This is Jan Ridders’ newest Stirling engine. It’s so small it uses a 1 Euro coin for the flywheel and a couple of 5 Euro cent pieces for the top and bottom plates of the displacer cylinder. Jan will tell you that he got the idea for building a micro- engine from a Swiss artist who goes by the name “jovallmen” on YouTube. His engine uses a couple of Swiss 5 centime coins and it may be even smaller than Jan’s. You can see a video of it here.