Hardware

Quasi-Direct Drive (QDD)

A quasi-direct drive (QDD) is an actuator that pairs a high-torque electric motor with a low gear ratio, typically around 6:1 to 10:1, preserving much of a direct drive's backdrivability and transparency while multiplying torque. Popularized by the MIT Cheetah robots, QDD actuators enable proprioceptive force sensing, estimating contact forces from motor current without dedicated sensors, and tolerate impacts that damage highly geared drives.

Why it matters for physical AI

Cheap, impact-robust force sensitivity is exactly what dynamic legged robots and contact-rich manipulators need, which is why QDD actuation spread from research quadrupeds to commercial platforms.