A Test Rig for Measuring Force and Torque Production in a Lorentz, Slotless Self Bearing Motor

An option to hybrid Maxwell/Lorentz type self bearing motors and their inherent trade-off between bearing force and motoring torque with PM magnet thickness is one which utilizes Lorentz forces for bearing and motoring force production. A slotless version of this type of self bearing motor, and its test rig, are discussed in this paper. The test rig includes the motor, along with a conventional magnetic bearing, a shaft assembly, radial position sensors and an optical encoder. Experimental results are presented showing the force versus current relation for the self bearing motor and indicates that several of the destabilizing side pull forces predicted by theory may be neglected in practice. In particular, the cross coupled bearing current gain for the motor is experimentally shown to be negligible as compared to the direct bearing current gain. This result provides the basis for stabilizing control of the motor. The current gain for the torque production was measured as 2.5 N-m/A, and that for bearing force production was measured as 48.2 N/A. These results are shown to agree well with theory.