15 speed Cambiogear Bicycle Transmission

15 speeds on front chainring (at the crank) made of Dupont Zytel (nylon strengthened with chopped fiberglass). Invented and designed by prolific engineer Royce Husted near Chicago for the Excel corporation. 6 segments expand and contract to produce 15 sizes of hexagonal chainring between two plates. Only 2 of the segments have teeth; the other 4 are just place holders. The fixed outer plate has radial grooves to lock the segments into place. The inside plate has 6 spirals (which act as inclined planes) w