SIMPLE PLANETARIES AND INVERIONS

Epicyclic gearing or planetary gearing is a gear system that consists of one or more outer gears, or planet gears, revolving about a central, or sun gear. Typically, the planet gears are mounted on a movable arm or carrier which itself may rotate relative to the sun gear. Epicyclic gearing systems may also incorporate the use of an outer ring gear or annulus, which meshes with the planet gears.


This table could summarize the ratio calculation of a simple planetary system and one gear inversor system:


Planetary drives are usually demanded on transmissions where the input-output ratio is very high. Also these type of transmission can be developed in a small volume. In some final drives, using a double planetary system ratios of 1:26 can be obtained.



Planetary system and Inversor system images and animations.

References:
Wikipedia
Mechanism & Mechanical Devices Sourcebook

Images and Animations by:
Vergara.