About this 3D model

This is a Public Domain OpenSCAD file with epitrochoids and hypotrochoids. These shapes are useful for making mechanisms like Roots Blowers http://www.thingiverse.com/thing:8068 Wankel Engines http://www.thingiverse.com/thing:8069 and Moineau Pumps http://www.thingiverse.com/thing:7958 An EPITROCHOID is a curve traced by a point fixed at a distance "d" to the center of a circle of radius "r" as the circle rolls outside another circle of radius "R". An HYPOTROCHOID is a curve traced by a point fixed at a distance "d" to the center of a circle of radius "r" as the circle rolls inside another circle of radius "R". An EPICYCLOID is an epitrochoid with d = r. An HYPOCYCLOID is an hypotrochoid with d = r. See http://en.wikipedia.org/wiki/Epitrochoid and http://en.wikipedia.org/wiki/Hypotrochoid