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Omni Wheels
Hi, I'm starting this thread to get a feel of how well omni-wheels worked for the teams that actually used them. I've been looking at many possible things for out robot for next year, this being one of them. The one problem I've always wondered about is the omni wheels making the robot easily pushable. I'm wondering if they have the same effect of casters, where they allow another robot to push you around easily. If anyone out there with omni wheels could tell me about your experiances with them and especially if you got into pushing matches with other robots, that would be appreciated.
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Team 122 has used omni-wheels for a number of years (notably, we lacked them last year ... which propelled us to using them again this year!) The amount of traction they provide all depends on how you make them, and we've explored a number of methods. The "omni" part of the wheels only need to give when the 'bot experiences a lateral force -- so just because someone pushes you on the front doesn't mean it should give. Particularly 3 years ago we built our bot to be a pusher (back when we had to move goals to different zones and keep them there); we used omni-wheels, and it all worked pretty well for us. Overall, I think omni-wheels are a great thing to have.
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this year team 293 made the switch to omni wheels. I feel that they performed better than casters do but if someone hit us on the side by the omnis we'd spin right around. We bought them from McMaster-Carr and they were excellent but next year we'll probaly make our own. The model number was 2289T3. I recomend them to any team that does not have the time or resources to make their own.
Ben Van Selous |
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I would think the issue with omni-wheels would be the simple fact that they give laterally. Thus, if you have all 4 omnis, you'd be pushed clear across the field if someone got on your side. If you have 2 omnis and 2 normal wheels, you don't have that problem, but I think you'll still have a problem of being easily turned to the side and knocked off course.
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Yeah..that's exactly what I've been thinking. If someone hits you on the side.....you can't really do anything about it.
-casters are something I wouldn't want anywhere near our robot |
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Team 79 has been using omni "crab" drive for two years now. We have a very powerful robot and we can hold our own in a pushing match. One thing that we did last year to keep people from pushing us off the top of the ramp was have a lock down system. Just by pressing a button on our controls each wheel would turn in, so that they are all facing a different direction. And the wheels that we used had a lot of traction on the top platform. I think that omni drive is a very cool thing to have and work great if the game calls for it.
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I think it all depends on what material you use for the "omni" part, and what design you use.
For instance wheels like this and ones likethis virutally don't slip at all, even though they have a different design. The first link is one 1018's robot (my team), and we didn't climb the step, so all we needed was grip on carpet. The second did, and they need the grip on the platforms. You should find a design, then get materials that will best suit you traction needs. |
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I'm surprised Pit Bull hasn't said anything on this thread. His Title is "Mr. Omni-wheels." (or something to that meaning)
It depends on your drive setup it you can be pushed (easily) or not. If you do something like a Killough Platform, you can never truly be hit from a "side." (If you don't know what a Killough Platform is, look it up on Google.) |
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anyways... omni wheels love em! i came up with them this year for our bot just so that we can turn in high gear and climb very easily and that was accompolished very well. if another bot did hit us on the right side all we needed to do we counteract it and drive towards that side and they couldn't push yes any more. they really work great and are wonderful. i will have a white paper up soon on my creation. check for it in a few weeks... p.s. we had 2 omnis in front 2 pn. wheels i the back... heres a pic pit out... |
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I'm trying to develop a drive system that can move freely in all directions for next year. And I rummaged through the whitepapers, and it the concept of using four omni-wheels, two in either direction, would work.
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-----====-----And again; with that design, if a robot pushed yours, you'd really only have two wheels of traction to push back with? Looking at a few designs of omni-wheels that use the metal spinners for the treads (rather than the plastic ones) what's the possibility of those damaging the carpet if you're in a pushing match and your wheel slips? Also, what's the advantage of using omni-wheels if not for all-direction travel? For example in the above robot picture; you have the two omni-wheels in the front. You said it was so you could turn in high gear easier; so the omni-wheels provide half decent forward-backward traction and little lateral traction. Are there any other benefits? Thanks for your time answering these. :D |
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Team 1083 and 180 both used omni wheels to make a holonomic drive train. It worked very well; we rarely were pushed, as we were so much more maneuverable than anything else out there. Also, unlike casters which just "sit" there and can rotate easily, our wheels were attached directly to the motors and gear box, so pushing them was not as easy as casters.
