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arXiv · 2509.23561

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
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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.

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Jianren Wang, Quanting Xie, Jie Han, Yang Zhang, Christopher G. Atkeson, Abhinav Gupta, Deepak Pathak, Yonatan Bisk. 2025-09-28. High Torque Density PCB Axial Flux Permanent Magnet Motor for Micro Robots. https://arxiv.org/abs/2509.23561

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