I threw away my primary concept. Not really stealthy. The new one is more
I exchanged the 18T 1/2"x1/8" frewheel sprocket for a 15T 8mmx3mm sprocket. That way the motor can be mounted below thebottom bracket.
Sadly I couldn't write the WYE tutorial, since I had too much to do. But here's the finished Tongxin motor, sadly I had no time for a mount yet
You can hope for next weekend
Notice the slots i sawed in to make it possible to push the motor into the extruded 90mm (100mm outer dia) alu alloy tube. The motor measures 91.05mm in diameter (edit: the upper cast piece is only 90.5mm). It was too hard to push it with the bench wise without the slots. I can pull it out again with a puller.
Notice the rather short chain
The sprocket has 15, the chainwheel 35 teeth.
Iknow that this is really thight, but it saves so much place. Let's see how long it will survive