Direct-drive

A direct-drive robot joint couples the motor's output directly to the joint without intermediate gear reduction. The mechanical opposite of geared architectures (harmonic drives, planetary stages, cycloidal drives). MIT's Cheetah quadruped is the canonical direct-drive leg architecture.

The distinction matters because direct-drive trades high torque density for natural backdrivability and high control bandwidth. Geared joints produce more torque per unit motor power but lose backdrivability; direct-drive needs larger, heavier motors. Most current humanoids use geared joints at major DOF because the torque-density math doesn't work at full body weight; MIT Cheetah works partly because quadrupeds distribute load across four legs at smaller scale. The architectural choice cascades through the rest of the control and safety design.