Tilting torque calculation of a novel tiered type permanent magnet spherical motor

This paper proposes a novel tiered type permanent magnet spherical motor (T-PMSPM) of which the output torque is relatively higher than that of the most existing spherical motors. The proposed T-PMSPM has three stators along axial direction; each of the stator is consisted of an iron core and a three-phase winding. An analytical method is developed in order to calculate the tilting torque based on the air gap magnetic field distribution generated with the specific pole-slot combinations. For performance verification and accurate calculation, three-dimensional finite-element analysis (FEA) is adopted. Two typical rotor configurations are compared and analyzed, focusing on the ability of large torque production, especially for the tilting torque. Finally, a prototype motor as well as the auxiliary apparatus used for experimental measurements has been manufactured. Considering that the friction torque is nonnegligible, a test procedure of torque measurement and separation is designed and performed. The tilting torque obtained from the experiments is compared with the FEA results after friction compensation.