Motor testing / matching for improvement of driving straight

I have a team that has a robot that enjoys turning on a slight arc rather than driving straight. They have gone through the usual checking for uneven friction routines and that has not shown to be an improvement.

I recall an old thread of testing motors under a load and pairing ‘matched’ motors together, but my searching hasn’t been able to turn up that thread.

Other than derating one side motors in code slightly, has anyone had any experience or success with improving the straightness of a drive path by pairing similar performing motors?

There are threads on building dynos, which should help your team test out motors. Here’s one that we used to build in IQ and program with RobotC and the Data Log capability. Motors

One of the kids on our IQ team tested all of the motors for the robot’s flywheel by going to the devices section of the brain and seeing the speed/RPM of each motor. That may be a quicker way to do it without having to build and program a dyno.

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One of the threads was our team from last year on gen 1 and IQ. Went through 10 brand new motors. Put both motors with a shaft and large gear. Same velocity; put a pin on gear and counted revolutions in same time frame. Deviance was high up to 40 or 50 rpm difference in a short (1 to 1.5 minutes). Found two gen 1 motors “close” (within 5) and called it “good “.

We had the same problem- everything symmetric, washers everywhere no drag; and the robot would veer 4-6” across the field. No comment on quality control.

If you can, compare several motors that way and use the closest difference for drive train.