[fox46]

There is no protection

No disrespect to your expertise Al and I don't pretend to be an expert on any of this but there must be *some* sort of protection- (a "tolerance" would likely be more appropriate) for backfeeding power. Every time you cut power and the motors are spinning down they are applying power to those terminals so there must be some sort of suppression. How much "reverse" power the controllers can handle is anybody's guess but watching kit robots "skate" in coast mode and get pushed around even in brake mode would suggest to me it is at least enough to tolerate it for a little bit. Sure- extensive "pushing around" a robot would certainly damage something but the big question is how much before this happens?

In 2000 when I was in grade 10, our school used to participate in the now defunct "Canada First" robotics competition- brainchild of the late Bruce MacMillan, a spinoff of FIRST before the GTR regional came into existence. That particular year the competition organizers had designed a custom control board that when interfaced with an RC aircraft system provided control to the robots. Unfortunately the system was plagued with problems in the form of exploding MOSFETs/Transistors and the on-board microprocessor. The cause was a poor design where the designer had overlooked this kind of protection. Voltages which backfed to the controller when the power was turned off (so we were told) was causing the processor to cook itself- just like you describe. The motors we were supplied with were windshield wiper motors with very little "spindown" and were virtually impossible to backdrive which meant only a very small amount of power was needed to cause this condition. This is why I am convinced the Victors and Jags have at least some tolerance to reverse voltages otherwise I am confident they too would cook. The solution to these issues that was implemented AT the competition was replacing all the power switching hardware on the boards with relays resulting in only "ON/OFF/ON" control.