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What is a planetary gearbox ?


Robotics, 3D printing and new means of transport (EV Cars) all have one thing in common: often they are driven by a planetary gearbox. Varitron as a manufacturer of planetary gearboxes, of course we are a professional in the gear system, but what if you encounter this technique for the first time? We have decided to explain it clearly for all – In this article we discuss the basics of the planetary gearbox.



So what is a planetary gearbox?


A planetary gearbox is a gearbox with the input shaft and the output shaft aligned. A planetary gearbox is used to transfer the largest torque in the most compact form (known as torque density).


The bicycle’s acceleration hub is a great example of a planet-wheel mechanism: Have you ever wondered how you can get so much power and capabilities in such a little hub? For a three-speed hub, a one-stage planetary gear system is used, for a five-speed hub a 2-stage. Each planet gear system has a reduction state, a direct coupling and an acceleration mode.


In mathematical terms, the smallest reduction ratio is 1:3, the largest reduction ratio is 1:10. At a reduction ratio of less than 3, the sun gear becomes too big against the planet gears. At a ratio greater than 10 the sun wheel becomes too small and the torque will drop. The ratios are usually absolute i.e. an integer number.



Whoever invented the planetary gearbox is not known, but was functionally described by Leonardo da Vinci in 1490 and has been used for centuries. WOW!


Why is it named a planetary gearbox, not solar system gearbox?

The planetary gearbox got its name because of how the different gears move together. In a planetary gearbox we see a sun (solar) gear, satellite (ring) gear and two or more planet gears. Normally, the sun-gear is driven and thus move the planet gears locked in the planet carrier and form the output shaft. The satellite gears have a fixed position in relation to the outside world. The system looks similar to our planetary solar system and that is where the name comes from. What helped was that ancient gear constructions were used extensively in astrology for mapping and following our celestial bodies.


In practice, we often speak from the perspective of the use of planetary gearboxes for industrial automation. That is why we call the sun-gear the input shaft, the planet gears and carrier the output shaft and the satellite gear (or ring gear) the housing.


Can I drive the planetary gearboxes from other ways?

It is possible to realize different speeds and turning directions with the same construction. This can be achieved by, for example reversing the gearbox, which offers the following possibilities: 

Driven From

Solid (Holding) stage

To be driven side


Input shaft


Output shaft


Input shaft

Output shaft


Reverse movement + Delay

Output shaft

Input shaft



Output shaft


Input shaft



Output shaft

Input shaft

Reverse movement + Acceleration


Input shaft

Output shaft


In and output shaft





Where is the planetary gearbox usually used (in the transmission)?


The planetary gearbox usually used in:

In a robot to increase the torque

- In a printing press to reduce the speed of the rollers

- For precise positioning

- In a packaging machine for a reproducible product

- Machineries with compact space design


The planetary gearbox is usually used in below industries:

-Automation Machineries for Solar panels

-Automation Machineries for chip manufacturing

-Automation Machineries for consume electronics manufacturing

-Packaging machineries

-Food machineries

-Automation Warehouse system

-AGV Cars


Planetary gearbox working with a servo motor


-The torque is divided over 3 gears (the planet gears), and therefore – at equal dimensions – the torque is almost 3-fold than a “normal” gearbox.

-Low backlash.

-Compact and therefore a low mass inertia.

-High efficiency.

-Closed system.

-Absolute reduction ratios between 3: 1 and 10: 1 per stage. And up to 1:1000 in 3-stages



Vatidel Gearboxes are ideal for, for example, modern-day servo technology, thanks to the sophisticated Viton seals, helical teeth and a balanced sun-gear shaft. Our wide product series of planetary gearboxes and offer unrevealed service, support and parts stock. That makes us an unbeatable supplier of low-backlashes gearboxes.


See Varitron Planetary Gearbox



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