Introduction of Planetary Reducer

Planetary reducers are used for applications where low reduction rate and precision are required.Except for the general reducer definition, let’s get to know planetary reducer in a little detail.

Planetary Reducer Input Side and Output Side

planet reducer input output

When viewed from the outside, the input side for the servo motor connection and the output side for the load connection are visible.

The input side of the reducer is designed according to the shaft output and flange dimensions of the servo motor to be connected.

In general, there are body sizes such as 40, 50, 60, 70, 80, 90, 100, 110, 120, 140 and 155. However, for now, we will proceed based on the body of 90 (in the image).

Internal Structure of Planetary Reducer

planet reducer internal structure input output

Planetary reducer consists of 3 basic parts as sun, planets and ring. The servo motor drives the sun, the planets around the sun spin in the ring. In this case, the sun gear transfers the power from 3 different points (for the 3-element reducer) to the outer planetary gears.The output power increases according to the ratio between the outer ring and the sun. At the same time, the speed decreases at the same gear ratio.

Calculation of Planetary Gear Ratio

planetary reducer ratio calculation formula

Planetary reducer calculation main formula.

Ratio= ( Tsun+ Tring ) / Tsun

Calculation Example of Planetary Gear Ratio

planetary reducer calculation example

For this example;

Numbers of teeth of the sun gear: 17

Numbers of teeth of the ring: 102



Frequency Calculation of Planetary Reducer Gears

In some cases, it may be necessary to calculate the frequency produced by the gears inside the planetary reducer to perform noise analysis.

planetary reducer frequency calculation

For example;

Input speed=4500rpm   / 75rps

Output speed = 75/7= 10,71 rps

for Ring


F=1092,42 Hz

for Sun Gear


F=1275 Hz

How To Assemble Servo Motor To Reducer

servo motor planetary reducer assemblyThis is a very easy operation. First check that the servo motor shaft and flange are compatible with the input side of the gear unit.If there is no keyway on the reducer input hole, remove key on servo motor shaft.Insert the servo motor shaft into the input of the reducer and push the flange until it clicks into place.Next, install the bolts that secure the motor and reducer bodies to each other.Finally, tighten the bolt in the hole on the reducer flange.This process is necessary to fix the motor shaft to the reducer’s input gear. In the video, you can see the installation example in 3D environment.

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