by the rules that have been there since the beginning.
Yeah, we get it.. That's the rule. I don't think anyone is arguing that you need to trip the sensor. The issue at hand is that there is some obfuscation in the method of doing so. Sure, there is plate you need to lift, and it takes some amount of force. But we as teams have no way to actually test what we believe will trip the sensor short of going to the regional and trying it. Sure we can guess all we want at what will and will not trigger the sensor, but in the end it turns out the process for tuning these things is not as black and white as you would hope for. Sure, things don't work perfectly, that's engineering. But there might be a more deterministic way to see who won the race. Beam breakers? We dump way too much time and money into these regionals for "just trust us" to cut it. Real time scoring has never been very reliable, we all know that. It's not an issue if there is an accurate backup. While I'm certain (now more than before with Al's post) that this issue can be resolved at the regional level, the wording of the update was a bit disconcerting. I also look forward Einstein Finals Match 2-2 when everyone's minibot is more or less the same speed.
TL;DR: We all just got told "you're holding it wrong".
MrForbes
16-03-2011, 10:12
Do you know if any teams built a TARGET using the field drawings, designed a minibot to make it work every time, and it's not working on the actual field?
If so, then I'd say we have a problem. If not, some teams just didn't do their homework.
Tom Bottiglieri
16-03-2011, 10:13
Do you know if any teams built a TARGET using the field drawings, designed a minibot to make it work every time, and it's not working on the actual field?
.
You can build poles until the cows come home. It's the triggering settings that are the issue.
Vikesrock
16-03-2011, 10:17
Do you know if any teams built a TARGET using the field drawings, designed a minibot to make it work every time, and it's not working on the actual field?
If so, then I'd say we have a problem. If not, some teams didn't do their homework.
Cory of 254 said exactly that in post 15 (http://www.chiefdelphi.com/forums/showpost.php?p=1040363&postcount=15) in this thread.
martin417
16-03-2011, 10:26
Yes...playing by the rules that have been there since the beginning.
As an engineer, I work to engineering specs. If I meet those specs, I expect to be paid. You can imagine that I might be a wee bit upset if I were to design a product that meets the customer's specs, deliver that product, and be told "I'm not paying you because the product didn't do what I expected it to do". If your specs are not written clearly enough, that is your fault, not mine.
In FIRST, the manuals and rules are the specs. Your argument that the 4N force was not in the rules is not valid. The peg heights are not in the rules either. The entirety of the game documentation is the specification document to which all teams work. Our minibot cannot hit the bolt heads, and I can guarantee that it imparts far more than 4N of force. Therefore, by any definition, it meets the specs. If we get to competition this weekend, and our minibot doesn't trigger the tower, am I supposed to just accept that and go on? Is that proffessional? In the real world, it would not be tolerated.
More importantly, this is supposed to be a race. The tower trigger is just a means of scoring that race. Imagine an Olympic sprinter that happens to be too short to reach the tape. If he crosses the finish line first, but runs under the tape, does that mean he didn't win the race? I think this whole argument is silly. The first minibot to reach the top should be declared the winner. All this argument about how to decide that winner is a side note. FIRST should come up with a foolproof method of determining the winer.
MrForbes
16-03-2011, 10:31
The spec is TRIGGERING the TOWER. The spec is not getting there first.
If 254's official towers use the design in the published field drawings, and the minibot does work on them, but not on the modified design tower switches, then I'd say we have a problem.
re: the force required to move the plate, vs. it's weight. If your minibot must lift the entire plate evenly, then it might take more than 4N to trigger the tower.
To lift the entire plate evenly it will take more than 4N.
If your robot contacts the plate on one side, then it only needs to lift that side of the plate. The plate should still rest on the two bolt heads on the other side of the pole. The force required to trigger the FMS should be significantly less than the full weight of the plate.
It's a simple second-class lever. I thought that was obvious so I didn't stated it explicitly. My bad.
martin417
16-03-2011, 10:51
The spec is TRIGGERING the TOWER. The spec is not getting there first.
If 254's official towers use the design in the published field drawings, and the minibot does work on them, but not on the modified design tower switches, then I'd say we have a problem.
G67> The RACE SCORE is assigned to each ALLIANCE based on the place of finish in the MINIBOT RACE (ties each receive the points for that place):
1st MINIBOT to TRIGGER the TARGET
30 points
2nd MINIBOT to TRIGGER the TARGET
20 points
3rd MINIBOT to TRIGGER the TARGET
15 points
4th MINIBOT to TRIGGER the TARGET
10 points
OK fine. Let's throw out the last paragraph of my post and concentrate on the rest. What is required to TRIGGER the TARGET? If I don't know the answer to that question, how do I design a minibot to reliably TRIGGER the TARGET? Does it take 4N of force? Does it take some force for a specified period of time? Do I need to hit the plate in a certain area? Do I need to tap out morse code on the plate when I get there? I don't care what the specs are, just let us know so we can design a device that meets those specs.
Where are these "published field drawings" I keep reading about?
2011 Game Field Elements_RevA.pdf (http://usfirst.org/uploadedFiles/Robotics_Programs/FRC/Game_and_Season__Info/2011_Assets/2011%20Game%20Field%20Elements_RevA.pdf) mentioned in Team Update #18 does not contain any information about the sensor, or its location, or any details concerning how the signal is processed by the computer equipment to which it is attached.
MrForbes
16-03-2011, 11:06
The TARGET is described in the ARENA drawings. As far as I can tell, the only way to make sure your MINIBOT will TRIGGER it is to build it and try it--or do a detailed analysis of how the plate will behave when struck by your MINIBOT. The 2N to 4N thing in the ARENA description gives you an idea of what's required, but you still need to look at the design of the TARGET to be able to figure out exactly what's required.
As for the sensors...I guess we just have to guess at how it works, and make sure the plate will move a long ways when the MINIBOT hits it?
As long as 1 of those contact points is hit for enough time for FMS to read the signal it will trigger.
There's the rub. How does FMS read the signal. What if FMS is busy doing something else when the switch is hit?
What are the wires from the switches attached to?
Are they generating an interrupt and being time-stamped? Is that happening locally and the information stored so that FMS can read it when it gets a chance?
The engineer in me wants to know.
I honestly don't think this is as big of a problem as it is being made out to be. So far as I could tell at Pittsburgh, the sensors were pretty darn reliable. The only times they did not trigger it seemed like 1 of these 3 were the causes:
1.) Hit the bolt
2.) Did not hit with enough force (like, creeped up really really slowly with the wheels slipping)
3.) Turned off / reversed immediately after hitting the bottom plate without pushing much at all
If your minibot avoids all those 3 things and are still getting false negatives during the practice day at Week 3's: talk to a FTA. They will help you work out whats going on. I think the practice day will be plenty of time to sort through those 3 issues and any others that come up. Like I posted before, the triggers are really simple, there are only a few possible causes for them not to go, so I really don't think it will be necessary to hit in an exact spot, other than not bolt, or with a super specific force or time (or tap out morse code :P)
Now, I must say that I am never crazy about automated scoring systems. I wouldn't have designed a minibot race at all because of how hard it is to score without some automation. However, this is the game thats been given to us and you can see my earlier posts about why I think that the automated scoring is necessary given this game. And only because I believe the automated scoring system is necessary am I advocating for teams to take whatever steps necessary to make sure they can trigger the setup.
But still, my gut instincts say that if those 3 little things are avoided, this whole thing will just not be an issue.
Alan Anderson
16-03-2011, 11:23
Quick math suggests about 4-5 newtons of force just to cancel out weight of polycarb plate.
You don't have to lift the entire bottom plate. You just need to tip one side of it up in order for the switch to make contact. A naive analysis says it would take between 1/2 and 3/4 the weight of the plate to trip a switch, or -- hey, lookie here -- about 2-4 newtons.
martin417
16-03-2011, 11:25
I honestly don't think this is as big of a problem as it is being made out to be. So far as I could tell at Pittsburgh, the sensors were pretty darn reliable. The only times they did not trigger it seemed like 1 of these 3 were the causes:
1.) Hit the bolt
2.) Did not hit with enough force (like, creeped up really really slowly with the wheels slipping)
3.) Turned off / reversed immediately after hitting the bottom plate without pushing much at all
I haven't witnessed it, but others have posted here that not all target triggers were reliable, ie: targets that should have triggered in week two didn't.
Now, I must say that I am never crazy about automated scoring systems. I wouldn't have designed a minibot race at all because of how hard it is to score without some automation. However, this is the game thats been given to us and you can see my earlier posts about why I think that the automated scoring is necessary given this game. And only because I believe the automated scoring system is necessary am I advocating for teams to take whatever steps necessary to make sure they can trigger the setup.
I don't agree that reliable automated scoring is difficult. I was a Cub Scout leader several years ago, and our pack had a home-made Pinewood Derby track. The scoring was automated and home-made. A simple beam break trigger and a timer. It was 100% reliable (I never saw a failure to trigger in 4 years of races).
You don't have to lift the entire bottom plate. You just need to tip one side of it up in order for the switch to make contact. A naive analysis says it would take between 1/2 and 3/4 the weight of the plate to trip a switch, or -- hey, lookie here -- about 2-4 newtons.
You're a little late to the party. That point has already been made.
DonRotolo
16-03-2011, 11:34
to make sure your mini bot does not hit in the bolt pattern on the bottom of the plate.if those 3 little things are avoided, this whole thing will just not be an issue.
I dunno, having only been at a Week 1 regional I haven't witnessed towers triggering properly.
But clearly there are some pitfalls to be aware of, just make sure they are addressed. IF someone witnesses a reasonable hit not being recorded in Week 3, please post a video here. Then we can argue the point.
MrForbes
16-03-2011, 11:37
Assuming the problem has to do with the time it takes to TRIGGER the field system, not the force exerted, it seems that some means of controlling the deceleration at the time of impact with the TRIGGER plate, might help. Perhaps add a springy finger to the top of your MINIBOT?
Perhaps add a springy finger to the top of your MINIBOT?
Great idea. And simple to implement. Perhaps just a small loop of surgical tubing at the point of contact would do the trick.
MrForbes
16-03-2011, 11:44
I was thinking of a thin section of large diameter PVC pipe. We use a few of these on the bottom of our (heavy) MINIBOT to cushion the fall back to the BASE.
Assuming the problem has to do with the time it takes to TRIGGER the field system, not the force exerted, it seems that some means of controlling the deceleration at the time of impact with the TRIGGER plate, might help. Perhaps add a springy finger to the top of your MINIBOT?
Or FIRST should fix their system. Why should the customer fix a part that came to them out of spec? We are paying for something and if FIRST doesn't deliver the onus should be on them to fix the problem, not on us to work around their broken implementation.
MrForbes
16-03-2011, 12:07
The spec is that your MINIBOT has to TRIGGER the TOWER. They didn't specify exactly what it takes to do that. But you still have to do it. If your MINIBOT does not do that, then modify your MINIBOT so it does. If that means slowing it down....oh well.....
pfreivald
16-03-2011, 12:07
Or FIRST should fix their system. Why should the customer fix a part that came to them out of spec? We are paying for something and if FIRST doesn't deliver the onus should be on them to fix the problem, not on us to work around their broken implementation.
Nominal measurements, nominal specs, last-minute changes to fix last-minute problems... These are common in FIRST, have been common in FIRST at least as far back as when I started 827 and got crushed by 254 at the Silicon Valley Regional.
Some level of overengineering, and not engineering things too close to your target, is required all the time, methinks.
The discussion seems to be divided into two groups: those who have a fast, high-impact minibot and have experienced first-hand a target not triggering when it clearly should have, and those who do not have this first-hand experience, but speculate on whether the system is or isn't reliable. I put more credence with those with first-hand experience.
Regarding "the bolts"....it seems that they should have been fixed to the lower plate, and moving through the upper plate, so that they move with the lower plate no matter where it is contacted, rather than being fixed to the top plate and protruding through the bottom plate, so that they create 4 areas which block the minibot from triggering. From my understanding of the drawings, this would be an easy change to make.
MrForbes
16-03-2011, 12:21
The discussion seems to be divided into two groups: those who have a fast, high-impact minibot and have experienced first-hand a target not triggering when it clearly should have, and those who do not have this first-hand experience, but speculate on whether the system is or isn't reliable. I put more credence with those with first-hand experience.
I put more credence with those who read the rules and understand what the rules require the TEAMS to do.
There is no "should have TRIGGERED the TARGET" in the rules. You do it, you get credit. You don't do it, you don't get credit for it.
Part of the design challenge is to make sure your MINIBOT TRIGGERS the TOWER. Some TEAMS seem to have missed that. Apparently they thought the challenge was to get a minibot up the TOWER as quickly as possible.
BrendanB
16-03-2011, 12:31
I put more credence with those who read the rules and understand what the rules require the TEAMS to do.
There is no "should have TRIGGERED the TARGET" in the rules. You do it, you get credit. You don't do it, you don't get credit for it.
Part of the design challenge is to make sure your MINIBOT TRIGGERS the TOWER. Some TEAMS seem to have missed that. Apparently they thought the challenge was to get a minibot up the TOWER as quickly as possible.
IF the triggering programs and times of triggering on the towers hadn't been changed by FIRST between week 1 and 2 then this wouldn't be a problem for me. What is a problem is that it is changed to a level of "it seems to be working" instead of "every minibot who goes up the pole and exerts the 2-4N of force will trigger the top".
And to top it off humans wont' be used as the backup when electronics fail... seems backwards to me.
I put more credence with those who read the rules and understand what the rules require the TEAMS to do.
That would be an example of speculating about what should happen, as opposed to experienceing what did happen. Surely you are not suggesting that there is no possibility of a malfunction.
The discussion seems to be divided into two groups: those who have a fast, high-impact minibot and have experienced first-hand a target not triggering when it clearly should have, and those who do not have this first-hand experience, but speculate on whether the system is or isn't reliable. I put more credence with those with first-hand experience.
