Let's Talk About The Bridge:

[davidthefat]

Does anyone think an active balancing mechanism, like a moving heavy object, on the robot to balance 3 robots? My guess is, like most years, the majority of the robots will be around 120 lb and it would be relatively easy to balance one or two on the bridge. I had the idea of putting the battery and electronics on a platform that can be shifted from the front and back of the robot and anywhere in between to actively balance the robot. Having the weight shift back and forth instead of the actually moving the robot will be better when trying to squeeze 3 robots on the platform.

Any one have any objections to that? Relatively, it would only add a weight of a motor and the mounting. All the other weight will come from other necessary components such as the battery and other electrical components, perhaps even the shooting mechanism itself.

[BrendanB]

It'll be a whole lot easier to just move the base at a slow speed then to actively shift the weight in your robot.

[davidthefat]

It'll be a whole lot easier to just move the base at a slow speed then to actively shift the weight in your robot.

Elaborate, what do you mean by move the base?

[gyroscopeRaptor]

It would be very likely in your idea that the cord could get caught or yanked from the connectors. The battery alone could work well if nothing would tangle on its cord, but a dead weight (if the robot has weight allowance enough for it) would serve the purpose just as well. No math to back this up, but anything lighter than the battery may not be worth spending the weight or motors on.

[Daniel_LaFleur]

It'll be a whole lot easier to just move the base at a slow speed then to actively shift the weight in your robot.

... and an understanding of who will move and (more importantly) who doesn't move to get the proper balance

[Ninja_Bait]

I was thinking of a lead screw with a "nut" that was just a huge chunk of steel with a threaded hole. But I also agree with BrendanB, that just careful driver control can be sufficient.

[BrendanB]

Elaborate, what do you mean by move the base?

Instead of having a mechanism move, just have your driver move at an extremely slow speed.

[Kevin Sevcik]

I'll second Brendan. Why not just move the whole robot instead? You presumably already have that system on your robot and working. Why make even more work for yourself when you already have a shooter, pickup, and bridge slapper to design and build?

[davidthefat]

It would be very likely in your idea that the cord could get caught or yanked from the connectors. The battery alone could work well if nothing would tangle on its cord, but a dead weight (if the robot has weight allowance enough for it) would serve the purpose just as well. No math to back this up, but anything lighter than the battery may not be worth spending the weight or motors on.

I've thought about the battery connector, since the electronics are on the platform with the battery, that would be fine. But the cords for all the other components to pose a threat, but isn't that black plastic, snake like thing, for exactly this application?

[davidthefat]

Instead of having a mechanism move, just have your driver move at an extremely slow speed.

Thought about actively balance the bot that way, it is a viable option for 1 robot on a platform, but with 3, it gets really tricky because there simply is no room to move.

[BrendanB]

Thought about actively balance the bot that way, it is a viable option for 1 robot on a platform, but with 3, it gets really tricky because there simply is no room to move.

The only way you are fitting three is with 3 robots that are at least 28 inches wide and you'll have 11 inches of overhang at best.

[Daniel_LaFleur]

The only way you are fitting three is with 3 robots that are at least 28 inches wide and you'll have 11 inches of overhang at best.

Believe me, a 38"wide robot can be valuble in the elimination rounds ;)

[BrendanB]

Believe me, a 38"wide robot can be valuble in the elimination rounds ;)

That's what we were thinking too but everyone on your alliance needs to think that way in order to get that bonus!

In the eliminations how does the coopertition bridge play out? I can't find that anywhere.

[akoscielski3]

I am wondering how robots are going to make the bridge go down form the neutral position. That may be hard. Is it just gonna be you run into it and it will move? or will we have to make a mechanism to lower it for us? Any thoughts?

[davidthefat]

I am wondering how robots are going to make the bridge go down form the neutral position. That may be hard. Is it just gonna be you run into it and it will move? or will we have to make a mechanism to lower it for us? Any thoughts?

Like I said before, little t-rex arms.

[Daniel_LaFleur]

That's what we were thinking too but everyone on your alliance needs to think that way in order to get that bonus!

In the eliminations how does the coopertition bridge play out? I can't find that anywhere.

Coopertition does not play any role in the elims which is why 3 robots on a teeter-totter is worth 40 points only in the elims.

