The rotor of the electric motor so that it can work, needs a torque so that it can begin its turning. This torque is normally developed by magnetic forces generated between the rotor and stator magnetic poles. An engine can never operate if it is designed solely with permanent magnets and this factor is easy to verify, since not only will it not have the initial torque to start the movement, if they are already in their equilibrium positions, as they will only hesitate, around this position if they have an initial impulse.
The attraction or repulsion forces generated between stator and rotor can pull or push the movable poles of the rotor, thereby producing torques, which will cause the rotor to rotate faster, until the frictions or charges attached to the rotor. shaft can reduce the resulting torque to zero. motor brakes
Both the rotor and the stator of the electric motor need to be magnetic, since these forces are between the poles that cause the necessary torque to make the rotor rotate. However, even if permanent magnets are often used, especially small motors, at least some of the magnets on an engine will need to be electromagnets.