🪐 Brass Orrery Gear Train: Planet Periods, Tooth Ratios and Kepler Drift (2D)

Top view of an orrery whose planets are driven by integer-tooth gear ratios, drawn next to the true Kepler motion. Change the largest gear size, the mass of the Sun, the eccentricity of Mars and the crank speed, and see how far each brass planet drifts from the real one per century, how the equation of centre bends an elliptical orbit and why period grows as distance to the power three halves. Kepler law, the Kepler equation, the best tooth ratios and orbital gravity are checked numerically, with four in-page numerical checks.