[Ernst]

Last year our robot had a "finesse" mode, that literally slowed down the arm motors and the drive motors. I think a similar mode (that can simply be activated by a button on the joysticks or a toggle switch) could be highly beneficial when trying to just drive your robot to balance.

If your robot this year ends up with any kind of swinging chute or arm, then you could probably use that to effectively shift the center of gravity.

ALSO:

That's what we were thinking too but everyone on your alliance needs to think that way in order to get that bonus!

In the eliminations how does the coopertition bridge play out? I can't find that anywhere.

My understanding is that the Coopertition bridge gives you only qualifying points, and is therefore not necessary in the elimination rounds.

[BrendanB]

Coopertition does not play any role in the elims which is why 3 robots on a teeter-totter is worth 40 points only in the elims.




My understanding is that the Coopertition bridge gives you only qualifying points, and is therefore not necessary in the elimination rounds.

Thanks my assumption was that it became null and void for elims.

[davidthefat]

Last year our robot had a "finesse" mode, that literally slowed down the arm motors and the drive motors. I think a similar mode (that can simply be activated by a button on the joysticks or a toggle switch) could be highly beneficial when trying to just drive your robot to balance.

If your robot this year ends up with any kind of swinging chute or arm, then you could probably use that to effectively shift the center of gravity.


Personally, I want to take all the human aspects out of the balancing. The operators are facing them head on, not to the side of the board. So my plan is to get all the alliance members up and tell them to drop all controls so the software can do its work.

[KrazyCarl92]

What about placing an accelerometer on the robot that allows it to autonomously balance on the bridge? You could have it detect when you are unbalanced on the bridge then press a button that activates the auto-balance and drives to correct the imbalance. Just tell whomever you are balancing with that you have this auto-balancing feature and you have yourself 20 points or 10 points and a 2 point CP bonus as the case may be!

[BrendanB]

Personally, I want to take all the human aspects out of the balancing. The operators are facing them head on, not to the side of the board. So my plan is to get all the alliance members up and tell them to drop all controls so the software can do its work.

Three robots operating on software to balance on a ramp in which they barely fit? Could work but you need all three to do that which will be extremely rare! It is almost like having a robot in 2010 that could hang off the tower and have two to hang off of it for bonus points. It only happened once all season and with two robots not all three.

[Ninja_Bait]

The only way you are fitting three is with 3 robots that are at least 28 inches wide and you'll have 11 inches of overhang at best.

Dear Everyone:

Please build a little robot like Team Thrust's in 2010, so we will all fit on our ramp during the match.

Thanks
694

[davidthefat]

What about placing an accelerometer on the robot that allows it to autonomously balance on the bridge? You could have it detect when you are unbalanced on the bridge then press a button that activates the auto-balance and drives to correct the imbalance. Just tell whomever you are balancing with that you have this auto-balancing feature and you have yourself 20 points or 10 points and a 2 point CP bonus as the case may be!

I was just thinking of going for 2 PID loops. One to actuate the platform to the right position and the second to find where to move the platform to. Personally, a gyroscope would be better. Since it gives us the angular velocity, I just integrate that over time and you get the net angle of the gyro.



edit: any legality on "latching" onto other robots? The "t-rex" arms to push the platform down can be used to latch onto robots.

[Ninja_Bait]

edit: any legality on "latching" onto other robots? The "t-rex" arms to push the platform down can be used to latch onto robots.

Interesting question. G27 prevents you from doing it on the coopertition bridge:

Deliberate or damaging contact with an opponent Robot inside its Frame Perimeter is not allowed.

But not with your own alliance partners. Hmmm....

[Kevin Selavko]

I am wondering how robots are going to make the bridge go down form the neutral position. That may be hard. Is it just gonna be you run into it and it will move? or will we have to make a mechanism to lower it for us? Any thoughts?

At our local kickoff we had a prebuilt one to play with, if there is no weight on it to make it offbalance it will automaticly rebalance itself. This means that you will probibly have to buld somthing to keep it down as your robot is getting on. They are also fairly high off the ground, so you cant just run into it unless you are trying to push it down for an aliance member on the other side.

