Joint Actuator Module

A robot joint unit that packages a motor, gearbox, encoder, and driver together into one part.

A joint actuator module is the standard way modern humanoid and quadruped robots build a joint: a brushless motor, a gearbox (planetary, harmonic, or RV), an encoder (to measure angle), a driver (to control current), and often even a torque sensor and a brake (which locks the joint when power is cut) are all packaged into a single unit, exposing only power and communication lines — commonly CAN, RS-485, or EtherCAT — to the outside. This lets a robot maker simply bolt the module into the frame and send it position or torque commands, which makes both development and repair much easier. Its torque, speed, weight, backlash (the play between gear teeth), and heat generation determine the robot's movement capability, and it's also one of the biggest cost items in the whole robot. MIT's open-source Mini Cheetah joint design helped popularize low-cost joint actuator modules.

ExampleUnitree's GO-M8010-6 is a common integrated joint motor used in quadruped robots, with a built-in planetary gearbox at roughly a 6.33:1 ratio.

Also called

Integrated Joint Module, Joint Motor Module

Related

Actuator · Quasi-Direct Drive · Planetary Gearbox · Strain Wave Gear (Harmonic Drive) · Rotary Encoder · Servo Drive (Motor Driver)

Sources

Mini Cheetah: A Platform for Pushing the Limits of Dynamic Quadruped Control (ICRA 2019)
Unitree GO-M8010-6 关节电机参数（宇树官网） (Chinese)