---
name: "Cycloidal Gearbox"
subtitle: "A fifteen-year-old's 1:9 gearbox, published with the version that didn't work"
date: 2026-08-02
shortlist: true
link: "https://github.com/tom-ilan/cycloidal_gearbox"
linkText: "GitHub"
source: "Hacker News — Show HN"
topics: [gadgets-and-toys, learning-and-reference]
tags: [3d-printing, cad, open-source, engineering]
description: "Three versions of a 3D-printed cycloidal drive — including the failed one — plus the Fusion 360 script that generates the tooth profile from scratch."
---

Version two is in the repo because it failed: a micro cycloidal drive squeezed to a NEMA 17's footprint, defeated by tolerances a 3D printer cannot hold. Version three works — 90mm across, ten outer pins, nine rotor lobes, 1:9. The real object here is the Fusion 360 script that draws the profile from pins, pitch radius and eccentricity, so you can generate a ratio the author never printed.