Omni wheels?

[Mentor08]

We are using 4 motors, 4 wheel drive, 2 drive chains per side, 2 high friction aluminum wheels, and 4 omni wheels (2 on left together, 2 on right together). Is it better to put the omni wheels on the front or on the rear?

[EricH]

Originally Posted by Mentor08

We are using 4 motors, 4 wheel drive, 2 drive chains per side, 2 high friction aluminum wheels, and 4 omni wheels (2 on left together, 2 on right together). Is it better to put the omni wheels on the front or on the rear?

How about opposite corners?

It would depend on your application, where you want the robot to rotate around, and how easily you want to be turned. Putting them in opposite corners reduces the last factor.

[Matt H.]

That depends on how you want your robot to turn. If you mount the omni's in the rear the robot will pivot on a point directly in between the front wheels. If you mount them in the front it will pivot around a point between the two rear wheels.

In our 2006 robot we used this system and found it hard to steer no matter what the configuration. If I had to make a choice I would say to put the omnis in the rear because this allows (from experience) the most normal steering.

[Mentor08]

The opposite corners...hadn't thought of that. I don't think that they are the same diameter.

We used casters on the front last year. Big mistake, no control. My thinking is that omni's on the front might end up being the same with a little more control. Hopefully putting them on the rear will give more control.

[Matt H.]

Omnis on the front will give you only marginally more control than casters--rear is the way to go.

If you wanted to be in the true engineering spirit then you could build your chassis such that the wheels are interchangeable and then try both varieties.

[Mentor08]

Good idea on trying it both ways.

Is it better to use 1 chain per side or 2 chains per side?

[Mark Holschuh]

Originally Posted by Mentor08

Good idea on trying it both ways.

Is it better to use 1 chain per side or 2 chains per side?

You want to maximize the amount of wrap of the chain around the sprockets to prevent the chains from slipping off. I recommend two chains, one going to the front wheel and one to the back. Make sure that your sprockets are aligned with each other.

[Mentor08]

Thanks!