Hello. A dream project of mine. I wanted to build a motor with just a magnet and an electromagnet. It was more complicated than I initially thought - but it works. An electro magnet 5 volts Ø20 x 15 mm 25N is required. Screws M3 x 12 mm (5x) M3 x 6 mm (1x) Grub screws M3 x 8 mm (3x) Magnets for the control disk Ø3 x 4 mm (min. 4 pcs. to 7 pcs.) Magnet for the piston Ø10 x 2 mm (1x) Reed switch 3 x 3 x 14 mm (1x plastic)

Important: The electromagnet must repel the piston when it is on. Everything must run smoothly and should have some play if it is to work. There is only one direction of rotation. The disc with the shift magnets are adjusted so that the start "magnet on" is at front dead center. Start with 4 magnets and stick more as needed. Don't give up right away if it doesn't run. The disc must be adjusted very finely. It runs best when it is standing upright.

A similar variant of this motor is also called a solenoid engine. There is a lot about this on the web.

https://youtu.be/1osCYgaJc2U