Planetary gears pack a lot of torque in a small package, making them a natural for today's rotary machine axes.
Planetary gears debuted in the early 1970's in automatic transmissions used in tracked and wheeled off-road vehicles. Planetary/parallel-shaft arrangements appeared in the first wave, followed by all-planetary travel drives. Eventually planetary technology split off into today's common forms, including swing drives, winch drives, concrete mixers, and others. Industrial applications developed over the same period, primarily in the form of gearboxes powered by electric motors.