I think this is an unfair categorization. I was standing on the side of the field at the end of almost every match at a week 2 regional and saw every minibot that did not trigger the post. There were not that many of them and of them and it could not be shown that they did not hit a bolt or did not turn and reverse before pushing up the pad.
If someone has a really good first hand account of a minibot that definitely did not hit the bolt and definitely did not bounce off too fast and still did not get triggered, please speak up so that the cause can be investigated.
Brandon Holley
16-03-2011, 12:39
Part of the design challenge is to make sure your MINIBOT TRIGGERS the TOWER. Some TEAMS seem to have missed that. Apparently they thought the challenge was to get a minibot up the TOWER as quickly as possible.
If thats the case, then why did the first two weeks of the season use manual scoring to determine minibot race winners? There's no way for a human to know if a trigger was sensored from the ground. The GDC referred to the endgame as a race, we all refer to the endgame as a race, because it is a contest for teams to get their minibot up the tower as quickly as possible. Yes there are constraints, size, weight, motor usage, battery usage etc. One of those is the 2-4 N measurement the GDC added in to the game documentation.
The sticking point to me is that some teams clearly are exerting that force on the top plate. Maybe some of us feel more comfortable calculating the exact force required, but I'm comfortable enough with our minibot to say it hits the target hard enough to trip the switch. Now, if our minibot hits the target LONG enough to trip the switch is the big question because there is no requirement in the rules about length of time required to trip the switch.
If the GDCs intention was to make the entire challenge not just complying with the deployment rules, minibot part usage and the actual challenge of ascending the pole, but to also include the tripping of the sensor as a key factor, there should have been much more information provided besides "2-4 N". Whether this includes an approximate timeframe this force needs to be applied in or something else. To have every team interpret the field drawings of the tower sensor to determine if their minibot trips the sensor or not is insane to me.
Thats my only gripe. Now I don't know how big of a deal this all is. Al has told me to rest easy, and I trust Al, so I will do just that. I'll also be making sure our minibot runs are recorded on video just incase a sensor doesn't happen to trip. At least we'll be able to try to break down why it didn't that particular run.
-Brando
... bind on the pole like I've seen the plate do.
This observation received very little attention in this thread. Could it be a significant factor in the reliability of the triggering?
It seems it would be possible for it to bind on the pole, especially if the contact point between minibot and plate is far off-center causing the plate to tilt. Does anyone know what is the coefficient of friction between polycarbonate and galvanized(?) steel?
If someone has a really good first hand account of a minibot that definitely did not hit the bolt and definitely did not bounce off too fast and still did not get triggered, please speak up so that the cause can be investigated.
I believe speaking up about such an account is exactly what several posters have done.
MrForbes
16-03-2011, 12:44
I don't doubt that there were several instances where MINIBOTs did reach the top, but did not TRIGGER the TOWER. Unfortunately, the rules do not let that count for anything.
How can you claim there was a field malfunction if the exact requirements to TRIGGER the TOWER are not specified? It could just as easily be that the MINIBOT in question does not close the switch for a long enough time to trigger the field system.
I do understand that the system was changed to make it less sensitive to false triggering. But since the whole thing was not specified, I won't say that the field system no longer meets the specs. The ultimate spec is still that you gotta trigger it. Rather than complain about FIRST following their own rules, work on your MINIBOT to make it trigger every time. Ask on the Q&A what exactly is supposed to be required to make it trigger.
Grim Tuesday
16-03-2011, 12:49
I don't doubt that there were several instances where MINIBOTs did reach the top, but did not TRIGGER the TOWER. Unfortunately, the rules do not let that count for anything.
How can you claim there was a field malfunction if the exact requirements to TRIGGER the TOWER are not specified? It could just as easily be that the MINIBOT in question does not close the switch for a long enough time to trigger the field system.
I do understand that the system was changed to make it less sensitive to false triggering. But since the whole thing was not specified, I won't say that the field system no longer meets the specs. The ultimate spec is still that you gotta trigger it. Rather than complain about FIRST following their own rules, work on your MINIBOT to make it trigger every time. Ask on the Q&A what exactly is supposed to be required to make it trigger.
How can you claim it was a MINIBOT malfunction, if you don't know what to design your minibot for. If FIRST made us guess on what the maximum peg height would be, I don't think anyone would be happy.
I believe speaking up about such an account is exactly what several posters have done.
Is there one that says: "Our minibots dimensions make it physically impossible to hit the bolts and we have a really tough to flip switch so that the plate must be pushed up and hit the contacts before it turns off"
If these cases can be organized and then demonstrated week 3 practice day then I will believe there are larger problems at work here.
If someone has a really good first hand account of a minibot that definitely did not hit the bolt and definitely did not bounce off too fast and still did not get triggered, please speak up so that the cause can be investigated.
Ken, what would be considered bouncing off too fast? What is the duration that teams need to contact the disc to ensure that the target is triggered?
Ken's point is a very valid one. Does anyone have any video of Minibots hitting the top target but not triggering the target during week 2? Right now we're just dealing in speculation which isn't leading to anything productive. From what I saw in Pittsburgh, the large majority of minibots were in fact triggering the top target. If this wasn't the case at a regional you were attending, let's try and figure out what the issue was that was causing these false negatives.
If the issue was minibots hitting the bolt heads, that's unfortunate but it can be argued that teams should have been prepared for that based on the published drawings. (I may consider that a flimsy argument, but that's neither here nor there) If the issue is that teams aren't contacting the top target for long enough, I'm more concerned as nowhere in any official specification or guideline have I seen a duration of impact clause.
Brandon Holley
16-03-2011, 12:57
I do understand that the system was changed to make it less sensitive to false triggering. But since the whole thing was not specified, I won't say that the field system no longer meets the specs. The ultimate spec is still that you gotta trigger it. Rather than complain about FIRST following their own rules, work on your MINIBOT to make it trigger every time. Ask on the Q&A what exactly is supposed to be required to make it trigger.
The reason I'm reading this thread is to gather as much information as possible to ensure our minibot hits the trigger every time.
The only course of action is to work on your minibot to ensure it hits the trigger every time. What I don't agree with is that this course of action was a necessary evil of this game. Had the specifications been laid out ahead of time I would certainly not be complaining one bit if my minibot didn't hit the switch. What bothers me is that there seemed to be some kind of a specification regarding force and now that specification seems less important than the time it takes to trigger the target.
This is a healthy discussion, but I think theres too many unknowns to really take it farther. I think we can agree that the teams responsibility is to trigger the target, what we need is some direction from FIRST on what exactly that entails (your Q&A suggestion is a good one).
-Brando
MrForbes
16-03-2011, 12:57
If thats the case, then why did the first two weeks of the season use manual scoring to determine minibot race winners?
That's a very good question. I guess the officials didn't understand the rules.
If the issue is that teams aren't contacting the top target for long enough, I'm more concerned as nowhere in any official specification or guideline have I seen a duration of impact clause.
If we'd all had our act together two months ago, we would have asked
:eek:
Ken, what would be considered bouncing off too fast? What is the duration that teams need to contact the disc to ensure that the target is triggered?
I do not have a answer for this. So far the only thing I heard of was the speculation of 75ms floating around in this thread. I can see if I can find an answer to this later.
It makes sense to me that if it turns out there are bots that definitely don't hit the bolt and hit the pad hard enough and still don't trigger that duration would be the next most probable cause. I can imagine a pretty violent bounce on some minibots. I would like to believe FMS would still catch those, just based on some of the minibots I saw at Pittsburgh which bounce pretty good that got picked up, however I can not say that bouncing too quick is an impossible cause of a false negative.
I think teams can alleviate the duration problem pretty easily as well by adding some cushioning or something, but I know a real hard number for duration time would help team immensely.
I put more credence with those who read the rules and understand what the rules require the TEAMS to do.
There is no "should have TRIGGERED the TARGET" in the rules. You do it, you get credit. You don't do it, you don't get credit for it.
Part of the design challenge is to make sure your MINIBOT TRIGGERS the TOWER. Some TEAMS seem to have missed that. Apparently they thought the challenge was to get a minibot up the TOWER as quickly as possible.
The challenge was to get the minibot to trigger the target as quickly as possible. This is an optimization problem. Many of us used the specifications given as we worked out the optimization.
As they say in Animal House: "You effed up! You trusted us!"
To imply that all teams should have built a slow super-overpowered minibot just to ensure they trigger the target if the FIRST specs were wrong is silly. We (as good engineers) should have worked within the specs given to us.
BTW - I have no idea if there is a problem or not, but I'm surprised by your dismissal of the fears of many by saying "you should have built your minibot to hit harder, not to the spec."
-John
MrForbes
16-03-2011, 13:34
Apparently not many (none?) of us realized the spec was incomplete.
I sure missed it.
Kims Robot
16-03-2011, 14:06
In FIRST, the manuals and rules are the specs... The peg heights are not in the rules either. The entirety of the game documentation is the specification document to which all teams work.
I beg to differ... the peg heights are in GE1100-1106 and are referenced on page 3/10 of the 2011 FRC Game Manual, Section 2 - The Arena. Yes they could have been better spelled out. In the "real" engineering world, engineers reference other documents all the time, rather than copy/pasting specs into every document they make because it reduces the risk of forgetting to update documents when a change is made. GE-11036 tells you exactly how to build a sensor plate, yet how many teams actually did it?
1.) Hit the bolt
2.) Did not hit with enough force (like, creeped up really really slowly with the wheels slipping)
3.) Turned off / reversed immediately after hitting the bottom plate without pushing much at all
Bingo!
IF the triggering programs and times of triggering on the towers hadn't been changed by FIRST between week 1 and 2 then this wouldn't be a problem for me. What is a problem is that it is changed to a level of "it seems to be working" instead of "every minibot who goes up the pole and exerts the 2-4N of force will trigger the top".
And to top it off humans wont' be used as the backup when electronics fail... seems backwards to me.
I am not sure what you call "it seems to be working" as week 1 they CLEARLY weren't working. There were a ton of false triggers (robots hitting the tower), and then when they implemented a duration, some robots were too fast, so they resorted to manual scoring for week 1. So FIRST fixed them. They did not change the plates, just the electronics/sensors.
In my mind there is absolutely no way a ref or any spectator can tell for certain that a minibot has put enough pressure on the plate, not hit a bolt and reliably triggered the top. The field crew will be able to test & determine if the tower sensors are working, and if a sensor breaks, I am certain they will fix it.
Ken's point is a very valid one. Does anyone have any video of Minibots hitting the top target but not triggering the target during week 2? Right now we're just dealing in speculation which isn't leading to anything productive. From what I saw in Pittsburgh, the large majority of minibots were in fact triggering the top target. If this wasn't the case at a regional you were attending, let's try and figure out what the issue was that was causing these false negatives.
If the issue is that teams aren't contacting the top target for long enough, I'm more concerned as nowhere in any official specification or guideline have I seen a duration of impact clause.
EXACTLY... I have yet to see a single video that convinces me otherwise. Everyone can do all the math they want, but without factoring in things like when does your robot reverse direction, what is its deceleration,etc, its impossible for me to conclude that the towers aren't working.
And I agree with everyone saying there is too much speculation in here... has anyone actually gone into the Q&A and asked the question? Asked what the sensor is? what the duration is? Your team leader has access to the Q&A forums... USE THEM.
martin417
16-03-2011, 14:16
I beg to differ... the peg heights are in GE1100-1106 and are referenced on page 3/10 of the 2011 FRC Game Manual, Section 2 - The Arena. Yes they could have been better spelled out. In the "real" engineering world, engineers reference other documents all the time, rather than copy/pasting specs into every document they make because it reduces the risk of forgetting to update documents when a change is made. GE-11036 tells you exactly how to build a sensor plate, yet how many teams actually did it?
You missed my point entirely. Squirrel was making the point that the 4N number was not in the rules (one of those things with the <Gxxx>), but in the arena drawings. My point was that the arena drawings ARE part of the specs and are just as important as the rules (<Gxxx> again).
Also, even if a team built the sensor plate, it is apparent that that is not enough. You have to know how that switch trigger will be detected. What algorithm is used to reject pole strikes by robots? how long does the switch have to be depressed? etc.
Kims Robot
16-03-2011, 14:21
Also, even if a team built the sensor plate, it is apparent that that is not enough. You have to know how that switch trigger will be detected. What algorithm is used to reject pole strikes by robots? how long does the switch have to be depressed? etc.
Ask in the Q&A.
Sorry if I misread your original post... I'm a little annoyed that everyone is blaming FIRST for this, when they are clearly trying to make an improvement over week 1, and no one can move that a minibot that should have triggered the pole didn't.
There was a question in the Q&A asking if the bot had to stay up for any period of time.
The response was that it just had to trigger the plate.
As far as padding goes, we tried this in week 1 with 1/2" of "grip-pad" and electrical tape formed into a cushion. This did not improve the reliability of triggering in week 1 at all.
I measured the force our light switch requires to activate. It was 5-6 newtons. 25-50% above the upper limit of the specification (2-4N). The minibot itself struck the top-plate of the practice pole (wood plate) violently enough that the 10' steel pole actually jumped about 1/8". This would make sense if you do the physics of a 1.25 kg object traveling at about 2 m/s (some minibots are even faster than this) being stopped in less than 7mm of travel. It is a pretty violent impact. If the impact absorbed perfectly, I would expect a If you do the math on this, you would expect 7ms impact with a peak force around 30-40N.
Of course, this was week 1. I did hear that week 2 was improved immensely.
Assuming an elastic collision, this could have a dwell under 14ms. If 75ms is required, a flexible member requiring about 4N to flex it, and around 2-3 inches of compression just might work. Shorter if you are slower, longer if you are faster. For you guys going 3 m/s... Good luck. Hope to be joining you soon.
