A planetary gear box is an equipment piece designed to provide the ability to elevate the torque and lower the speed of an electric motor, such as stepper motor, thus altering the power and enhancing the control of the electro-mechanical system.

High-quality planetary gear boxes offer high torsional stiffness, low backlash, and high levels of efficiency, which makes them suitable for industrial automation applications. Moreover, they are suitable for working in high torque applications where feedback is essential.

Planetary gear boxes are constructed from three gears: a sun gear, a ring gear and planet gears.


  • Sun Gear: Just as the sun is located in the centre of the solar system, the sun gear is positioned in the center of the gear box.
  • Ring Gear (Annulus): The ring gear is the outermost gear. It features inward-facing teeth to mesh with the inner planet gears.
  • Planet Gears: Just as all the planets, the planet gears orbit the sun gear and mesh with the ring bear.

This gear got its name due to its resemblance to the solar system – the center of the ring gear turns around the center of the sun gear. Simply said, the sun gear is fixed while the planetary gear rotates around it. The teeth of the ring gear interlock with the inward teeth of the sun gear, allowing a smooth transmission.

Planetary Gear Boxes Applications

Planetary gear boxes are highly used in automatic transmission vehicles. What differs this type of gear boxes from the others, is that a planetary gear box can use any of these three elements as the input or the output. That explains their popularity in applications that require transmission of high torque-to-weight ratios, such as lifting machines, cranes and other machine tools for the construction, agriculture and marine industry. With torque ranging from 1000nm to over a million of nm, this makes planetary gear boxes ideal for continuous, intermittent, and reversing operation. Moreover, these boxes can be installed in just any mounting position, which means they can accommodate high radial and axial loads.

Planetary Gear Boxes Benefits

When compared to traditional gear boxes, planetary gear boxes have numerous advantages. One of the main advantages is their unique combination of both compactness and exceptional power transmission efficiency. Typically, efficient loss in a planetary gear box is only 3% per stage, which ensures that a high proportion of the energy being input is transmitted through the gear box, rather than wasted on mechanical losses in the gear box. Better load ability and higher torque density are also among the other great benefits of planetary gear boxes.