Orrery: Gear-Driven Solar System

A fully 3D-printable mechanical orrery: a hand crank (or optional stepper motor) turns a gear train that drives nine planets plus the Moon around a glowing Sun, each at its own scaled orbital period. Measured in the CAD motion study, the ten drive ratios match their targets to better than 0.01 percent and every planet turns the same way. The Moon runs off its own gear path up the Earth post, independent of the Earth arm.

It is built from 105 printed parts with no screws, nuts, glue or bearings: snap rivets, snap-fit arms and posts, printed D-shafts and integral thrust rings. Only steel rod is bought (one 8 mm x 306 mm central post, short 8 mm idler pins, a 4 mm Earth post). Long arms (Saturn, Uranus, Neptune, Pluto) split in two with a sliding dovetail; gas giants are two-hemisphere shells with banded colours; Saturn has a tilted three-colour ring set; the Sun is a translucent two-piece shell that hides an LED. A year dial sits on the lid, and a motor cradle, electronics tray and USB-C base wedge are optional extras. The sweep is about 0.88 m across.

From the project's own verification report (CAD, not physical): no interference over 26 layshaft positions, arm droop under 2 mm in every arm, and every snap feature below the 0.02 strain limit. The model shows all 110 printed pieces in their assembled positions (each 3MF holds one part in its own coordinates, so the gear groups and the extra base wedges and snap rivets are placed using the transforms from the Fusion model), plus the purchased steel rods and pins and the optional 28BYJ-48 motor, which are not in the 3MF set and were taken from the Fusion model. STATUS: this page is a conversion of the exported 3MF parts; its build status is whatever the project's own handoff notes say, and printing and running it is not confirmed here. Known compromises listed by the project: a 0.45 mm inner lip on the gas-giant seam sockets, and some small tree supports. Parts file sizes are large (about 130 MB of 3MF).