I haven't been to a competition yet, so i don't know, but are they letting you test your mini bot on the field before hand? Just to make sure it works. As far as the bolts go, if i was a ref i would put some chalk or something on the bolt heads. Something that would leave a mark. Or, before the comp the bots get checked to see if they can contact the bolt. Maybe a green mark on bot that can't touch bolt and a red mark if it can. This would end a part of the problem or questions that might arise.
Ken Streeter
16-03-2011, 15:16
What bothers me is that there seemed to be some kind of a specification regarding force and now that specification seems less important than the time it takes to trigger the target.
Before I say anything else, let me start with a few caveats:
Our team (1519) was at a week zero (pre-ship) scrimmage (Nashua, NH) with the official field, and a week one tournament (NH).
At week zero, we had a minibot of around 3.5 pounds and 3-4 seconds.
At week one, we had a minibot of around 2.3 pounds and <2 seconds.
We did not compete at week two, so I don't have first-hand experience as to whether or not the field changes helped fix the problems.
At week zero, there were lots and lots of "false positives" occurring on the minibot towers from robots bumping into the base of the towers. My understanding is that this was due to very sensitive limit switches combined with an FMS sampling time of 20ms where only one sample was required to report a trigger. However, I don't recall any "false negatives" where a minibot climbed the pole, but didn't result in a successful trigger. Then again, I think there were only a couple minibots being successfully deployed at the scrimmage and these were still > 3 seconds in climb time.
At week one, in order to remedy the problem with false positives, the FMS software was changed (at least at GSR) so that a "trigger" would only occur when 8 consecutive positive samples were detected, with the samples still occuring at a 20ms rate. This FMS change effectively required minibots to hold at least one of the trigger limit switches closed for approximately 150ms. This change eliminated false positives from robots bumping into the base of the towers, and worked fine for slow minibots, but fast minibots were then having trouble hitting the trigger for LONG enough. On Thursday, our minibot was one of the ones which was regularly smashing into the top of the tower (with plenty of Newtons) but which was also not holding the switches closed long enough to result in a "trigger." Team 40 had a similarly quick minibot and was seeing the same problem.
We started adding a mechanical "impact absorber" to the top of our minibot in order to have it remain in contact with the switch plate a little longer, but this had two problems -- it didn't always extend the contact long enough, and sometimes failed to activate our off switch.
In the last match on Friday (a replay of Match 11), we unintentionally found a sure-fire solution to the problem of not contacting the tower for long enough (simply leave the motors on) as shown in the photo below:
http://www.chiefdelphi.com/media/img/046/046d46a28eed8b3651805057241d4bb9_m.jpg
(Separate photo discussion thread at http://www.chiefdelphi.com/forums/showthread.php?t=93430 )
However, our team budget isn't sufficient to afford cooking thermal protection wires and motors in every match, so we needed to come up with a different solution! We ended up increasing the reliability of our off-switch a little, but were still at the edge of triggering / not-triggering the FMS limit switches for long enough. Some matches it would work, and others it would not. I can only presume our contact time was very close to the required threshold.
In Week Two, it's widely known that FIRST made mechanical changes to the trigger assemblies. I'm curious as to whether or not they also changed the needed "contact time". (Maybe to the 75ms described earlier in this thread?) I do think that once a "contact time" is determined by FIRST, it would be helpful to release the information to teams.
That said, I'm still concerned that really fast minibots may not hold the trigger plate up for long enough to result in a positive trigger. It sounds to me that everything worked great at some regionals (Kettering and Pittsburgh have reported that) while other regionals may not have had as much success (San Diego?) This sounds to me that the problem may not yet be completely solved.
I'm curious to see what happens in Week Three regionals and hope that FIRST and teams continue to get this worked out. 1519 doesn't compete again until week Five.
I do know that with ever-faster minibots and deployment systems, anything other than automated scoring (except maybe official video replay) will have a hard time distinguishing between four minibots that all hit the top of the tower with between 9 and 8 seconds remaining in the match! At the Week One Granite State Regional, Finals-2 was determined by the minibot race, (see http://www.chiefdelphi.com/forums/showthread.php?t=93314 ) where all 4 minibots hit the top with between 8 and 6 seconds remaining on the clock. Not all of the minibots activated the trigger. The referees manually made the correct on-field call, but there was a fair bit of debate about whether or not they had. Counting on the referees to always be the adjudicators puts them in a really tough spot, so I hope that the automatic triggering system can be made to work reliably without having to pose major additional constraints on teams (such as requiring them to hold the trigger plate up for a long time.)
However, since there presumably is some sort of "contact time" required to have a successful trigger recorded, it is very important (as Brandon mentions) to have teams know what that time is in order to be able to adapt their minibots to satisfy the requirement.
sanddrag
16-03-2011, 15:40
I think we can agree that the teams responsibility is to trigger the target, what we need is some direction from FIRST on what exactly that entails (your Q&A suggestion is a good one).
At week one, in order to remedy the problem with false positives, the FMS software was changed (at least at GSR) so that a "trigger" would only occur when 8 consecutive positive samples were detected, with the samples still occuring at a 20ms rate. This FMS change effectively required minibots to hold at least one of the trigger limit switches closed for approximately 150ms. This change eliminated false positives from robots bumping into the base of the towers, and worked fine for slow minibots, but fast minibots were then having trouble hitting the trigger for LONG enough. On Thursday, our minibot was one of the ones which was regularly smashing into the top of the tower (with plenty of Newtons) but which was also not holding the switches closed long enough to result in a "trigger." Team 40 had a similarly quick minibot and was seeing the same problem.
This is the problem exactly. An engineering specification of what constitutes the act of TRIGGERing the tower has not been provided beyond that it takes 2-4 Newtons of force, and unspecified magic happens in the FMS to determine if it is TRIGGERed.
To the best of my knowledge, the manual or arena did not provide any specifcation as to how the tower switches are being sampled, or what they're connected to. I think it's fair enough to say we don't care about the speed of the electrons in the wires, but beyond that, whatever is happening post-switches could make a difference in the design, or in who wins.
For this sort of thing, 20ms is a ridiculously long sample time, and to require 8 consecutive samples at that slow of a rate is just absurd. If that's what it takes to prevent hostbot shakes from triggering it, it needs a redesign. Did FIRST seriously not think teams would build minibots that would bounce off the top in less than 1/10 second?
It was never specified for what duration the force must be applied.
I'd like to see a specification that says something like:
The TOWER is considered TRIGGERed when the switches, connected through _________ to a ________ controller, running code available for download from _____, cause the ____ variable to become true.
Jared Russell
16-03-2011, 16:35
In Florida, it appeared the vast majority of races resulted in the towers triggering properly, whether the minibot was slow or fast (and Florida had several sub-1.5 second minibots).
However, I do remember a couple of specific instances where the tower was not triggered for one reason or another (but not the teams involved - all I know is it wasn't us!).
Regarding "the bolts"....it seems that they should have been fixed to the lower plate, and moving through the upper plate, so that they move with the lower plate no matter where it is contacted, rather than being fixed to the top plate and protruding through the bottom plate, so that they create 4 areas which block the minibot from triggering. From my understanding of the drawings, this would be an easy change to make.
At Lake Superior, one of the FTAA thought of this solution as well. However, it was not implemented because it adds to the weight needed to push the plate up. I believe it was Bill Miller himself who said the FIRST folks thought of your idea, but realized the issue.
For the record, with the exception of issues across the entire field in the second finals match, I did not know of any issues with the towers at Lake Superior with the exception for one team that initially was hitting the bolt heads (they made a tiny modification to fix the issue). That said, the minibots were used by under half of the teams.
Lil' Lavery
16-03-2011, 17:16
I put more credence with those who read the rules and understand what the rules require the TEAMS to do.
There is no "should have TRIGGERED the TARGET" in the rules. You do it, you get credit. You don't do it, you don't get credit for it.
Part of the design challenge is to make sure your MINIBOT TRIGGERS the TOWER. Some TEAMS seem to have missed that. Apparently they thought the challenge was to get a minibot up the TOWER as quickly as possible.
By this logic, should the "false positives" from week 0 and thursday/friday in week 1 have counted so long as they occured in the last 10 seconds of a match? Should slamming your minibot into the tower hard enough to trigger the target count as winning the minibot race, even if your minibot never even leaves the hostbot?
MagiChau
16-03-2011, 17:18
By this logic, should the "false positives" from week 0 and thursday/friday in week 1 have counted so long as they occured in the last 10 seconds of a match? Should slamming your minibot into the tower hard enough to trigger the target count as winning the minibot race, even if your minibot never even leaves the hostbot?
Trigger is listed as the plate being pushed.
TRIGGERED – the act of pushing the bottom disk of the TARGET so that the sensors are tripped and a
signal is sent to the Field Management System (FMS). When a TARGET is TRIGGERED, the
MINIBOT RACE on that TOWER is complete.
Mike Copioli
16-03-2011, 17:47
Trigger is listed as the plate being pushed.
TRIGGERED – the act of pushing the bottom disk of the TARGET so that the sensors are tripped and a
signal is sent to the Field Management System (FMS). When a TARGET is TRIGGERED, the
MINIBOT RACE on that TOWER is complete.
So........... were does it state HOW the plate must be pushed? To Seans point, stating that it merely needs to be triggered is ignoring the intent of the rule....To determine the WINNER, AND THE SUCCESSIVE PLACES, of the minibot race.
MagiChau
16-03-2011, 18:10
So........... were does it state HOW the plate must be pushed? To Seans point, stating that it merely needs to be triggered is ignoring the intent of the rule....To determine the WINNER, AND THE SUCCESSIVE PLACES, of the minibot race.
Found the rule G46 the minibot may only be used to climb the pole.
<G46> MINIBOTS may only be used to climb the TOWER.
Violation: PENALTY plus YELLOW CARD
Regarding "the bolts"....it seems that they should have been fixed to the lower plate, and moving through the upper plate, so that they move with the lower plate no matter where it is contacted, rather than being fixed to the top plate and protruding through the bottom plate, so that they create 4 areas which block the minibot from triggering. From my understanding of the drawings, this would be an easy change to make.
This change would probably have unintended consequences. The bottom plate would likely be more susceptible to jamming. The slightest tilt could bind the threaded bolts in the holes in the upper plate.
jvriezen
16-03-2011, 18:18
In retrospect, I think a better trigger design would have been to have a stationary aluminum lower target plate, insulated from the pipe, and specify that TRIGGERING requires completing a circuit by connecting the pole to the plate with some electrical conducting material in your MINIBOT. Nothing would need to move, you just have to electrically connect the two. This would have the downside of sidestepping the engineering tradeoffs surrounding speed and weight and time to reverse power, making it a simpler (but more well defined) challenge.
John
FRC Team 2530 "Inconceivable"
Mentor, Inspector, Drive coach
Chris is me
16-03-2011, 18:19
Ken's point is a very valid one. Does anyone have any video of Minibots hitting the top target but not triggering the target during week 2? Right now we're just dealing in speculation which isn't leading to anything productive. From what I saw in Pittsburgh, the large majority of minibots were in fact triggering the top target. If this wasn't the case at a regional you were attending, let's try and figure out what the issue was that was causing these false negatives.
358 didn't trigger their pole at WPI despite clearly causing the polycarbonate to deflect. I will try and get our video.
Other than them, few had any problems at WPI
Tristan Lall
16-03-2011, 18:28
With respect to the act of triggering, here are some cases based on the way the rule is constructed in the manual:
Hit the tower base, tripping the switch: false positive
Push on the plate, tripping the switch and causing FMS to register it: true positive1
Push on the plate, tripping the switch only momentarily (but long enough to send a signal), and the FMS misses or ignores it: false negative2
Push on the plate, tripping the switch and causing FMS to receive the signal, but a bug prevents the FMS from registering it: false negative3
Push on the plate with 100 N, bending it visibly, causing the tower to sway, emitting magic smoke, but failing to trip the switch: true negative4
Minibot reaches the height of the plate, but FMS doesn't register it, so referee grants it: educated guess (could be either true positive of false positive, but the ref didn't have anything to do with that fact)
Some of these are quite perverse. I've left out field faults, but in some of the above situations, they're an additional complication that can perhaps restore some equity, if identified properly. (If replaying the match suits you.) I've also left out GDC intent—because although the high-level intent is clear, they have offered no substantial guidance about the actual sequence of events they had in mind for triggering the tower.
If you think this is crazy, don't blame me. I didn't design the game that way.
1 Which won't count toward the race if it wasn't the minibot doing the pressing!
2 The rules have no provision for a minimum duration. If the switch is tripped, an ideal system would not wait.
3 It's basically impossible to identify this false negative if the FMS doesn't throw an error code or something.
4 The force isn't part of the determination of triggering. And since sending the FMS a signal is an integral part of the act of triggering, if the sensor doesn't work right, you didn't trigger it. Doesn't that suck?
Mike Copioli
16-03-2011, 19:36
=MagiChau;1040834]Found the rule G46 the minibot may only be used to climb the pole.
You missed the point.
Besides this states nothing about HOW the PLATE gets pushed only about what may climb the pole. There are many forces that can 'PUSH' the plate without actually climbing the pole or even contacting the plate at all.
In case you have not figured out my point, I will clarify: To differentiate between TRIGGERING first and WINNING the race is lawyering the rules as the obvious intent is to determine who is first, second, third and fourth and assign a point value to represent each place.
If we lose a match because the other alliance scored more points than us. I can accept that and applaud the victors.
If we lose a match because our alliance partner goes into the opposing alliances scoring zone contacting a robot incurring a red card. I can accept that and commend the refs for making the correct call.
But if we lose a match because the field did not operate as intended or described in the user manual as interpreted by the TEAMS, FIRSTs customers, using a minibot that was built to operate under said parameters....This I cannot accept and will not accept and will result in a student standing in the little ? box at the end of the match every time it happens.
If TRIGGERING requires some amount of debounce time to register, or something greater than 4 Newtons, or Coke turning into Pepsi, this should be CLEARLY published in one of the many user manuals put out by FIRST.
