In finite element analysis, the energy derivative is obtained by the sum of the contributions from each element in
the airgap to obtain the total torque.
The finite element method is used to determine the cogging torque and the electromagnetic torque.
The cogging torque characteristics are determined when only the magnet in the rotor excites the motor.
It is repeated every fifteen degrees due to the number of slots.
The cogging torque is measured experimentally by using a wheel apparatus and applying known weights to a string.