View Full Version : For those who are skeptical about propellers - Team 2526
http://i127.photobucket.com/albums/p129/zrop/IMG_6038.jpg
http://i127.photobucket.com/albums/p129/zrop/IMG_6039.jpg
The props both spin at about 7000 rpm, but they haven't been properly calibrated yet, so we may get quite a bit more power out of them.
Videos:
http://www.youtube.com/watch?v=mlUPGUfgrHo#
http://www.youtube.com/watch?v=crKvPEwvf-U
And for those safety nazis -- why yes we do have a safety cage for it :)
http://i127.photobucket.com/albums/p129/zrop/IMG_6031.jpg
What type of props are those? They look like 9"x something. Are they balanced? If not, I can tell you how to balance a prop.
Also, I'm not quite sure that that cage is going to be enough. I'd put another layer on on top or underneath so that the area of each open area is divided into four areas--if the props do explode, I'm pretty sure they could get through the pictured version. Reducing the open area will also reduce the risks.
Wow that totally is a unique and different propulsion system! I cant wait to see that in actual competition!
I would tend to agree with Eric though, I'd add some more protection to that cage. The cage will protect from reaching hands, but if those props were to ever break, (and going 7000 rpm, they very well might) you dont want blades going flying... I'm not a safety Nazi, I just like being safe.
Overall though, Awesome!
safety cage we are going to use is designed to keep balls outs rather than keeping blade shrapnel in. :ahh:
engunneer
01-02-2009, 00:30
Cool.
What are the pegs on your rollers? What's the diameter of them? If they are too small, you might have inspection problems.
safety cage we are going to use is designed to keep balls outs rather than keeping blade shrapnel in. :ahh:
The inspectors will be looking for both. One piece of prop shrapnel gets through, and <S01> is probably going to be called. Then you have to remove both.
Let's say those are 9" blades going at 7000 RPM. That's C=pi*d=pi*9=28.26" per revolution. That's about a 2' circumference (rounded down to emphasize the need for protection here). So, the tips of that prop are traveling at 7000RPM=116.7RPS over a 2' circle. That's a tangential speed of 233.3 feet per second--or about 4 FRC fields in one second. If a tip breaks off at that speed, you WILL get a safety violation if it leaves the robot! And, if I were the head ref, I'd make you either remove the props or add protection to the cage. Play it safe and add material now.
Edit: I just saw this: http://www.chiefdelphi.com/forums/showthread.php?p=812049#post812049
I would consider this, or something similar, much safer than your current setup.
Woodworker88
01-02-2009, 00:43
Nice work, looks like you put some thought into the design. Good use of model airplane props.
Are you worried that having the props mounted in a biased configuration (not dead-center on the robot) will tend to make the robot turn or move awkwardly? I assume you offset them to make room for a ball-handling system. Will the airflow pass through the ball system or will you reverse the rotation to reverse the direction of the robot?
On a separate note, have you checked the metal hardware on your collector to make sure it's not going to rip up the balls? Looks iffy to me.
=Martin=Taylor=
01-02-2009, 00:44
What you should do is put them up high, so they will both propel your bot and blow-away balls.
If it can move a 120 lb. bot it should be able to deflect a few rocks :yikes:
Greg Peshek
01-02-2009, 00:49
What you should do is put them up high, so they will both propel your bot and blow-away balls.
If it can move a 120 lb. bot it should be able to deflect a few rocks :yikes:
Sadly that hasn't worked with the tests our team has doen, the porous nature of the ball's geometry tends to not move it at all. Our tests were all done with a 22" blade with a 3D-10A pitch blade that was moving a lot of air at a 1:1 ratio from a CIM. YMMV.
Looking good guys, keep it up.
-Greg
The inspectors will be looking for both. One piece of prop shrapnel gets through, and <S01> is probably going to be called. Then you have to remove both.
Let's say those are 9" blades going at 7000 RPM. That's C=pi*d=pi*9=28.26" per revolution. That's about a 2' circumference (rounded down to emphasize the need for protection here). So, the tips of that prop are traveling at 7000RPM=116.7RPS over a 2' circle. That's a tangential speed of 233.3 feet per second--or about 4 FRC fields in one second. If a tip breaks off at that speed, you WILL get a safety violation if it leaves the robot! And, if I were the head ref, I'd make you either remove the props or add protection to the cage. Play it safe and add material now.
Edit: I just saw this: http://www.chiefdelphi.com/forums/showthread.php?p=812049#post812049
I would consider this, or something similar, much safer than your current setup.
The propellers are perfectly safe as long as they don't exceed their maximum rpm, the rate at which we are spinning them is no where near their maximum rpm (the maximum is about 13k rpm). Having them spontaneously exploding is not a huge concern to us, having balls getting in the way of the props is a much bigger concern. (oh and its 12.25 in in diameter btw ;D)
Akash Rastogi
01-02-2009, 00:59
I'm taking Eric's word on this one.
I highly doubt that the inspectors will give a crap ( or too much) about the safety of the precious orbit balls.
I say that if a finger or even a hand can pass through the cage, then it is not safe.
+$0.02
Sadly that hasn't worked with the tests our team has doen, the porous nature of the ball's geometry tends to not move it at all. Our tests were all done with a 22" blade with a 3D-10A pitch blade that was moving a lot of air at a 1:1 ratio from a CIM. YMMV.
Looking good guys, keep it up.
-Greg
Yeah, that's why we have a 3.5 multiplier on our props. So the 2.5 k rpms you get on a CIM motor at peak power output you don't have nearly enough pushing power. Our props are actually push them at about a walking pace.
See, ideally you reach 88% - 94% the speed of sound on the tips of your props in order to get maximum power.
I'm taking Eric's word on this one.
I highly doubt that the inspectors will give a crap ( or too much) about the safety of the precious orbit balls.
I say that if a finger or even a hand can pass through the cage, then it is not safe.
+$0.02
Who is dumb enough to stick their fingers in there?? Plus the props are far enough inside the cage that even if you can get your fingers in, they wouldn't touch the props.
PLUS who's running around the field trying to catch a robot by sticking their fingers into the cage with spinning blades???
synth3tk
01-02-2009, 01:07
Who is dumb enough to stick their fingers in there?? Plus the props are far enough inside the cage that even if you can get your fingers in, they wouldn't touch the props.
PLUS who's running around the field trying to catch a robot by sticking their fingers into the cage with spinning blades???
Pit area? Although safety should always be first, sometimes mistakes are made.
Greg Peshek
01-02-2009, 01:09
Yeah, that's why we have a 3.5 multiplier on our props. So the 2.5 k rpms you get on a CIM motor at peak power output you don't have nearly enough pushing power. Our props are actually push them at about a walking pace.
See, ideally you reach 88% - 94% the speed of sound on the tips of your props in order to get maximum power.
Well, our blade/s pull too much power to gear it up any. We start tripping a 40A breaker at a 1:2 ratio. The size of our prop combined with the really high pitch, and the fact that the blade is cut to give a lot of thrust in one direction.. gave us a pretty good acceleration to around the speed you're describing at 3/4 ratio.
Of course we're going for different things. You have them for turning and maneuvering plus a good amount of power. And we're going for sheer power, mainly for getting across in a straight line fast, pinning, and then dumping.
Tell you what, you make it to Atlanta for Championships, we'll have an Overdrive style race. ;)
-Greg
Pit area? Although safety should always be first, sometimes mistakes are made.
How about we put safety whistles behind the props so everyone can hear when they're on and uh.. think?
Akash Rastogi
01-02-2009, 01:11
Who is dumb enough to stick their fingers in there?? Plus the props are far enough inside the cage that even if you can get your fingers in, they wouldn't touch the props.
PLUS who's running around the field trying to catch a robot by sticking their fingers into the cage with spinning blades???
Who's dumb enough to accidentally turn on a robot when someone is working on the blades???
Who's dumb enough to move the wheels when someone is fixing a sprocket on the drive train?????
I can make lots of question marks too. You can get as defensive as you want about your robot design itself, but when it comes to the safety of others don't take suggestions lightly.
If you're not in it for the safety and well being of your members and others in the pit, that's fine by me.
Well, our blade/s pull too much power to gear it up any. We start tripping a 40A breaker at a 1:2 ratio. The size of our prop combined with the really high pitch, and the fact that the blade is cut to give a lot of thrust in one direction.. gave us a pretty good acceleration to around the speed you're describing at 3/4 ratio.
Of course we're going for different things. You have them for turning and maneuvering plus a good amount of power. And we're going for sheer power, mainly for getting across in a straight line fast, pinning, and then dumping.
Tell you what, you make it to Atlanta for Championships, we'll have an Overdrive style race. ;)
-Greg
You might want to reduce your pitch then. High pitches are made for high speeds, therefore you're being really ineffective and ideally you'd have about 1-2 pitch prop from max speeds of about 7-15 mph. Otherwise, even with our pitch of 3.75, we hit ideal speeds at about 30 mph.
And yes, prop race at Atlanta ;D
The propellers are perfectly safe as long as they don't exceed their maximum rpm, the rate at which we are spinning them is no where near their maximum rpm (the maximum is about 13k rpm). Having them spontaneously exploding is not a huge concern to us, having balls getting in the way of the props is a much bigger concern. (oh and its 12.25 in in diameter btw ;D)12.25 inches????
Let's run the numbers. That's 374.15 feet per second if something breaks! If a prop breaks, it's going 7, yes 7, FRC fields per second.
As for perfectly safe if they don't exceed maximum RPM, that's all well and good, but R/C aircraft don't hit things. That's the facts of it--if they hit anything, they crash (or just crashed) and the prop is broken anyway. These props are going to be jostled through shock loads when they get hit. This could potentially weaken them. If they're weak, and they get one hit too many, somebody is going to get hit, hard. I haven't run the numbers on KE for, say, 1/3 of a prop, but that's far more than I want to have hitting anybody!
As for who's going to poke hands in, I can think of a few things--little kids, poles from a tipped trailer, unsuspecting students... I am pretty sure I could get my hand in enough to contact at least one prop.
Bottom line, don't worry about keeping balls out, worry about keeping the props in. If you do that (better than the cage shown will), the balls will take care of themselves.
Oh, and I just remembered--if you reverse those blades while they're going full bore, that's a pretty hefty acceleration force you put them through. This will contribute to propeller weakening. They aren't designed to run in reverse.
XaulZan11
01-02-2009, 01:22
Yes, the cage does make it more safe, but why isn't it on during testing? In the 2nd video, I think the person bending down gets a little too close; one slip and people will be watching the video for different reasons...
Creative design, but make sure it's safe
tanmaker
01-02-2009, 01:22
I believe the KE for 1/3 of the prop will be over 2000 joules so yeah, it's not something I want to be in front of when it comes flying off.
12.25 inches????
Let's run the numbers. That's 374.15 feet per second if something breaks! If a prop breaks, it's going 7, yes 7, FRC fields per second.
