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.