Stirling Engine
Version 0.1
Design
Two beta style engines coupled together.
Piston
I want to use a piston instead of a diaphragm because it has a larger displacement, more displacement equals more power. I want to build my diaphragm using a steel wool core and some small pieces of metal (coat-hanger?) to reinforce it, pour concrete over that and seal the whole thing with silicon. This should allow me to make any shape I want while still getting a good smooth seal.
Notes
I saw a video using metal water bottles for the chamber - metal and already very smooth.