PID loops and motor flame out

Could a PID loop flame out a motor? What dose it take to flame out a motor? My team has not found the limits and we would rather not find out if possible.

Different motors behave differently. A Neo is much different than a Neo 550. Neo 550s are much easier to kill make sure they have a current limit set. A falcon is much different from a 775 pro.

That being said a poorly tuned PID or poorly designed system can kill any motor.

Stalling a motor with relatively high loads is a recipe for disaster. If your are controlling position and need the motor to hold it. Make sure the gearing and or loads are such that you have very little current/voltage needed to hold the motor in place. Vex Pro had some motor testing data that they published that show various motor lives at various voltages.

Thermal failures in motors come from heat buildup. Heat buildup happens when you give the motor lots of electrical energy as input, force it to dissipate it as heat (rather than mechanical energy), and don’t adequately get the heat away from the motor before things start to melt or deform.

Thankfully, other companies have done the research for you on approximately when this happens.

For example, for the 775 pro, let’s say you lock the output shaft of the motor in one spot (100% of the electrical energy input goes to heat, none to mechanical energy). at 2V and 4V inputs, the motor will push for a long time without major issue. At 6V, that will only happen for about a minute and a half or so. At higher voltages, the motor burns out almost instantly.

FWIW on terminology - flame out frequently refers to jet engines losing combustion. In motors, they tend to just get smokey and stop rotating. This is because at high heat, the most common failure mode I’ve seen is the insulation on the wire in the windings starts to melt (smoke) and short-circuits the windings together. This short circuit lowers the resistance of the windings overall, which increases current, which puts even more heat into the motor, which just melts things faster.

Note the 775Pro is the extreme example. It was designed to air cool itself while running, which doesn’t happen when you stall the motor. Other motors are built differently to allow them to survive a stall condition much longer.


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