There are several free 3D printable models at this site, related to various types of gears, as well as much information.
The globoid explanation was helpful.

http://www.otvinta.com/globoid.html

I'll try to print some next winter...
The Eccentrically Cycloidal (EC) drive was interesting, but has recent patents.
It is easily modeled in MoI using the epicycloid script...

- Brian