Design and Analysis of High Torque-to-weight Ratio Motors for Legged Robot Joints

This paper investigated the influence of the motor size changing and magnetic materials with different saturation levels on the torque-to-weight ratio (TWR) of joint motors for legged robots. Firstly, based on scaling laws, the TWR formula related to motor parameters is derived, which shows that radial stretching of the motor contributes more to increasing the TWR. Therefore, a 36-slot/34-pole motor with a flat structure is investigated. It is found that the TWR is increased by 14.8% and the motor efficiency is increased by 0.9% using annealed cobalt-iron alloy than standard electrical steel sheets. Besides, the rotor material can be replaced by low saturation level stainless steel for simple structure at the expense of nearly 3% TWR.