How to understand planetary gear system 

Planetary gear set is widely used in many fields. Planetary gear system is called epicyclic gear system too. You can find planetary gear sets on robots, cars, helicopters, 3D printers, CNC machines, and much more. To design this type of transmission system, you need to be very skilled in this area. But now there are many planetary gear manufacturers, and as a user, what you need to do is to choose the best planetary gearbox.

Before choosing a planetary gearbox, you need to have basic knowledge about this technology. So this article is for a user who wants to understand the planetary gear transmission, and it is not for a skilled gear engineer.

Figure 1
1. Ring gear; 2. Sun gear; 3. Carrier; 4. Planet gear

There are four main components in a planetary gear system. In this figure, Carrier is connected onto Planet gears. The planet gears rotate around the sun gear as planets rotate around sun.

Three shafts can be assembled on the sun gear, planetary gears (via the carrier), and the outer ring gear. Each of them can be input or output. You can get different turning directions and speeds without changing the construction, depending on the constructive tasks. The input shaft and output shaft are aligned in a planetary gearbox. By choosing which of the components is to be fixed, you can get a different reduction ratio.

Load is shared among several planet gears, so a planetary gear system can produce a lot of torque. By combining several planet stages and having them work together, you can get much higher torque and almost unlimited transmission ratio.

The following is a simple planetary gear set which designed for 3d printing or laser cutting. You can download the files and make them by yourself. Note: If you print the models on a FDM 3d printer, there may be some problems, because the tolerance is not enough for FDM 3d printers. But you can modify them or sand the parts as needed.

Ravigneaux gear

There are two planetary gears and two sun gears in a Ravigneaux gear system.

Planetary gear sets can be used on iris mechanism too.
More videos are on YouTube. You can get more 3d models on twothreed.com, cgtrader or Etsy

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