Omni Wheel Drive Train 2020(?)

FIRST General Forum
1

I am a newer coach of a 3rd year team. This year they want to try a 6 wheeled drive train with 4 omni wheels with a center traction wheel. They are also talking about using a chain drive on all 6 wheels.

I have never worked with omni wheels before and am concerned with this configuration that we might not have any defensive control and be easily pushed around.

I want the students to have the right information going into this project and let them decide on their robot design, but I do not want to let them make uninformed decisions.

I have seen a design of 2 traction wheels (driven) with a third loose omni wheel in the front. Thoughts?

Any help with some drive train configurations for this year’s game would be greatly appreciated, with or without omni wheels.

2

Some scattered thoughts:

  1. Yes power all of the wheels - this gives you much more ability to push and move.
  2. The center traction helps you resist being slid across the floor / pushed around, but it will be easy to spin your robot. This may not be what you want in a shooting game, though it’s much less of an issue in a pick and place game.
  3. What are the advantages the students want to get out of this style of drive versus a six traction wheel drop center drive? Have you run into problems with that setup before? It is similar in turning performance but much more resistant to being spun.
3

What benefits is your team considering? If you are trying to score powercells, omnis can make your robot easier to push around. This could stop you from intaking or shooting accurately sometimes.

4

What is there reason for having the omnis? Are they trying to solve a specific problem or do they just want them on the robot because they are cool?

Driving all your wheels is advantageous in most cases. I’d say they are on the right track there.

It might be easy to turn you if they hit your corner. Straight front back and straight on in the side you’d probably be ok.

This is a design that works.

I would suggest going with all traction wheels and a center drop. (And I’d probably choose 6" wheels.)

5

This is used to change the axis around which you rotate - we’ve historically done omnis on the back, never the front, but based on your own robot’s weight distribution maybe the front would be better for your case.

7

We used a west coast drive with pneumatic wheels last year and they said it was very hard to steer. So they thought the omni wheels would help… I’m still very skeptical of using the omnis, but it’s the students robot…

8

Thank you, that is what I thought, but just wanted to be correct since I have never used them before.

9

We used a west coast drive with pneumatic wheels last year an they said it was very hard to steer. So they thought the omni wheels would help…but I was concerned about being pushed around.

10

There’s definitely a range of wheel scrub between pneumatic and omni. If you’re running WCD it’s easy to swap wheels. Try colsons or a treaded wheel and see how you like the turning, are you dropping the center wheel? I think you’ll find it very difficult to shoot under even the slightest defense with 4 omnis on the bot this year.

11

We are considering pursuing the same setup, the only way I see the robot losing traction is if we got hit in the corner, you could always do a 4 traction and 2 Omni put on the side that turns, which is something we might do. If you want a reference that pulled a 4 Omni and 2 traction wheel, Team 5190 (Green Hope Falcons) had that setup ran in 2019.

12

Ah I see. Pneumatic wheels can make turning difficult. They scrub like nobody’s business. I’d recommend against omnis at this stage. Have your students read up on center drop and pick a drivetrain that uses all of the same wheel. There certainly is a case for using different wheels on the same drivetrain. But it sounds like it’s in your best interest not to this year.

13

How much drop was on the center axle? It sounds like you may not have had enough, or the balance of the robot was off. A 6 wheel drop center that is well balanced is very maneuverable. I have seen recommendations between .0625" and .250".

14

Corner omnis with a high traction center wheel will give you a very maneuverable drivetrain capable of turning on a dime. You will be easier to push around if you do that, though. If you decide to go with all high traction wheels dropping the center wheel will help you turn. Pneumatic wheels in particular require the center to be dropped a fair amount.

15

Would one need more drop with pneumatic wheels than with the non-pneumatic wheels? I could imagine the center wheels compressing and negating some of the drop that is designed in.

16

I’ve heard that it’s more about keeping the tires inflated than anything. I don’t have firsthand experience with it. Since I’ve been involved we’ve only run 4 pneumatic wheel setups.

17

I guess you mean to pump up the middle tires so they don’t compress. Unfortunately, one could lose the cushioning effect that caused one to choose pneumatic tires in the first place.

18

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