[pfreivald]

I'm thinking "robot one moves onto the ramp, robot two moves onto the edge. Robot one stops moving, robot two balances with accelerometer or gyro assist."

If three robots, it becomes, "robot one moves onto the ramp, robot two moves onto the edge. Robots one and two creep forward until robot three can move onto the AAAAAAAAAAAAAAAAAAAAAGH! THIS IS SO HARD!"

Should be awesome!

[davidthefat]

How much force is required to bring the ramp down?

[BrendanB]

How much force is required to bring the ramp down?

None of us could tell. Can't bring it down with your finger but put your foot on it and with a little pressure it came down. No exact measurements.

[davidthefat]

None of us could tell. Can't bring it down with your finger but put your foot on it and with a little pressure it came down. No exact measurements.

So I'll have to keep torque in mind. Really heavy weight is needed to tilt it from the middle area of the bridge.

[nighterfighter]

None of us could tell. Can't bring it down with your finger but put your foot on it and with a little pressure it came down. No exact measurements.


On the video on Youtube they stated that if you place 2 batteries next to each other, 28 inches out, the bridge should stay level. Move it an additional 2 inches I believe, and it would tilt.

Use physics, convert and stuff, and there's your answer! :p

[Mongai]

My guess is, like most years, the majority of the robots will be around 120 lb and it would be relatively easy to balance one or two on the bridge.

Ah, but remember that robot weight isn't evenly distributed.

[KrazyCarl92]

What about this scenario:

Eliminations, you have two robots on your alliance bridge and one robot on the coopertition bridge (and thus prevent your opponent from scoring on the coopertition birdge):
You get 20 points for the 2 robots on the alliance bridge and 10 points for the robot on the coopertition bridge, meanwhile preventing your opponent from scoring 10 points because you prevent them from using the coopertition bridge.

Unless your opponent could get 3 robots on their bridge, this scenario would come out the same as if you got 3 robots on a bridge and they got one robot on the coopertition bridge in terms of point differential.

I think the bridge will prove to be pivotal because not only do I think the points are weighted more balanced than in past years (...minibots), but also because FIRST reserves the right to change the point values come Championships.

[Ninja_Bait]

The Coopertition bridge scores no match points.

G40:
When the final score is assessed per [G37], a Balanced Alliance Bridge, per Section 2.2.5, earn points
(note that the coopertition bridge is excluded from this rule)

And G41:
If a Robot from each Alliance is balanced on the Coopertition Bridge when the final score for a Qualification Match is assessed per Rule [G37], each Alliance earns 2 Coopertition Points.
(note that the coopertition bridge scores only coopertition points in this rule)

[davidthefat]

So in other words, go big or go home.

[Marc S.]

If you made a wide base robot you could have a larger intake and more easily fit 3 bots on a ramp.

[Peyton Yeung]

I think getting 3 bots on will work well if the last bot to get on has a bridge lowering device.

[Djur]

How much force is required to bring the ramp down?

It's ~10 lbs at an end of the bridge. (estimation)

What about placing an accelerometer on the robot that allows it to autonomously balance on the bridge? You could have it detect when you are unbalanced on the bridge then press a button that activates the auto-balance and drives to correct the imbalance. Just tell whomever you are balancing with that you have this auto-balancing feature and you have yourself 20 points or 10 points and a 2 point CP bonus as the case may be!

That's actually ridiculously easy; I coded that from scratch on the 1hr drive back from the kickoff.

[Andrew Y.]

just put your battery on a linear slider and rack and pinion...::safety::

[jreuter]

[G37] Final scores will be assessed 5 seconds after the Arena timer hits zero.

So, whatever you do to balance, make sure it stays in position after you lose power.

[pfreivald]

If you made a wide base robot you could have a larger intake and more easily fit 3 bots on a ramp.

An omnidrive robot can more easily fit, too.

[Djur]

An omnidrive robot can more easily fit, too.

Omniwheels wouldn't be too useful because they can slide very easily and don't have good traction; Mecanums are a bit more helpful because they don't slide as easily and have better traction; holonomic drive would be best because it doesn't sacrifice traction for mobility, but it's difficult to create. Just my 2 cents.

[PayneTrain]

I guess this thread would be good to talk about how teams plan on moving the bridge from the static position down to court level so the robot can get on the bridge.

