Harmonic Drive

thingiverse

A 3D printable harmonic drive is now available, offering several advantages over traditional drives such as no backlash, high gear ratios, and position holding without power. Harmonic drives contain an elliptically deformable inner gear (flex spline) that meshes with a ridged outer gear (circular spline), controlled by an elliptical horn (wave generator) attached to a motor. This design features 32 teeth on the flex spline and 34 on the circular spline, costing around $3 in parts and plastic, along with a servo. The drive's main addition is a stabilizer that constrains output force to the radial axis, reducing shearing forces on the flex spline. With refinement, it may be used in bipedal robots like FOBO. A full parts list and pricing information can be found here, while assembly instructions are available here. Testing can be done with any microcontroller controlling a servo, following the Servo/Knob example from the Arduino development environment.