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GSL Series Zero-Backlash Strain Wave (harmonic) Gearboxes

GAM’s GSL series zero-backlash strain wave gearboxes use harmonic gearing to provide zero-backlash and high torque in a small, lightweight gearbox. Collaborate with GAM engineers to customize the GSL series robotic strain wave gear reducers for easy integration into machines and mechanisms.

  • Drops in for popular competitor gearboxes
  • Strain wave harmonic gearing for high precision
  • Backlash ≤ 0.5 arcmin (≤ 30 arcsec)
  • High reduction ratios in a single stage: 50:1 to 160:1
  • Simple design for integration into a mechanism or machine
  • High torque density with low inertia
  • Wide selection of models and configurations
  • Collaborate with GAM engineers to design a strain wave gearbox assembly for easy integration
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Strain Wave Design & Operation

Stain wave harmonic gearing has a simple design with 3 basic parts: wave generator, flexspline, and circular spline.


  • Wave Generator: Made up of an elliptical cam and a ball bearing. It is usually attached to the driving  component. The inner ring of the bearing is fixed around the cam causing the bearing to deform to an  elliptical shape.
  • Flexspline: An elastic, thin-walled component with gear teeth on the outer surface. The flexspline is  either cup or hat shaped, with a rigid base for  transmitting torque. It has 2 less teeth than the circular spline. Most commonly the output
  • Circular Spline: Rigid steel ring with internal teeth. It has 2 more teeth than the flexspline. Most commonly the fixed component.

The deformation of the flexspline into an elliptical shape causes the teeth to sequentially engage and disengage the teeth of the circular spline. This results in the flexspline rotating at a significantly slower speed relative to the wave generator producing the gearbox's high ratios.


GSL Operational Overview

Strain Wave (Harmonic) Gearing in Action

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

In this style, the flexspline is the outermost diameter. Useful for applications requiring a gearbox with a rotating housing such as an AMR or AGV wheel or a robot joint


Rotation Direction

The GSL strain wave gearbox can be driven in two ways depending on which component is fixed and which is the driven, or output, component:

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

GSL Series Models

Compact / Ultra Thin Gearboxes

GSLC Components

The component form of the strain wave gearboxes includes only the Wave GeneratorFlexsplineCircular Spline. For easy, full integration into your mechanism or machine.

Collaborate with GAM

We have the ability to customize & modify all our products. Our team of engineers will collaborate with you to produce your desired result.

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