Are you going to stick a wedge on top of your robot to push it down on the other side for an alliance member? Are you going to build something that knocks it down on your side? Are you going to put legs on the robot so it can jump, or something else?

[pfreivald]

Omniwheels wouldn't be too useful because they can slide very easily and don't have good traction; Mecanums are a bit more helpful because they don't slide as easily and have better traction; holonomic drive would be best because it doesn't sacrifice traction for mobility, but it's difficult to create. Just my 2 cents.

I meant omni-directional, not necessarily "omni wheels" -- so this would include mecanum, swerve, etc, etc.

Some kind of deployable traction device would be desirable if these are used, of course.

[slijin]

How much force is required to bring the ramp down?

The tipping point seems to be ~54 lbft of torque, as per the 5th Field Tour video.

[davidthefat]

The tipping point seems to be ~54 lbft of torque, as per the 5th Field Tour video.

So at 1.5 feet out from the center, around 36 lb is required to tip it. How much does a battery weigh?

[Dmiller28]

Iv got a question... are we able to grab onto the bridge and hold onto the side of the bridge opposed to driving onto the bridge itself?

[PAR_WIG1350]

So at 1.5 feet out from the center, around 36 lb is required to tip it. How much does a battery weigh?

13-13.5 pounds


Iv got a question... are we able to grab onto the bridge and hold onto the side of the bridge opposed to driving onto the bridge itself?

[G10]
Robots may not grab, grasp, grapple, or attach to any Arena structure. (Robots may push or react against any elements of the Arena that is not protected by another rule.)
Violation: Foul

[Frenchie461]

\

[G10]
Robots may not grab, grasp, grapple, or attach to any Arena structure. (Robots may push or react against any elements of the Arena that is not protected by another rule.)
Violation: Foul

This means you can still push down on the bridge though.

[Mr_D_Mentor]

If you made a wide base robot you could have a larger intake and more easily fit 3 bots on a ramp.

Of course you make your robot more prone to tipping over if you want to go over the 4" bump.

[Tetraman]

So in other words, go big or go home.

Taking from the new will.I.am song, you mean "You can go hard, or you can go home."

Anyway, here is a bit of thought that I'm sure many have thought about already: (please excuse the bad Sketchup drawing. I'm not finished with the final field.)

http://i48.photobucket.com/albums/f242/ErwinTheSketcher/BreakingTheGame.png

Step 1: Carry Bot is on one side, with the other two on the other side.
Step 2: Carry Bot puts the Bridge on the top of their robot, allowing a robot to drive onto them.
Step 3: Carry Bot or the Third Bot moves the bridge down for the Two bots to get up.
Step 4: Two bots move to allow the Third Bot to get up.
Step 5: +40 Points.

[Kusha]

Taking from the new will.I.am song, you mean "You can go hard, or you can go home."

Anyway, here is a bit of thought that I'm sure many have thought about already: (please excuse the bad Sketchup drawing. I'm not finished with the final field.)

http://i48.photobucket.com/albums/f242/ErwinTheSketcher/BreakingTheGame.png

Step 1: Carry Bot is on one side, with the other two on the other side.
Step 2: Carry Bot puts the Bridge on the top of their robot, allowing a robot to drive onto them.
Step 3: Carry Bot or the Third Bot moves the bridge down for the Two bots to get up.
Step 4: Two bots move to allow the Third Bot to get up.
Step 5: +40 Points.

Heh, this came up yesterday.
You'd need something like this, and it would be pretty hard. Look at other '07 bots
http://www.youtube.com/watch?v=zgHanZXFweg

[MechEng83]

Has anyone built the "cheap" version of the bridge? Ours is pretty much built to spec but doesn't have dynamic properties coming close to the competition bridge in the FIRST video on their site.

Using 2 batteries, our bridge tips at about 15 inches out, rather than the 28" claimed. I did some math (explained below) and came up with a weight for our bridge around 70 pounds, whereas the competition bridge should be more like 170 pounds. Anyone else notice this, and what are your recommendations? I've thought about just adding 100 lbs of weights to the underside of the bridge, but didn't know if other people had more elegant solutions.


