Effect of Winding Process on Performance of Rhombic-Wound Slotless Motor

With the continuous advancement of the manufacturing industry, slotless motors are widely adopted for their compact structure and stable torque output. Slotless windings are categorized by geometry into skewed, rhombic, and hexagonal types, and by manufacturing process into enameled wire and flexible printed circuit board (FPCB) windings. Enameled wire windings involve sophisticated fabrication but feature dense conductor arrangement, while FPCB windings have the limitation of fixed inter-conductor spacing and enable flexible layout, facilitating integrated manufacturing and performance optimization of small-sized motors. Meanwhile, stator outer diameters of slotless motors vary with different power requirements. Thus, this paper focuses on rhombic-wound slotless motors to investigate how the two winding processes affect electromagnetic performance under different power configurations (i.e., different stator outer diameters). Four stator outer diameter specifications ( 13 mm, 22 mm, 30 mm, 40 mm ) are selected in ascending order within the typical range of slotless motors, and finite element models (FEMs) are established for both winding processes to analyze performance differences. Results show that enameled wire winding yields superior performance for large stator outer diameters; for small diameters, the two processes deliver comparable performance, yet FPCB winding excels in integral motor molding and winding optimization. In addition, FPCB windings incur higher conductor eddy current losses due to conductor geometric effects.