Planetary Gearboxes: An Ancient Technique with Modern Advantages

Planetary gears have 2,000-year-old roots in Greek history when they were used to predict the movements of the planets in the solar system. Today’s more sophisticated planetary gearboxes are used to drive a variety of machinery.

What is a Planetary Gearbox?

Planetary gears are a simple configuration of a central “sun” gear and orbiting “planet” gears used in applications that require compactness, high torque or high speed, efficiency and ruggedness.

A planetary gearbox typically includes three main components:

  • The central “sun” gear;
  • Two or more orbiting “planet” gears fixed to a carrier ring; and
  • An outer “ring” gear.

Inside a planetary gearbox, the central sun gear typically serves as the input, the planet gears and their carrier ring act as the output and the outer ring gear acts as the fixed housing for the assembly. Alternatively, the planet gears and their carrier ring could be fixed with the outer ring gear as the output or the sun gear could be fixed. Clearly, there is a lot of versatility. The main benefit is that the load from the central sun gear is distributed to multiple planet gears for higher torque capability and smoother operation. Because the torque is distributed between the teeth of the different gears, it allows over 95% of the energy input to be to delivered to the output.

Not only are planetary gearboxes highly efficient, they are also very compact, durable and reliable. The arrangement within the planetary gearbox provides a high degree of rigidity, which is critical in applications that require abrupt start-stop cycles or abrupt changes in rotational direction.

Types of Planetary Gearboxes

There are three main types of planetary gearboxes, including:

Wheel Drive Planetary Gearbox: Here, the central sun gear drives the surrounding planetary gears, which are connected to a fixed carrier ring within the gearbox. As the central sun gear rotates, the planetary gears in turn drive the outer ring gear and the outer housing to which the wheels are usually mounted.

Shaft Output Planetary Gearbox: In shaft-drive types, the sun gear drives the planetary gears which are connected to a rotating carrier ring. The outer ring gear remains stationary while the rotating carrier ring drives the output shaft.

Spindle Output Planetary Gearbox: The operation of a spindle planetary gearbox is the same as the shaft-output type, but it uses a flange instead of a regular shaft for the output.

Where are Planetary Gearboxes Used?

In manufacturing planetary gearboxes tend to be used in applications that require efficiency, precision, reliability and high-torque or high-speed transmission. They can be found in machines such as automobiles, conveyors, mixers, printing presses, 3D printers, robots, CNC machines, packaging machines and many others.

How Do I Choose a Planetary Gearbox?

Selection of a planetary gearbox is highly dependent upon the application in which it will be used. It is recommended to contact a reputable supplier of planetary gearboxes with specific information about your application, including the necessary mounting features, gear, ratio, backlash, speed, torque, efficiency, available space and the environment in which it will operate (industrial environments often contain moisture, dirt and dust which will corrode the gearbox, so a corrosion-resistant body may be needed). Other factors to consider include the price, delivery time and service. With a planetary gearbox that meets all the requirements of the application, you will likely find that it provides years of reliable, trouble-free and cost-effective service. For assistance determining whether a planetary gearbox is right for your application or specifying the proper size and features, please contact John Henry Foster.