MIT Mode

A single joint-motor command carrying target position, velocity, Kp, Kd, and feedforward torque, with the drive computing torque via a PD formula.

This joint-motor command format originates from the motor controller of MIT's Biomimetic Robotics Lab's Mini Cheetah quadruped (open-source firmware by Ben Katz). Chinese motor makers such as Damiao followed and made their drives compatible with it, and Xiaomi calls it ‘motion control mode’ on its CyberGear motor. In a single CAN frame, the host sends a target position p_des, target velocity v_des, stiffness Kp, damping Kd, and a feedforward torque τ_ff; the drive's internal loop computes τ = Kp(p_des − p) + Kd(v_des − v) + τ_ff (p and v being the measured position and velocity) and passes that to the current loop. Changing the parameters switches behavior: a large Kp approximates position control, Kp = 0 gives velocity or damping control, and Kp = Kd = 0 gives pure torque control. Reinforcement-learning locomotion and humanoid policies, which output joint target positions, are often executed through this mode with fixed Kp and Kd. It is a single-joint PD-plus-feedforward format, not the direction-split hybrid force/position control described elsewhere.

ExampleThe Damiao DM-J4310 manual notes that with Kp = 0 and Kd ≠ 0, giving v_des spins the motor at constant speed; with Kp = Kd = 0, giving τ_ff outputs exactly that torque; and when doing position control, Kd must never be set to 0, or the motor will oscillate or even lose control.

Also called

MIT Cheetah-style Joint Command, MIT Control Mode

Related

Proportional-Derivative Control · Stiffness and Damping Gains · MIT Mini Cheetah Actuator · DAMIAO DM-J4310-2EC Joint Motor · Xiaomi CyberGear Micro-Motor · Torque Control

Sources

bgkatz/motorcontrol 固件 foc.c（torque_control: kp·(p_des−θ) + kd·(v_des−ω) + t_ff） (Chinese)
DAMIAO DM-J4310-2EC V1.1 手册（Operating modes: MIT mode） (Chinese)
Xiaomi CyberGear 说明书英译版（Operation control mode 五参数指令） (Chinese)