Hardware

Backdrivable Actuator

A backdrivable actuator is an actuator whose output can be moved by external forces without damage and with low resistance, allowing the mechanism to be pushed by hand or by contact with the environment. Backdrivability generally requires low gear ratios, as in quasi-direct-drive designs popularized by the MIT Cheetah, since high-ratio gearboxes like harmonic drives reflect large apparent inertia and friction to the output.

Why it matters for physical AI

Backdrivable joints let robots sense contact through motor currents and yield safely on impact, enabling proprioceptive force control and kinesthetic teaching without dedicated force sensors, and reducing injury risk around people.