Math:
The hinges are 7" apart, meaning the pivots are 3.5" on each side of center.
Since the batteries weigh approximately 14 pounds each, and the center of gravity is approximately 3 inches inboard of that, we can calculate the balanced gravitational moment of the bridge and battery. For our home-built bridge, the battery side moment is (15"-3"-3.5") X 28 lbs. The balance bridge moment must be 3.5" X W[bridge]. Solving for W we get ~70 lbs.
Now, take the competition bridge in the FIRST video -- replace our 15" with 28" and you get 170 for W[bridge]. No wonder they said the field was particularly heavy this year!

[ThaneS]

I've just finished our bridge and I note the same thing. Ours tips with the batteries at around 13". However, we haven't put a sheet of polycarbonate over the top yet. I think this should make the bridge less prone to tipping, as there is more weight keeping it in the center position (if my brain is thinking about physics correctly). Getting a 4x8 sheet of .25" polycarb isn't the easiest thing for us, but another sheet of .5" plywood weighs about the same (50 lbs), so that's probably what we're going to try first. The only other discrepancy between our bridge and the plans is that the plans seem to dimension the nominal thickness of the plywood, and not the actual, easily available, thickness that we used (15/32" instead of 1/2").

On a completely different note, I haven't seen much discussion of robots falling off the bridge. There's no lip on the sides, and if a wide robot tries to go over it, there's only 5" of clearance on either side. I expect to see a lot of tipped robots.

[Djur]

On a completely different note, I haven't seen much discussion of robots falling off the bridge. There's no lip on the sides, and if a wide robot tries to go over it, there's only 5" of clearance on either side. I expect to see a lot of tipped robots.

There actually is a metal bracket on the edge to prevent robots from driving off; it's about 1 inch high if I remember right.

[speedbuggy76]

We ran into the same problem with our inexpensive version of the bridge today as well. Let us know what you decide to do to fix it, we need to work on ours too. We figure if our programmer can get it to work on this more finicky bridge, it should be good to go for the competition one :)

[ThaneS]

Ah yes, I see you're right. I should have read the drawings more carefully. In that case I expect somewhat fewer tipped robots.

[MechEng83]

We figure if our programmer can get it to work on this more finicky bridge, it should be good to go for the competition one :)

Another mentor on my team made that same point... on the other hand, the competition bridge will take significantly more force to push down than the economy model. These two features need to be balanced (no pun intended)

[vamfun]

Taking from the new will.I.am song, you mean "You can go hard, or you can go home."

Anyway, here is a bit of thought that I'm sure many have thought about already: (please excuse the bad Sketchup drawing. I'm not finished with the final field.)

http://i48.photobucket.com/albums/f242/ErwinTheSketcher/BreakingTheGame.png

Step 1: Carry Bot is on one side, with the other two on the other side.
Step 2: Carry Bot puts the Bridge on the top of their robot, allowing a robot to drive onto them.
Step 3: Carry Bot or the Third Bot moves the bridge down for the Two bots to get up.
Step 4: Two bots move to allow the Third Bot to get up.
Step 5: +40 Points.

We had the same idea.... seems like an interesting way to go. Need to get rule clarifictions about robot piggy backing.... I wonder about possible bumper zone violations for the upper robot.

If all robots can be designed to climb a 30 deg ramp... then they could just drive over the robot using 14in ramp extensions and then you don't require the use of a bridge to mount. This would have to be a very low profile specilized robot.

[Marc S.]

We had the same idea.... seems like an interesting way to go. Need to get rule clarifictions about robot piggy backing.... I wonder about possible bumper zone violations for the upper robot.

If all robots can be designed to climb a 30 deg ramp... then they could just drive over the robot using 14in ramp extensions and then you don't require the use of a bridge to mount. This would have to be a very low profile specilized robot.

See the rule updates, all robots must be touching the ramp to be supported by the ramp. So now you just have to build a robot that can lift itself high enough to allow a robot to fit underneath. Maybe some team collaboration is needed.

[Chris is me]

Omniwheels wouldn't be too useful because they can slide very easily and don't have good traction; Mecanums are a bit more helpful because they don't slide as easily and have better traction; holonomic drive would be best because it doesn't sacrifice traction for mobility, but it's difficult to create. Just my 2 cents.