As for perfectly safe if they don't exceed maximum RPM, that's all well and good, but R/C aircraft don't hit things. That's the facts of it--if they hit anything, they crash (or just crashed) and the prop is broken anyway. These props are going to be jostled through shock loads when they get hit. This could potentially weaken them. If they're weak, and they get one hit too many, somebody is going to get hit, hard. I haven't run the numbers on KE for, say, 1/3 of a prop, but that's far more than I want to have hitting anybody!
As for who's going to poke hands in, I can think of a few things--little kids, poles from a tipped trailer, unsuspecting students... I am pretty sure I could get my hand in enough to contact at least one prop.
Bottom line, don't worry about keeping balls out, worry about keeping the props in. If you do that (better than the cage shown will), the balls will take care of themselves.
Oh, and I just remembered--if you reverse those blades while they're going full bore, that's a pretty hefty acceleration force you put them through. This will contribute to propeller weakening. They aren't designed to run in reverse.
How about this: We'll put extra thick mesh on the sides of the safety cage because any flying props would.. exit there. But to keep proper airflow, the current cage in the front and back should suffice.
Akash Rastogi
01-02-2009, 01:24
I believe the KE for 1/3 of the prop will be over 2000 joules so yeah, it's not something I want to be in front of when it comes flying off.
Yup. It is by my account also. (Emphasis mine)
How about this: We'll put extra thick mesh on the sides of the safety cage because any flying props would.. exit there. But to keep proper airflow, the current cage in the front and back should suffice.
Thick mesh, or a sheet, would probably work. Even if it doesn't fully stop the prop, it'll slow it down to the point where it isn't nearly as great a danger.
Yes, the cage does make it more safe, but why isn't it on during testing? In the 2nd video, I think the person bending down gets a little too close; one slip and people will be watching the video for different reasons...
Creative design, but make sure it's safe
Haha. It just looks like I got close, but really, i grabbed it about a foot in front of the props. And as for the cage, we didn't have the mounting brackets completed at the time of testing... and we were anxious. :D
Yup. It is by my account also. (Emphasis mine)
Don't worry. It's double nylon nutted on. :D
TotalChaos
01-02-2009, 01:28
Who is dumb enough to stick their fingers in there??
I have to agree with Akash and Eric. I wouldn't just assume that common sense will prevent all accidents. Why do you think they put "HOT" warning labels on coffee cups? Or warnings on electrical things, such as hair dryers, not to submerge in water? ... Sometimes things can happen, and there's no reason not to play it safe...
Other than that, very cool propulsion system! I was one of those skeptical about using fans, but it turns out I was wrong and they work great after all!
Good luck at the competition!
- Austin
synth3tk
01-02-2009, 01:29
How about we put safety whistles behind the props so everyone can hear when they're on and uh.. think?
Even if I wasn't safety captain for my team two years in a row, I would still like to think that safe practices are of the utmost importance in every FIRST member's mind during the season. While this isn't as deep as thousands of people dying, you still need to take some caution in the real world, and all the FRC is doing is preparing you to make safety second nature.
Afterall, we don't want this:
http://www.chiefdelphi.com/forums/showthread.php?t=65978
or this:
http://www.chiefdelphi.com/forums/showthread.php?t=59436
to sound like something that might happen as a result of your team's machine. I take safety seriously, and hope that everyone else does too. If not, you need to sit back, forget drilling another hole, and think about that.
I would still have finger-proof mesh in the front and back, and possibly even wire the props so that they cannot be turned on with the mesh removed. Never count on "people won't be stupid" as a saftey feature. Take Murphy's law one step further, "Everything that can and cannot go wrong will go wrong."
*From someone who got his finger caught in Vex chain one time too many.*
tanmaker
01-02-2009, 01:30
Remember we are taking into account 1/3 of a propeller. For all of the smashing that could be happening, those props will no doubt be subjected to forces they are not designed for. These abnormal forces will weaken the propeller, causing it to ultimately fail.
I would still have finger-proof mesh in the front and back, and possibly even wire the props so that they cannot be turned on with the mesh removed. Never count on "people won't be stupid" as a saftey feature. Take Murphy's law one step further, "Everything that can and cannot go wrong will go wrong."
*From someone who got his finger caught in Vex chain one time too many.*
Alrighty.. We'll take care of it. We really posted this here for more the propulsion design rather than safety concerns.
synth3tk
01-02-2009, 01:34
Alrighty.. We'll take care of it. We really posted this here for more the propulsion design rather than safety concerns.
Think of it this way: Now we saved you some time, hassles, and [possibly] stitches this season.
tanmaker
01-02-2009, 01:35
I think we all understand that, and it is a great design, don't get me wrong. We just want you to be safe and take these recommendations into consideration early rather than having the safety inspector telling you the same thing a few hours before a match.
Akash Rastogi
01-02-2009, 01:38
Alrighty.. We'll take care of it. We really posted this here for more the propulsion design rather than safety concerns.
I love the design. Great work. I hope you get Xerox creativity for it at the least.
engunneer
01-02-2009, 01:40
There's a theory that I give to students in the machine shop. Whenever something is moving, look for the "plane of destruction". It's the plane where things go flying when (not if) things go bad. You never want to be in the plane of destruction.
A denser mesh on the sides are a great idea. also, get some of those big "remove before flight" flags and use them and some kind of peg or clip to prevent rotation whenever it's not on the field. (even better, tie them to the cart so you can't lose them).
Woodworker88
01-02-2009, 01:42
get some of those big "remove before flight" flags and use them and some kind of peg or clip to prevent rotation whenever it's not on the field. (even better, tie them to the cart so you can't lose them).
Excellent idea, this is what combat robots (battlebots) are required to use to safeguard rotating weapons. Physical pins prevent rotation until the robot is in place on the field.
There's a theory that I give to students in the machine shop. Whenever something is moving, look for the "plane of destruction". It's the plane where things go flying when (not if) things go bad. You never want to be in the plane of destruction.My Aero Design team has a rule: NEVER stand in the same plane as the prop while the engine is a) running or b) about to be started. In front or behind is OK (or required, depending on who you are), but never to the side. Shield the plane of the props, and a little in front of and behind that plane, and you *should* pass inspection. By doing so, you also get a "ducted fan", where there is almost a funnel for air to pass through. These are just as good as unshielded props, if not better.
Woodworker88
01-02-2009, 02:17
My Aero Design team has a rule: NEVER stand in the same plane as the prop while the engine is a) running or b) about to be started. In front or behind is OK (or required, depending on who you are), but never to the side. Shield the plane of the props, and a little in front of and behind that plane, and you *should* pass inspection. By doing so, you also get a "ducted fan", where there is almost a funnel for air to pass through. These are just as good as unshielded props, if not better.
This is the same rule we have when working on props and jet turbines at the aerospace museum where I volunteer. All of our APUs (jet turbine powered generators) have distinct red lines painted on the enclosures to show the plane of the turbine blades.
My Aero Design team has a rule: NEVER stand in the same plane as the prop while the engine is a) running or b) about to be started. In front or behind is OK (or required, depending on who you are), but never to the side. Shield the plane of the props, and a little in front of and behind that plane, and you *should* pass inspection. By doing so, you also get a "ducted fan", where there is almost a funnel for air to pass through. These are just as good as unshielded props, if not better.
I'd have to agree about the ducted fans. Close ducts around the blades SERIOUSLY improve propulsion force because less air is thrown off to the sides because of centripetal force. The duct creates a high-pressure zone around the edges of the blades that focuses all the air from front to back. Not to mention, if you narrow the end of the duct a little (toward the back), you get higher pressure, which should help you to move forward faster.
Insulation foam (like the kind used in insulation board) is very good for fan ducts, as it's easily formed, strong, and light weight, not to mention will catch any flying pieces that should come off in the foam itself, so you don't get any ricochets.
I can see how under normal circumstances that cage should be safe, but think about what could happen if a nut popped off either your robot or another one in a collision (as it looks like you'll be hitting pretty hard!) and fell into the propeller, you've basically got a "low-speed" bullet, probably combined with a shattered propeller blade that is no longer bound by centripetal force. Sure, all the drivers, coaches, and human players (minus maybe the two in the middle) would be perfectly safe behind half-bullet proof glass, but the judges and refs (who give you points, by the way) could be in serious danger. I think spending a couple hours lathing some foam into ducted fans is more than worth it to improve performance and keep people saying, "Dude, that was awesome!" instead of, "Ow. Hey, can I get a -- no, seriously, ow."
SWEET robot though! Really like the numbers on those things, looks like you'll be having some very fun matches at nationals!
Wayne Doenges
01-02-2009, 08:29
It's a great design but IMHO I don't think it will push a 120 pound robot with trailer around the arena. Just my $.02. I'll take our wheels on regolith to move any day.
I do take offence though that just because allot of people have concerns about the safety of the props being call "safety nazis" :mad:
Also, concerning your ball gatherer you may want to look at this rule:
Exterior or exposed surfaces on the ROBOT shall not present undue hazards to the team members, event staff or GAME PIECES. Reasonable efforts must be taken to remove, mitigate, or shield any sharp edges, pinch points, entanglement hazards, projectiles, extreme visual/audio emitters, etc. from the exterior of the ROBOT. All points and corners that would be commonly expected to contact a GAME PIECE should have a minimum radius of 0.125 inches to avoid becoming a snag/puncture hazard. All edges that would be
commonly expected to contact a GAME PIECE should have a minimum radius of 0.030 inches. All of these potential hazards will be carefully inspected.
* gets off soapbox and puts on flame suit :ahh:
Sean Raia
01-02-2009, 10:10
Interesting
I'd have to agree about the ducted fans. Close ducts around the blades SERIOUSLY improve propulsion force because less air is thrown off to the sides because of centripetal force. The duct creates a high-pressure zone around the edges of the blades that focuses all the air from front to back. Not to mention, if you narrow the end of the duct a little (toward the back), you get higher pressure, which should help you to move forward faster.
Insulation foam (like the kind used in insulation board) is very good for fan ducts, as it's easily formed, strong, and light weight, not to mention will catch any flying pieces that should come off in the foam itself, so you don't get any ricochets.
I can see how under normal circumstances that cage should be safe, but think about what could happen if a nut popped off either your robot or another one in a collision (as it looks like you'll be hitting pretty hard!) and fell into the propeller, you've basically got a "low-speed" bullet, probably combined with a shattered propeller blade that is no longer bound by centripetal force. Sure, all the drivers, coaches, and human players (minus maybe the two in the middle) would be perfectly safe behind half-bullet proof glass, but the judges and refs (who give you points, by the way) could be in serious danger. I think spending a couple hours lathing some foam into ducted fans is more than worth it to improve performance and keep people saying, "Dude, that was awesome!" instead of, "Ow. Hey, can I get a -- no, seriously, ow."
SWEET robot though! Really like the numbers on those things, looks like you'll be having some very fun matches at nationals!
I've always known that closed ducts increases thrust (thanks mythbusters :D ) but have never known how proceed in making them. Thanks for the suggestion on how do make that possible.
I've always known that closed ducts increases thrust (thanks mythbusters :D ) but have never known how proceed in making them. Thanks for the suggestion on how do make that possible.
Just keep in mind that the same rules of production apply here as do in MythBusters, i.e. there will be foam everywhere wherever you do this. I would recommend getting layers of foamboard and cutting out circles close to the end diameter with a knife, and then shaving off the remaining parts as close as you can. Then glue the layers together as closely lined up as possible (epoxy/gorilla glue works well), let cure, and then take some sandpaper to the inside to get it perfectly smooth. Make sure that the inside diameter is NO MORE than 1/4" off the tip of the blade, and that's REALLY pushing it. Try to get it about 1/8" if possible. This is the easiest way I know how to do it, it'll be really friggin' strong, and it'll look pretty cool. Make sure to put a grating on both the front and the back that fingers cannot penetrate at all and will resist nuts and screws. If it ends up looking dorky, you can always put some LED's inside the foam to light it up into a cool blue (as the foam is already blue).
Team2883
01-02-2009, 11:29
very cool design, but i beleive steering could be an issue, but heck with that it will still be the most recognized bot at any venue. I know I would be leaving the pit area to watch you fire that thing up.
writchie
01-02-2009, 14:13
Haha. It just looks like I got close, but really, i grabbed it about a foot in front of the props. And as for the cage, we didn't have the mounting brackets completed at the time of testing... and we were anxious. :D
Wow, one foot! That's a safe distance. Two weeks ago in response to safety concerns you said:
Yeah I agree with what you said. We just rushed to mount the prototype in order to disprove any skepticism our team had. So inevitably, safety was the first thing that was overlooked... Atleast everyone wore safety glasses...
After the safety advice you received over the last two weeks ago, you're now educated enough to make the following comments
....Alrighty.. We'll take care of it. We really posted this here for more the propulsion design rather than safety concerns.
....And for those safety nazis -- why yes we do have a safety cage for it
...safety cage we are going to use is designed to keep balls outs rather than keeping blade shrapnel in.
...The propellers are perfectly safe as long as they don't exceed their maximum rpm, the rate at which we are spinning them is no where near their maximum rpm (the maximum is about 13k rpm). Having them spontaneously exploding is not a huge concern to us, having balls getting in the way of the props is a much bigger concern. (oh and its 12.25 in in diameter btw ;D)
Reply With Quote
...Who is dumb enough to stick their fingers in there?? Plus the props are far enough inside the cage that even if you can get your fingers in, they wouldn't touch the props.
...How about we put safety whistles behind the props so everyone can hear when they're on and uh.. think?
...PLUS who's running around the field trying to catch a robot by sticking their fingers into the cage with spinning blades???
Reply With Quote
It's pretty obvious that you guys are a team of know-it-all invulnerable teenagers without adult supervision, never mind engineering mentors. Many people have tried to point out the safety issues and like all Darwin candidates you smugly dismiss them with flippant comments.
I don't expect that you will change your ways and since children, drunks, and idiots are often protected by providence I expect you'll survive without incident. I also expect that if you show up with anything like your present wire cage, you'll be promptly thrown out of the pits.
But you do provide a service that draws useful advice that less arrogant individuals may use to reduce the risk that their machines pose to themselves and any onlookers. By the way, here's one example of what can go wrong:
http://www.youtube.com/watch?v=hmcTyBxSL00
The R/C hobby has a pretty good safety record over the years, although it is not been free of de-capitations and other fatalities and many serious injuries. There are no perfectly safe propellers and no perfectly safe anything for that matter. It's a matter of understanding risks and reducing them to acceptable levels. Mostly, this happens by eliminating "UNNECESSARY" risk and you guys are a shining example of those.
Every decade or so, something changes (like mass, blade dia, rpm's, etc) and accidents skyrocket until best practices change.
Do the math. The risk potential comes from the velocity and energy of the parts when they fail and fly. Yes, the propeller arc and thrust line are the most dangerous in the open, but the blades can bounce off obstructions and continue in any direction. Vibrations and flutter can cause rapid failures. A foreign object sucked into the airstream can damage the prop or cause an immediate blade failure, especially if it impacts near the tips. Given this years robot collisions, failure modes not encountered in R/C flying can be expected. Anything short of full containment just isn't going to cut it.
Few of those who loose fingers or suffer other serious injuries intended to do so.
FIRST has a safety culture for very good and valid reasons. If you are unwilling to accept that culture and consider those looking out for your safety and that of the public to be Nazi's, then you are of no benefit to the FIRST program.
writchie beat me to the rant post about how ignorant you're being.
The idea is cool, yes. You need to keep in mind though you have some of the most respectable people on Chief Delphi telling you about what you're doing wrong, and you're just shaking off like "oh yeah we'll fix that"
Inspectors will stop you if your props look remotely unsafe. They're looking out for everyone's safety not just how cool your robot is. If a 12 year old can put a finger inside your guard, they'll rule it unsafe, judging by that picture I think a 12 year old could fit his whole arm in there.
What's the over/under on the number of propeller robots on Einstein?
Any takers?
Akash Rastogi
01-02-2009, 17:46
What's the over/under on the number of propeller robots on Einstein?
Any takers?
0/6
Sorry 1771...I still love you guys.
What's the over/under on the number of propeller robots on Einstein?
Any takers?
1/6 at best
sdcantrell56
01-02-2009, 18:00
0/6
Sorry 1771...I still love you guys.
Awe come on Akash. This is our year to make it. I'm feeling it in my bones...now if we can just get our bots finished we might actually have something. :D
David Brinza
01-02-2009, 18:18
I wouldn't be surprised if FIRST issues guidelines regarding safety measures for propellers (just remember the guidelines for last year's catapults). FIRST is (and should be) risk adverse when it comes to safety.
As an inspector, I'm going to ask a lot of questions about the safety provisions and considerations in high-energy, potentially lethal features in robots.
What margin of safety do you have in the hazard containment? (Prove to me that you've got at least a factor of five in keeping all parts from penetrating your safety shields.)
How do you verify that there are no flaws in the propeller and attachment components? Do you have proof of inspection for cracks in the propeller, shaft, etc.? Do you have safety-wired fasteners and a fail-safe design (i.e., if a fastener fails, do you still have margin against catastrophic failure)?
Sound tough? This is nothing compared to the aftermath of a failure where someone is seriously injured or worse.
Akash Rastogi
01-02-2009, 18:23
I wouldn't be surprised if FIRST issues guidelines regarding safety measures for propellers (just remember the guidelines for last year's catapults). FIRST is (and should be) risk adverse when it comes to safety.
As an inspector, I'm going to ask a lot of questions about the safety provisions and considerations in high-energy, potentially lethal features in robots.
What margin of safety do you have in the hazard containment? (Prove to me that you've got at least a factor of five in keeping all parts from penetrating your safety shields.)
How do you verify that there are no flaws in the propeller and attachment components? Do you have proof of inspection for cracks in the propeller, shaft, etc.? Do you have safety-wired fasteners and a fail-safe design (i.e., if a fastener fails, do you still have margin against catastrophic failure)?
Sound tough? This is nothing compared to the aftermath of a failure where someone is seriously injured or worse.
I was thinking, what if there was a way for teams to have a touch sensor near their fan mounts, like really really really close, so that if the propeller moves even like .125" from its original mounting position, the motors to the fans shut off when the limit switch or touch sensor is touched? Seems simple enough to me.
I was thinking, what if there was a way for teams to have a touch sensor near their fan mounts, like really really really close, so that if the propeller moves even like .125" from its original mounting position, the motors to the fans shut off when the limit switch or touch sensor is touched? Seems simple enough to me.
I had the same thought, my afterthought though was teams that would take this precaution would probably have very good safety precautions already for any other situation.
writchie
01-02-2009, 19:51
I was thinking, what if there was a way for teams to have a touch sensor near their fan mounts, like really really really close, so that if the propeller moves even like .125" from its original mounting position, the motors to the fans shut off when the limit switch or touch sensor is touched? Seems simple enough to me.
A 12 inch prop rotating at 7500 RPM has a wing tip speed of about 120 meters per second. It stores considerable energy. Even if you could anticipate ALL of the possible fault scenarios and detect when they occur, removing the energy source is not going to change the mechanical energy much over the short term. It's too late to have any effect.
IMHO The only realistic measures are distance from the hazard (used in R/C flying) and containment and only the latter is available to us. For the containment scenario, I think that teams will have to demonstrate that their containment materials and configuration can easily contain a prop failure at max RPM.
There are tradeoffs. Using steel mesh wire, the open area drops dramatically as you increase wire size and reduce mesh spacing. Engineering a mechanism that is both effective and safe is a challenge and either one without the other is just not acceptable.
All safety considerations aside...
Have you done any performance testing as compared with a standard kitbot drivetrain? How about one with some basic traction control?
I'm not overwhelmed by your performance videos, and I'm curious why your team made the design decision to go this direction. Was there testing or prototyping involved? All about theoretical calculations? None of the above?
If the decision was all about "cool factor" then... rock on.
However, if you believe this has higher performance than using those CIMs in the traditional "rubber meets the road" way, I'm curious why you believe so, and if you have supporting data. If you DO have supporting data, I'd absolutely LOVE to get a peek. :)
Enlighten a man who sometimes has difficulty understanding why others stray outside the box, when the box appears to be an optimized and elegant solution. ;)
-John
"plastic meets the road"
fixed.:P
I'm curious on your reasoning also, the main reason I dismissed propellers was not only safety, but slowing and stopping. How well does it stop and change direction to reverse?
fixed.:P
I'm curious on your reasoning also, the main reason I dismissed propellers was not only safety, but slowing and stopping. How well does it stop and change direction to reverse?
Theoretically, we're supposed to be getting 30-some newtons of thrust from the current arrangement... and with the calculations (which i long forgot) it was supposed to be able to accelerate faster than bots that use standard wheel drive. However, I emphasize that this is not the final arrangement -- we should have standard triblade props delivered this monday with a pitch of 4, and furthermore, if we get more thrust out of that, we'll try to custom order triblabe or quadblade props with a pitch between 1 - 2, idealizing our max speed (at around 7-15 mph) while boosting rpms and increasing power. THEN, with the addition of a duct (ideally, increasing power by an addition 5%) we should be operating at pear conditions.
Also, the idea of hybridizing our bot has came up: i.e. powering the back two wheels for extra acceleration. Although that's a ton of power stress on the battery, the 3rd CIM for the powered wheels would only work during acceleration, so we should be alright. =)
Ok, My thought: I know this is probably asking alot...But could the regionals have walls along the perimeter to protect the crowd? I don't mean to be overly cautious, but I think I'd feel a little uncomfortable sitting in the crowd while some of the possible bots are going to be running. I'm not asking for anything too fancy. Perhaps just a wall like there is between the drivers and the field. I know, props could easily go over this, but at least it would cut out the worst case scenario.
Otherwise, a cool design. Good luck with the competition. And I hope nobody gets hurt.
Ok, My thought: I know this is probably asking alot...But could the regionals have walls along the perimeter to protect the crowd? I don't mean to be overly cautious, but I think I'd feel a little uncomfortable sitting in the crowd while some of the possible bots are going to be running. I'm not asking for anything too fancy. Perhaps just a wall like there is between the drivers and the field. I know, props could easily go over this, but at least it would cut out the worst case scenario.
Otherwise, a cool design. Good luck with the competition. And I hope nobody gets hurt.
Or FIRST could just solve the problem directly and not allow unsafe robots to compete
$0.02
CraigHickman
02-02-2009, 02:00
Ok, My thought: I know this is probably asking alot...But could the regionals have walls along the perimeter to protect the crowd? I don't mean to be overly cautious, but I think I'd feel a little uncomfortable sitting in the crowd while some of the possible bots are going to be running. I'm not asking for anything too fancy. Perhaps just a wall like there is between the drivers and the field. I know, props could easily go over this, but at least it would cut out the worst case scenario.
Otherwise, a cool design. Good luck with the competition. And I hope nobody gets hurt.
Should be fine. If you'll be at the Portland regional, I'll have a Kevlar helmet you can borrow, as well as glasses capable of withstanding a shotgun's deerslug at 5m. (Yay ROTC!)
I honestly don't want to see FIRST turn into battlebots, where the field is contained by walls. It blocks viability, and makes the competitions ugly and slow due to access.
Or FIRST could just solve the problem directly and not allow unsafe robots to compete
$0.02
Only thing. Just because FIRST says it safe, is everyone going to make the same ruling? For instance: We've all seen those "smart" cars. They are ruled to be safe. However, I will never drive one. I just wouldn't feel safe, regardless of whether or not I am. You have to remember when it comes to safety, apparent safety is close to the same importance of actual safety.
Al Skierkiewicz
02-02-2009, 08:09
Time for my two cents...
I am a lead inspector, and yes I am concerned about the safety of anyone at any time. This includes participants, volunteers, camera people (many of whom I know), judges and refs. If that makes me a Safety Nazi then I can live with that label. I am concerned about safety when your robot is in your pit, on the practice field, on the competition field or anywhere in between. Pits are crowded places in which I spend a lot of time and I have seen things over the years that curdle my blood. First is about innovation and creativity in design and we should encourage those ideals for the betterment of the program, but not at the loss of other equally important ideals such as safety. We have low voltage power sources for your safety, electrical rules for your safety and pneumatic rules for your safety. Expect inspectors to take a close look at your designs not only for safety but I would be prepared to show accoustic output as well. Should the GDC issue guidelines for prop driven robots we will follow those guides explicitly. Until then good luck with your development.
Should be fine. If you'll be at the Portland regional, I'll have a Kevlar helmet you can borrow, as well as glasses capable of withstanding a shotgun's deerslug at 5m. (Yay ROTC!)
I honestly don't want to see FIRST turn into battlebots, where the field is contained by walls. It blocks viability, and makes the competitions ugly and slow due to access.
I really think you guys believe that props are bound to spontaneous explode or something. As long as balls or anything of a significant mass does not touch them, there is no reason for them to catastophically fail. We'll most likely be replacing props after every round / two rounds, just to rule out any failure chances due to wear. Beside that, I believe any other precautions are just silly. I mean, I trust the machine... I stand a foot away from it while it's on. Idk if others trust my contruction, but i sure know i do.
Vikesrock
02-02-2009, 12:28
I mean, I trust the machine... I stand a foot away from it while it's on. Idk if others trust my contruction, but i sure know i do.
Our robots have never had props on them and I'm always more than a foot away from them while they are on unless they are propped up on blocks.
I can't say I understand why your blatant disregard for the safety advice posted by members with experience with these systems means that I should trust your robot to be safe.
If this robot manages to pass inspection with the safety cage shown in those pictures, I will be instructing my team to at the very least put on safety glasses in the stands every time your robot is on the field.
Wayne Doenges
02-02-2009, 12:29
Have you ever been to a competition? After each match you will see various parts from the robots on the floor. What if a bolt or nut was to be flipped into your props.Even if they didn't damage your props where does the part go after hitting the props.
Also, on a safety note. In your videos it shows your robot going along the floor PAST all the students with uncage props. When I'm around running R/C aircraft I NEVER put myself in the plane of rotation. I've seen first hand what a prop can do if it breaks and flies free. I've seen them imbed themselves into 2x4 park benches.
PLEASE BE SAFE!!!!!
Our robots have never had props on them and I'm always more than a foot away from them while they are on unless they are propped up on blocks.
I can't say I understand why your blatant disregard for the safety advice posted by members with experience with these systems means that I should trust your robot to be safe.
If this robot manages to pass inspection with the safety cage shown in those pictures, I will be instructing my team to at the very least put on safety glasses in the stands every time your robot is on the field.
I'm not blatantly disregarding, I'm taking them into consideration and adding just enough safety features so that the props can still function.
We will upgrade the cage, in particularly in the 'plane of destruction'.
And really, say a prop was coming at you, I wouldn't be that concerned about my eyes, but rather, other parts of my body. Becuase theoretically (depending the mass of the fragment ofcourse), you'd get some penetration in the skin if that hit you. And then... surgeons would have fun dislodging a 'plastic knife' from your body. Not really the best image, but.. atleast you'd be able to see your own masacre. [sorry for the sarcasm, I'm just a little angry about our progress XD]
Have you ever been to a competition? After each match you will see various parts from the robots on the floor. What if a bolt or nut was to be flipped into your props.Even if they didn't damage your props where does the part go after hitting the props.
Also, on a safety note. In your videos it shows your robot going along the floor PAST all the students with uncage props. When I'm around running R/C aircraft I NEVER put myself in the plane of rotation. I've seen first hand what a prop can do if it breaks and flies free. I've seen them imbed themselves into 2x4 park benches.
PLEASE BE SAFE!!!!!
Yes. Debris would be an interesting encounter. I'm thinking of loosing the set screws on the gears just at the point of slipping. Then if there is any added resistance [ideally] the prop would simply slip through and maximum damage could be eliminated.
I really think you guys believe that props are bound to spontaneous explode or something
It won't be spontaneous, it'll be in response to a large object passing through your porous safety cage and into the props. Maybe an orbit ball will come apart above your bot and the plastic shards will fall on your bot. Maybe another team's robot will shed bolts, or maybe a human player will accidentily toss their watch. Maybe a wire will break or come loose and will get ingested. Maybe a robot will fall on your cage and bend it inwards, hitting the prop.
Also keep in mind that every time your robot hits a wall or another robot at speed, your props will endure forces well beyond what a normal R/C plane ever encounters. An impact with the wall may decelerate a bot at 10gs, which means your fast-spinning props have to deal with that deceleration and not vibrate themselves to death. An R/C plane never sees accelerations like that.
If you don't want to change your design on safety grounds, not believing that it is a risk, change it based on pragmatic grounds: despite any "no that won't happen" arguments from your team, inspectors will mostly likely not permit your robot to compete. So even if you don't personally believe it is a safety risk, it seems that pragmatism would compel you to make a better safety cage.
Two words. ducted fan.
Bruce
It won't be spontaneous, it'll be in response to a large object passing through your porous safety cage and into the props. Maybe an orbit ball will come apart above your bot and the plastic shards will fall on your bot. Maybe another team's robot will shed bolts, or maybe a human player will accidentily toss their watch. Maybe a wire will break or come loose and will get ingested. Maybe a robot will fall on your cage and bend it inwards, hitting the prop.
Also keep in mind that every time your robot hits a wall or another robot at speed, your props will endure forces well beyond what a normal R/C plane ever encounters. An impact with the wall may decelerate a bot at 10gs, which means your fast-spinning props have to deal with that deceleration and not vibrate themselves to death. An R/C plane never sees accelerations like that.
If you don't want to change your design on safety grounds, not believing that it is a risk, change it based on pragmatic grounds: despite any "no that won't happen" arguments from your team, inspectors will mostly likely not permit your robot to compete. So even if you don't personally believe it is a safety risk, it seems that pragmatism would compel you to make a better safety cage.
I've already mentioned that we'd construct a better cage. I'll get pics of it up as soon as possible just to stop all these continual scoldings. XD
I really think you guys believe that props are bound to spontaneous explode or something. As long as balls or anything of a significant mass does not touch them, there is no reason for them to catastophically fail. We'll most likely be replacing props after every round / two rounds, just to rule out any failure chances due to wear. Beside that, I believe any other precautions are just silly. I mean, I trust the machine... I stand a foot away from it while it's on. Idk if others trust my contruction, but i sure know i do.
I can think of all kinds of examples of things that "should" not happen that end up happening. I know in the chemical industry and know in others, things are designed to account for failure scenarios. Why? Because it will happen at some point. That is why people spend weeks doing things like a Layers of Protection Analysis and Failure Modes Effects Analysis for big projects. Do you need to spend weeks doing that? No, this is much smaller, but spending a few hours thinking about things that could go wrong would not be amiss.
Listen to Al, a lead inspector. Listen to all the others who have years of experience both with FIRST and in industry. If it is anything to you, I will be inspecting teams at your regional on Thursday and reffing on the field on Friday and Saturday.
I like that you are thinking of changing the fans and making a better cage. Just remember, the folks on here are trying to help you so that you don't have to scramble on Thursday at the regional.
I think it is an interesting design. I will withhold judgment on it until I see it in action.
Good luck to you!
synth3tk
02-02-2009, 13:10
I've already mentioned that we'd construct a better cage. I'll get pics of it up as soon as possible just to stop all these continual scoldings. XD
As stated before, we're all inspectors, spectators of horrible accidents, or Safety Captains, that just want to make sure you (and the event attendees) stay safe. I truly hope that you change your view on the safety procedures of your team.
Hopefully your team has a competent safety captain, good practices for your heavy (and light, for that matter) machinery, procedures to deal with an accident (should one occur), etc. It looks like a great design, very innovative, but remember: Safety FIRST!
Woody1458
02-02-2009, 14:19
I encourage your team to take a look at this post:
http://www.chiefdelphi.com/forums/showthread.php?threadid=73389
That is the kind of safety precautions that are necessary. More fencing to keep fingers and smaller parts out, and extremely safe plane protection.
Also I would like to note that all of us here at FIRST truly believe in the ideals of Safety and GP. Not just as a way to get an award. If these ideals are ignored by anyone the competition breaks down at it's core. I encourage you to visit a local senior team and check out their safety procedures, our you can email me at xanderjanz@gmail.com to find out about 1458's safety procedures. This is no joke and we expect you to take safety seriously.
Cyberphil
02-02-2009, 15:13
Good, intresting design, but i have one question. Isn't there a rule about the wheels being parallel to each other? In the one picture you can clearly see how the frontwheels turn with the propelers while the back wheels just stay stationary. Is this still legal? From how i read it and heard, it doesn't seem legal.
Good, intresting design, but i have one question. Isn't there a rule about the wheels being parallel to each other? In the one picture you can clearly see how the frontwheels turn with the propelers while the back wheels just stay stationary. Is this still legal? From how i read it and heard, it doesn't seem legal.
You're thinking of <R06>, which specifies that the axis of rotation of the wheel must be parallel to the floor. It doesn't say anything about the axis of rotation of the axis of rotation.
MrForbes
02-02-2009, 15:15
There's a rule about the wheels being perpendicular to the floor...I don't know about any rule saying they can't steer.
