Planetary gearbox

A sun gear, orbiting planets, and an internal ring.

A planetary (epicyclic) gearbox puts a sun gear at the centre, several planets orbiting it, and an internal ring around the outside — a compact, coaxial reduction. The generator enforces the epicyclic relations (ring teeth = sun + 2×planet, the equal-spacing assembly rule) and phases every gear so the teeth interlock. With the ring fixed, the sun driven, and the carrier as output, the reduction is 1 + ring/sun. The gears are separate bodies — print the sun, planets, and ring and add your own carrier.

1. Set the sun and planet tooth counts and the number of planets.
2. Set the shared module, pressure angle, thickness, bore, and ring rim width.
3. Generate: the sun, planets, and ring drop in meshed and phased, with the reduction shown.