What's going on with the Cortex when motors generate electricity?

I’ve noticed that when my kids force their unpowered robot’s motors to move (for example, when they force their robot’s arm to move down), the speaker attached to their Cortex will emit the kind of BEEP BEEP associated with powering up the robot. I’ve always presumed this to be a case of the motors acting as little electric generators when being forced - no surprises there. But what does surprise me is that this generated current appears to turn on the Cortex.

Is that true? And, if so, is there any potential (no pun intended) for excessive amounts or prolonged durations of such generated current to cause problems with the Cortex? for example, to mess with its memory? or allow operations to continue even after the Cortex has been turned off?

The reason I’m asking is that the new SkyRise game involves lifting substantial weights to impressive heights, so when these tall robots are dropping down, I could foresee current being generated that perhaps could cause problems.

I’m just curious what happens when this generated electricity is apparently dumped back into the Cortex. Could it pose a problem? or does the Cortex circuitry make that unlikely?

This is not as much as of a problem when the brain is on. If the robot is off the only thing counteracting reverse current is the stopping power of the battery, but when the brain is on the electrical components will resist these revers currents more. Hence why it is easier to hand crack motors when the robot is off or unplugged than when it is on.

Here’s my guess:

Motor outputs on the Cortex have 3 pins: PWM, power and ground. The PWM signal is the one that controls the motor, and is almost directly connected to the microcontroller chip. Power and ground are power rails connected straight to the battery with some kind of fuse to prevent overcurrent. But the cortex power regulator is also connected to the battery, so when a motor is turned by hand, it generates a voltage that can go all the way back up to the battery, then to the cortex. If the motor is turned fast enough, the voltage generated is high enough to power the voltage regulator and start the microcontroller.

As far as problems go, I can’t see too much voltage being an issue, since I’d expect the regulator to handle something like 7-16V (or higher) normally, so it’s not going to explode. The battery should also be ok, for a short time at least; just don’t do it continously.

In game, the robots are never actually turned off all the way. There’s a “disable” command sent from field control such that it disables all the motor outputs, not turning off your robot. It’s still on, and it’s still connected. It won’t cause a falling arm to intermittently turn the robot on and off from low power.

I don’t know how the motor controller 29 works either, but since there has to be some kind of power transmission, I assume there’s a way for the 2 wire output to feed power back into the 3 wire port, unless there’s some really clever circuits in there.

I’m surprised they don’t have flyback diodes in the motor controllers.