This is one way to do it ...
I wanted to run the motor through the bicycle gearing system including the front chainring set. Got it done, but plenty of concept and engineering work went into the bottom bracket arrangement. Anyway, here it is for anyone interested: Youtube videos
Wow , nicely done. I cant blame ya for wanting to use teh front gearing, as I've seen a few hills that had "make my day" written on them. There is a company using the mid drive concept. http://www.ecospeed.com/index.html Of course, if you are wanting to stay within legal range in markets, e-bikes are limited to 20mph cutoff of the assist, have you figured out how to implement that?,, orrrr :-) just a thought :-) Great clean build though.
I'm currently abusing the daylights out of a Currie E-zip Trailz that has been rode hard many times. My "project' was a $1250 mistake from a now defunct "Ecruizers" commuter, a 500watt SLA scooter styled ebike that was built by Changzhou New-District Benshen Bicycle Co. Aside from the pedals, which are needed to be a legal bicycle, its a fair build, but I'm having to machine a crankset from scratch. When I'm through, the pedals will work solidly... until then, its a private property toy.
The crankset on the scooter is very unique, and poorly designed. The arm are fairly scalvageable, but the spindle, nightmare. It appears to have started out life as a cylindrical tube, with the interface for the arms pressed down square, retaining the pedal arms with a "socket style" checkball. The corners of the shaft are rounded, so not a good fit, even if it had been the right size for the arms. Three turns of the pedals, the arms fall off, ... great system eh?