path sun → carrierratio 5 : 1direction same waytorque × 4.85
InputOutputHeld stillSun 12 teeth, planets 18, ring 48. Hold the ring, drive the sun, and the carrier comes out at 1 + 48/12 = 5:1, same direction. This is the usual gearbox setup, and you can stack stages for 25:1 or 100:1. Hold the carrier instead and the ring runs backwards at 4:1. Hold the sun and you only get 1.25:1. Three planets share the load, which is why a planetary is so compact for the torque it carries. Each stage also leaves a few arcminutes of backlash.