On the Bowden brake theme , its amazing how things evolve . I know I'm way out in left field , but in the 16th century a form of firearms ignition involved a flat spring that was the lever , rotating a wheel through a short length of link chain . the system was refereed to as the Wheel Lock .
They were expensive and time consuming to build , but all three elements we need to pedal forward were there .
Jim "maybe too much time on my hands" McCoin
Fremont Ca.