Gears are complicated, fallible lumps of suspect metal, with thousands of stress points.... anyone considered using a solid bit of kit to change speed??
Nip back to your textbooks and look at the Eddy Current Dynamometer...
Or if that doesn't grab your intellect, put an alternator (solid) in the same axis as a motor and multiply/divide frequency electronically.
Can't visualise it??? Should be coming to a hybrid vehicle near you soon....