LEAP#200 Mini Solenoid Engine
Some people take it to a whole other level (like this V8 model).
What I have here is much more modest - a single-cylinder engine powering an impromptu-wire-art drive train. The mini-solenoid used here has a very small effective stroke - about 8mm - which necessarily constrains the gearing. I was inspired by 30GB's similar model for the layout.
As always, all notes, schematics and code are in the Little Arduino Projects repo on GitHub.