Cyberphil
02-02-2009, 16:09
ok, thank you. I was just a little confused.
JGecko146
02-02-2009, 16:13
Zrop,
It's not your design we're bashing. The design is really cool. It's that you seem to blow people off with a flippant comment every time someone mentions safety. Everyone wants to have a blast at FIRST but we also want to go home to our families intact. Therefore safety is huge. It especially concerns those of us who know things can go wrong even when you are being safe. That's why "trusting a robot" is a scary thing. I've been in and around FIRST for 13 years now and I still wouldn't "trust a robot" when it comes to my own personal safety. Just think about it.
Woodworker88
02-02-2009, 17:41
Have you ever been to a competition? After each match you will see various parts from the robots on the floor. What if a bolt or nut was to be flipped into your props.Even if they didn't damage your props where does the part go after hitting the props.
On military aircraft carriers, twice a day or more all members of the crew stop all operations to perform a FOD (Foreign Object Disposal) walk, in which they walk shoulder to shoulder across the flight deck looking for any foreign object as small as 1/8" in diameter. This is to prevent the disasterous consequences that could result if one of these objects were sucked into a jet intake or blown around by jet exhaust or prop wash. Keep this in mind as you work on your systems.
Robert103
02-02-2009, 17:51
I think this is a good idea, but i have one question, won't using propellers make stopping harder?
I think this is a good idea, but i have one question, won't using propellers make stopping harder?
Not if they quickly pivot 360 degrees ;D
Robert103
02-02-2009, 18:45
Nice :D
Cyberphil
02-02-2009, 19:42
But how will they rotate quickly if they move with the steering of the wheels?
Not if they quickly pivot 360 degrees ;D
Look up rotational inertia. It would seem the laws of physics do not agree with you on this stopping method. Good luck on trying to find a different way of stopping.
Not if they quickly pivot 360 degrees ;D
Rotational inertia. As said before the props aren't intended for anything more than spinning and moving an R/C plane. The vibration from the robot is already more forces than intended, let alone the sudden accelerations from crashes, and now rotational inertia. You should really start rethinking some of these issues. You're making it seem like this is all a joke and you're just shrugging off every suggestion. I think most people reading this thread have the same mindset that that's what you're doing with every single one of our posts.
Woody1458
02-02-2009, 22:48
Rotational inertia.
If you have no experience with this force (i didn't until last year) spin a wheel on a rod then try to rotate it like you would the props. You get very interesting results
Yeah I'm really concerned about the gyroscopical effects of the props. But hey, I've seen videos of hovercrafts using rotating prop bases, so i think it's feasable. We're going to figure out controlling this stuff this week, so we'll get back on the results. XD
Rotational inertia. As said before the props aren't intended for anything more than spinning and moving an R/C plane. The vibration from the robot is already more forces than intended, let alone the sudden accelerations from crashes, and now rotational inertia. You should really start rethinking some of these issues. You're making it seem like this is all a joke and you're just shrugging off every suggestion. I think most people reading this thread have the same mindset that that's what you're doing with every single one of our posts.
Alternatively, the motors could be thrown in reverse. The problem with that though is that the leading edge of the props would become on the wrong side, greatly decreasing thrust.
Al Skierkiewicz
03-02-2009, 12:54
Alternatively, the motors could be thrown in reverse. The problem with that though is that the leading edge of the props would become on the wrong side, greatly decreasing thrust.
If you are using the Jaguar I would recommend you use the limit switch function to prevent a change in direction. If using a Victor, install a line in software to prevent counter rotation.
David Brinza
03-02-2009, 12:57
I hope you appreciate that the comments and concerns about the safety of your propellers is HELP from the CD community. I know several teams have given this approach serious consideration (including our team).
Team 980 chose an alternative drive concept, not because of safety concerns with fans, but for performance needs to support our game strategy. We felt we could contain a failed propeller and avoid having debris getting sucked in and becoming a dangerous projectile by using a "ducted fan" approach with steel mesh over the ends. I don't think your robot can detect a problem with your props and react fast enough to insure no shrapnel will be produced. It's better to have a design which is not going to allow anything dangerous to escape. With the ducted fan, you'll get better thrust performance as well.
I look forward to seeing videos of your robot on the move!
If you are using the Jaguar I would recommend you use the limit switch function to prevent a change in direction. If using a Victor, install a line in software to prevent counter rotation.
Why would this be necessary??
martin417
03-02-2009, 13:05
If you are using the Jaguar I would recommend you use the limit switch function to prevent a change in direction.
The limit switch function of the Jaguars is off limits this year (by rule, see Q&A). You may not use them. The jumpers must remain in place
Rick TYler
03-02-2009, 13:06
I'll have a Kevlar helmet you can borrow, as well as glasses capable of withstanding a shotgun's deerslug at 5m. (Yay ROTC!)
Perhaps the glasses would withstand a 12-gauge deerslug, but your face behind them won't. Just saying...
The limit switch function of the Jaguars is off limits this year (by rule, see Q&A). You may not use them. The jumpers must remain in place
What is this 'limit switch function' you refer to?
billbo911
03-02-2009, 15:07
The limit switch function of the Jaguars is off limits this year (by rule, see Q&A). You may not use them. The jumpers must remain in place
Confirmed, maybe.
Here is the quote from the Q/A:
No, the limit switch inputs on the Jaguar speed controllers are not legal for use this year. This would be a violation of Rule <R62>. The rules in the Manual supersede all other documentation.
The problem is, <R62> is about the Solenoid breakout board, not the limit switch inputs on the Jaguars.
<R62> Solenoid Breakout outputs shall be connected to pneumatic valve solenoids only. No other
devices shall be connected to these outputs.
<R61> Talks about the CAN Bus, but also does not limit the use of the limit switch inputs.
<R61> Every speed controller, relay module, and servo shall be connected via PWM cable to the
Digital Sidecar, and be controlled by signals provided from the Mobile Device Controller via
the Digital Sidecar. They shall not be controlled by signals from any other source.
A. Support for the CAN bus port on the Jaguar speed controllers is prohibited for this
competition, and the port is not to be used. Nothing shall be connected to the CAN bus
port. It is recommended that the port be protected with a piece of tape to prevent debris
from entering the port.
So, not trying to be contrary to the GDC's responses, just exactly where in the manual does it specifically rule out the use of the limit switch inputs??
I would ask this question myself of the GDC, but I do not have permission to post on the Q/A forum, only read.
Al Skierkiewicz
03-02-2009, 15:15
Martin,
I was just asking myself the same thing. I think there may be confusion between the CAN bus and the limit jumpers. BTW, I did not see the Q&A response.
Second, please disregard Rev F there were errors now superceded by Rev G.
Russ Beavis
03-02-2009, 15:19
http://forums.usfirst.org/showthread.php?t=11658&highlight=jaguar
billbo911
03-02-2009, 15:34
I just took my own advice and re-read <R61>. I now see why the answer is as it is. Their original post was mentioning <R62>, it has now been corrected.
I concur, Limit switch input is off limits via the Jaguar. See the BOLD section of the <R61> quote above. It shows the answer.
Make sure you are looking at the latest rev of the manual and the latest rev of the question. They were out of sync for one rev due to a numbering problem (thank you, Microsoft). But that seems to have now been addressed and corrected. The Q&A answer appears to be pointing to the correct rule, as correctly numbered (again) in the manual.
-dave
.
Woody1458
05-02-2009, 03:07
Make sure you are looking at the latest rev of the manual and the latest rev of the question. They were out of sync for one rev due to a numbering problem (thank you, Microsoft). But that seems to have now been addressed and corrected. The Q&A answer appears to be pointing to the correct rule, as correctly numbered (again) in the manual.
-dave
This just in, Dave Lavery is a Apple supporter. Spread the word.
rspurlin
05-02-2009, 09:43
A couple of years ago at the Peachtree regional, one team added ballast to their robot using a container filled with bb's. We only discovered this when the container ruptured during a match and spilled this former ballast across the floor. Despite a serious vacuum session immediately and at every break thereafter, we were still finding bb's when we packed up the field.
I've been a regional and a championship ref and every year we pick up a small box full of parts dropped off robots during competition. Please do not underestimate this hazard that others have already described to you.
Your design has to take into account safety in conditions which are out of your control. This is why we have negative reactions to your insistence that some of these failure scenarios won't or can't happen. What might seem safe while working in your own controlled environment is possibly highly unsafe when surrounded by hundreds of people completely unaware of your design and dozens of robots that might not be as well built as yours.
I would not be surprised at all if a lead inspector deems your design as it stands too unsafe for competition. The head ref at each regional also has the prerogative to prevent an unsafe robot from competing and might not take an engineering inspired view. It might be more of an emotional view like the previous poster who would not drive a Smart car no matter what the safety engineers say.
Personally I hope to see your robot on the field, even if just to see the backwash clear the scoring table of all its paper.
This just in, Dave Lavery is a Apple supporter. Spread the word.
Next year's game involves apples. What could it be? Let's all head to our local orchards to do research!:P
David Brinza
05-02-2009, 16:46
This just in, Dave Lavery is a Apple supporter. Spread the word.
Dave's Mac is autographed by "Woz".
I don't think he's very shy about being an Apple supporter...
Next year's game involves apples. What could it be? Let's all head to our local orchards to do research!:P
Don't ask Dave about apples, he'll start talking about penguins,
my team has one and it only creates two punds of thrust
AdamHeard
05-02-2009, 17:07
I know others have said it, but I'm concerned about the safety here.
If those blades break, which could happen, they will be sent flying at extremely high speeds, with lots of energy.
I'm usually the guy telling people worried about safety to shut up, it's fine. But this is one case where it seriously scares me. You could send shrapnel at extremely high speeds into the audience, which could kill somebody if hit right. It's unlikely, but too high a risk for my liking.
Rick Wagner
05-02-2009, 17:10
With two equal weight robots in a pushing contest on this regolith surface, a pound or two of thrust will make a big difference. Done properly (a good safety cage), a propeller in addition to all-wheel drive makes a lot of sense. The robot that pushes another robot into a hostile corner can decide the game.
DarkFlame145
05-02-2009, 17:13
I know they will work, I'm just a little frightened by them on a robot =P
AdamHeard
05-02-2009, 17:25
With two equal weight robots in a pushing contest on this regolith surface, a pound or two of thrust will make a big difference. Done properly (a good safety cage), a popeller in addition to all-wheel drive makes a lot of sense. The robot that pushes another robot into a hostile corner can decide the game.
I totally agree with that.
I've seen similar sized objects with similar energy and similar speeds break up; it will take a serious, serious object to hold it in. A cage won't suffice, plates of metal or polycarb will be needed, and not thin stuff at that.
Rick TYler
05-02-2009, 18:33
I've seen similar sized objects with similar energy and similar speeds break up; it will take a serious, serious object to hold it in. A cage won't suffice, plates of metal or polycarb will be needed, and not thin stuff at that.
The propeller blades are pretty low mass. Put a curved Lexan duct around the fan and call it good. The nice thing is that you know the blades are going to fly straight out -- it's not like they're made of C4. Wrapping the perimeter with a 6-inch wide Lexan duct should do the trick. Even if the blade hits the Lexan and bounces back to penetrate the finger-grid, there certainly won't be enough energy left to kill someone standing around the field.