Holonomic drives sacrifice traction in the same direction mecanum drives do. Holonomic drives have just as little traction as a rubber wheel, in theory. In practice omni wheels don't have very much traction in any direction unless you double or triple them up. Combine that with a low friction well greased gearbox and you will realize the wheel wastes power scrubbing motion in the wrong directions with any holonomic system. I would not recommend one.

[vamfun]

See the rule updates, all robots must be touching the ramp to be supported by the ramp. So now you just have to build a robot that can lift itself high enough to allow a robot to fit underneath. Maybe some team collaboration is needed.

.......any Robots touching it are fully supported by it.”
I am not sure that the new update precludes robot on robot. The bottom robot is touching the ramp and it is supported by the ramp. It doesn't matter that there is another robot on top of it.

However, one could also argue that the upper robot must be supported by the ramp by default since it is on a robot completely supported by the ramp.

Hmmmm seems more clarification is needed here for sure.

[Gray Adams]

.......any Robots touching it are fully supported by it.”
I am not sure that the new update precludes robot on robot. The bottom robot is touching the ramp and it is supported by the ramp. It doesn't matter that there is another robot on top of it.

However, one could also argue that the upper robot must be supported by the ramp by default since it is on a robot completely supported by the ramp.

Hmmmm seems more clarification is needed here for sure.

I would say the intent of the rules doesn't preclude robot on robots, but that's just my interpretation. It's hard to believe the GDC wouldn't want you to get points for balancing robots like that, unless you're trying to use it as a loophole of sorts so you could touch the ground or something.

[Jim Wilks]

There actually is a metal bracket on the edge to prevent robots from driving off; it's about 1 inch high if I remember right.

2" angle stock as per the drawings

[Ernst]

Completely unrelated to all of the posts in this thread so far, but I have a new question:

Do these measurements seem accurate?
If not, are they close enough that it doesn't really matter?
http://i.imgur.com/xUuI8.png

[Chinoman27]

OUr team was mulling over an idea like this. Two non driven wheels with no interaction with the drive train are on the end of a rotating arm of sorts. THis arm is left horizontal at the base of the robot within all wheels and bumpers while drivng. When robot is approaching the bridge the arm is pushed down, pushing the wheels onto the ground lifting the front end of the robot off the ground high enough to place front wheels on bridge. Back wheels can still drive robot forward to get front wheels over bridge edge. Then the arm is pulled back and the robots weight pulls the bridge down with the front wheels already on and alternate wheels stowed back below.

[Siri]

Interesting question. G27 prevents you from doing it on the coopertition bridge:



But not with your own alliance partners. Hmmm....Hmm...<G27> prevents contacting opposing robots within their frame perimeter. Any rule about the bumpers?

[LinuxArchitect]

Personally, I want to take all the human aspects out of the balancing. The operators are facing them head on, not to the side of the board. So my plan is to get all the alliance members up and tell them to drop all controls so the software can do its work.

I don't follow... you're expecting each alliance partner to have such software and that it is compatible? That would be taking coopertition to a new level.

[LinuxArchitect]

Hmm...<G27> prevents contacting opposing robots within their frame perimeter. Any rule about the bumpers?

You're expected to make contact within the bumper zone. Normally to push an opponent, but pulling/pushing a partner even with the aid of a mechanism would seem ok to me.

IMHO, each robot should have a bumper grabber to aid in bridge balancing by latching on to their neighbor. You have a pretty good (but not perfect) idea where your partner's bumper will be so it shouldn't be too difficult. Perhaps not a top priority though.

[PayneTrain]

OUr team was mulling over an idea like this. Two non driven wheels with no interaction with the drive train are on the end of a rotating arm of sorts. THis arm is left horizontal at the base of the robot within all wheels and bumpers while drivng. When robot is approaching the bridge the arm is pushed down, pushing the wheels onto the ground lifting the front end of the robot off the ground high enough to place front wheels on bridge. Back wheels can still drive robot forward to get front wheels over bridge edge. Then the arm is pulled back and the robots weight pulls the bridge down with the front wheels already on and alternate wheels stowed back below.

Why not save your arm idea the stress of lifting a 140 pound fully loaded robot and just push the bridge down in the front?

