Driving Striaght

Problem: Our robot won’t drive straight whether with the controller or during programming.
Possible cause: Omni Wheels in the rear?

Setup: typical two motor rear wheel drive, 4 wheels obviously. Front two wheels are normal wheels, the back two are Omni. We are using gears to power the wheels, testing done with 36 and 24 gears (3:2 gear ratio) (we’ve also used the same gearing with 36 tooth sprocket and chains to drive as well). Our wheel base is a little longer than a standard build, about 4.5". Everything was taken off the robot except the drivetrain and base and the brain to make sure there was nothing else to cause it.

The main issue is when driving with the controller that we see it, but since the same issue happens when coding as well, I can eliminate calibration in the controller. So when driving with the controller or programming, our robot always starts veering to the right shortly after going. We did all the testing in coding move (drive forward 60"). We thought it was maybe motors, swapped things around with no change in curving still. We then swapped the rear wheels for regular ones and things got better. We then tried a setup of FWD power with two regular wheels and then putting the omni back on the rear and again was getting much better results again. The problem with doing a FWD is now the robot is front heavy (thus it wobbles when picking things up or turning more). The other issue is with FWD, turning on the controller is almost to fast now. We really want the Omni wheels on the rear with RWD because turning is so much more accurate in that setup, but hate having to drive a couple feet, stop turn the robot a little, and then start driving again.

Just looking to see if anyone has experienced this before and any other options we could try.

It’s pretty clear it’s a mechanical/build issue. I think that swapping the omnis for regular wheels and seeing improvement is a clue that the issue is connected to the right rear. The regular wheels are slightly more narrow than the omni wheels, so it could be something on that right side rear is binding. Is the brain centered and the weight equally distributed? Is there any visible uneven sag? Have you tried removing the motors and rolling it down a ramp to see if the problem persists?


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