Strain analysis of stator coil holders for permanent magnet spherical motors

An analytical model of air-gap flux density and the Lorenz force law were used to establish radial and tangential electro-magnetic force models in the spherical coordinate system for the stator coils. Then, a finite element model of the stator casing and coil holder was applied to compute the strain of the coil holder caused by electromagnetic force, and the influences of the stator casing's thickness, the diameter and the length of the coil holder's connecting rod on this strain were analyzed. Finally, the finite element method and the analytical method were used to analyze a prototype motor and their results were compared, which verified the validity and accuracy of the analytical models. This analysis shows that when the stator casing becomes thin or the connecting rod slenderizes, the strain of the stator coil holder produced by electromagnetic force increases linearly within a certain range and then grows significantly.