I highly recommend holonomic drive when you want to be maneuverable. |
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we opnly used two because of the game, we wanted to get on that ramp very qucikly in which it did b/c we had a 1/2" lip to catch the edge of the 6" platform. anything else or i missed? |
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Team 931 used them for the first time this year. We wanted a robot design that was longer than it was wide, for stability with a long arm, and knew that our robot would not turn well with four standard wheels. There are two omnis on the front and two pneumatics on the back.
When we switched to the omnis, it turned too well. Think about it - omnis act as casters when the robot turns. The operator would push the stick to turn and the robot would turn, but it would keep turning when the operator moved the stick back to neutral! The polar moment of inertia kept us going. If you want to go with omnis, I recommend one of three things: -holonomic drive -exponential stick control for better turning sensitivity at low speeds -(best option in my mind) a gyro to counteract the overshoot I'm trying to get a white paper out on these wheels by midsummer. Brandon Heller Mentor Team 931 Alum Team 449 Quote:
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Ah, you're referring to Patrick's 3DOF whitepaper right? After driving the Cornell robocup robots for a while with an XBOX controller, I have to say that such a design is just plain awesome for being mobile. If someone tries to push you, there are so many ways to move. Google Cornell Robocup and check out some of their videos for a demonstration. Patrick is also updating the Cornell team's status at the American Open in New Orleans (their first match should've been 30 min ago) in this thread: http://www.chiefdelphi.com/forums/sh...ad.php?t=28159 In addition, our team has used omniwheels in 2002 and 2003... search these forums for pics of them (and descriptions) or PM me. They've worked beautifully. We switched to tank treads this year. |
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Omni wheels actually worked great for my team this year. But, we didnt have them on the ground the whole time. We had ours attatched to a pnumatic cylinder and when the stoke was out the wheels were down and when the stoke was in they were up. We saw early in the build season that the pnumatic wheels that were provided in the kit didn't allow for smooth turning. So our drive/chassie team came up with the idea of having a set of omni wheels stowed up under the robot and that could be deployed when ever the driver wanted them to. This turned out to be a great asset for out team this year because our driver could easliy maneuver the robot. :D
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For anyone considering the use of omni wheels on their robot, Andy Baker put out a great white paper on how team 45 made theirs and it has all the specs you need to make a great pair yourself. We on team 177 used a slight variation of these wheels on the back of our robot (we kept pneumatic tires on the front) and they allowed for excellent turning. Despite what people say you do not need at least 3 of these wheels by any stretch of the imagination. We recieved many comments from people attending the Philly regional and nationals that they thought we would be very easy to push out of the way with omni wheels and that they were surprised to see us do all of the pushing. If you saw any of our matches you know that defense was a big part of our game, and these magnificent wheels made that possible.
