Extreme Electronics designed this easy-to-build solenoid engine:

I’ve always loved solenoid engines. The first one I built was many,many years ago out of Mechano. Many others have followed since, But they always ran badly and only for a short while as the accuracy of the construction medium was poor. I am not a metal worker, making a “proper” engine out of cast pieces is out of my (and many other peoples) capabilities.

With modern laser cutting it is easy to make accurate components, it is relatively cheap and fairly quick.

So the Acrylic Solenoid Engine came into being

The initial driver is using a small PIC 12F675 and and an IR detector to give me pulse timing information from the solenoid. I went the IR sensor route rather than a mechanical switch so there was no rubbing parts that could wear as acrylic is rather soft. To get a good timing signal aluminum foil is placed on one side of the flywheel to give a good reflection back to the IR emitter receiver pair on the PCB.