Miniature working traction engine. 0:51 video:
https://www.youtube.com/watch?v=MC0Gpl9e1YQ
Previously:
https://www.homemadetools.net/forum/...2579#post96643
https://www.homemadetools.net/forum/...2043#post75628
https://www.homemadetools.net/forum/...964#post133843