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.
