[DonRotolo]

The concerns expressed are valid, but one needs to have only one motor that can be backdriven, not both.

Our first arm joint on out 2005 robot has a setup similar to what you describe - the van door motor (for power, but backdriveable) and the denso window motor (weak but not backdriveable) on the same shaft, driving a 12 or 15 tooth sprocket to a 50 or 60 tooth sprocket at the arm joint, #35 chain.

We did experience one failure of the plastic shaft coupler, and one failure of the window lifter motor, during the NJ regional. Neither failed again at Nationals, but we took a more defensive stance there.

I do agree it is not an ideal situation for longevity, but it's not a guaranteed failure either.

Don