Hardware

Strain Wave Gear

A strain wave gear, widely known by the trade name harmonic drive, is a compact speed reducer consisting of an elliptical wave generator, a flexible externally toothed flexspline, and a rigid internally toothed circular spline, achieving reduction ratios of roughly 50:1 to 160:1 in a single stage. Because many teeth engage simultaneously, it offers near-zero backlash, high torque density, and compact form. It is the standard joint reducer in industrial and collaborative robot arms.

Why it matters for physical AI

Joint transmissions define an arm's precision and back-drivability; the strain wave gear's zero-backlash accuracy — and its compliance and friction quirks — pervade manipulator control design.