September 2026 – Present · Solo project

Custom Cycloidal Robotic Actuator

Onshape
NEMA 17
AS5600 Encoder
3D Printing

A compact, low-backlash cycloidal-drive actuator prototyped over three PLA iterations, with a 13:1 reduction, delivering about 70% of its theoretical output torque in static testing.

Overview

This actuator is the first step toward a desktop robot arm with custom actuators, joint encoders, and 3D-printed links. The goal is an actuator that runs continuously and transmits torque efficiently.

I chose a cycloidal drive for its low-backlash potential in precision robotics, and because the load is shared across many lobe contacts, which gives it a high contact area.

Design

The gearbox uses 13 lobes and 14 rollers for a 13:1 reduction. It is a dual-disc design: two cycloid discs run out of phase to balance the drive’s internal forces.

Assembled cycloidal gearbox — The assembled gearbox.

Cycloidal gearbox with the cover removed, showing the disc and rollers — Cover removed, showing the cycloid disc and rollers.

Section view of the dual-disc cycloidal reduction — Section view of the dual-disc reduction.

For testing, the input is a NEMA 17 stepper rated at 17 N·cm.

NEMA 17 stepper motor — NEMA 17 stepper used as the test input.

Test Results

1.33–1.77 N·m

Output torque: 60–80% of the 2.21 N·m theoretical output (17 N·cm × 13:1).

3+ hours

Continuous run with no failure; only slight wear on the cycloid discs.

Lever + probe

Torque from a force-probe reading on a lever arm fixed to the output shaft.

The torque benchmark is the motor’s stated rating multiplied by the reduction.