How to Select the Right Harmonic Reducer

Torque, reduction ratio, backlash, size and mounting — the five parameters that decide which model fits your machine.

1. Required torque

Start from the load. Calculate the rated torque your application needs and add a safety margin, then check the reducer rated torque and peak (acceleration) torque. Never size a reducer only by rated torque if the machine sees frequent starts, stops or shock loads.

2. Reduction ratio

Ratio = input speed ÷ output speed. Common harmonic ratios run from 30:1 up to 160:1. A higher ratio gives more torque and finer positioning but lower output speed. Match the ratio to your target output speed and required resolution.

3. Backlash and stiffness

For servo and robot axes, look for low or zero backlash (often specified in arc-seconds) and high torsional stiffness. Lower backlash means better repeatability; higher stiffness means the axis holds position under load without wind-up.

4. Size, weight and mounting

Harmonic reducers are chosen when space is tight. Decide whether you need a hollow shaft (to pass cables or a through-shaft), a cup, hat or integrated bearing-flange structure, and how the unit mounts to your motor and frame. Compact "short" variants save axial length at equal torque.