Cycloidal drives are effective speed reducers known for their compactness compared to traditional gearboxes, but they often consist of multiple components. A recent finding by Raph introduced a revolutionary design: the harmonic pin-ring drive, utilized in certain TQ electric bicycles. This innovative drive simplifies construction by utilizing only two discs, prompting Raph to 3D model his version for experimentation.
The mechanics behind this cycloidal drive are thoroughly detailed in a related article on Pinkbike. While conventional cycloidal drives use load pins to stabilize rotation, making them bulkier, the harmonic pin-ring design employs two toothed discs that are offset by 180°. This configuration effectively cancels out wobble while maintaining a more compact form.
The harmonic pin-ring drive resembles strain wave gearing, a technology first patented by C.W. Musser in 1957 and popularized under the Harmonic Drive brand, which has historical applications including in NASA’s Lunar Rover. Although this technology isn’t new, its resurgence is notable. For those interested in hands-on experience, the 3D model files are accessible on GitHub and MakerWorld.