Cogging torque is a result of the permanent interaction of the magnet produced with the permeability of the air gap manifested by the tendency of the rotor to look for stable positions, even when the motor is off, which results in a pulsating torque that does not cooperate for the total torque of the system. The cogging torque is quite harmful when it comes to precision applications because it introduces small variations in speed that generate vibrations in the engine that are felt when it operates at low speeds and with light loads.
In order to reduce this effect, some changes are made in the design of the machine, such as determining the width of the openings of the stator slots, the angle of inclination of those grooves and creation of auxiliary teeth. In cases where the cogging torque is not very extraordinary, it is customary to tilt the stator grooves, at most one groove ac motors. Theoretically, it is possible to eliminate the cogging torque by using a stator configuration which is based on the construction of a flat stator where the windings are not housed in grooves. It is a configuration that would be good for running at high speeds, as iron losses would be very low and the engine would see its weight reduced.