MagiChau
16-03-2011, 19:51
Only the minibot is allowed to trigger the plate and be awraded points and the minibot is only allowed to climb the pole so only the minibot is allowed to climb the pole to trigger the plate and scores points according to the race's results. Is this not the intent of the rule and the wording of it? Why can a flawed field not be accepted as possibly existing? Week one after all usually has delays from fixing some electronic errors. I, myself, got frustrated in week 1 trying to fix why the robot sat still for 2 qualification matches when the drive-team reports they have communication, we already tested in the pits, and it was working earlier.
Humans only have so much insight before forgetting something. The GDC might have thought saying 4N of force acting on the trigger plate was enough but apparently it did not happen so. I cannot say anything on what they should have or should not done.
...bind on the pole like I've seen the plate do.
Using the nominal dimensions on the field drawings for the pole OD, the threaded bolts, and the hole diameters and location in the polycarbonate plate, plus the apparent location of the sensors, it appears that if the plate is lifted off-center so that it pivots on the bolts it will reach an interference condition with the bolt threads and the pole before it travels 1/4" at the switch. FWIW.
Grim Tuesday
16-03-2011, 20:45
Simple solution: Use camera backup, officaly fed into the field system, and read post match by a scoring personel. You could set cameras up on top of the alliance station walls, or pretty much anywhere as long as they have a clear field of view.
boomergeek
16-03-2011, 20:55
At week 1, with one sample, "force of 2-4N" was a complete rule.
If an X sampling time requirement is added to a trigger event and not reflected in a rule update: then FIRST is not being completely open and honest.
Some teams will end up with more access to more information than other teams.
I didn't know sampling was added. All that was officially reported was it was being fixed to prevent false triggers from robot collisions.
Some teams found out some of the sampling changes- was any of the that information given outside the Q&A?
(I could not find any discussion of sampling on FIRST Q&A)
[EDIT] Originally referenced a post later removed by author later, so I wont quote that, but I still think a post about attitude is generally relevant, so I will leave the rest even though it is now somewhat out of context.
I understand the frustration of losing a match because of something that you think is out of your control. Back when I was driving in HS, I felt the same way. As a volunteer, I can tell you it gets pretty old pretty fast to have teams getting in your face and giving you an attitude about these types of issues. I know it sucks to lose matches, but please remember the greater purpose we are here for and how negative attitudes affect that.
So even if you can prove that something unfair happened, please lets all keep a calm and professional composure and remember our true greater purpose here. Let's debate issues, but in a civil and professional manner. I am not saying that this conversation has turned into this, but what type of example is being set for the students if after a match the minibot doesn't trigger and you start complaining about FIRST and the field staff to your students.
Schnabel
16-03-2011, 21:00
The triggers are designed with multiple sensors, and the FMS only looks for 1 of those to be triggered for any amount of time. Thus making the minimal amount of force still trip the tower. The towers have been tested and proved to be much more accurate since week 1, so I think this should be a non-issue now at week 3.
NO IT DOES NOT. From looking at the way that these are designed at the Kettering District, there are 3 trigger switches, they are connected in series!
Graphical Representation:
___________ (Power in)
.................|
................[ ] (Sensor 1)
.................|
................[ ] (Sensor 2)
.................|
................[ ] (Sensor 3)
.................|
__________| (Reading out)
This means that all three switches must activate in order to trigger the tower. What I noticed with most of the fast minibots is that they actually hit the plate so hard that it wouldn't go up horizontally, thus not triggering all three sensors. We did have one minibot that I loved that was the slowest one there (wish I knew what team it was), BUT because it took more time to make it to the top it triggered the tower every time. Just for reference it came down as soon as it hit, just it did both in a slower manner than say 33's or 51's which were super fast.
Also another note for the fast minibots. When you go up so fast that you hit the plat and skew it from horizontal you actually bind it against the threads of the bolts holding it together. This means the plate won't move past a certain point, which just may be before the trigger point.
NO IT DOES NOT. From looking at the way that these are designed at the Kettering District, there are 3 trigger switches, they are connected in series!
They look like they are in series, but I believe they act in parallel. Check out attachment. I helped make the tower mods and this is how I remember it working.
If any of the contacts are closed, the whole switch is closed.
Please correct if wrong.
Vikesrock
16-03-2011, 21:09
NO IT DOES NOT. From looking at the way that these are designed at the Kettering District, there are 3 trigger switches, they are connected in series!
Two things here:
1. The GDC has said in the Q&A that only one switch needed to be triggered. If they were wired in series they must have been wired normally closed.
2. This is somewhat irrelevant as the microswitches were replaced in the Week 2 retrofit kit for the towers.
Using the nominal dimensions on the field drawings for the pole OD, the threaded bolts, and the hole diameters and location in the polycarbonate plate, plus the apparent location of the sensors, it appears that if the plate is lifted off-center so that it pivots on the bolts it will reach an interference condition with the bolt threads and the pole before it travels 1/4" at the switch. FWIW.
So...impacts within 2" of the pole (which is where every one of the "fast" minibots that occasionally didn't trigger hit) are less likely to lift the plate in an exaggerated off-centered manner right? This suggests an off-centered lift isn't the culprit in those cases in my mind.
It would be great if the trigger design itself provided whatever dwell was necessary for the system sample rate to detect, was not sensitive to bumping the tower, did not matter where it was contacted, did not have any bolts or obstructions that kept it from working every time, and required only the specified force with no other mystery requirements.
Such as:
So...impacts within 2" of the pole (which is where every one of the "fast" minibots that occasionally didn't trigger hit) are less likely to lift the plate in an exaggerated off-centered manner right? This suggests an off-centered lift isn't the culprit in those cases in my mind.
I don't follow your logic.
Mike Copioli
16-03-2011, 21:46
So even if you can prove that something unfair happened, please lets all keep a calm and professional composure and remember our true greater purpose here.
I am well aware of the greater purpose here....are you? It's to inspire. It is not inspiring to work as part of a team, to inspire others to strive for excellence and success only to have that under minded by a poorly documented field condition that changes the outcome. As far as unprofessional and uncalm at what point did you think my post was any of those things?
You may want to consider these points before you appoint yourself mediator in a battle that has not even happened yet.
I am not saying that this conversation has turned into this.
Then what are you saying?
I'll tell you what, when and if it happens to your team you can pretend it did not affect the outcome and then later face the disappointing faces your student members who worked so hard on solving a problem only to have the question change after answering it correctly. Oh if first can't find 4 dudes with a button I know three that would be happy to help with this problem.
As far as unprofessional and uncalm at what point did you think my post was any of those things?
The simple answer is: at no point. :P
I wasn't referencing your post. It was a different one where the author deleted after reconsidering its GPness. Without that post for context, I think mine seems overdramatic.
The intention of the post was not really meant to chastise a single individual or set of individuals, but to remove some of the tension in the air, which seemed to be coming up after the now deleted post. So if it came off that way, I apologize, like I said, wasn't the intent.
I don't follow your logic.
Given the amount of play/spacing between the floating plate and the bolts as well as the pole itself as you referenced, wouldn't a push on one side far out at the perimeter cause more of a "tilting" effect than a push near the center of the plate?
Matt Krass
16-03-2011, 22:16
I for one am on the bandwagon of wanting a final official specification from FIRST. I want to know exactly the force I'm expected to exert, for exactly how long, and exactly how clean the signal needs to be. I want to know what kind of sample rates, sensor wiring, and hysteresis is in place here. FIRST owes us that.
Before anyone jumps on me for blaming FIRST, I want to make it clear that I'm not mad at them. They gave us a very vague specification, we designed to it, we did our best, and it appears we have fallen short.
FIRST also designed to it, they designed a system to react to that vague specification, it seems they also have fallen short. They're now taking steps, within reasonable bounds, to correct that. I agree it's not wonderful, and it is unfortunate that teams in prior events are not going to benefit from this system, but I think we can all agree we'd rather improve it, then have everyone suffer in the name of fairness, especially on a playing field that will never be entirely level anyway.
Also, I agree with the people here that are concerned the system still isn't reliable, my inner engineers hunch is telling me it's not going to work as well as they want, and I don't agree with their approach of "We fixed it, trust us, and deal with it.".
But wait! I hold the teams responsible as well! We were given a vague specification, and everyone made their own interpretation of it, and many of us were wrong, and this is our mistake. Questions should have been asked weeks ago, more research done by teams, we all dropped the ball. I'm not saying people should assume failure, or injustice, but just one team asking FIRST for more information could have made a world of difference.
As I said before, I'm glad FIRST is stepping up and trying to fix their foul-up, now it's our turn to return that professionalism, ask questions and see what we have to work with, and do our best to meet the most accurate specification we can wrangle out of them.
Matt
I know this has been suggested already, but I think the right place to pose questions is directly to the Q&A:
http://forums.usfirst.org/forumdisplay.php?f=1465
You need to have the team leader account to post there, but I am sure that FIRST will be more than receptive to answer all the questions posed here. If people do get an answer to some of the common questions, can they please post them here as well?
The main questions that seem to need answering is:
How long must the contacts be connected for FMS to trigger / what other technical constraints of the triggering system should be kept in mind by the teams?
I do not have an account for this, otherwise I would pose the question myself. I do think teams have full right to ask these questions though.
Chris Hibner
16-03-2011, 22:33
Also another note for the fast minibots. When you go up so fast that you hit the plat and skew it from horizontal you actually bind it against the threads of the bolts holding it together. This means the plate won't move past a certain point, which just may be before the trigger point.
Thank you Eric, and Ether for your analysis. I was starting to doubt my eyes and memory. I remember when the refs tested the plate with a stick at Kettering, the first couple of pushes bound the plate.
As one of the teams with the light, fast, tiny minibots, here's hoping the new solution works.
Given the amount of play/spacing between the floating plate and the bolts as well as the pole itself as you referenced, wouldn't a push on one side far out at the perimeter cause more of a "tilting" effect than a push near the center of the plate?
All else being equal it would seem reasonable to suppose that. But there are other dynamic factors at play whose effect on jamming due to tilting is difficult to quantify.
..... Questions should have been asked weeks ago, more research done by teams, we all dropped the ball.......
Questions were asked. Here's one:http://forums.usfirst.org/showthread.php?t=16174
The answers were vague. We didn't drop the ball. We built a pole, with lexan plates, three limit switches & timer. Worked 100% with our minibot during development.
At NY, our minibot triggered the pole most of the time, pole didn't trigger once, but it was counted. I can only hope they are all counted at our next competition in DC.
If a time specification has been introduced, that has changed the specs and the game. We expected and designed to "Only one limit switch needs to be actuated" as per the Q&A Jan 16th.
I have submitted the following question to the FIRST Forum Q&A:
"With any electro-mechanical contact closure that is sensed by a programmable control system, there is both a force component required to perform the closure, and a time/dwell component for the control system to register the closure. The Competition Manual provided the force component necessary to activate the minibot trigger contacts, but did not provide the time/dwell required for this contact to register with the FMS. What is the minimum length of time that the specified force (2N-4N) must be applied to the trigger plate in order to be recorded/registered by the FMS?"
Just for fun (for those who are so inclined):
A 3 pound minibot is traveling up a pole at 7 feet per second.
It is depowered and a downward force of 4 Newtons (plus gravity) is immediately applied to it.
1) Assuming no friction, how far will the robot continue to rise until it reverses direction?
2) Instead of 4 Newtons, how much (constant) force would need to be applied to limit the rise to 1/4" ?
Note: The purpose of this exercise is to show that the force exerted on such a minibot by the plate assembly (and thus the force exerted by the minibot on the plate assembly) far exceeds 4 Newtons.
MrForbes
16-03-2011, 23:53
It looks like we're making progress on figuring this out.
Just for fun (for those who are so inclined):
A 3 pound minibot is traveling up a pole at 7 feet per second.
It is depowered and a downward force of 4 Newtons (plus gravity) is immediately applied to it.
1) Assuming no friction, how far will the robot continue to rise until it reverses direction?
2) Instead of 4 Newtons, how much (constant) force would need to be applied to limit the rise to 1/4" ?
Note: The purpose of this exercise is to show that the force exerted on such a minibot by the plate assembly (and thus the force exerted by the minibot on the plate assembly) far exceeds 4 Newtons.
1. 0.586 ft.
2. 474 N
1. 0.586 ft.
2. 474 N
Yup.
Yup.
WooHooo! I've still got it!
Chexposito
17-03-2011, 00:58
to trip it, you have to be traveling ~.39 meters per second or ~1.28 fps for a 1 kilogram minibot using EBE assuming no friction, the minibot is not back driving, there is no rotational inertia, and pretty much everything else.
pretty much if you're not going that fast you are not winning anyways (~15 sec with more rounding and constant acceleration)
to trip it, you have to be traveling ~.39 meters per second or ~1.28 fps for a 1 kilogram minibot
I doubt you would ever successfully trigger the switch with those numbers.
Please explain your reasoning and show your calculation.
I'm not so sure it's that simple Ether. Such a simple model isn't explaining what's being seen on the field. Additionally, why a 1/4" stop? Why not 3/4", which may be just as valid a distance that prevents the sensors from triggering (I'm assuming the plates are ~1" apart, which may be wrong since I still haven't examined the field drawings).
Additionally, how does your model take into account any mechanical (dis)advantage that plate exerts due to binding on the bolts opposite the minibot's impact point?
wireties
17-03-2011, 08:39
I am well aware of the greater purpose here....are you? It's to inspire. It is not inspiring to work as part of a team, to inspire others to strive for excellence and success only to have that under minded by a poorly documented field condition that changes the outcome.
I hope this all gets resolved in a way that satisfies everyone. BUT this is a good life lesson for aspiring engineers. We have to respond to technical specifications all the time that are vague (where our potential customer knows much less about the problem/solution domain than we do). On some level, it is our responsibility to request clarification BEFORE designing/building a solution.
And BTW Linux == Embedded, my company has put it on several satellites and on some tiny tiny platforms. Linux does soft real-time quite well these days and is closing in on hard real-time performance.