http://www.chiefdelphi.com/forums/pa...le&paperid=226 |
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we should get all the robots that have omni wheels and make a big gallery of them, that would look cool.. :cool: |
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well it was our first year with omini wheels-- we actually have to fix them up-- only problem i saw was the rubber on the wheels-- a lot of driving just wore them down-- all well-- i'm sure S.P.A.M. won't mind sharign our design-- nobody we saw had a drive system like us-- and we plan on making them better
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I saw a few teams using omni wheels bought from this site:
http://www.omniwheel.com They have an interesting selection. Rob |
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we actually did buy some from that site-- took the whole supply actually for that time period but the wheels didn't work for us--didn't hold our load and no clearance-- i had to actually take down the plastic but that didnt' help much either--so we had to fabricate our own wheels at the end of the 6th weeks-- but we did it-- many teams have seen our wheels they are really cool |
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/-------\ |oooooo| |oooooo| |oooooo| \-------/ for some reason the spaces arent staying between the two walls of my robot so i put o's in the middle when that robot is moving "up" on the page, all the motors will be applying force in that direction. The one thing i can't seem to figure out is wether 100% of their force is in that direction or 1/sqrt2 of it is in that direction because the wheels are at 45deg angles to the direction we are measuring force in. Now basic physics would say that yeah, its 1/sqrt2 because the force is being applied at a 45deg angle, but the odd thing is, when you get out the other xy component vector, it doesnt seem to be applying a force when the robot drives straight assuming the omniwheels have no significant friction to lateral movement. Now im sure no one got that, but if you did, help me cause im really stumped by this. |
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i'm pretty confident that that you're right with the second one ,[sqrt2]% of available motor power (but then again, i've been awake way too long). that is the reason i think the mecanum/ilon wheel setup is better, since it allows the motors to apply 100% of their power to full forward/back or left/right movement. |
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::GASP:: Not only have you guys seen one, but it was at the Florida Regional with you. |
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Both systems get [(sqrt2)/2]% efficiency in the x and y directions. Mecanum wheels have the rollers at 45* angles which produces the same vectors as a normal holonomic platform with its wheels at 45* angles. |
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Wildstang has used a variety of different designs for omni wheels over the years. We scratch build our own and have modified the design each time we used them. This year we used two driven omni (we call them BUPODfor Biased UniPlanar Omni Directional) and two crab drive modules for four wheel drive. In crab from side to side we had to add some software to help the robot drive straight which we called "Drive Straight". The omni wheels tend to go where they want when they are not driving.
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If the mecanum wheels produced 100% power in the forward or reverse direction, it would be impossible to strafe. We know that this setup can strafe, so the power must be in the direction that the rollers are facing.
Another proof is to watch a video of a holonomic platform with mecanum wheels. Watch what happens when 2 wheels on a diagonal are powered. The robot moves in the direction that the rollers are facing. |
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George, i know 1083 wants to try to build its own omniwheels next year and i was wondering if you were planning to make them bigger than those 4.72" ones from omniwheel.com. I can't actually think of a valid reason why wheels that small are bad, but very few teams seem to use wheels that small, so there is probably a reason. Maybe a larger wheel gives you the potential for better traction. (yes, i know in theory traction is only dependent on the weight of the robot and the materials contacting each other, but in practice, it isnt that simple) Your grooved omniwheels seemed to have better traction than any others, bought or built.
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sorry i took so long replying...
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<hare-brained idea> on that note (prop. blades) i'd also like to throw out an idea that i got from watching the bots strafe back and forth. what if you were able to change the angle of the rollers? decreasing the angle would move you less distance per each "wheel" rotation, but would give you more pushing force.the angle of the rollers could be changed by a mechanism similar to the ones used to change the blade pitch on prop. aircraft. </hare-brained idea> |
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That's probably the best argument for us using them again in the future. |
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Thank you, Jake Mazotas |
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sry george meaning that nobody made wheels like us-- design that james came up with and that i got to help make and well yeah get to fix them again :ahh: :) |
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We (X-CATS 191) used Omni wheels for the first time this year as well... They worked very well and we even made them from scrath recycling old copier parts we pulled out of some dumpster. I'll have to get some closer pictures for ya.
We made an 8 wheel drive system that walked up the platform. It worked well except for the side traction when we were halfway up a step and then we had issues sliding.. Oh well you live and learn... Ellery |
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I think everyones forgetting (or you just werent around) one of the proven bots out there with large omni wheels and they happend to use 6 of them they went in all directions they didnt get pushed around and there was no easy side to push them from they turned marvelously and speed and power to boot
MIM Metal in Motion 343 2002 bot still one of my fav robots of all time check them out and youll see there design ... i wanted to build something like that but i couldnt get the whole building omni wheels thing started any suggestions or things only expirience teaches u when building this nice lil wheels? things i should watch out for when tyring to build and use them? |
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