[noceradave]

the center of gravity of your own robots's a counterweight

[Joe Johnson]

Based on the calcs that I have done (from the info the video provides plus the other data from the rules, etc.),


at level, it takes about 15lbs at the edge to tip to an empty bridge
the bridge must weigh about 200lbs and it's CG must below 9" above the barrier top or else their would be zero restoration torque when down - I estimate it is at 7" FWIW
If two robots with their combined CG on the centerline of the bridge (and they weigh 143 lbs each), it takes 35lbs to push the edge of the bridge down and their combined CG can move +/-5” without tipping the bridge. If one robot is stationary, the other robot can move +/-10”!
Further, assuming each has a CG 20” above the plane of the top of the bridge and they are in their nominal balance position, if the bridge is tipped to the ground, it will take 39lbs at the edge of the ramp to lift them back up.
Continuing… if they move from their together from their nominal position, they will have to move more than 6” up the ramp to make the bridge neutrally balanced (+ a bit more to get it to move). Note that this is beyond the 5" they have from nominal (see above) and they then have to stop the bridge so they will have to move maybe 3" back once they start tipping.
If only one robot does the rebalancing, they will have to move 12" up the ramp ...
I could go on, but this is all physics guys…



There's a lot to think about... ...fun fun fun...


Joe J.

[vamfun]

Thanks for the analysis Joe....

Do we know exactly how far the Bridge edge is from the wall. We have it at around 1 inch. Can anyone confirm this from taking measurements from the actual demo field?

[rscheer]

Does anyone have the wieght of a battery handy?

[plnyyanks]

IIRC, they're ~15 lbs

Edit: looking it up, they're 6.2 kilograms = 13.6686603 pounds (from the datasheet (http://www.yuasabatteries.com/pdfs/NP_18_12_DataSheet.pdf))

[RRLedford]

[Semi-teaser] Once you realize that getting FOUR full size robots on the bridge is quite possible without them overlapping, then the ways for easily getting three on and balanced start to look a lot easier to accomplish.

-RRLedford

[372 lives on]

I would love to see if anyone builds "minibots". Yeah of you can get your robot down to 10x10 that would be intense :) but would probably not be very usefull so how about other weird sizes like 10x 20 :) I want to see something crazy like that designed for 3 bots on a bridge but still able to function during normal game play.
:eek: :eek: :ahh:

[artdutra04]

I would love to see if anyone builds "minibots". Yeah of you can get your robot down to 10x10 that would be intense :) but would probably not be very usefull so how about other weird sizes like 10x 20 :) I want to see something crazy like that designed for 3 bots on a bridge but still able to function during normal game play.
:eek: :eek: :ahh:You can fit three normal sized robots on the bridge (http://www.youtube.com/watch?v=GytK9Sl1RwY).

While smaller robots would make it easier, it's not impossible with "normal" sized robots.

[RRLedford]

You can fit three normal sized robots on the bridge (http://www.youtube.com/watch?v=GytK9Sl1RwY).

While smaller robots would make it easier, it's not impossible with "normal" sized robots.

You can fit four normal size robots on the bridge too, even the outer ones.

-RRLedford

[372 lives on]

You can fit four normal size robots on the bridge too, even the outer ones.

-RRLedford

LOLOLOL

i want to see your math.

no really...

28*4=112 inches
+ bumpers=136 inches


ok so how do we get 136 inches onto 88 inches???

finishies lolrage realizes we have three robots per alliance.........:mad:

[RRLedford]

LOLOLOL

i want to see your math.

no really...

28*4=112 inches
+ bumpers=136 inches


ok so how do we get 136 inches onto 88 inches???

finishies lolrage realizes we have three robots per alliance.........:mad:

I didn't say that any match would be having an actual 4 bots on a bridge result.
I only said that four full size bots CAN be balanced on the outer bridges, and without overlapping each other
In order to imagine what I am saying you will have to start thinking more "outside the bridge"

Now that I consider it further, even five (5) full size bots can balance on the bridge
-RRLedford

[RRLedford]

I didn't say that any match would be having an actual 4 bots on a bridge result.
I only said that four full size bots CAN be balanced on the outer bridges, and without overlapping each other
In order to imagine what I am saying you will have to start thinking more "outside the bridge"

Now that I consider it further, even five (5) full size bots can balance on the bridge
-RRLedford

I now believe that even without trolling or overlapping, as many as eight (8) 27" x 37" robots could balance on the bridge.

