I HAVE ALWAYS ENJOYED MEETING NEW GUYS IN TOWN WITH MOTORBIKE INTERESTS.
(I do NOT enjoy the cap lock button) One fellow from Enid Ok. told me and later showed me their method. They take the field housing off a car generator and replace it with pieces of pipe on the bolts. It is mounted behind the seatpost by the mounting hole on the castings and the motor is mounted on the rear carrier. The armature rotates on the rear wheel held there with a spring and clutched by pulling it up. The belt is tight when in contact with the tire. FWIW
Keith (trackfoddder) Williams