What is Planetary Gear Set?

April 21, 2021

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The planetary gear set is made up of the planet gear, sun gear, and inner ring. A set of planet gear is called a single-stage planetary gearbox. The stage number of planetary gear refers to the number of planet gear sets. A planetary reducer consists of a planetary gearbox and a motor. The backlash of a planetary reducer: fix the output end and rotate the input end clockwise and counterclockwise to make the input end produce rated torque ( +-2% torque), there is a slight angular displacement at the input end of the planetary reducer, which is the return stroke clearance. The unit is “arc minute”, which is equal to one-sixtieth of a degree. Some people call it backlash. Planetary reducer is an industrial product with a wide range of applications, which can reduce the speed of the motor while increasing the output torque. The planetary reducer can be used as a supporting component in industries such as lifting, excavation, transportation, and construction.

As mentioned above, one set of the planetary reducer is called the single-stage gear reducer. The second-stage planetary reducer means that there is a two-stage planetary gear train, and the three-stage planetary reducer means that there is a 3-stage planetary gear system. Since one set of planet gears cannot reach the larger transmission ratio, sometimes 2 or 3 sets are required to meet the user’s requirements for larger transmission ratios. Due to the increase in the number of the planetary gear set, the overall length of the 2-stage or 3-stage reducer will increase, and the efficiency will decrease.


Generally, the number of stages of the planetary reducer is divided into 1, 2, and 3. The commonly used reduction ratio of planetary reducer:

Level 1: 3, 4, 5, 7, 10

Level 2: 15, 20, 30, 35, 40, 50, 70, 90, 100

The difference between the single-stage planetary gearbox and two-stage planetary gear train:

The difference in the number of gear sets.
The difference in efficiency, the efficiency of the two-stage planetary gear train is lower than that of the single-stage gear reducer.
The difference in length, the two-stage planetary reducer is longer than the single-stage planetary reducer.
The difference in transmission ratio, the two-stage planetary gear train has a larger transmission ratio than the single-stage planetary gearbox.