Small Banebots Motor Issue - Lessened torque and smoke

[Al Skierkiewicz]

The snap action breakers are thermal devices capable of up to 600% over current for a few seconds before they trip (They can actually handle 200% of rated current for 10-15 seconds). It is conceivable that a 20 amp breaker will not trip at the stall current of this motor unless it is sustained. As with all motors of this type, there is a very high thermal resistance from the armature to the outside world. The only thing conducting heat is the shaft and bearings.
The breakers are sized to match with the wire size to prevent fires on the robot. A dead short on any branch circuit will trip these breakers as they are expected to. The stall current in your little motor will rapidly raise the temperature of the windings causing the insulation on the internal wires to fail which in turn causes shorts between windings. The smoke is the insulation burning as the wires short. When this occurs, the current skyrockets and the power falls while the motor is in self destruct. It is conceivable that the motor will still turn while drawing more than rated stall current with shorted windings.
Please remember that in raising an arm, there is a change in force/load. The greatest demand (load) on the motor will occur when the arm is passing through the horizontal plane. I am sure that Dr. Joe can explain this better than I can.