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What are Planetary Gear Sets?

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A planetary gear set consists of the planet gear, sun gear, and inner ring, and is known as a single-stage planetary gearbox. Planetary gears stage numbers are indicative of the number of planetary gear sets. A planetary reducer consists of a planetary gearbox and a motor. The backlash of planetary reducers: fix the output end, and rotate the input end clockwise and counterclockwise to make the input end produce rated torque ( +-2% torque). The input end of the planetary reducer has a slight angular displacement, which is the return clearance. The unit is known as "arc minute", which equals to one-sixtieth of a degree. Some refer to it as backlash. A planetary reducer is a widely used industrial product. It reduces 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 a single-stage gear reducer. A second-stage planetary reducer means that there is a two-stage planetary gear system, and a three-stage planetary reducer means that there is a three-stage planetary gear system. Since a set of planetary gears cannot reach a larger transmission ratio, sometimes 2 or 3 sets are needed to meet the user’s requirements to achieve larger transmission ratios. Due to the increase in the number of planetary gear sets, the overall length of the 2-stage or 3-stage reducer increases, decreasing efficiency. 

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:

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

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