How often do RC plane propellers spontaneously explode? This is a really mature technology -- I would be surprised if they weren't overbuilt for safety. How about replacing those 2-blade props with 3- or 4-blade units? For the same power you can have shorter blades with much lower tip velocities. At least, that's how it works on real airplanes.
AdamHeard
05-02-2009, 18:39
The propeller blades are pretty low mass. Put a curved Lexan duct around the fan and call it good. The nice thing is that you know the blades are going to fly straight out -- it's not like they're made of C4. Wrapping the perimeter with a 6-inch wide Lexan duct should do the trick. Even if the blade hits the Lexan and bounces back to penetrate the finger-grid, there certainly won't be enough energy left to kill someone standing around the field.
How often do RC plane propellers spontaneously explode? This is a really mature technology -- I would be surprised if they weren't overbuilt for safety. How about replacing those 2-blade props with 3- or 4-blade units? For the same power you can have shorter blades with much lower tip velocities. At least, that's how it works on real airplanes.
RC airplanes aren't hit by other things very often.
Rick TYler
05-02-2009, 18:40
RC airplanes aren't hit by other things very often.
A properly mounted propeller on an FRC bot shouldn't ever get hit at all. If they are mounted out in the open like the prototype in the first item in this thread -- that's unsafe and negligent. I was assuming (I know, I know) that it would be properly protected from ball-strikes and other structural indignities.
A properly mounted propeller on an FRC bot shouldn't ever get hit at all. If they are mounted out in the open like the prototype in the first item in this thread -- that's unsafe and negligent. I was assuming (I know, I know) that it would be properly protected from ball-strikes and other structural indignities.
The R/C airplanes don't get hit either, at all (other than maybe on a hard landing or a midair collision). It's not the props getting hit that we're worried about, it's the robot getting hit and jarring around.
I'm pretty sure that if the props can resist any vibrations that they and the motors generate, they should hold in a robot collision. I mean yeah, it will be a significant change in acceleration, but that's still no reason for the props to spontaneously explode.
Oh and update: We've decided to add power to the back 2 wheels powered by a CIM motor. So basically, that'll add some extra acceleration that we lack, and the props should handle well with the turning. ;D
I'm pretty sure that if the props can resist any vibrations that they and the motors generate, they should hold in a robot collision.
Thats two completely different forms of impact. First is vibration. That usually slowly tears something up. The second is turbulence and blunt force. Basically your comparison is as reasonable as stating, 'This doesn't break when I shake it so it shouldn't when I take a baseball bat to it.' Not really a valid statement at all.
A personal request: Once you build your robot so it can drive, purposefully run it into a couple of walls at full speed. See what happens. If it doesn't do any damage, you might be ok in competition, but you still might have trouble.
Daniel_LaFleur
05-02-2009, 22:11
I'm pretty sure that if the props can resist any vibrations that they and the motors generate, they should hold in a robot collision. I mean yeah, it will be a significant change in acceleration, but that's still no reason for the props to spontaneously explode.
Oh and update: We've decided to add power to the back 2 wheels powered by a CIM motor. So basically, that'll add some extra acceleration that we lack, and the props should handle well with the turning. ;D
Why is it that I shudder every time I hear "I'm pretty sure" when they are talking about engineering?
I'm not too concerned about the vibrations of the motors. I'm far more concerned with the shock of impact from another robot.
**Gets up on soapbox**
Why not be "sure" rather than "pretty sure" by running the bending calculations. I am "pretty sure" that your robot will see a better than 10G impact with another robot or the wall (this will be transmitted throughout the robot and anything cantilevered will feel the full force across its beam.). Calculate that force across the beam of your prop and use the weight of your prop divided by the number of blades. Personally I'd use 20G as a safety margin. If the material does not bend further than where it will permanantly deform then I'd call it fairly safe for the forces it will see ... then you need to protect it from outside forces like other robots and orbit balls.
Props can be very effective. Lets just make sure they're safe as well.
**Gets off soapbox**
writchie
05-02-2009, 22:16
The propeller blades are pretty low mass. Put a curved Lexan duct around the fan and call it good. The nice thing is that you know the blades are going to fly straight out -- it's not like they're made of C4. Wrapping the perimeter with a 6-inch wide Lexan duct should do the trick. Even if the blade hits the Lexan and bounces back to penetrate the finger-grid, there certainly won't be enough energy left to kill someone standing around the field.
How often do RC plane propellers spontaneously explode? This is a really mature technology -- I would be surprised if they weren't overbuilt for safety. How about replacing those 2-blade props with 3- or 4-blade units? For the same power you can have shorter blades with much lower tip velocities. At least, that's how it works on real airplanes.
It's called a propeller explosion because that what it looks like when contained.
A 12 inch prop rotating at 9000 RPM has a wing-tip velocity over 470 RPM. A 22 inch at that RPM is traveling at over 3/4 the speed of sound.
Propellers do not spontaneous explode when standing still, nor undamaged and moving within their design limits in the applications for which they were designed, tested, and proven. They explode when forces beyond their material strength limits essentially rip them apart. When that occurs two things happen; the failed piece (maybe an inch of tip) no longer has any centripetal force and begins moving in a straight line (usual outward and a bit forward) while aerodynamic forces still act on it, often causing it to tumble; At the same time, the remains are now horribly unbalanced and the remaining rotational energy goes into ripping off the other tip and maybe some other parts - hence the term explosion.
Back to the tip - it will usually bounce off something but since it will be at an angle its direction will change. This happens maybe 200 microseconds after tip separation. If the tip is wood it may splinter into dust. If its nylon it may elastically deform and retain a good deal of its energy after the bounce. Murphy then takes over and the path of the tip may cause it to pass through any protective screening if the opening are wide enough. Or it may bounce inside, hitting the rotating remains. You are told to stay out of the propeller arc because in the open air setting of an R/C field, that is where the prop is likely to go (except if the prop nut loosen off with a tractor prop and the prop travels forward until it hits the face looking at the front of the propeller (i've found props 100 feet away).
On a FIRST field, the whole chain of events could be triggered by the robot hitting the wall, inducing abnormal loads. The point is that if Murphy has his way the collision may be on the side of the field where people like referees, MC's, and cameramen are standing. Tragedy does not require that someone be killed. A nylon tip is plenty sharp, especially when its travelling at 200 fps.
Yes, R/C propellers are a mature technology for the conditions and best practices in which it has been used. That is not what we have here, especially as configurations stray from the conventional. Exactly how are you going to predict the vibrations and resonances of a pimped up belt drive for the prop?
When you move outside the envelope, the technology is no longer mature. And prop failures in R/C do occur surprisingly often where the envelope is being pushed.
I have no doubt that some thruster designs will be deemed insufficient to be operated within a reasonable margin of safety for the conditions present on the field (5 other 150 lb robots sliding under marginal control all over the field.) I'm hoping that some teams will have confronted and surmounted the challenges presented and be allowed to demonstrate their engineering on the field.
I do like this added dimension to the competition. But to paraphrase a movie quote "The lack of humility before nature that's being displayed here, uh ... staggers me."
writchie
05-02-2009, 22:20
I think the following comments on propeller safety from a manufacturer are worth the lengthy quote- From APC.
APC Propeller Safety Concerns
All propellers are inherently dangerous. Model airplane propellers are especially dangerous. Model airplane propellers used in high performance racing are extremely dangerous. Model airplane engines designed and modified to achieve maximum operating capabilities create unpredictable and potentially severe loads, leading to various forms of potential propeller failure. Ignoring reasonable safeguards may likely be catastrophic. This concern is the motivation for the following discussion.
Warnings included with propellers are intended to protect consumers. They also protect manufactures against claims resulting from misuse of the product. Most products with potential for causing injury contain ample warnings about misuse. Some advertisements for products now contain warnings, even before the product is sold! There is a strong proliferation of warnings in most products having potential for creating injury or damage. This inundation of warnings may cause consumers to become inured to product warnings.
The warnings about propeller use must be taken seriously, especially for racing applications. It is very risky to assume that a racing propeller blade will not fail, especially when used with state-of-the-art racing engines. Yet, nevertheless, occasionally model aircraft operators are observed standing in the plane of propeller rotation of high performance racing engines running at full power. This is very frightening. The following information reinforces the assertion that dangers of misuse are very real.
Ideally, a product can be designed with credible knowledge of the environment (loads acting on the product) and capabilities of the product to withstand that environment (not fail). There is nothing ideal about designing a model airplane propeller because some major components of propeller loads are very uncertain. The principle load components acting on a propeller are:
Centrifugal (from circular motion causing radial load)
Thrust/drag (from lift and drag acting on blade sections)
Torsional acceleration ( from engine combustion and/or pre-ignition)
Vibration (from resonant frequencies or forced excitation)
Another potential source of loading is aero elastic tip flutter. This may be caused by self exciting aerodynamic loads at a resonant frequency.
These loads are discussed next in order.
Centrifugal loads are very predictable, given rotational speed and mass density distribution of a blade. Their contribution to total stress is relatively small.
Thrust/drag loads are somewhat uncertain due to complexities of aerodynamic environments. The relative axial speed at the prop (at any radial station) is aircraft speed plus the amount the air in front of the blade is accelerated by the mechanics creating thrust. The latter may be approximated using first order classical theory. Much empirical lift/drag data (from wind tunnel tests) exists to quantify lift/drag loads, once relative velocity and angle of attack distributions are established.
Torsional acceleration loads are generally not known. Analytical estimating technique used by Landing Products to quantify torsional acceleration loads suggests that they can become dominant when pre-ignition or detonation occurs. These analytical observations are supported by test experience with very high performance engines running at elevated temperatures. The latter causes a high torsional load (about the engine shaft) which creates high bending stresses, adding to those from centrifugal force and lift/drag effects. These torsional acceleration loads depend on unique conditions for specific engines. Engines "hopped up" for racing appear to be especially prone to create high torsional loads when lean mixtures lead to high cylinder temperatures and pre-ignition/detonation.
Vibration causes additional loads from cyclic motions. These motions occur when resonant frequencies are excited or when cyclic load variations exist on the blade. The magnitude of these variations depends on how close the driving frequency is to the resonant frequency and the level of damping in the propeller material. Engine combustion frequency is an obvious excitation. Obstructions in front of or behind the blade can cause cyclic variations in thrust load. Once a blade starts to flutter, those motions alter the flow, causing variations in loading. High performance engines have caused propeller tips to break, presumably due to fatigue failure from vibration.
Aero-elastic flutter is speculated to be a dominant mechanism causing rapid fatigue failure near a tip when insufficient or destabilizing tip stiffness exists. The interaction between variable loading and deflection induces a high frequency vibration with unpredictable magnitude.
