GSL Series Robotic Strain Wave Gearbox Operation

GAM’s GSL Series Robotic Strain Wave Gearboxes provide zero-backlash and high torque in a small, lighweight gearbox for integration into machines and mechanisms.

Learn more about GSL strain wave gearbox features and models here

Strain Wave Design

Stain wave gearing has a simple design with 3 main parts:

wave generator

Wave Generator

  • Elliptical cam drives inner race of ball bearing
  • Usually the input driver for gear reduction



  • Thin-walled cylinder with teeth on the outside.
  • Fits over outer race of bearing and continuously deforms as the wave generator rotates
  • Usually the output component
circular spline

Circular Spline

  • Rigid steel ring with inner teeth
  • Usually the fixed component

Strain Wave Gearbox Operation

Cup vs. Hat Style

The terms "Cup" and "Hat" refer to the shape of the Flexspline. When viewed in cross-section, the flexspline looks like a cup or a hat.Cup vs. Hat

Cup Style

Mounting flange output (bottom of the cup) is easy to bolt to for components such as pionions

Hat Style

The flexspline is outermost diameter. Useful for applications requiring a gearbox with a rotating housing such as an AGV wheel or robot joint

Rotation Direction

The GSL strain wave can be driven in two ways:

Common Operation

Input Wave Generator
Output Flexspline
Fixed Circular Spline
Rotation Opposite Direction
Ratio Nominal Ratio, e.g. 50:1

Alternate Operation

Input Wave Generator
Output Circular Spline
Fixed Flexspline
Rotation Same Direction
Ratio Nominal Ratio + 1, e.g. 51:1