Epitrochoids and Hypotrochoids

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