I had a dashpot lying around and decided it would make a perfect
piston-cylinder for an LTD (Low Temperature Differential) Stirling
engine.  I wanted to build a Ringbom engine but, in a personal
correspondence with Dr. James Senft, the guru of all LTD Stirling, I was
advised that it was a tricky proposition and would only run in a very
narrow temperature range if, indeed, it ran at all.

Despite this good advice, I cobbled together a Ringbom using proportions
that 'looked right to me'.  Well, the good Doctor was right and it
didn't want to run - a fact that didn't surprise me given the
(non)effort I had expended in its design.

Then, while fooling around with it, I decided that it didn't run because
I made the displacer a tad bit heavy and it couldn't generate enough gas
pressure to lift it if run in the position pictured below.  So, no worry
- I turned it on its side (flywheel horizontal and displacer chamber
vertical), heated it gently with a small alcohol lamp, and it took off
very nicely.

Ringboms will run with the flywheel rotating in either direction and
this one does that, making a tiny tump-tump sound as the displacer is
driven in and out by the changing gas pressure.  Their utter mechanical
simplicity is mesmerizing.