HTH
Ian Curtis
17-03-2011, 08:45
I'm not so sure it's that simple Ether. Such a simple model isn't explaining what's being seen on the field. Additionally, why a 1/4" stop? Why not 3/4", which may be just as valid a distance that prevents the sensors from triggering (I'm assuming the plates are ~1" apart, which may be wrong since I still haven't examined the field drawings).
Additionally, how does your model take into account any mechanical (dis)advantage that plate exerts due to binding on the bolts opposite the minibot's impact point?
I think the point is that that is a lot of force. If it really requires 2-4 newtons to trigger the plate, 474 newtons should definitely trigger the plate. It obviously does not always do this, so there are other issues at play like you said.
474 newtons is the equivalent force of an FLLer (~100 pounds) standing on the plate.
Paul Copioli
17-03-2011, 08:48
474 newtons is the equivalent force of an FLLer (~100 pounds) standing on the plate.
... or Karthik.
Sorry, I couldn't resist.
I'm not so sure it's that simple Ether. Such a simple model isn't explaining what's being seen on the field.
It was never intended to model or explain what's being seen on the field. Please re-read the disclaimer at the bottom of my original post. All it shows it that minibots which DO successfully trigger the tower are exerting way more than 4 Newtons.
Additionally, why a 1/4" stop? Why not 3/4", which may be just as valid a distance that prevents the sensors from triggering (I'm assuming the plates are ~1" apart, which may be wrong since I still haven't examined the field drawings).
AFAIK, we have no official drawing or specification of the switch mechanism, but colt527 provided a sketch as an attachment to this post (http://www.chiefdelphi.com/forums/showpost.php?p=1040602&postcount=69) which shows 1/4" travel required to trip the switch.
Additionally, how does your model take into account any mechanical (dis)advantage that plate exerts due to binding on the bolts opposite the minibot's impact point?
It doesn't, and wasn't intended to.
I think the point is that that is a lot of force. If it really requires 2-4 newtons to trigger the plate, 474 newtons should definitely trigger the plate. It obviously does not always do this, so there are other issues at play
Precisely. I couldn't have said it better myself. In fact, I didn't :-)
wireties
17-03-2011, 09:10
Or FIRST should fix their system. Why should the customer fix a part that came to them out of spec? We are paying for something and if FIRST doesn't deliver the onus should be on them to fix the problem, not on us to work around their broken implementation.
The teams, of course, pay FIRST to compete. In that sense the teams are customers. But FIRST is largely a set of volunteers, at least the staff at the regional events. If we think of this game as a simulated engineering exercise, FIRST is actually the customer (having provided a specification).
Our team, like most, did not query the "customer" about a vague requirement. This is totally "our bad" though one hopes FIRST does not intentionally put out vague specs. Our first heavy-ish 4 second minibot triggered the sensors every time in week 1 at The Alamo but our evolving optimized minibot design is now gonna be a little stronger and stay in contact with the plate a little longer than originally designed.
Chris is me
17-03-2011, 09:13
I think Cory's point is that FIRST shouldn't be let "off the hook" every time they do something at the expense of teams just because it's a volunteer organization. We do still pay to compete, after all.
It was never intended to model or explain what's being seen on the field. Please re-read the disclaimer at the bottom of my original post. All it shows it that minibots which DO successfully trigger the tower are exerting way more than 4 Newtons.
Sorry to be pedantic, but...
You're basically saying that it's OK to imply an assumption for the calculation and then ignore the assumption for the conclusions of overall system characterization. You did this with your Mecanum analysis a few months ago as well.
I think Cory's point is that FIRST shouldn't be let "off the hook" every time they do something at the expense of teams just because it's a volunteer organization. We do still pay to compete, after all.
Which would probably be a great broad stroke to paint, yet the whiners haven't proposed a solution. The fact of the matter is, Physics beat the crap out of FIRST's system during Week 0 and Week 1 by exposing a severe flaw. Why are we complaining that FIRST had to adapt to it? Why should they put out a specific spec in the form of a rule that teams WILL simply complain about regardless? The referees already made concessions to manually score the towers even though it wasn't in the rules.
Honestly, the only concession FIRST can make at this point is to give us dedicated MINIBOT time on Thursday. 4 teams at a time can have their MINIBOTs climb, uninhibited, yet with the real field's triggering/scoring system. If it's dedicated minibot time, then every team should be able to test their ascent and triggering 4-5 times in an hour or two.
wireties
17-03-2011, 09:33
As an engineer, I work to engineering specs. If I meet those specs, I expect to be paid. You can imagine that I might be a wee bit upset if I were to design a product that meets the customer's specs, deliver that product, and be told "I'm not paying you because the product didn't do what I expected it to do". If your specs are not written clearly enough, that is your fault, not mine.
This is a good lesson for the students and for mentors that do not typically address similar challenges at work. Think more like an engineer that owns the company or an engineer helping to form a response to a proposal. Taking a risk (being able to satisfy) a vague requirement from a customer is NOT a good idea. You very well might not get paid and it does not matter if one is correct or not. In this case, the customer (FIRST) supplied a vague spec but did provide a compliance test.
If the specs are not written clearly, it is ALSO our responsibility to request clarification or we risk NOT getting paid (or tripping the sensor).
Chris is me
17-03-2011, 09:41
yet the whiners haven't proposed a solution.
Proximity sensors and light sensors are two common proposed solutions.
Personally, I don't see what's wrong with a photo finish here. Yes, "instant replay" is a dirty word, but it would clearly be the best.
You're basically saying that it's OK to imply an assumption for the calculation and then ignore the assumption for the conclusions of overall system characterization.
Could you be a bit more specific? What "implied assumption" are you referring to?
The only assumptions used in the calculation were to ignore friction (which was explicit, not implied) and to ignore additional stored kinetic energy (rotational). These tend to cancel each other out. Over very short distances (such as 1/4"), the stored rotational KE easily overcomes friction, so it's actually a conservative assumption. You can demonstrate this for yourself, if you like: with the wheels raised, power your minibot with 12V and then remove the power. Observe how much the wheels turn after the power is removed.
If you have questions about the mecanum analysis I would be glad to discuss those, but not in this thread.
Proximity sensors and light sensors are two common proposed solutions.
Personally, I don't see what's wrong with a photo finish here. Yes, "instant replay" is a dirty word, but it would clearly be the best.
1.) Proximity sensors may work, yet are subject to calibration and vibration for a single data point. If you're using the difference of two data points, you still have to either increase sampling rate or # of sample to prevent false positives. Thus, changing to proximity sensors could pose the same issues/risks of the current system, which means there's no reason to change to proximity sensors.
2.) Light sensors are subject to noise and calibration. These may work better than proximity sensors since the noise is most likely easy to isolate, yet the tolerances in spacing would have to be tight to ensure even the slightest movement of the plate triggers the sensor. The designers simply may not have the time to implement something so quickly across all of the regional events for this week or even next week. This one seems the most feasible to me from a technical perspective though.
3.) Any instant replay sets a dangerous precedent. There will always be those who make assumptions based upon what's happened before, regardless of what's stated in the manual and regardless of what's talked about at driver meetings. I think FIRST just doesn't want to go there unless there's more thought put into it. That desire is reasonable in the longer term just to simply avoid stress during competition. Yet assuming a photo finish for 1 specific aspect of every game could probably also open up the types of activities we'd perform in future games. So I'm with you on this one ... subject to that caveat.
Could you be a bit more specific? What "implied assumption" are you referring to?
The only assumptions used in the calculation were to ignore friction (which was explicit, not implied) and to ignore additional stored kinetic energy (rotational). These tend to cancel each other out. Over very short distances (such as 1/4"), the stored rotational KE easily overcomes friction, so it's actually a conservative assumption. You can demonstrate this for yourself, if you like: with the wheels raised, power your minibot with 12V and then remove the power. Observe how much the wheels turn after the power is removed.
Alright, I did say implied and you were explicit about the friction. Yet it was still ignored in the conclusion without any explanation in the original posts. Ok, so there's the explanation, which I still don't think allows for a valid conclusion based upon the calculation. Your latest statement makes the implied assumption that the unloaded motors act identical to the real system during impact. Impact forces induce shock into the gearing which momentarily increases the friction in the gearing/bushings with a positive correlation to the amount of force applied to the plate. Impact forces induce friction in the bolts on the triggering mechanism, which may be bind on the plate if the impact causes a torque moement. Thus it may take 474 newtons at a specific instance in time to slow a minibot down without taking friction into account -- yet until we characterize the friction in the system we're making a dangerous* conclusion that "more than enough force is applied to moving the plate".
*dangerous because the process of coming to the conclusions would then be acceptable to use elsewhere.
I can't characterize the friction with numbers or equations, which I will concede. Interestingly, that's the very specific reason we [industry] do shock testing for our real world complex systems. The equations simply don't match the results of the real implementation.
... or Karthik.
Sorry, I couldn't resist.
I'm counting the days down until Waterloo. Get your popcorn ready.
I still don't think allows for a valid conclusion based upon the calculation.
I think the calculation allows a valid conclusion. Even if the gearbox were to completely lock up, the only effect it would have for purposes of this calculation would be the resulting friction between the (locked) wheels and the pole. Compared to 474 Newtons, such friction can reasonably be ignored for purposes of the conclusion, which is simply that a 3lb minibot traveling at 7fps which is decelerated to zero speed in 1/4" is exerting much more than 4 Newtons on the plate.
If the specs are not written clearly, it is ALSO our responsibility to request clarification or we risk NOT getting paid (or tripping the sensor).
I don't feel the specification was unclear. There is a force given in the rules. The original tower used limit switches.
Logically one would think that a setup using limit switches would be momentary-ie not having to be triggered for some finite time period.
We should have foreseen that there was not enough real world testing done to show how robots hitting the towers would affect the response of the triggers?
In the future I guess when we see things like this you're saying we should assume FIRST will not be able to implement them properly and as such we should ask way more questions than necessary to ensure that everything works right?
I think Cory's point is that FIRST shouldn't be let "off the hook" every time they do something at the expense of teams just because it's a volunteer organization. We do still pay to compete, after all.
...I've been chastised for championing this point for years.
So the refs, judges, and staff at the events are VOLUNTEERS. According to the people who don't see it my way, they should be forgiven any and all shortcomings, because they're VOLUNTEERS. Everyone claims that a cornerstone of the FIRST program is the tenet of GRACIOUS PROFESSIONALISM. To me, doing your job poorly, or worse, outright incorrectly (as in 2008 SVR Finals Match 2), is UNPROFESSIONAL. Not only that, but each and every team has mentors. All of whom are, themselves, VOLUNTEERS. The mentors are expected to know and follow the rules, because if they don't, and their teams robot doesn't comply with the rules, they don't get to play.
This isn't even what this argument is about, though. FIRST HQ is NOT run by volunteers. Many of the staff at FIRST HQ take a salary, paid for by our entry fees, and the sponsorships provided by industry. They are being paid to provide the teams with a product, a competition.
While I might be able to be convinced to forgive the shortcomings of a ref based on the "volunteer" argument, I will never be able to be convinced to forgive FIRST HQ for shamelessly doing things at the expense of their customers, the teams.
Does a standard scale, such as the ones used to inspect the robots at competition, give us the weight or mass of the robot? In other words, is the number we see equal to mass*[accel due to gravity] or equal to only mass?
Using a direct weight-equals-mass calculation, I get 0.586 feet stopping distance and 488N for stopping @ 1/4".
Dividing by the acceleration of gravity, I get a stopping distance of 0.060 feet (~3/4") and ~50N to stopping @ 1/4".
Does a standard scale, such as the ones used to inspect the robots at competition, give us the weight or mass of the robot? In other words, is the number we see equal to mass*[accel due to gravity] or equal to only mass?
The scale measures force.
If you measure something on Earth, then you can use that force to calculate the mass, as follows: kilograms = pounds * 0.4535924
If you use the same scale on the Moon, you will get a force reading about 1/6 of what you got on Earth, even though the mass is the same.
Does a standard scale, such as the ones used to inspect the robots at competition, give us the weight or mass of the robot? In other words, is the number we see equal to mass*[accel due to gravity] or equal to only mass?
Using a direct weight-equals-mass calculation, I get 0.586 feet stopping distance and 488N for stopping @ 1/4".
Dividing by the acceleration of gravity, I get a stopping distance of 0.060 feet (~3/4") and ~50N to stopping @ 1/4".
In imperial units, a scale measuring pounds gives the weight of an object, not the mass. The imperial unit of mass is slugs, which is equivelent to approx. 32 lb-mass. When doing Newtonian calculations in imperial units, you must use the units slugs, lb-force, feet, and seconds. This yields the results you mentioned first, .586 ft and ~480 N (107 lbs).
, yet the whiners haven't proposed a solution.
I wouldn't say I'm a whiner, but I did propose a solution: http://www.chiefdelphi.com/forums/showthread.php?p=1040957#post1040957
pfreivald
17-03-2011, 12:07
Not only that, but each and every team has mentors. All of whom are, themselves, VOLUNTEERS.
I am paid a coaching stipend, so technically I am not a volunteer.
(I was asked to itemize it out this year because we're doing budget negotiations and it looks like the admins are trying to cut compensation for extracurricular advisors, so I did the math and discovered that when it comes down to brass tacks I get paid about $0.07/hour if we keep it to only one summer project, but still...)
@pfreivald: ok, so maybe not ALL the mentors on FRC teams are 100% volunteers, but my point is still valid since you're in the overwhelming minority.
pfreivald
17-03-2011, 12:30
@pfreivald: ok, so maybe not ALL the mentors on FRC teams are 100% volunteers, but my point is still valid since you're in the overwhelming minority.
I EARN that seven cents an hour, dag-nabbit!
(I hope you realize I was just playing with you.)
Matt Krass
17-03-2011, 12:32
I am paid a coaching stipend, so technically I am not a volunteer.
