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Comments:

A Planetary Gearbox is a set of gears, shafts, and bearings that are enclosed in a housing and are arranged in a way that resemble a solar system, with one or more planet gears orbiting around a sun

gear. Such gearboxes are known as speed reducers. They convert input speed (typically provided by an electric motor) into a lower output speed while correspondingly creating higher torque. In other words, gear-boxes reduce RPM, turning it into power for use in low-RPM high-torque applications. Gearboxes come in different arrangements including planetary (as shown), bevel, cycloid, helical, harmonic, spur, and worm. Our focus here is on the planetary arrangement.

Much larger planetary gearboxes exist for industrial processes, providing output torque in excess of 6,000,000 pounds per square inch. The input power to the illustrated planetary gearboxes comes from a small electric motor (as shown). Small motors are found in many household devices such as fans, clocks, timers, cassette players, printers, computer disc drives, etc.

How Does a Planetary Gearbox Work?

The planetary system has 3 main components: a central sun gear, a planet carrier (carrying one or more planet gears), and an annulus (an outer ring). The central sun gear is orbited by planet gears. The planet gears are meshed with the sun gear.  An outer ring (the annulus) has teeth facing inward that also mesh with the planet gears.

There are several configurations for planetary systems. Typical configurations require that out of the 3 components: one is the input, one is the output, and one is stationary.

For example, one configuration is where the sun gear is the input , the annulus is the output, and the planet carrier is stationary. In this configuration, the input shaft rotates the sun gear. The planet gears rotate on their own axes, simultaneously applying a torque to the rotating planet carrier, that in turn applies torque to the output shaft (which in this case is the annulus).

The rate at which the gears rotate (gear ratio) is determined by the number of teeth in each gear. The torque (power output) is determined by both the number of teeth and by which component in the planetary system is stationary.

Planetary Gearbox Advantages

The planetary gearbox arrangement is an ingenious engineering design that offers many advantages over traditional gearbox arrangements. One advantage is its unique combination of both compactness and outstanding power transmission efficiencies. Typical efficiency losses in a planetary gearbox arrangement is only 3% per stage. This type of efficiency ensures that a high proportion of the energy being input into the gearbox is multiplied and transmitted into torque, rather than being wasted on mechanical losses inside the gearbox.

Another advantage of the planetary gearbox arrangement is load distribution. Because the load being transmitted is shared between multiple planets, torque capability is greatly increased. The more planets in the system, the greater load ability and the higher the torque density.

The planetary gearbox arrangement also creates greater stability (it's a balanced system) and increased rotational stiffness.

Possible disadvantages to the planetary arrangement include design complexity and accessibility issues.

Artwork comments:

This private illustration project took a total of 5 days to complete. Applications used: Caligari trueSpace, Adobe Photoshop CS,  Adobe illustrator CS.

Electric Motor & Planetary Gearbox