Cycloidal drive
A cycloidal drive is a compact gear system that reduces input speed while delivering high torque and very little backlash. It uses an off-center input within a bearing to make a cycloidal disc wobble inside a fixed outer ring gear. The edge of the disc has holes that align with pins on the ring gear. As the disc wobbles and pushes the pins, the output shaft turns. The wobble itself doesn’t move the output directly; the pins moving through the holes produce smooth rotation. The output turns in the opposite direction to the input.
The reduction ratio depends on the ring gear pins and the lobes on the cycloidal disc. Single-stage drives go up to about 119:1, and two-stage drives can reach about 7,569:1. Efficiency is typically around 93% for a single stage and about 86% for two stages.
Because the input motion is eccentric, the drive can vibrate unless balanced. To reduce this, designers often use two discs offset by 180 degrees. For even less vibration, three or more discs can be used, with the outer discs moving together opposite the middle, which is heavier.
Modern precision cycloidal drives often use several output shafts arranged around the same circle and driven by central input gears, forming a planetary-like configuration. This layout can be driven by a fast motor and is common in robot actuators. Bearings are used to carry loads, reducing surface wear.
Advantages include zero backlash, high torque in a small package, and larger contact areas than many gearboxes, though they rely on sliding contact. They are ideal when you need high torque at low speed.
The concept traces back to Lorenz Braren in the 1920s. He patented the cycloid gearbox in 1925, started Cyclo GmbH in 1931, and licensing with a Japanese company in 1937 allowed production in Japan by 1939.
This page was last edited on 2 February 2026, at 16:31 (CET).