This is a beguiling patent. It covers a very elegant design using a cable operated pulley to drive a peg on the pulley cage laterally along a helical groove. As such it prefigures the Le Cyclo design by 6 years.

In many ways it is more sophisticated than the Le Cyclo design. It uses a single cable and spiral spring, where the Cyclo used a fiddly arrangement with two cables. Also, in this patent the pulley cage is off-set, which should give a tighter chain gap than the Cyclo design, where the pivot of the pulley cage is concentric with the top pulley wheel.

Hats off to Romain-Gaston Chauveau - whatever became of him and his marvelous invention?

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• Publisher: L’Institut national de la propriété industrielle
• Inventor: Romain-Gaston Chauveau
• Country: France
• Date: French application January 1918
• Derailleur brands: unknown
• Derailleurs: unknown