This video shows how a servo motor works.
This is a permanent magnet DC (PMDC) servo motor, also known as an asynchronous motor. As the back-EMF as the motor is turning is sinusoidal, some refer to this as an AC servo motor. This however should not be confused with an induction (synchronous) motor which the stator induces a magnetic flux on the rotor.
Shows electronic commutation.
Explains slotless, slotted and bridged stator designs.