Planetary gearboxes, also known as planetary reduction boxes or gearboxes, are basically composed of multiple planetary gears rotating around a sun gear. This structure not only reduces the transmission speed ratio, but also proportionally amplifies the torque of the motor. Planetary gears can generally be divided into simple planetary gears and complex planetary gears. Simple planetary gears include a sun gear, an outer gear ring, a planetary gear and a planet carrier. Complex planetary gears contain more gear trains, which may include multiple planetary gear trains and sun gear trains, and have the characteristics of high reduction ratio and high torque.