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.
- Simple design: Only three main components
- Video about strain wave operation
- Two main styles: cup or hat
- How operation affects rotation direction
Learn more about GSL strain wave gearbox features and models
Strain Wave Design
Stain wave gearing has a simple design with 3 main parts:


Wave Generator
- Elliptical cam drives inner race of ball bearing
- Usually the input driver for gear reduction

Flexspline
- 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
- 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 Style
Mounting flange output (bottom of the cup) is easy to bolt to for components such as pinions
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 |