High Torque Density PCB Axial Flux Permanent Magnet Motor for Micro Robots
Jianren Wang, Quanting Xie, Jie Han, Yang Zhang, Christopher G. Atkeson, Abhinav Gupta, Deepak Pathak, Yonatan Bisk
TL;DR
This work tackles the challenge of delivering high torque at low speed in micro-robotic joints by developing a PCB-wound axial-flux permanent-magnet motor with IC-substrate HDI technology. The design stacks four 12-layer modules to form a 48-layer stator, achieving a record copper fill ≥45% in a 5 mm thick, 19 mm diameter package, while retaining an iron core to boost flux. Electromagnetic and thermal analyses guide optimization, and a prototype demonstrates superior stall torque and density compared to a commercial reference, with back-EMF and thermal performance aligning with simulations. The result is a compact, high-torque actuator suitable for quasi-direct-drive micro-robotics and scalable manufacturing using HDI PCB-winding techniques.
Abstract
Quasi-direct-drive (QDD) actuation is transforming legged and manipulator robots by eliminating high-ratio gearboxes, yet it demands motors that deliver very high torque at low speed within a thin, disc-shaped joint envelope. Axial-flux permanent-magnet (AFPM) machines meet these geometric and torque requirements, but scaling them below a 20mm outer diameter is hampered by poor copper fill in conventional wound stators, inflating resistance and throttling continuous torque. This paper introduces a micro-scale AFPM motor that overcomes these limitations through printed-circuit-board (PCB) windings fabricated with advanced IC-substrate high-density interconnect (HDI) technology. The resulting 48-layer stator-formed by stacking four 12-layer HDI modules-achieves a record 45\% copper fill in a package only 5mm thick and 19mm in diameter. We perform comprehensive electromagnetic and thermal analyses to inform the motor design, then fabricate a prototype whose performance characteristics are experimentally verified.