-DIck Ledford

[Daniel_LaFleur]

I now believe that even without trolling or overlapping, as many as eight (8) 27" x 37" robots could balance on the bridge.

-DIck Ledford

I don't believe more than 3 could stay on as the bridge changes from tipped to balanced due to the angular momentum.

Thus, theoretical maximums are not valid compared to the real world physics of making it happen.

In fact, I believe we will see a number of rolled robots as in the elims as they try for 3 robot balances. Build your robot robustly :ahh:

[RRLedford]

I don't believe more than 3 could stay on as the bridge changes from tipped to balanced due to the angular momentum.

Thus, theoretical maximums are not valid compared to the real world physics of making it happen.

In fact, I believe we will see a number of rolled robots as in the elims as they try for 3 robot balances. Build your robot robustly :ahh:

Our robot plays defense and then goes on the bridge first. We head for the balance point and we go just past it enough to tip it down toward our two alliance partners, who can then roll right up with both of them bumper to bumper.

Since we are able to hang off the SIDE edge of the bridge with less than 1/2 of our width located above the bridge, our partners can drive right past us, stopping near the middle. This lets all of three of us remain closer to the center of the bridge as we balance it, making the job much easier than if we had two bots hanging off the ends. None of our alliance needs to go anywhere near the ends to still have a 3-bot balance in elimination round, and we all have plenty of bridge length to work with as we balance it.

-Dick Ledford

[Tom Ore]

Since we are able to hang off the SIDE edge of the bridge with less than 1/2 of our width located above the bridge, our partners can drive right past us sitting near the middle. This lets all of three of us remain closer to the center of the bridge as we balance it, making the job much easier than if we had two bots hanging off the ends. None of our alliance needs to go anywhere near the ends to still have a 3-bot balance in elimination round.

-Dick Ledford

We pursued this same idea for a few days very early in the season. We took it far enough to get a rough CAD and even named it Harold. In the end, we abanded it with the other two "out there" ideas we were thinking of (the 179 style and the trollbot style.) It's really cool to see that teams actually built all three of these ideas.

[davidthefat]

This is what I have observed about balancing after practice and going to a scrimmage: it is all about knowing when to just "stop driving". So far, I have consistently balanced the robot in 4 to 10 seconds every time. I realize that you just require a lot of that "gut feeling". You just have to "know" when to stop driving. Once you overshoot, it gets fairly hard to balance. Also, about balancing two robots, I found hand signals to be the best way to communicate with the opposing alliance; have the coach watch and do hand signals.

[RRLedford]

This is what I have observed about balancing after practice and going to a scrimmage: it is all about knowing when to just "stop driving". So far, I have consistently balanced the robot in 4 to 10 seconds every time. I realize that you just require a lot of that "gut feeling". You just have to "know" when to stop driving. Once you overshoot, it gets fairly hard to balance. Also, about balancing two robots, I found hand signals to be the best way to communicate with the opposing alliance; have the coach watch and do hand signals.

We made it to balance in 3 seconds from first wheel touching bridge for out best time in our first real driving tests today. Only ~14" lateral inches of our robot (including the bumper) is above the bridge, and the rest (~19") is hanging off the left side of our bridge. We have only 2 of our 3 right wheels (6 wheel tank drive) making decent contact with the bridge and are just able to make it up with wheels slipping all the way. We can over shoot to send bridge down at opposite end and then spin wheels slowly to hold that tilted position at near mid way down at the low end. After our alliance partners from the scoring end roll right up the bridge going past us, we can then get back up toward center and balance with them near center, along side them.

We really had to get as much of our mass as possible assembled as far over to the right side as possible and we are still needing a bit more far right placed ballast to improve our bridge traction for the 2-3 driven wheels that remain in contact as we go up it. We will likely just keep adding weight there right up to the point where we hit 120 lbs. so we can max out our traction for the right side (on bridge) wheels. Our left wheels are just spinning in the air as we climb up using only the left <1/3 of the bridge. It is a very cool looking DOUBLE balancing act.

-Dick Ledford