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.
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.
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
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.
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
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.
I think it all depends on what material you use for the “omni” part, and what design you use.
For instance wheels likethis 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.
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.)
sorry a little late had a party here last night the people didn’t leave till 2 am.
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…
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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Okay; that’s a pretty bad drawing; but you get the idea. By running the two sets of wheels at different speeds, you can strafe your robot in different directions. This means you’ll have a seperate gearbox/transmition/motors for each set of wheels, correct? Say you have two motors per set of wheels. Does that mean you can really only apply two motors worth of power in any one direction? So if you were up against a robot that had a tank drive with four motors of power in one direction, you’d only have two to their four? Now I’m just learning the basics of these engineering principles, so tell me if I’m way off.
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.
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.
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?
omni wheels = motorable casters…that can or can’t be movable sideways… like mine, they can’t move sideways but they rool b/c of the rollers…
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?
I think you are confusing “omni drive” with “omni wheels”.
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
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/showthread.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.
Yeah…you were one of the teams I saw that got me thinking about the omni wheels. We were in the pits right next to you at the MWR…and someone showed them to me.
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.
this is the main reason that i (personally) don’t like “traditional” holonomic setups. mecanum/ilon wheels (such as the ones on these robots) solve this problem to a degree, since it allows you to harness the power of all 4 motors whenever the bot is moving in a direction perpindicular or parrallel to that of wheel rotation. this setup is weakest when it is moving diagonally when only two of the wheels are being powered. in addition, since the rollers overlap, and are rounded, there isn’t as much bumping present as there is in the traditional omni-wheel.
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/papers.php?s=&action=single&paperid=226
i am interested in your omni wheels, and why u guys choose to put them in the back… please explain.
we should get all the robots that have omni wheels and make a big gallery of them, that would look cool…