teeth on the sun gear and the number of teeth filled by the planet gears respectively for example the difference between the ring and the sun filled by the planet gears might be as many teeth as are on the sun gear in the same set in that situation the speed of the ring gear would be the sum of two thirds the speed of the carrier and one third the speed of the sun if the sun gear or the planet carrier rotates in an opposite direction the arithmetic sign is negative for that speed in mathematical calculations if the sun gear were to be held stationary then a carrier with inner and outer sets of planet gears will turn in the same direction as the rotating ring gear of that set on the other hand if the sun gear were to be held stationary and the carrier were to be driven then planet gears in the inner set that engage the sun gear roll or u201c walk u201d along the sun gear turning in the same direction that the carrier is rotating pinion gears in the outer set that mesh with pinion gears in the inner set will turn in the opposite direction thus forcing a meshing ring gear in the opposite direction but only with respect to the planet gears with which the ring gear is meshingly engaged the planet gears in the outer set are being carried along in the direction of the carrier the effect of the rotation of the pinion gears in the outer set on their own axis and the greater effect of the orbital motion of the planet gears in the outer set due to the motion of the carrier are combined so the ring rotates in the same direction.