Motor Install
There is no easy way to do this, you just have to cut out the front between the drive sprockets, use a dremel with a large cutting disc and go slowly and carefully.
For details of the motors
see this page
Next you need to fit the motors by removing the existing axel for each sprocket, use a 12mm drill to drill down through the center of the existing axels, drill mounting holes for the motor screws (I used a template to mark the hole positions)
To mount the motor solidly I had to insert a 2mm plastic plate onto the sidewall of the Kettenkrad, see black plastic infill on picture too left.
This is the finished cutaway, both motors fit (just!)
To finish off I will have to make a metal (perhaps plastic) cover that screws on at the back, where you can see the two screw holes and also attaches too the front behind the front wheel (without screws)