After 4 months of design changes and approx. one year of use without problems, here my solution to power a bicycle by using a electric drive, mounted mainly by using 3D printed parts:

eBike toothed belt wheel To avoid dirt accumulation in between the tooths of the belt disk there is a small gap. Snow or small particles can fall through.

eBike motor

belt pulley

battery pack

Winter 2012

openings under each tooth prevent snow...

Part list:

Technical details: