Spine Fit

First increase in speed – An increase in speed results when the sun gear is held stationary and planet the planet-pinion carrier is turned. As the carrier turns on, the planet pinions rotate on their shafts. This turns the internal gear faster than the carrier.
Second increase in speed – Another combination is to hold the internal gear stationary and turn the carrier. This drives the sun gear faster than the carrier.
First reduction in speed – If the internal gear is turned and the sun gear is held stationary, the planet-pinion carrier turns more slowly than the internal gear. This arrangement provides second gear.
Second reduction in speed – If the internal gear is held stationary and the sun gear is turned; the carrier is driven at reduced speed. The planet pinions must rotate on their shafts. As the pinion rotate, carrier also rotates. Thus carrier rotates at lower speed used to get first gear.