Planetary Gear Reducer Guide

A planetary gear reducer is a type of planetary gearbox that aims to transmit a maximum torque in the most compact form. It decreases the number of motor revolutions and ensures high torque through the speed sensor. But how exactly does it work? In this article, we will first explain its basic structure so that you can better understand the mechanism. Later, we will take a closer look at its advantages and various applications.

Figure 1. Planetary Gear Reducer, SunUs



The main transmission structure is the planetary gears, sun gear, and ring gear. The sun gear driven by an external power is located in the center of the gear set. As the sun gear rotates around the driving shaft, the three planetary gears revolve around the sun gear. The planetary gears are distributed equally on a so-called planet carrier. The ring gear is in close contact with the internal gearbox housing. Below is a picture showing the construction of these planetary gearbox components.

Figure 2. Structural Components of a Planetary Gearbox

These three gears are directly supported by the output shaft, ring gear, and sun gear, which float in it. When the sun gear is driven by the input power, the planetary gears start to rotate around the center as well as the orbit of the ring gear.

Design & Working Principle of Planetary Gear Reducer, Wittenstein Group



If you want to achieve high torque while reducing the processing speed, a planetary gearbox might be an ideal choice. In real life, you’ll find them not only small machines like electric screwdrivers but large units like bulldozers. They are better than both helical and spur gears when it comes to efficiency, durability, and horsepower. Now, let us look at all of the advantages of it:

High Power Density

Several planets or airplanes share the load instead of one gear. The more of these planets are incorporated into a gearbox, the better the shared load efficiency. This leads to higher power density.

High Efficiency

A planetary gear reducer is highly efficient due to its unique design. Although many speed gear reducer manufacturers do not disclose efficiencies in their catalog directly, there is a simple calculation you can use to obtain the value:

Input Power/Output Power=Efficiency

Compact Size and Low Weight

These devices have a very compact design compared to other speed reducers and as a result, usually weigh less than other types. With this device, you can achieve as much as a 50% size reduction while maintaining the same torque output.

Excellent Durability and Longer Life

Thanks to the torsion rigidity and better rolling properties of planetary gear reducers, they usually last longer and are not as prone to malfunctions. Bearings help reduce the damage caused by rubbing the shaft directly on the box. Therefore, higher gear efficiency and smoother operation are achieved.

Increased Repeatability

Higher radial and axial load speeds provide reliability and sturdiness, which results in a significantly lower risk of gear misalignment. Besides, planetary gear reducers ensure a constant and uniform transmission and greatly reduced vibration under different loads. All these result in higher precision and therefore increased repeatability.

Increased Torque Transmission

As more teeth come into contact, the mechanism can transmit and withstand greater torque and transfers the power more evenly.

Maximum Versatility

The mechanism is installed in a cylindrical gearbox and can be installed in almost any space. On top of that, planetary stages can be stacked which allows for high customizability.


Planetary gearboxes have the aforementioned benefits of compact size, lightweight design, strong load capacity, high reliability, low noise, large output torque, large speed ratio range, high efficiency, and incredible versatility. Thanks to these advantages, planetary gear reducers are suitable for lifting and transportation, construction machinery, metallurgy, mining petrochemicals, construction equipment, light industry and textile industry, medical equipment, instrumentation, automobiles, ships, weapons, aerospace, and many other industrial sectors.

Some models have a square flange design, with simple installation in mind, which makes them suitable for AC/DC servo motors, stepper motors, and hydraulic motors, etc.

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