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-   -   Omni Wheels Survey (http://www.chiefdelphi.com/forums/showthread.php?t=28168)

Ryan F. 24-04-2004 21:03

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.

mtrawls 24-04-2004 22:10

Re: Omni Wheels Survey
 
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.

Ben.V.293 24-04-2004 22:43

Re: Omni Wheels Survey
 
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

Kevin Sevcik 24-04-2004 22:45

Re: Omni Wheels Survey
 
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.

Ryan F. 24-04-2004 22:48

Re: Omni Wheels Survey
 
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

UNFkrunch79 24-04-2004 22:51

Re: Omni Wheels Survey
 
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.

Ben Lauer 24-04-2004 23:31

Re: Omni Wheels Survey
 
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.

Ryan M. 25-04-2004 07:24

Re: Omni Wheels Survey
 
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.)

Alex Cormier 25-04-2004 08:58

Re: Omni Wheels Survey
 
Quote:

Originally Posted by Texan
I'm surprised Pit Bull hasn't said anything on this thread. His Title is "Mr. Omni-wheels." (or something to that meaning)

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...

FizMan 25-04-2004 09:36

Re: Omni Wheels Survey
 
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. :D

Nathan Pell 25-04-2004 09:58

Re: Omni Wheels Survey
 
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.

Alex Cormier 25-04-2004 10:15

Re: Omni Wheels Survey
 
Quote:

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?

Tom Bottiglieri 25-04-2004 10:34

Re: Omni Wheels Survey
 
Quote:

Originally Posted by UNFkrunch79
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 you are confusing "omni drive" with "omni wheels".

bheller 25-04-2004 12:11

Re: 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

Quote:

Originally Posted by rforystek
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.


Yan Wang 25-04-2004 13:26

Re: Omni Wheels Survey
 
Quote:

Originally Posted by FizMan
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.


Code:

-----====-----
|            |
|            |
||          ||
||          ||
|            |
|            |
-----====-----

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. :D


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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