Worm Gear

A gear pair where a screw-shaped worm turns a wheel, giving a large reduction ratio and a 90° change in axis.

A worm gear is a classic gear pair: one full turn of the screw-shaped worm advances the meshing worm wheel by only one or a few teeth, so a single stage can produce a reduction ratio of tens to one, while also turning the rotation axis 90 degrees. A common and useful feature is self-locking — an external force applied to the wheel can barely turn the worm backward — so the mechanism holds its position with the power off, and no separate brake is needed. The downside is high sliding friction between the tooth surfaces, which means low efficiency, heat buildup, and essentially no back-drivability, ruling it out for joints that need compliance or force control. In embodied-AI hardware, worm gears mostly show up in dexterous-hand fingers, camera gimbals, and lift mechanisms — small spaces where holding a fixed pose matters — a different tradeoff than harmonic or planetary reducers make.

ExampleSome low-cost dexterous hands drive their fingers with a small motor and a worm gear, so the fingers stay closed around an object even with the power off.

Also called

Worm Drive, Worm Gear Reducer

Related

Speed Reducer / Gearbox · Gear Ratio · Backdrivability · Strain Wave Gear (Harmonic Drive) · Planetary Gearbox · Trapezoidal Lead Screw & Self-Locking

Sources

Worm drive - Wikipedia