[Ether]

Originally Posted by MrForbes

Are you sure about the voltage thing? I don't really understand the whole voltage/current/percent power relationship with speed controllers...but my guess is you're providing it quite a bit more than 1.2 volts if you're commanding 10% power, using PWM.

Everything Adam and Thad said, plus this minor item, which may be key to understanding:

If you're commanding the motor controller via PWM, you're not commanding power, you're commanding output PWM duty cycle.

If the motor controller is linear, then 10% command will create 10% output duty cycle which will effectively cause 10% of the battery's voltage¹ to appear at the motor's input, which -- if the motor is stalled -- will create 10% of the motor's stall current to flow through the motor which will create 10% of the motor's spec stall torque.

The electrical power being put into the motor is Pin = current*voltage, which will equal (10% of spec stall current)*(10% of battery voltage) which will equal 1/100th of the input power at motor stall at spec voltage.

That's why the motor doesn't overheat.



¹Let's assume, for sake of simplicity, that the battery is a constant 12 volt source (same as motor spec voltage).

2The output mechanical power at the motor's output shaft is Pout=shaftSpeed*loadTorque. When the motor is stalled, shaftSpeed is zero so Pout=0. Therefore all the input power Pin is dissipated inside the motor as heat.