Planet gears rotate around axes that revolve around a sun gear which spins in place. A fixed ring gear holds the planet gears in orbit about the sun gear and meshes with both the ring and sun gears.

Called epicyclic CVTs, or planetary CVTs, these transmissions use planet gears to transfer torque. Toyota used one in the Prius back in the late 1990s. Planetary gears work for hybrids, too., GM ...

When the planet gears of the intermediate system are held reactionary, the ring gear of the its system moves in a direction opposite that of its sun gear. This is where reverse motion begins.

Planetary designs also cannot have ratios less than 3:1 because then the pinion and outer ring gear would need to be nearly the same size, leaving no room for the planet gears.

The Uni Wheel obviates the need for a separate gear reduction, as that job is handled by the sun and planet gears. (Right now, Hyundai is working with a 6.241:1 ratio, but this may be tweaked for ...