Comparison of inner and outer rotor configurations in slotless PM machines with PCB windings

For low power applications, two kinds of topologies and configurations of PM machines exist, the slotted and slotless topologies and the inner and outer rotor configurations. When searching for high torque densities, e.g. in robotic applications, it has been shown that the outer rotor configuration outperforms the inner rotor configuration in the slotted topology. In this paper, these two configurations are compared but for the slotless topology based on both an optimized motor constant and a nominal torque. It is shown that the inner rotor configuration is superior in terms of motor constant compared to the outer rotor configuration. On the contrary, in terms of nominal torque, the outer rotor configuration outperforms the inner rotor configuration because of its higher heat dissipation capabilities.