Efficient propeller design practice utilizes analytical/computational models to predict propeller performance and stresses. However, the uncertainty in impressed and inertial loading from complex phenomena requires testing to assure safe performance. Unfortunately, it is not possible to assure testing that convincingly replicates worst case conditions. The large combinations of engines, fuels, temperature, humidity, propeller selection, aircraft performance and pilot practices creates an endless variety of conditions. If the origins of severe loads were well understood, quantified, and measurable, structured testing might be feasible that focuses on worst case stack up of adverse conditions. However, since the origins of severe loads are really not well understood, it is essential to provide sufficient margins in material properties and design to assure safe performance. Propellers that are used in fairly routine and widespread applications (sport and pattern) lend themselves reasonably well to test procedures that provide reasonable confidence. In time, a sufficient data base develops that can be used to empirically quantify performance and "anchor" or "tune" assumptions used in analytical models.
However, propellers that are used for increasingly extreme performance applications do not benefit from the large empirical data base sport and pattern propellers enjoy. Assumptions and design practices developed for current generations of engines may not be valid for emerging engines whose technologies continue to push engine performance to greater extremes. Consequently, propellers that are used in applications where performance is already relatively high (and expanding) must be used with great caution.
An adverse cascading effect occurs when propellers are permitted to absorb moisture in high humidity environments. Composite strength, stiffness and fatigue endurance all reduce with increased moisture content. Reduction in stiffness typically causes resonant frequencies to move toward the driving frequency (increasing torsional loads) and, the reduction in strength reduces fatigue endurance. Composite propellers should be kept dry.
In summary, please abide by the safety practices recommended by propeller manufactures. This is especially important for high performance propellers. Assume that propellers can fail at any time, especially during full power adjustments on the ground. Never stand in or expose others to the plane of the propeller arc.
In FIRST, safety has always been #1, and its imperitive that teams take it seriously. As several others have mentioned, and linked to in this thread, accidents DO happen, and CAN cause serious injury. For the 2008 season, 1075 built a robotic forklift cart, driven by an IFI system from 2004. When we built it, we knew for sure that the safety advisors would be all over us about it, since driving a vehicle through the crowded pits has the potential to be quite dangerous, never mind that the vehicle itself has its own concerns. It was built with a very long list of safety features designed to prevent accidental operation, as well as to reduce possibility of serious injury as a result of its use. It was also built to reduce RSI's in our own team members, associated with lifting the robot, and working on it at the wrong height.
Its features are as follows:
on the old white joysticks:
trigger: enables the lift to be operated with aux1 and aux2
trigger + thumb button: enables the X and Y axes of the joystick to drive the cart
other lockouts:
seat is spring loaded, with a switch to prevent operation of the cart without a driver IN the drivers seat
front bumper on the end of the deck has a switch in it as well to stop the cart from continuing to drive into something (people, walls, whatever)
the lift has holes crossdrilled in the legs for safety pins, to ensure the deck doesnt fall.
the motor driving the deck up and down has a shroud over the chain, to protect any stray fingers, etc
it has a rotating light off our 2003 robot, to warn the area of its presence and ability to move unexpectedly.
for 2009 I believe we are planning to add an automotive horn, for an audible warning.
AND, its ALWAYS operated with a crew of flagpeople to clear the path and raise awareness to its presence.
As for benefits it provides to us, it was designed to be able to reach over the edge of the field, however, none of the events we've taken it to so far have allowed us to do so. This was to reduce back strain associated with lifting it on and off the field.
It allows us to raise up the robot to a proper height to work on in the pits without back strain and similar issues.
It also has a number of features to aid in testing and debugging the robot at competition.
This is the kind of attention to detail required in FIRST when it comes to safety. I hate to use my own team as an example, because it sounds like i'm bragging or gloating, but when there's a high risk for danger (ie. props breaking up at thousands of rpm, with the potential for sending shrapnel flying at high velocity), safety should be paramount.
I'm taking Eric's word on this one.
I highly doubt that the inspectors will give a crap ( or too much) about the safety of the precious orbit balls.
I say that if a finger or even a hand can pass through the cage, then it is not safe.
+$0.02
Not just breaking and having shrapnel in the field, but if something flies into the stands it's going to be trouble.
synth3tk
06-02-2009, 21:57
Just a reminder of how important safety is:
http://chiefdelphi.com/forums/showthread.php?p=815540#post815540
Russ Beavis
07-02-2009, 09:04
To any teams that will be using propellers on their robot, be prepared for serious scrutiny from your robot inspectors. I'm still developing the inspector training materials for this particular design element and I'm leaning towards placing a lot of the burden of safety verification on the teams.
Be prepared to defend your design. I would strongly encourage you to bring a "standard finger" to demonstrate general protection.
I would strongly encourage you to calculate the amount of energy stored in your propeller(s) at max speed and determine whether that energy is sufficient to punch through your enclosure. For example, how much energy is required to "rip" a steel wire of diameter X? Maybe you can find such destructive limits on online materials databases.
Bring plenty of documentation to support your design.
Good Luck and BE SAFE!
Russ Beavis
Chief Inspector
ChuckDickerson
08-02-2009, 20:39
To any teams that will be using propellers on their robot, be prepared for serious scrutiny from your robot inspectors. I'm still developing the inspector training materials for this particular design element and I'm leaning towards placing a lot of the burden of safety verification on the teams.
Be prepared to defend your design. I would strongly encourage you to bring a "standard finger" to demonstrate general protection.
I would strongly encourage you to calculate the amount of energy stored in your propeller(s) at max speed and determine whether that energy is sufficient to punch through your enclosure. For example, how much energy is required to "rip" a steel wire of diameter X? Maybe you can find such destructive limits on online materials databases.
Bring plenty of documentation to support your design.
Good Luck and BE SAFE!
Russ Beavis
Chief Inspector
Russ,
Thank you very much for addressing the safety issue of propellers here on CD as a warning. I have two questions though:
1) Will the "inspector training materials for this particular design element" be officially released on the FIRST website so that teams will know exactly what they need to be prepared for?
2) Will the "standard finger" be defined? Something like a 3/4"D x 3"L wooden dowel or something? If left to the teams to define I would expect as many different definitions of a "standard finger" as there will be propeller designs. Actually it seems like this should be something that the inspectors provide at inspection rather than the teams if it is to become a "standard" similar to the sizing box or scale.
I ask because the safety considerations for propellers should be taken seriously but the only defined requirements that teams have access to at the current time is the Inspection Checklist (http://www.usfirst.org/uploadedFiles/2009%20FRC%20Inspection%20Checklist%20Rev%20B.pdf) . Maybe a section could be added to the checklist covering minimum propeller safety requirements?
Al Skierkiewicz
09-02-2009, 08:00
Chuck,
The standard finger that Russ speaks of is a test fixture used by UL to test fan guards. As I understand it, the device takes into account the distance from the guard to the blade and the size of the openings in the guard as it would pertain to a finger intrusion. As this is a new concept in robot design for First, and has potential safety issues, I am sure that several different disciplines are involved in setting a standard for inspections.
Finger intrusion is only one of those concerns. As have been discussed above, noise, flying debris, robot damge, etc. are all concerns as well.
Rex Woodu
09-02-2009, 08:21
Dude. Those props are still awesome.
Warren Boudreau
10-02-2009, 08:46
I look forward to seeing all documentation and substantiation that will support the safety guidelines that Russ will be issuing to the inspectors.
David Brinza
10-02-2009, 10:05
I look forward to seeing all documentation and substantiation that will support the safety guidelines that Russ will be issuing to the inspectors.For those who are curious about how serious fan blade containment is the aerospace industry, check out this certification test (http://www.msm.cam.ac.uk/phase-trans/2002/RR.html) performed by Rolls-Royce.
Think of all of the analysis that went into the design of that engine to ensure survival from such a catastrophic failure. The FAA and other aerospace agencies require proof that the design is robust, hence the analysis is backed by this very dramatic (and expensive!) test.
I'd be interested in seeing what came out of the the exhaust of that engine. I bet it wasn't pretty...
BTW, I didn't post this to discourage propeller advocates for robots. I just want them to see what kinds of challenges engineers sometimes encounter.
Collin Fultz
10-02-2009, 10:16
For those who are curious about how serious fan blade containment is the aerospace industry, check out this certification test (http://www.msm.cam.ac.uk/phase-trans/2002/RR.html) performed by Rolls-Royce.
You're right. Years of effort goes into these fan designs in the hope that you only have to run this test once.
Some of the coolest testing we do is this test and the bird strike test, which basically involves shooting ducks at an engine running at full power. As was recently proven in NY, it's a good thing we do it. A friend of mine in the test department designed the equipment to do our most recent bird strike test.
As an MC and announcer...I hope the safety restrictions are very tight on prop-driven robots. Otherwise, I'll be announcing from outside.
Rick TYler
10-02-2009, 10:57
As an MC and announcer...I hope the safety restrictions are very tight on prop-driven robots. Otherwise, I'll be announcing from outside.
As a scorekeeper about three feet from the edge of the arena, who has the added disadvantage of sitting down most of the time and is therefore less mobile, I couldn't agree more.
Steigerwald
10-02-2009, 11:20
I agree that that needs some serious protection. Don't underestimate the energy in large diameter spinning objects.
Perhaps you could make a ducted design that turns with the blades. Then you would get more performance, while reducing the chance of pieces coming out of the fan space.
GaryVoshol
10-02-2009, 19:13
Check out the protection requirements in Team Update 11.
Check out the protection requirements in Team Update 11.
Only problem is that the update 11 doesn't have any specific requirements. It gives an example of a safe setup. It does not state any need for this particular setup. I personally won't feel that this is adequately covered until they specify max blade size, max rpm, and mandatory specific protective equipment. Any less and it will be too ambiguous.
Only problem is that the update 11 doesn't have any specific requirements. It gives an example of a safe setup. It does not state any need for this particular setup. I personally won't feel that this is adequately covered until they specify max blade size, max rpm, and mandatory specific protective equipment. Any less and it will be too ambiguous.
They "expect that propellers...will be protected in a comparable way." That's not exactly just an example...
I'm not sure that they want to specify those items. They've already spec'd the bumpers to death, so it's either "Do we REALLY want to go farther?" or "Why stop there?". Judging by team reactions to the bumpers, I'd guess the former. I could be wrong.
If they do specify one thing, I would say they should do specific minimum protective equipment, possibly with relation to the size of the prop and the speed.
Daniel_LaFleur
10-02-2009, 21:31
Only problem is that the update 11 doesn't have any specific requirements. It gives an example of a safe setup. It does not state any need for this particular setup. I personally won't feel that this is adequately covered until they specify max blade size, max rpm, and mandatory specific protective equipment. Any less and it will be too ambiguous.
First off, Max blade size has little to do with the safety of a prop. A 32" prop can be made safe while a 10" prop could be very unsafe.
Max RPM is a function of prop size and construction. some props are perfectly happy at 20,000 RPM whil others are dangerous at 5,000 RPM. To set an arbitrary 'MAX RPM' may actually encourage poor design and unsafe robots.
As far as mandatory specific protective equipment goes, what may hold a 32" 5,000 RPM prop may not hold a 11" 20,000 RPM prop. Instead of blanket protective equipment (which may or may not work in all cases), require the teams to prove that the setup is safe with proper engineering numbers. Show that the cage will completely contain a catastrophic failure of the prop.
