Mecanum wheels

Is it possible to position 4 omni wheels in such a way that it has the effects of mecanums? i don’t have omnis to test it with. I was thinking of a bot with a square chassis. position the wheels so they are at a 45 degree angle away from each other. here is a crude way of showing you (i don’t have a camera) pretend the \ and / lines are the omnis are the {} is the chassis.

                              \ /
                              / \

that idea popped into my head like 2 minutes ago and i didn’t feel like thinking it over. and i’m sure many of you will feel like thinking right now, so will it work?

I think it work, but it wouldnt allow you to turn. it would be possible to slide around though.

If you arrange them like this:

\ /

Wouldn’t that give you the same mecanum-like drive, and allow for spin as well?

  • Dean

yes, this is the standard arrangement for an omni-directional robot using omniwheels, instead of holonomic. instead of turning, you will be spinning, rotating all of the wheels in the same direction.

That would work, but isn’t it called holonomic?

Good question. According to wikipedia, any system that has as many (or more) controllable degrees of freedom as controlled degrees of freedom could be described as holonomic. I’m not sure if the word “holonomic” is being used this way in practice, though.

[INDENT][edit]I think I might have mixed up “controlled degrees of freedom” and “controllable degrees of freedom” in the wikipedia definition. So, depending on which is which, I may have the meanings of “holonomic” and “non-holonomic” flipped. Somebody in the know please post and clear things up.[/edit][/INDENT]

Mecanum refers to a particular wheel design. Going by the wikipedia definition, a mecanum-based 'bot might or might not also be holonomic, depending on the exact configuration.

In the configuration I posted above, you have 4 controlled degrees of freedom (one motor on each wheel). But you only have 3 controllable degrees of freedom (translate along X, translate along Y, and rotate around Z).

The reason this configuration is mecanum-like, is that it would take the same types of control signals that mecanum wheels would normally need.

So you get a omni-wheel-based non-holonomic robot that drives like a mecanum-wheeled non-holonomic robot. :smiley:

I’d love to see a site with a definitive guide to drive train geometries, along with their various common names.


  • Dean

How could you spin with this setup, i know with the holonomic you simply spin all motors in the same direction, clockwise for instance, but i cannot think of a way to spin or turn this new wheel setup.

like i said, i didn’t really think it over. now that i look at it i see it can’t spin, but only goes forward and sideways.

I wish i had some omnis! but they’re so expensive!

The first arrangement could still be classified as having a mecanum-style movement, as mecanum wheels don’t necessarily involve rotation. The other configuration would work better though.

For clarification of the Wikipedia-definition of holonomic, the first configuration is not holonomic, whereas the second is. In robotics, holonomic drive means that the robot in question can rotate and move along all possible axes. The key word there is “rotate.” Without the ability to rotate, the robot can’t truly be considered holonomic. That’s how I interpreted the definition at least.

Almost completely unrelated, but tied to the subject by my strange brain: we passed a motion in Model UN stating that Wikipedia is always right.

like i already stated, rotating all of the wheels in the same direction (CW or CCW) the robot will spin. i know this to be true because i have done it, and ArtDutra has repeatedly posted links to his awesome omni robot.

Nobody here is disagreeing with you. We are discussing two wheel configurations on this thread.

The first one (wheels arranged like an X) would allow you to translate just like mecanum wheels, but would not allow you to spin in place.

The second configuration is like the standard omni configuration, with the wheels mounted at the corners, and slanted at 45d. This configuration lets you translate like mecanum wheels but also lets you rotate in place.

I don’t see anybody asserting that the second configuration is unable to spin in place.

  • Dean

sorry, i guess i just misinterpreted what was going on. sorry for that.

both systems are certainly possible. My experience with the traditional omni wheel setup has been less than impressed. I have seen it at the last world competition and at a qualifier this year. They do give a very different and arguably more maneuverable setup. That’s where i see the advantages end. They are characteristically slow and awkward from a control standpoint. Another disadvantage in a competition is that they are very easy to push around. Maybe in another application they could be of use, but in competition they certainly dont seem to give a competitive edge

I’ve been meaning to build a standard omni-bot for a while now just to try this out, but I haven’t had a chance.

The way I’ve typically used Omni wheels thus far is to replace the rear wheels of a standard 4-wheel drive bot. This provides for much better turning (you pivot on a point between the two front wheels). Of course you can’t slide sideways with this configuration like you could with a pure-omni setup, but it isn’t hard to control.


  • Dean

These are a couple of CAD model I created earlier this year of Holonomic Drive trains. I’ve never had a chance to build them:
This one is designed with a pivot in the middle so that you have a better chance of keeping all 4 wheels in constant contact with the ground.