Small Motor Creations 6 - Orbital Gearboxes

Our little motors are great, but they spin so fast that its hard to use them directly for things that require lower RPM's, like wheels. To make the little FA-130's more useful we need to build a gearbox to slow the motor down and transform some of that speed into torque.

Orbital Gearboxes are one of my favorite solutions. They offer a range of input and output options in a nice compact package.  You'll find them in power drills, cars, cranes, pretty much everywhere there is an electric motor. These two gearboxes are bases on the same set of components, with different sections of the mechanism being used as the output.

In the Orange Gearbox Input through the Sun Gear at the center and output is through the Ring Gear that runs around the outside. The three Planet Gears act as idler gear, carrying movement from the Sun to the Ring.

The Sun Gear has 12 teeth and the Ring Gear has 60 teeth. In this case the Planet Gears don't affect the gear ratio because as idlers they are just carrying movement from one place to another. To get the gear ratio for this gearbox we divide the number of teeth on the output gear by the number of teeth in the input gear. That gives us a Gear Ratio of 5:1, so for every 5 turns of the input gear we get 1 turn of the output gear.

The Gray Gearbox uses the Sun Gear as its input and the Planetary Gear Carrier as its output while the Ring Gear is held stationary. The Carrier is the structure that holds the Three Planet Gears. As the Sun gears turns, the planets are spun between the Ring and Sun. The Carrier makes a revolution each times the Planets go around the Sun, Thus the name Orbital Gearbox.

The Gear Ratio for this gearbox is a bit more complex.  In this configuration the ratio is the number of teeth in the Sun Gear divided by the Sum of the Number of Teeth in the Ring and Sun Gears.  So in this case 12/(12+60) = .0138. For every input turn we get 0.0138 output turns. To clear things up we'll divide 1 by 0.0138, which is approximately 72. This gearbox has a ratio of 72:1, so for every 72 turns of the input we get 1 turn of the output.  And that is why I love orbital gearboxes, big ratios in tiny little packages.

For more information about orbital gearboxes I would highly recommend this article at 

Download the Orbital Gearboxes Files From Thingiverse:

FA-130 Size Motor At Pololu: