I REALLY like the tin can and balloon ingenuity.
Sterling engines are actually REALLY amazing. With a proper seal, a beta style engine can be run at high rpm's and relatively high power output.
Want to know a really amazing piece of trivia. A basic sterling engine (with a few extra modifications of course) is how compressed gas companies produce liquified air and ultimately liquid nitrogen. Chemical cooling is the first stage where a "freezer" uses the carnot cycle to extract heat into a heat exchanger but the working fluid can only go so far AND the inefficiencies in exchangers become too great. From that point, the chilled air is passed over the head of an externally powered stirling engine (electric motor driven into the crankshaft) so that the working fluid inside the engine (one of the noble gasses) is forced around and around. Even at RIDICULOUSLY low temperatures (down into the single digit kelvin) the "cold" side of the stirling engine will still be getting colder and the "hot" side of the stirling engine will still pass off heat. The limit comes at the triple point of helium, 4.3K or -452 degF at which point the liquid becomes super critical and containment becomes an issue as it has no viscosity and begins climbing the container walls!
