Internal gears are gears with their teeth pointing inwards. They mesh with regular (external) gears. One application of an internal gear is the planetary gear drive. This amazing mechanism packs a very high gear ratio in a very compact design. Electric screwdrivers take advantage of the planetary mechanism to provide powerful torque with just a small battery-powered motor.
This tutorial explains how to design all the components of a planetary gear system in Blender, and test it using Blender's rigid body physics engine. Tooth profiles and other useful parameters for the planetary gears are obtained from the internal/external gear calculator we have developed.
The end result of this tutorial, a .blend file containing a smoothly running planetary mechanism, can be downloaded via the link below. The simulation runs slowly, so please be patient when running it for the first time.