(I was asked to itemize it out this year because we're doing budget negotiations and it looks like the admins are trying to cut compensation for extracurricular advisors, so I did the math and discovered that when it comes down to brass tacks I get paid about $0.07/hour if we keep it to only one summer project, but still...)
For those 7 cents I expected more from you!
Just kidding. :)
Proximity sensors and light sensors are two common proposed solutions.
Personally, I don't see what's wrong with a photo finish here. Yes, "instant replay" is a dirty word, but it would clearly be the best.
The biggest problem I see with a 'photo finish' is something still needs to trip the camera. Taking constant video of the poles at a frame rate of 29.97fps may work, but close minibots will still be very close there, it may be hard to determine accurately. I'm not saying it isn't possible, but it's certainly something to think about.
I don't feel the specification was unclear. There is a force given in the rules. The original tower used limit switches.
Logically one would think that a setup using limit switches would be momentary-ie not having to be triggered for some finite time period.
We should have foreseen that there was not enough real world testing done to show how robots hitting the towers would affect the response of the triggers?
In the future I guess when we see things like this you're saying we should assume FIRST will not be able to implement them properly and as such we should ask way more questions than necessary to ensure that everything works right?
Logically a computer system can only sense a condition that exists for a finite period of time related to the sampling rate. Since no specification was given regarding how long the force must be sustained, nor the sampling configuration of the system, it was an incomplete specification. Also, the force specification given appeared to be a rough estimate of the minimum required, not a clear definition of what we had to attain. I believe, as other posters have stated, you're hung up on that number.
Real engineering specifications are pretty explicit, I'm working on a project here at work that has an entire page explaining that the power LED must turn on when I apply power to the system. It even states how fast the LED must turn on when power is applied. The 'spec' we got from FIRST, if you can even call it that, was most definitely incomplete, and yes we should have foreseen complications from a lack of real world test data. I stand by my original argument, both the teams and FIRST are responsible for this.
Matt
Rick TYler
17-03-2011, 12:45
... or Karthik.
Is that an Imperial Karthik or a new metric Karthik? Either way, I like the idea of saying, "Our robot imparts a force of 1.2 Karthiks on the playing surface."
Or, "most FRC robots are about 1.2 Karthiks, but FTC robots are usually .25 Karthiks, and VRC robots about .15 Karthiks." I think this could catch on.
Matt Krass
17-03-2011, 12:46
Is that an Imperial Karthik or a new metric Karthik?
Now I'm imagining some bizarre Star Wars-esque theme song when Karthik walks around. Sort of an Imperial Karthik March...
Paul Copioli
17-03-2011, 13:01
Now I'm imagining some bizarre Star Wars-esque theme song when Karthik walks around. Sort of an Imperial Karthik March...
So is it wrong that I just started humming the imperial march score?
I guess I just found the entrance music for Karthik at Waterloo! I wonder how long it will take before someone shuts down the webcast at Waterloo?
Matt Krass
17-03-2011, 13:11
So is it wrong that I just started humming the imperial march score?
I guess I just found the entrance music for Karthik at Waterloo! I wonder how long it will take before someone shuts down the webcast at Waterloo?
I imagined it sounding like the Imperial March, with a mix of power drills, and the FMS sound effects...
Is this what happens if you stay in FIRST too long?
Matt
Mike Copioli
17-03-2011, 13:11
yet the whiners haven't proposed a solution..
What makes you think they haven't. If they did, what makes you think FIRST will listen?
The fact of the matter is, Physics beat the crap out of FIRST's system during Week 0 and Week 1 by exposing a severe flaw. Why are we complaining that FIRST had to adapt to it? Why should they put out a specific spec in the form of a rule that teams WILL simply complain about regardless? .
Because it is their job and responsibility. A 'spec' is not a rule, it is the specifics of how something should work, hence the name 'spec.' A rule or ruling is what update 18 is and I do not consider "Oh well trigger it or else it does not count" as adapting to it.
Honestly, the only concession FIRST can make at this point is to give us dedicated MINIBOT time on Thursday.
A spec would be easier and much more efficient since teams have unlimited access to the minibot.
I wouldn't say I'm a whiner, but I did propose a solution: http://www.chiefdelphi.com/forums/showthread.php?p=1040957#post1040957
Think the design of the solution through, including its problems and how to solve them. Then analyze if the new problems present risks in implementation, and determine if the solution really solves the overarching problem or if it simply introduces different problems from the current implementation. You've presented an entirely new configuration -- if you can lay out more than just a picture, then you've presented a solution rather than an idea.
======================
As for the force required, I don't think it's relevant in retrospect; I do concede that it's improbable for the minibot to stop before it hits the sensor. I do still believe the friction greatly effects the deceleration rate of the minibot, which then effects the sensor contact time while the minibot decelerates moving up the pole after cutoff. (I don't know why I keep arguing irrelevant points). So below I'll present the case where there is no external force, as you've recommended and as I can't properly characterize. We can assume that the times will be less during deceleration if there is friction. Thus, deceleration comes from ~17N (plate + bot weight) of force on a 3lb minibot.
If the sensor contact points have a length L, and the minibot weight 3 lbs, and the bound off of the top plate provides no acceleration downward, then the data follows (times in milliseconds):
L (in) upward downward total
====================================
0.25 27.0 36.0 63.0
0.375 33.1 44.1 77.2
0.5 38.2 50.9 89.2
0.625 42.8 56.9 99.7
0.75 46.8 62.4 109.2
0.875 50.6 67.3 117.9
1.0 54.0 72.0 126.1
====================================
If we figure out what can make these times less, we may be on our way to finding the real problem:
1.) A gap between contact points -- this is necessary to prevent vibratory false positives. The gap means that the sensor makes contact for less time than the minibot is in contact with the tower.
2.) A bounce of the minibot off of the top plate that increases downward acceleration would decrease the time.
3.) Friction that increases deceleration moving up. In retrospect, perhaps the bounce has more of an effect that could make this negligible anyways?
4.) What others are there?
So if we try to solve any of these inherent problems, without introducing any new problems by regression, then (1) isn't really solvable except by sampling rate adjustments to ensure the most accurate initial contact time, (2) means we need a damping mechanism, and (3) just might be negligible. Cory wants the limit switches with increased sampling rates, but isn't that the setup that induced the false positives? Or did the false positives come as a result from FIRST not using the limit switches for some reason? It's important to note that even the limit switches have a contact length, L, and that the sampling rate of the switch could still mean a false negative given the data above. If a custom circuit was created to sample the sensors, then adjustments may not be possible (unless it's a simple resistor replacement, which could still introduce errors during replacement).
Thus I suspect the greatest contributing factor to the problem (as of Week 2) is the bounce off the top plate (stated before I'm sure).
IMO, the simplest 'fix' that would solve the problems is a simple dampening mechanism that attaches to a current configuration. If you're the GDC, is it easier to get teams to add a simple dampening mechanism to their minibots, for you to add your own (think logistics here...), or both? If the GDC has to add a rubber bumper, they have to give a new Force spec to teams. If the onus is on teams to add their own dampening mechanism, then the teams can customize it to their minibots. So Cory, I think you should be grateful the GDC isn't trying to perform a fix that could simply introduce more problems.
Thus, the GDC should give the teams some extra test time with the minibots in the real system with the Week 2 fixes.
What makes you think they haven't. If they did, what makes you think FIRST will listen?
Because the "solutions" in this thread haven't been well thought-out solutions so much as they've been ideas that would introduce the same magnitude of risk as the current implementation did 2 weeks ago. The GDC would be vilified further if they implemented a "new" design that had the same issues as the current/old (Week 1) design.
Because it is their job and responsibility. A 'spec' is not a rule, it is the specifics of how something should work, hence the name 'spec.' A rule or ruling is what update 18 is and I do not consider "Oh well trigger it or else it does not count" as adapting to it.
The Update simply enforces the rule as it was before referees made their decisions to manually score it. The spec and the update have nothing to do with each other in that regard. The Update simply points out a spec that was available before (though this is more opinion in regards to what the intention of putting that note in an official rule update is).
A spec would be easier and much more efficient since teams have unlimited access to the minibot.
Yet the argument that has been made very clear (and most accurately) is that the specs provided by FIRST haven't been 100% complete or accurate thus far.
I do agree that it's an insane amount of information in too many different places that make things confusing, but I'm more inclined to think that (right now, moving forward) more test time would be less time consuming and less frustrating that expecting teams to believe a new specification at this point.
Al Skierkiewicz
17-03-2011, 14:03
So is it wrong that I just started humming the imperial march score?
I guess I just found the entrance music for Karthik at Waterloo! I wonder how long it will take before someone shuts down the webcast at Waterloo?
I am thinking that temperature in Texas is spiking today.
Logically a computer system can only sense a condition that exists for a finite period of time related to the sampling rate.
You're forgetting about interrupts. If the switch is connected to an IO port which can be configured to generate an interrupt then there is no sample rate involved.
wireties
17-03-2011, 14:14
You're forgetting about interrupts. If the switch is connected to an IO port which can be configured to generate an interrupt then there is no sample rate involved.
And it certainly possible (though I guess not used here) to latch rising or falling edges of a signal so they are preserved till the computer gets a chance to poll them or run the ISR that reads them.
wireties
17-03-2011, 14:25
I don't feel the specification was unclear. There is a force given in the rules. The original tower used limit switches.
Logically one would think that a setup using limit switches would be momentary-ie not having to be triggered for some finite time period.
We should have foreseen that there was not enough real world testing done to show how robots hitting the towers would affect the response of the triggers?
In the future I guess when we see things like this you're saying we should assume FIRST will not be able to implement them properly and as such we should ask way more questions than necessary to ensure that everything works right?
I was drawing an analogy to a classic real-world engineering quandary (so students and young mentors can learn something from this problem), not stating that FIRST was doing anything wrong, intentional or not.
It is not uncommon to get requirement/s or a proposal from a real-world customer that is vague or contradictory or impossible. In such cases it is prudent to ask for more detail before starting a design/build process. In the real world, it costs $$$ to pursue vague requirements, a risky course of action!!
it's improbable for the minibot to stop before it hits the sensor.
I wouldn't take that possibility entirely off the table, in view of some of the testimony given in this thread. It's at least possible that on some occasions where the minibot visibly whacked the plate but failed to trigger, the cause was a tilted/jammed plate which prevented switch contact.
We can assume that the (contact) times will be less during deceleration if there is friction.
It's not at all obvious that this assumption is valid. It is arguable that a faster-moving object with no friction hitting a switch may ricochet off faster and have less contact time than a slower-moving object with friction.
(if) the bound off of the top plate provides no acceleration downward
When the minibot drives the bottom plate into the switch, there will be rebound acceleration of the minibot. This acceleration is very large and cannot be ignored. The only time there would be no rebound acceleration would be if the speed had become near zero by the time the minibot hit the switch.
wireties
17-03-2011, 14:42
In the future I guess when we see things like this you're saying we should assume FIRST will not be able to implement them properly and as such we should ask way more questions than necessary to ensure that everything works right?
Surely there is some middle ground. And asking more questions than is necessary is preferable to asking too few questions, don't you think?
HTH
Chris is me
17-03-2011, 14:54
Surely there is some middle ground. And asking more questions than is necessary is preferable to asking too few questions, don't you think?
HTH
So we're supposed to assume FIRST's specs are a little incomplete instead of complete or completely wrong? Why?
Mike Copioli
17-03-2011, 15:12
Because the "solutions" in this thread haven't been well thought-out solutions so much as they've been ideas that would introduce the same magnitude of risk as the current implementation did 2 weeks ago. The GDC would be vilified further if they implemented a "new" design that had the same issues as the current/old (Week 1) design.
That's because the spec is incomplete. Debounce time is a necessary component for solving this problem. Without it you can apply 100 newtons or Karthiks or grains or whatever unit you like until you turn blue, if you do not apply that force for at least the time needed to debounce the switch it does not matter.
. The Update simply points out a spec that was available before (though this is more opinion in regards to what the intention of putting that note in an official rule update is).
Yes, an incomplete spec.
I do agree that it's an insane amount of information in too many different places that make things confusing, but I'm more inclined to think that (right now, moving forward) more test time would be less time consuming and less frustrating that expecting teams to believe a new specification at this point.
Ok, if you think that clarifying a spec is more difficult then every team in FIRST using trial and error to find what works then FIRST is less efficient than I thought.
So fine I have a simple solution.... Use the sensor plates as primary feed back and four dudes with a button as secondary. This is how it is done in swimming events, including the Olympics.
When the minibot drives the bottom plate into the switch, there will be rebound acceleration of the minibot. This acceleration is very large and cannot be ignored. The only time there would be no rebound acceleration would be if the speed had become near zero by the time the minibot hit the switch.
The basic cause-effect of this, as an example, is that even if the minibot moves the plate 1", causing the sensor to be in contact for 3/4" of that movement, the contact time of the sensor is much less than the 100ms I listed. So we need either a higher sampling rate to allow finer granularity in the false-positive algorithm, or we need a dampening mechanism that's implemented by the "GDC" or by teams.
====
As far as I can tell, interrupt-driven signals have just as much probability for false-positives as sampling does in this setup. The interrupt would have to be held high/low for a certain amount of time to ensure it's a valid trigger, which still requires some sort of 'time' specification for teams to ensure they don't lose contact with the sensor too quickly.
So fine I have a simple solution.... Use the sensor plates as primary feed back and four dudes with a button as secondary. This is how it is done in swimming events, including the Olympics.
How do you safely account for paradox? The refs would need to be up on a ladder (or something similar) to ensure they hit the button at the actual impact time and not a microsecond later. In swimming the judges are able to stand over the lanes to get the best view (from what I've seen).
The issue with sending out a time spec isn't efficiency, but rather accuracy. If it's wrong in 1 case at 1 regional, causing a tower to not be triggered and a match to be lost, was it worth it to argue over what the actual number is to begin with?
I'm not defending FIRST so much as I'm trying to be pragmatic about this from a project engineering perspective.
Chris is me
17-03-2011, 15:22
How do you safely account for paradox? The refs would need to be up on a ladder (or something similar) to ensure they hit the button at the actual impact time and not a microsecond later.
All of the refs are standing from more or less the same spot on the floor relative to their respective towers.
Mark McLeod
17-03-2011, 15:22
I think pole-sitting refs would add greatly to the amusement factor, as well as, giving them a kick in the pants to push their button. :)
c-parent
17-03-2011, 15:40
I think pole-sitting refs would add greatly to the amusement factor, as well as, giving them a kick in the pants to push their button. :)
I think you may be on to something for next years game...I'm seeing dunk tanks maybe? :D
boomergeek
17-03-2011, 15:45
I think we have one ref concentrating on every tower anyway looking for penalties and disablement.
I think we can trust ref's to press an "enablement" button as soon as the minibot crosses the starting line, then use the sensors on the plate integrated over 40 milliseconds to record the time I.e., the tower plate is inactive until after the ref decides the minibot crossed the start line fairly.
Whatever the triggering mechanism: it NEEDS to be published and the sooner the better. If not, then some teams will end up getting an advantage over others because of the multiple hats of developers, testers and facilitators.
wireties
17-03-2011, 15:52
So we're supposed to assume FIRST's specs are a little incomplete instead of complete or completely wrong? Why?
I don't want to seem too flippant but YES - because that is how the real world works. It is not fair and/or uniform. Go thru a career as an engineer who assumes the provided specs are always perfect and you will lose a lot of money and be frustrated. You'll probably quit and end up a sales-person!! ;o)
JaneYoung
17-03-2011, 16:09
I am thinking that temperature in Texas is spiking today.
We continue to monitor the impact of Copioli-isms in Texas, shoring up weaknesses in mounting pressures and potential collisions caused by strong wind. In other words, we are doing the best we can with what we have to work with. Temps are still spiking in some areas but we're continually adapting in preparation for the next generation. :)
Jane
AFAIK, we do not have official drawings or specs (of the sensor) from FIRST so I cannot say this definitively... but if the drawing that was posted earlier in this thread by colt527 is a reasonable representation of the hardware then the minibot moves the plate 1/4" and then closes the "switch" (which appears to be 2 metal pieces coming into contact) which acts as a hard-stop. High speeds of impact into this hard stop could arguably mean less contact time, not more.
The damping mechanism was suggested earlier in this thread by Squirrel (minibot) and jspatz1 (tower).
Everyone agrees that requiring multiple consecutive positive samples lowers the incidents of false positives.
The comment about interrupts was simply a clarification, for the benefit of students who may be reading, to an unqualified statement made about sampling. It may or may not be part of an eventual solution. Another clarification: an interrupt does not have to be "held". The ISR can spawn a high-sampling-rate temporary thread to run an algorithm to test for false negatives. Then it's just* a matter of adjusting the software.
* "just software". I hate that phrase. Don't you?
The damping mechanism was suggested earlier in this thread by Squirrel (minibot) and jspatz1 (tower).
Yea, I was close to squirrel's idea with a slightly different idea (http://www.chiefdelphi.com/forums/showpost.php?p=1040475&postcount=43) that was totally ignored. Jspatz's damping idea looked like an entire rework that introduced as many questions as it had answers. But that's neither here nor there at this point. The math and the arguments solidify that a simple damping mechanism is probably the simplest way forward from both a technical and a holistic program perspective. Personally, at this point, I'd much rather implement the damping mechanism myself rather than expect the numbers FIRST puts out are perfect and without tolerance. We still need test time on Thursday though. I don't exactly have a "springy finger" or "squishy surgical tubing" down to a mathematical science yet.
I'm thinking the root cause of the problem is more related to the rate of evolution of minibot designs. With the full-size competition robots, even when teams see robots with really amazing features, they are just too complicated to copy in the time available. The design time of one iteration of a minibot is fairly short and teams which so choose can keep iterating as long as they want. My guess would be that the GDC envisioned 4 or 5 second minibot times and the triggering system on the tower would have been fine. Early in the build season, talk of 3 second minibots surfaced. Then 1625 posted their video and the times fell to 2 seconds and now times near 1 second have been demonstrated. Put 2000 teams on a problem and allow them to iterate over and over again and give them a big payoff or iterating over and over and the result is that by St. Louis any team that wants an awesomely fast minibot will have one and maybe they all will exceed what the GDC envisioned.
AdamHeard
17-03-2011, 16:59
I'm thinking the root cause of the problem is more related to the rate of evolution of minibot designs. With the full-size competition robots, even when teams see robots with really amazing features, they are just too complicated to copy in the time available. The design time of one iteration of a minibot is fairly short and teams which so choose can keep iterating as long as they want. My guess would be that the GDC envisioned 4 or 5 second minibot times and the triggering system on the tower would have been fine. Early in the build season, talk of 3 second minibots surfaced. Then 1625 posted their video and the times fell to 2 seconds and now times near 1 second have been demonstrated. Put 2000 teams on a problem and allow them to iterate over and over again and give them a big payoff or iterating over and over and the result is that by St. Louis any team that wants an awesomely fast minibot will have one and maybe they all will exceed what the GDC envisioned.
Within a few hours of the update clarifying we had to use FTC motors, we had already calculated (with darn simple math), that sub 1 second minibots were possible. This should not have been overlooked, that's as if they made a field border that could only handle impacts of robots going 7 ft/s, because they assumed none would go faster.
Within a few hours of the update clarifying we had to use FTC motors, we had already calculated (with darn simple math), that sub 1 second minibots were possible.
Would you be willing to post this math, for the benefit of students on teams who do not have mentors/teachers who know how to do motor calculations.
Within a few hours of the update clarifying we had to use FTC motors, we had already calculated (with darn simple math), that sub 1 second minibots were possible. This should not have been overlooked, that's as if they made a field border that could only handle impacts of robots going 7 ft/s, because they assumed none would go faster.
I hear what you are saying and it seems reasonable, but if the GDC anticipated 1 second minibots it seems like they should have built some and tested them on their triggers. Most team minibots were probably "tinkered" into existence rather than engineered into existence. Is it possible that the GDC did likewise?
Would you be willing to post this math, for the benefit of students on teams who do not have mentors/teachers who know how to do motor calculations.
16.8 watts max power output w/o gearhead
= 12.4 ft-lb/sec
x2 motors = 24.8 ft-lb/sec max power output
2.3 lb estimated robot weight
(24.8 ft-lb/sec) / (2.3 lb) = 10.8 ft/sec (neglecting friction)
Matt Krass
17-03-2011, 18:49
You're forgetting about interrupts. If the switch is connected to an IO port which can be configured to generate an interrupt then there is no sample rate involved.
I considered interrupts, but even interrupts have a minimum latch time on most systems I've used, it may be on the order of microseconds, but it's there, and the point is, it was omitted, so we don't know if it's a fast interrupt or a slow poller, or a shift register that only gets clock in every 300ms, etc. The system must have some time component to it, which was my point. To assume it can behave instantaneously was erroneous, especially since no time component was specified. If you told me it took 100us for the interrupt to latch and take hold, then I'd say it's a negligible amount of time, but at least I'd have concrete evidence to work with.
EDIT: As also pointed out before, even interrupts cannot guarantee a clean signal without some decent debounce time on the signal, which still brings you back to a time component. Which we weren't given, and FIRST may not (yet) have.
Matt
AdamHeard
17-03-2011, 19:05
16.8 watts max power output w/o gearhead
= 12.4 ft-lb/sec
x2 motors = 24.8 ft-lb/sec max power output
2.3 lb estimated robot weight
(24.8 ft-lb/sec) / (2.3 lb) = 10.8 ft/sec (neglecting friction)
Beat me to it. We ran the math in metric units, but it's the same nonetheless.
We then assumed instant acceleration, and used distance = velocity x time to solve for an approximate "perfect" time.
I guess I just found the entrance music for Karthik at Waterloo! I wonder how long it will take before someone shuts down the webcast at Waterloo?
It'd get shut down a lot faster if we went with my own personal choice of entrance music, Shots by LMFAO.
even interrupts cannot guarantee a clean signal without some decent debounce time on the signal, which still brings you back to a time component.
For reference I'm linking to a post (http://www.chiefdelphi.com/forums/showpost.php?p=1041280&postcount=204) made a couple hours earlier here in this thread.
Matt Krass
17-03-2011, 19:42
For reference I'm linking to a post (http://www.chiefdelphi.com/forums/showpost.php?p=1041280&postcount=204) made a couple hours earlier here in this thread.
I recall your post, though I don't think my post was unqualified, merely incomplete. I should have mentioned interrupts in my original post, I was thinking more conceptually (against the notion of instantaneous detection taking zero time) and didn't see much relevance at the time.
Matt
16.8 watts max power output w/o gearhead
= 12.4 ft-lb/sec
x2 motors = 24.8 ft-lb/sec max power output
2.3 lb estimated robot weight
(24.8 ft-lb/sec) / (2.3 lb) = 10.8 ft/sec (neglecting friction)
Continuing the calculation:
(16.8 watts @ max power)/(0.0475 Nm torque @ max power) = 353.7 radians/sec shaft speed @ max power
(10.8 ft/sec)/(353.7 radians/sec) = 0.03045 ft shaft radius = 0.73 inch shaft diameter (for direct drive)
Probably want to reduce that diameter by 15% or so for losses and margin
someone please check my math
I recall your post, though I don't think my post was unqualified
Poor word choice on my part; the word has multiple meanings which could be taken the wrong way. I intended definition #2:
un·qual·i·fied (n-kwl-fd)
adj.
2. Not modified by conditions or reservations; absolute
I referenced the previous post mostly for the remarks about debouncing interrupt-serviced switches.
Folks,
If I were to carefully read this entire thread, instead of only quickly scanning the last 100 or so posts, what useful information/conclusions would I acquire?
I have gathered that the tower targets are close to FUBAR status and many mini-bot designs are consequently pseudo-randomly finding themselves up the proverbial creek. It that all we have here?
My goodness, does it take 200+ posts of grouching at each other, and at FIRST, to convey that clearly?
I know everyone is tired, but this could be a fun topic.
Who has tested some work-arounds and can reports their results to teams that need to modify their mini-bots???? Is slower better? Would putting a broad squishy nose on a mini-bot help? Would leaving the mini-bot motors energized an extra few fractions of a second after target-contact help? Anything else?
Blake
Matt Krass
17-03-2011, 20:32
Folks,
If I were to carefully read this entire thread, instead of only quickly scanning the last 100 or so posts, what useful information/conclusions would I acquire?
I have gathered that the tower targets are close to FUBAR status and many mini-bot designs are consequently pseudo-randomly finding themselves up the proverbial creek. It that all we have here?
My goodness, does it take 200+ posts of grouching at each other, and at FIRST, to convey that clearly?
I know everyone is tired, but this could be a fun topic.
Who has tested some work-arounds and can reports their results to teams that need to modify their mini-bots???? Is slower better? Would putting a broad squishy nose on a mini-bot help? Would leaving the mini-bot motors energized an extra few fractions of a second after target-contact help? Anything else?
Blake
I don't believe this has been 200 posts of people grouching at each other, instead it's been a very lively, interesting debate of the technical details of the situation. And since this is just coming out now, nobody has publishable results yet, just a lot of hypotheses on what may or may not be occurring, and how to possibly improve the towers or minibots.
Nobody has a definitely answer for you, other than expect to have to work at this some more.
Personally I think this group has done a fantastic job dissecting the situation and working to figure out the information FIRST has woefully failed to provide once again, but give them a chance, this isn't old news yet.
I thought it was a fun topic, though I wish I could contribute more effectively to it.
EDIT: I wanted to answer to this as well.
Poor word choice on my part; the word has multiple meanings which could be taken the wrong way. I intended definition #2:
I referenced the previous post mostly for the remarks about debouncing interrupt-serviced switches.
Sorry to misunderstand you, your intended wording makes a lot more sense!
Matt
My goodness, does it take 200+ posts of grouching at each other, and at FIRST, to convey that clearly?
There is a large number of posts because it is a topic of interest and importance to everyone, not because folks are looking to grouch at each other. The volume, to which you have contributed, is an accumulation of many individuals, of which you are now one. It is the result of many people sharing their 2 cents, like you did. Nearly every post has dealt with the topic, the only one I've read that really grouched at others is yours.
boomergeek
17-03-2011, 23:14
16.8 watts max power output w/o gearhead
= 12.4 ft-lb/sec
x2 motors = 24.8 ft-lb/sec max power output
2.3 lb estimated robot weight
(24.8 ft-lb/sec) / (2.3 lb) = 10.8 ft/sec (neglecting friction)
Here's a different way to get at approximately the same point.
At kick off, the video of the FIRST built minibot showed about 1.3 ft/sec for a robot that looked to be more than 5 lbs and using a pair of Tetrix motors and gearboxes.
Its not hard to cypher that a 2 lb robot can be 2.5 times faster than a 5 lb robot. By the same token, if you throw away a near 50% inefficient transmission, you should be able to obtain another doubling of speed. That gets you in the 7-8 ft/sec range. Add additional lowering of friction in the attachment to the pole mechanism and you approach the magically 10.8 ft/sec. Add topping off the battery to get to a better motor curve is gravy on top.
Chris Hibner
17-03-2011, 23:23
Just as a note:
We had 3 minibots up the pole today at the Detroit district, all three triggered just fine. I'll keep my eye on it this weekend.
Lil' Lavery
18-03-2011, 00:08
Just as a note:
We had 3 minibots up the pole today at the Detroit district, all three triggered just fine. I'll keep my eye on it this weekend.
