[chadr03]

I don't think you would like the results.

If you back drive a motor it becomes a generator and feeds power back into the system. With a 100:1 reducton gearbox if it is backdriven makes it a 100:1 increaser so you would have a generator moving pretty quick. This is putting power on the wrong end of your speed controllers and can damage them.

Also have you ever tried to backdrive a 100:1 recuction. It takes quite a bit of torque even if it is not trying to generate electricity.

I think your best best is to find a middle of the road solution or try some shifting/clutch mechanism that will allow your mechanism to work without having to backdrive the unused motor.