Anyone know what the gear ratio is?
Just checked one — it is about 4:1, or slightly less.
I just count the number of rotor rotations for one full rotation of the crank.
The other method that works on a lot of spinners — is to divide the number of teeth on the pinion gear into the number of teeth on the main gear.
The Mitchell museum will also have these specs, as will Google.
Best,
Fred