Harmonic Drive–Inspired 3D Printed Model

This is a 3D printed model inspired by a harmonic drive (strain wave gear), a compact and precise reduction mechanism commonly used in robotics.

Harmonic drives are known for their high gear ratios, minimal backlash, high positioning accuracy, and coaxial input and output shafts.

This model has a gear ratio of 39:1, making the motion reduction easy to observe and understand.

The flexspline is printed in TPU, allowing it to flex and deform in a way similar to a real harmonic drive, while the other parts are printed from rigid materials for strength and stability.

In addition, a new printing profile called the PLA Flex Drive Profile has been introduced.

This profile achieves the required flexibility using only standard PLA — no TPU or specialty filament required. By relying on structural compliance rather than material softness, it allows makers to build the mechanism using widely available and affordable materials.

Multiple units can be stacked and connected, creating a modular, multi-stage setup.
When stacked, the reduction becomes extreme — you have to turn the handle many, many times just to get a single full rotation, which makes the effect very clear (and a bit exhausting!).

Because of the complex shapes involved, support material is required.

This model is designed for demonstration and educational purposes rather than for handling heavy loads.