Review of High-Torque Electric Machines Applied in Biorobotics and Wearable Devices

Nowadays, the market for wearable devices and biorobotics is growing rapidly. In active prostheses and exoskeletons, joints are typically driven by electric machines. The critical challenge is balancing the generated torque with the size and mass of the motor, ensuring the overall weight does not hinder the user’s mobility. This paper presents a comprehensive review of high-torque electric machines based on an analysis of 162 publications, primarily from the last decade. The study systematically compares geometric, electrical, and efficiency parameters across various electromechanical converters to identify the optimal limits for bionic applications. Data suggests that an electric machine aiming to align with typical biorobotic requirements would likely fall within an outer diameter of 150 mm, an axial length of 85 mm, and a mass of 1200 g. Furthermore, the required parameters for advanced applications include an efficiency above 95%, a safe nominal voltage of up to 48 V, and the ability to generate torques up to 65 Nm. The analysis highlights that while conventional motors (such as BLDC and PMSM) dominate the market, achieving a torque density exceeding 35–45 Nm/kg—necessary to approach biological muscle capabilities—often requires adopting emerging topologies, such as magnetic gears or Vernier machines. This review provides clear quantitative guidelines for engineers designing optimal drive systems for biorobotics and wearable devices.