DIY Stirling heat difference engine with 3d printed parts

Doug Conner developed a 3d printable homemade Stirling engine, a type of motor that creates mechanical motion from temperature differential of a medium which is air in this case. The engine is made in ABS on a Stratasys FDM printer.

This engine has some metal (brass, aluminum) parts, couple of metal screws and some rubber O-rings, but that is unavoidable due to the nature of the technology and ABS material limitations.

It takes some 50 deg F (or 28 deg C) of heat differential to move at stable speed at about 300 rpm without additional weight or load.
Project homepage:

http://www.solarheatengines.com/2012/10/29/3d-printed-stirling-engine/

All the 3d files and plans to make this Stirling engine can be found at:

http://www.thingiverse.com/thing:34709

Here is video demonstration of the engine in action:

Doug's DIY 3d printed Stirling engine from the project homepage