Hardware

Gear Ratio

Gear ratio is the ratio between input and output rotational speeds of a transmission, equal to the factor by which torque is multiplied and speed divided in an ideal reducer. Robot joints commonly use harmonic drives, planetary gearboxes, or cycloidal reducers with ratios from about 5:1 to over 100:1. Higher ratios raise torque density but amplify reflected inertia, friction, and backlash, degrading backdrivability and the fidelity of torque control through the transmission.

Why it matters for physical AI

The choice between high-ratio precision and low-ratio quasi-direct-drive transmissions shapes whether a robot can feel and control contact, a hardware decision that directly constrains what contact-rich policies can achieve.