Well, you can spin the armature of a motor and use it as a generator of sorts. The main drive motor of choice in the DIY CNC world are stepper motors. When ballscrews became more in use, this caused some problems in the Z axis because a ballscrew is not self-locking like a single-thread ACME or trapezoidal screw, causing the Z axis to drop when the power was shut off. An electric or mechanical brake can be used, but adds a lot to the cost and a little bit to the complexity, while adding weight to the Z axis. The DIY trick was to add a relay that would short the coils when the power was off. This, believe it or not, generated enough juice to create enough holding torque to keep the axis from dropping! One can actually test which wires go to which coils on a stepper by simply pairing wires till resistance is felt when trying to spin the armature. Great when you have a 8-wire stepper and no wire color codes available.
yes on the crappy cb talkies i remember in the 70’s this was true.
when making a toy you cut that parts count any way you can.
and iirc green leds were used as detectors on a solar array tracker.