Were any additional modifications made to the towers since the last time this field was used? What was the last event this field was used at?
sanddrag
18-03-2011, 01:30
16.8 watts max power output w/o gearhead
= 12.4 ft-lb/sec
x2 motors = 24.8 ft-lb/sec max power output
2.3 lb estimated robot weight
(24.8 ft-lb/sec) / (2.3 lb) = 10.8 ft/sec (neglecting friction)
Thank you Ether! This is the first post I've seen all season to do a proper (yet quite simple) calculation of how fast a minibot of given weight can get up the pole. I've been meaning to do this with my students all season long, but was too busy with the arm and other things. I think now is the time to revisit it.
Trial and error is one thing. Knowing what you're shooting for, because you did some calculation first, is quite a different (and much better) thing.
GaryVoshol
18-03-2011, 06:58
Were any additional modifications made to the towers since the last time this field was used? What was the last event this field was used at?The field from Waterford went to Detroit.
martin417
18-03-2011, 07:03
Update from Peachtree:
We deployed our minibot in 2 practice matches, and had no issues triggering the tower. For reference, the minibot weighs about 2.8 lb.s and runs the pole in about 1.6-1.8 sec.s We are using a 3-way household light switch to turn off the juice and short the motor leads for the return trip. I haven't measured the force required to flip that switch, but it is more than 4N.
boomergeek
18-03-2011, 07:30
Thank you Ether! This is the first post I've seen all season to do a proper (yet quite simple) calculation of how fast a minibot of given weight can get up the pole. I've been meaning to do this with my students all season long, but was too busy with the arm and other things. I think now is the time to revisit it.
Trial and error is one thing. Knowing what you're shooting for, because you did some calculation first, is quite a different (and much better) thing.
I believe Ether's number are based on actual lab trials.
I.e., the specification provided by Tetrix was no where near sufficient to extrapolate to a 10.8 ft/sec estimate. It was only a team member that went in a lab with dynamometer capability and did lab trials with and without the gearbox attached that allowed for the calculation.
Thank Richard for the creating the data AND sharing the data that allows physics teachers to let this rise above tinkering status.
http://www.chiefdelphi.com/forums/showthread.php?t=89072&highlight=richard+dynamometer
I believe Ether's number are based on actual lab trials.
I.e., the specification provided by Tetrix was no where near sufficient to extrapolate to a 10.8 ft/sec estimate. It was only a team member that went in a lab with dynamometer capability and did lab trials with and without the gearbox attached that allowed for the calculation.
Thank Richard for the creating the data AND sharing the data that allows physics teachers to let this rise above tinkering status.
http://www.chiefdelphi.com/forums/showthread.php?t=89072&highlight=richard+dynamometer
He (along with many others) already thanked Richard in post#5 of the thread you linked. But thanks once again, Richard :-)
Be aware that the calculation does not include any consideration of the time it takes the bot to accelerate to the indicated top speed. So if you use the top speed to calculate how long it will take to get to the top of the pole, the answer will be optimistic.
I'm going to take a look at a calculation that includes acceleration. I'll have to eyeball data from Richard's power vs torque curve (I didn't see raw data posted anywhere - is it available?). From other Tetrix curves I have seen, the motors are a lot less linear than other motors we've worked with, so I'll least-squares-fit a polynomial. Since the torque depends nonlinearly on speed, and the speed is the integral of acceleration which in turns depends on torque it's an interesting differential equation.
boomergeek
18-03-2011, 10:51
He (along with many others) already thanked Richard in post#5 of the thread you linked. But thanks once again, Richard :-)
He was giving you credit for seemingly being the first to provide the physics formulas I think Richard had provided that in post #7 of that now famous thread.
I guess there is always a healthy back and forth between thinking of the academic physics (thought experiments) and going into the lab to make fundamental measurements AND sharing them.
Those that have sophisticated tools like a dynamometer and share the results with everyone are making the math/physics very valuable.
Speed is a relatively easy thing for most teams to measure: actual motor performance is not and the vendor published curves are not always sufficient to the challenge.
FIRST also inadvertently made understanding of physics more important in the trigger mechanism. It's all good. There are physics lessons everywhere.
Going through the thread and looking for last week's events:
San Diego had issues (Cory (254), Jon (987))
Waterford worked okay (Kara (1189) (assume this is where she was), Zach (2337))
Wisconsin worked fine (Al (111))
Kansas City had issues (Jeff (1986))
Pittsburgh seemed to work (Ken (527))
Florida worked mostly (Alex (744), Jared (341)), Jared mentioned some issues, but did not have specifics
Lake Superior worked (me (next to the field all four days))
WPI had an issue for team 358 but few other issues (Chris (2791))
NYC and Israel have no reports in this thread.
For this week:
Detroit has had success (Chris (51))
Peachtree is working (Martin (1771))
Here's a fun image, generated here (http://www.chiefdelphi.com/media/papers/2469). Red line is Ether's theoretical diameter, and the motor load is indeed at max power. Yet the iterations show that a slightly different diameter can squeeze out a bit more due to acceleration being a slightly larger-than-anticipated factor.
Assumes:
Battery voltage of 14.4V
6755 RPM Free Speed
0.095 Nm Stall Torque
(Extrapolated the stall/free currents based upon a realistic efficiency curve)
2 motors
100% wheel-to-pole efficiency
direct-drive minibot straight off the motor
2.3 lb weight
Minibot goes exactly 7.5 feet straight up
He was giving you credit for seemingly being the first to provide the physics formulas I think Richard had provided that in post #7 of that now famous thread.
Not to start an argument here Dick, but the calculation I provided is somewhat different from the one Richard posted in #7. It's more similar to the one jreuter posted in #25. For the record, I hadn't read either of those posts until just now when I went back to re-read the thread after seeing your post. So Kudos to Richard and jreuter. I invite anyone interested to read that entire thread.
Does anyone know if raw (numerical) dyno data has been posted anywhere, which includes motor current and speed?
Katie_UPS
18-03-2011, 11:10
Wisconsin worked fine (Al (111))
While I'd normally take Al's word like one might of God, I'm not sure if this is true. There was an elims match where 234 deployed a minibot which didn't trigger, but definitely made it to the top. I was in the pits (save for 1675 matches), so this might've been the only time (freak incident or something like that).
.....
NYC and Israel have no reports in this thread.
.....
I reported only our experience at NY. There was one instance where our minibot did not trigger the top, but it was counted. All of our other deployments wee successful.
Mike Soukup
18-03-2011, 13:31
While I'd normally take Al's word like one might of God, I'm not sure if this is true. There was an elims match where 234 deployed a minibot which didn't trigger, but definitely made it to the top. I was in the pits (save for 1675 matches), so this might've been the only time (freak incident or something like that).
In the match you're referring to, 234's minibot was moving up the pole so slowly that I doubt it hit the top with enough force to trigger the sensor. From what I saw, it pretty much died as it hit the top, if it even reached the top. All minibots that I saw climb the pole with decent speed, triggered the sensor.
XaulZan11
18-03-2011, 13:43
234's minibot was moving up the pole so slowly that I doubt it hit the top with enough force to trigger the sensor. From what I saw, it pretty much died as it hit the top, if it even reached the top.
Yeah, the head ref had to take out a ladder and a piece of paper to determine if there was space inbetween the minibot and the top of the tower. The decision would have determined the match (and who advanced to the semifinals) if it wasn't for a red card on the other alliance.
Here's a fun image, generated here (http://www.chiefdelphi.com/media/papers/2469). Red line is Ether's theoretical diameter, and the motor load is indeed at max power. Yet the iterations show that a slightly different diameter can squeeze out a bit more due to acceleration being a slightly larger-than-anticipated factor.
Assumes:
Battery voltage of 14.4V
6755 RPM Free Speed
0.095 Nm Stall Torque
(Extrapolated the stall/free currents based upon a realistic efficiency curve)
2 motors
100% wheel-to-pole efficiency
direct-drive minibot straight off the motor
2.3 lb weight
Minibot goes exactly 7.5 feet straight up
This graph matches our experimental results. Our climb time was minimum at .40" dia.
Lil' Lavery
18-03-2011, 13:54
Just witnessed a false positive on the Bayou webcast. Minibot was about halfway up the tower when the lights triggered.
Al Skierkiewicz
18-03-2011, 14:07
Katie,
I discussed this in another thread I think. I was in the scoring area about ten feet from the minibot. It was spinning it's wheels as it climbed and when it reached the top, the wheels continued to spin but not enough force was applied to the plate. The Head Ref performed the paper test and initially determined that it had reached the top. Then he remembered a ruling about moving the plate. After checking the rules, I watched him and the rest of the refs do this, they determined that the plate had to move. Although I was not close enough to hear the refs conversation, I was sure that there was a a ref at the base of the tower when the minibot went up. A second check proved that the plate didn't move when the minibot was removed from the tower. His change in ruling was based on this second and critical check.
Katie_UPS
18-03-2011, 14:39
Katie,
I discussed this in another thread I think. I was in the scoring area about ten feet from the minibot. It was spinning it's wheels as it climbed and when it reached the top, the wheels continued to spin but not enough force was applied to the plate. The Head Ref performed the paper test and initially determined that it had reached the top. Then he remembered a ruling about moving the plate. After checking the rules, I watched him and the rest of the refs do this, they determined that the plate had to move. Although I was not close enough to hear the refs conversation, I was sure that there was a a ref at the base of the tower when the minibot went up. A second check proved that the plate didn't move when the minibot was removed from the tower. His change in ruling was based on this second and critical check.
I wasn't sure. I was on the sidelines rooting for their alliance. Thanks for clearing that one up :)
Actually, that's quite good. You're right: any bot with the potential of winning the match (being the first to the top) will have enough velocity to trigger the pole. A lighter robot, unless it had an illegal battery or power source, would not have the velocity to create enough force, and the larger robot would being expending force on getting up the pole, therefore sacrificing velocity.
sanddrag
18-03-2011, 15:24
Be aware that the calculation does not include any consideration of the time it takes the bot to accelerate to the indicated top speed. So if you use the top speed to calculate how long it will take to get to the top of the pole, the answer will be optimistic.Keep in mind, there may exist a design in which the minibot is accelerated (reaching top speed) before it ever gets to the pole...
This graph matches our experimental results. Our climb time was minimum at .40" dia.
But how much did your minibot weigh during this test, which found this diameter to be optimal?
Josh Fritsch
18-03-2011, 16:24
Not sure if someone has updated everyone, but we have not had any issues at West Michigan so far :)
martin417
18-03-2011, 18:50
Peachtree update:
No false positives, no false negatives (that I witnessed). Every minibot that made it to the top of the tower triggered the tower. It looks like, for peachtree at least, all this worry was for naught.:)
pfreivald
18-03-2011, 19:07
Peachtree update:
No false positives, no false negatives (that I witnessed). Every minibot that made it to the top of the tower triggered the tower. It looks like, for peachtree at least, all this worry was for naught.:)
That's wonderful!
Just witnessed a false positive on the Bayou webcast. Minibot was about halfway up the tower when the lights triggered.
Impossible event since everything was fixed according to the update:rolleyes:
wireties
18-03-2011, 21:02
Keep in mind, there may exist a design in which the minibot is accelerated (reaching top speed) before it ever gets to the pole...
I don't think so. When it grabs the pole it will slow down and then accelerate again. It can't climb faster than it can free spin or even travel horizontally, not on Earth anyways.
Mark McLeod
18-03-2011, 21:37
I've seen a couple of teams (190 at WPI) with a clever deployment design that uses the same sized pipe curved to mate to the tower.
The minibot starts out accelerating downward off the hostbot (gravity a plus), then follows the curving pipe to start up the tower at full speed.
boomergeek
18-03-2011, 21:44
Keep in mind, there may exist a design in which the minibot is accelerated (reaching top speed) before it ever gets to the pole...
<G19> MINIBOTS must remain completely autonomous and move up the POST solely through electric energy provided after the start of DEPLOYMENT by the permitted, unaltered battery and converted to mechanical energy by the permitted unaltered motors (and associated, appropriate circuitry). Violation: The TOWER on which the MINIBOT is DEPLOYED is disabled. If the MINIBOT is DEPLOYED on something other than a TOWER, then the ALLIANCE’S TOWER upon which the highest RACE SCORE was earned will be discounted.
<G19> means that HOSTBOTS are not allowed to launch the MINIBOT up the pole at the TARGET, or otherwise contribute to the vertical movement of the MINIBOT. Energy for vertical movement may not be stored in the MINIBOT before DEPLOYMENT (except that which is contained within the battery and excluding incidental kinetic energy stored in the motors or wheels, but NOT, for example, in a flywheel).
(My highlighting, not FIRST's)
Since DEPLOYMENT starts when the miniboot crosses into the cylinder, it cannot have energy other than "incidental" kinetic energy in the wheels.
Incidental horizontal running starts prior to crossing into deployment-i.e., the length of the minibot will probably be overlooked as incidental.
Converting the horizontal energy produced by the minibot while over the cylinder is allowed: so the speed at the point of crossing the start line for a ramp can be higher than a minbot that uses an arm to place the minibot on the pole. I think a ramp bot can reach a higher top speed but the question is how much faster can other mechanisms get the bot to the start line as compared to the ramp bot. If the non-ramp bots do not start with a significant lead, the ramp bots can pass them (Assuming equal efficiency).
Also of note: the ramp needs to be well below the start line such that none of the minibot is in contact with it when any of the minibot crosses the start line.
My bet is that a ramp bot will record the fastest time. (We do not have a rampbot: at least not yet ;))
Also of note: rampbots need to demonstrate that their hostbot does NOT provide horizontal momentum to the minibot: E.g., a host bot that suddenly decelerates as it is reaching the tower and is not completely motionless as it deploys the minibot COULD be imparting non incidental kinetic energy. Referees will need to watch out for that.
Paul Copioli
18-03-2011, 21:57
I've seen a couple of teams (190 at WPI) with a clever deployment design that uses the same sized pipe curved to mate to the tower.
The minibot starts out accelerating downward off the hostbot (gravity a plus), then follows the curving pipe to start up the tower at full speed.
In my opinion, this is illegal per the rules mentioned above. The hostbot is providing a track that is pushing the minibot up vertically.
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