Cycloidal Drive

An eccentric cam wobbles a lobed disc against a ring of pins — and in doing so, 60% of those pins share the load simultaneously.

Reduces the high speed, low torque rotation of a servo motor to low speed, high torque output at very precise angular positions. Used primarily as the joint actuator in industrial and collaborative robots, where positioning repeatability of better than 1 arc-minute is required alongside the ability to survive sudden shock loads.

An eccentric input shaft causes a lobed disc — the cycloidal disc — to orbit inside a housing lined with hardened pins. Because the disc has one fewer lobe than there are pins, each full input revolution advances the disc's output by exactly one pin pitch. At any instant, roughly 60–70% of all lobes are simultaneously in contact with pins, so the load is shared across many rolling contacts rather than a single gear mesh. Nabtesco's RV series adds a spur-gear first stage to reduce the eccentrics' rotational inertia and further damp vibration, yielding the two-stage reduction principle that has been standard in industrial robots since 1985.

In plain terms

Imagine a coin with bumps rolling inside a ring of pegs. Every bump pushes against several pegs at once instead of just one, so the whole thing is incredibly strong and precise — like many people carrying a heavy table instead of one person trying to do it alone.

Also called: cycloidal reducer, RV reducer, cyclo gearbox, cycloidal speed reducer.

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A short history

The cycloidal gearbox was invented in the late 1920s by German engineer Lorenz Braren, who patented a mechanism using rollers and pins instead of gear teeth to transmit power. Originally conceived for camera mechanisms and later adopted in heavy crushing machinery, the design was largely overlooked in precision applications for decades. The modern industrial chapter opened in 1980, when Nabtesco (then Teijin Seiki) introduced a cycloidal travel drive for excavators. In 1985, Nabtesco launched its RV (Rotor Vector) precision gearbox — the two-stage spur-plus-cycloidal design now standard in robot joints worldwide. As articulated-arm robots proliferated through the late 1980s and 1990s, the RV reducer became the dominant actuator for shoulder, elbow, and wrist axes, a position it still holds today.

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