Re: Real vibration resolution...shaft drive.
I dunno, I always thought one of those heavy duty string trimmer motors would make a far out drive line choice. I had one, I think it was an Echo or a maybe a Stihl, it put out a lot of power for it's size and was amazingly well made. If you could engineer a gear box for it or run a sprocket onto the cutter head . . . I'm sure the bike would wear out Long before the motor gave out.
Just my two cents