There was a gentleman at an airpark near Sacramento CA who
made a single rotor Timing belt, reduction,13B.
Installed it on a Dragonfly, Tandem Wing.

Last time I talked to him he was having a bad time
with it.

A Single Rotor has a very strong Reverse Torque that
is distructive at RPM's less than 1500.....Got a Big Flywheel?

Reggie