Geared steam locomotives. 13:36 video, queued to 3:00:
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More: https://en.wikipedia.org/wiki/Geared_steam_locomotive
Previously:
https://www.homemadetools.net/forum/...799#post133292
https://www.homemadetools.net/forum/...717#post143724
https://www.homemadetools.net/forum/...370#post142445
https://www.homemadetools.net/forum/...718#post136780
https://www.homemadetools.net/forum/...444#post131719
https://www.homemadetools.net/forum/...710#post108194
https://www.homemadetools.net/forum/...1817#post75199