They "expect that propellers...will be protected in a comparable way." That's not exactly just an example...
When it says comparable. It says that it is in respect to the danger of the blades. In reality, it really isn't saying much.
Also, I know it is the blade size that makes it dangerous. I also know it isn't the rpm that makes it dangerous. Lets compare to electricity. The current alone won't kill you and voltage alone won't kill you. It has to be together. However, there are standards for both. If nothing else, they could set up a simple formula that would allow for various rpm/diameter possibilities while still restricting the real danger.
When it says comparable. It says that it is in respect to the danger of the blades. In reality, it really isn't saying much.
I have to ask: How do you draw that conclusion? Sorry, but I just don't see it. They just say, this is one example of a safe design, and we expect comparable ones. They don't say what it's in respect to, just that it has to be comparable. The design given is for a general propeller, that's it.
Daniel_LaFleur
10-02-2009, 22:06
When it says comparable. It says that it is in respect to the danger of the blades. In reality, it really isn't saying much.
Also, I know it is the blade size that makes it dangerous. I also know it isn't the rpm that makes it dangerous. Lets compare to electricity. The current alone won't kill you and voltage alone won't kill you. It has to be together. However, there are standards for both. If nothing else, they could set up a simple formula that would allow for various rpm/diameter possibilities while still restricting the real danger.
Prop size isn't the issue, nor is RPM. It's people not understanding the forces that they are attempting to control.
Unfortunately, there is no simple formula that makes a prop of a specific size safe at a specific RPM. There are many factors that go into max prop RPM. While diameter is one of the factors there are others such as composition of the prop (wood? Nylon? etc ...) as well as pitch, and design (Master airscrew, APC, etc). What is safe for one type is dangerous for another.
All props should have a specification sheet that will tell Max RPM for that prop. I would expect teams to have a safety margin built in so that the prop cannot ever exceed that speed (In fact I would stay well below the manufacturers recomended max RPM).
Again, teams will need to prove that their design is safe and that the protection they have put in will work in the event of a catastrophic propeller failure. Anything less should not be allowed on the field.
I have to ask: How do you draw that conclusion? Sorry, but I just don't see it.
Yeah, I don't either now. I drew the conclusion through misreading. Sorry.
Note to zrop: Good luck meeting all the updates' standards.
Al Skierkiewicz
11-02-2009, 07:59
Lets compare to electricity. The current alone won't kill you and voltage alone won't kill you.
To be picky on this item, it's the current. That is why GFI devices are calibrated at current only. Voltage causes current to flow so that is why it is often labeled "Dangerous". A person with highly conductive skin and tissue will cause a greater current to flow than a person with poor conductivity for the same applied voltage.
Al Skierkiewicz
11-02-2009, 08:00
As to Team Update 11, there is three significant specifications there. The prop must be protected by a 1/4" mesh. The shroud needs to be at least 16 guage aluminum and it's length should be 1/2 of it's diameter. Those are at least easily determined by your inspector.
Zrop & others, any updates? Do you guys have any automation built-in, i.e. automated yaw functions to keep you going straight, etc?
I can see that you guys are putting much effort into the design of the props, and are experimenting to get the maximum bang out of the props. This is the process that FIRST loves to see. I remember seeing a team from Florida doing a prop design -- anyone remember who they are? Assuming good safety practices, I definitely look forward to seeing this in person! (Even if bumper impact forces wreak havoc on a blade who's tip is spinning over 200mph :ahh: :cool:)
As to Team Update 11, there is three significant specifications there. The prop must be protected by a 1/4" mesh. The shroud needs to be at least 16 guage aluminum and it's length should be 1/2 of it's diameter. Those are at least easily determined by your inspector.
Al -
Not to put too fine of a point on it, but Team Update #11 provides an example of "what will be considered safe," not specific regulations on what must be done. The example shows one way to cover the three things that I would consider important:
- protection from ejected debris in the event of prop failure
- protection from ejected debris in the event of FOD ingestion
- protection from insertion of body parts (fingers, toes, noses, etc)
The update leaves enough room for teams to come up with alternate designs for their protection methods. As long as that alternate method covered the three items listed above with equivalent or better levels of protection, then it would appear there is still some design flexibility here.
-dave
.
Al Skierkiewicz
11-02-2009, 10:18
Al -
The update leaves enough room for teams to come up with alternate designs for their protection methods. As long as that alternate method covered the three items listed above with equivalent or better levels of protection, then it would appear there is still some design flexibility here.
-dave
.
Agreed!
Zrop & others, any updates? Do you guys have any automation built-in, i.e. automated yaw functions to keep you going straight, etc?
I can see that you guys are putting much effort into the design of the props, and are experimenting to get the maximum bang out of the props. This is the process that FIRST loves to see. I remember seeing a team from Florida doing a prop design -- anyone remember who they are? Assuming good safety practices, I definitely look forward to seeing this in person! (Even if bumper impact forces wreak havoc on a blade who's tip is spinning over 200mph :ahh: :cool:)
Currently we are working on replacing our props with a similar 3-prop version of the one shown. The good news is that mostly everything is mounted and working to some extent (just needs a little tweeking). The bad news is that something happened with our computers causing a lot of our code to get erased or damaged (i don't know exactly what happened). I was actually talking with some of the people are Superior Tools who are machining some stuff for us and one of the guy is a model plane enthusiast, and i started talking with him. He actually recommended a 3-prop blade for low speed high torque. He also mentioned that those props we were using are so strong that its actually illegal to make props bigger than 16 inches (somewhere around here) out of that material, and he was saying how the only thing that would break them would be foreign objects coming in direct contact. He said that sudden changes in force due to collisions would have no effect on them or cause them to break and same with vibrations. He also mentioned that little objects like nuts and bolts and washers probably won't have to much effect on the prop its self, but its best not to find out (it may just turn that nut into a bullet).
As for the safety part, we are planning on having 2 cages, the first one as shown on the first page, will be used to keep large objects (mostly orbit balls) away from the props, then inside of that cage will be the aluminum housing and mesh.
I am not sure if this has been said yet, but in addition to being prop driven, we have the option of a wheel drive. We are using a modified bike gear where it will freely spin if the speed surpases the speed its being driven at, we hope this combined with the props will allow for faster acceleration (what we were lacking only prop powered).
Well its time to pull the all nighters to get this thing working, tomarrow i think we will be ready for the triblade + driven axle test to see what kinda performance we get out of it :).
Best of luck to all teams in this final week
He also mentioned that those props we were using are so strong that its actually illegal to make props bigger than 16 inches (somewhere around here) out of that material, and he was saying how the only thing that would break them would be foreign objects coming in direct contact. He said that sudden changes in force due to collisions would have no effect on them or cause them to break and same with vibrations. He also mentioned that little objects like nuts and bolts and washers probably won't have to much effect on the prop its self, but its best not to find out (it may just turn that nut into a bullet).
As for the safety part, we are planning on having 2 cages, the first one as shown on the first page, will be used to keep large objects (mostly orbit balls) away from the props, then inside of that cage will be the aluminum housing and mesh.
I've seen props made of carbon fiber break. That's pretty strong stuff, right? Especially if it's done right, and the company that makes them does it right. And they still break. There is, for safety consideration at any rate, no such thing as an unbreakable prop. Same goes for wood. Those plastic ones that you show? I've seen plastic ones break too.
Also, if you have the aluminum housing and mesh, you probably won't need the outer cage. It's a very good idea, though, as it adds a second line of defense against various things getting into the prop.
I've seen props made of carbon fiber break. That's pretty strong stuff, right? Especially if it's done right, and the company that makes them does it right. And they still break. There is, for safety consideration at any rate, no such thing as an unbreakable prop. Same goes for wood. Those plastic ones that you show? I've seen plastic ones break too.
Also, if you have the aluminum housing and mesh, you probably won't need the outer cage. It's a very good idea, though, as it adds a second line of defense against various things getting into the prop.
I know they are likely to break, but it just makes me feel better that the chances they will break are very low compared to what i first thought.
My biggest concern about the aluminum housing for the props is that if a orbit ball hits it at a high speed (don't know how fast the bots can throw them) it will potentially warp or displace the housing, and if we have it within a 1/4 inch from the props we could potentially hit the housing with the prop. Using the outer cage will prevent and bigger object (and more likely to cause damage) from getting to our props.
Who's dumb enough to accidentally turn on a robot when someone is working on the blades???
Who's dumb enough to move the wheels when someone is fixing a sprocket on the drive train?????
Be aware, one of our mentors this build season was helping with the chains when the driver asked for "Is everything clear?" and a guy said out loud "CLEAR!" He was clear himself but not the mentors. Of course, guy behind the joystick was smart enough not to move the chains, but had the driver guy just looked down to check the voltage and move the chains at the same time, who knows if we'll still be in build season.
The guy who yelled our clear is mentally impaired and is in the special ed program. We can't quite "exclude" people so he's part of us, but it's hard dealing with having a safe season and excluding people who can not be safe. We have those "liability" forms for the school but they won't save anyone's fingers or hands.
Be aware, one of our mentors this build season was helping with the chains when the driver asked for "Is everything clear?" and a guy said out loud "CLEAR!" He was clear himself but not the mentors. Of course, guy behind the joystick was smart enough not to move the chains, but had the driver guy just looked down to check the voltage and move the chains at the same time, who knows if we'll still be in build season.
The guy who yelled our clear is mentally impaired and is in the special ed program. We can't quite "exclude" people so he's part of us, but it's hard dealing with having a safe season and excluding people who can not be safe. We have those "liability" forms for the school but they won't save anyone's fingers or hands.
Oh what I love even more is how "No!" sounds very close to "Go!". We've already experienced a problem with that.
I think the formal testing terms are now "Red light", "green light". ;D
dooey100
12-02-2009, 22:56
I don't mean to derail, but I didn't think this was worthy of its own topic: Has anyone done the math on a verticle propellor pushing the robot down harder?
I don't mean to derail, but I didn't think this was worthy of its own topic: Has anyone done the math on a verticle propellor pushing the robot down harder?
Yes. The GDC has. Their math says that you have to divide by zero, then integrate with respect to X, then again with respect to Y...
Or, to put it more simply, you can't. I've brought this up here before, and in another thread that went on a similar tangent: http://forums.usfirst.org/showthread.php?t=11025
dooey100
12-02-2009, 23:20
Sorry, I didn't see that thread, I'm actually a FTC team member so I haven't looked the FRC Q+A
sxysweed
14-02-2009, 17:36
RC airplanes aren't hit by other things very often.
Except the ground...
The (plastic) prop on my Electric Firebird XL stood up to everything. Flew into trees, fences, all that, handled it just fine... But, your hand grazing a spinning prop HURTS. Almost cut a few fingers off once...
I like the idea, but safety first man. Better safe than sorry. The lexan sheet wrapped around should be fine, me thinks. The Blades aren't super heavy and shouldn't penetrate too far. Plus with the lexan you can add the little lip-thing they do on automotive ITB's/Carbs to help clean up the airflow coming in. And it looks fairly cool.
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