TL;DR: Sun, planet and ring gears explained simply, plus gear ratios, real uses and a 2,000-year story from the Antikythera Mechanism to 3D printing. An Engineering Analysis of Planetary Gear Systems from Antiquity to High-Performance Additive Manufacturing The architecture of modern motion control is fundamentally defined by the planetary gear set, a mechanism that started from the sophisticated analogue computing of the Hellenistic era to the high-torque, energy-dense drivet...