|check valves allow pedaling and free wheeling|
When I see a drum brake I think: In the same volume a hydromotor fits with about the same mass. With that motor one could drive and brake the velomobile. While braking energy may stored in a nitrogen volume to be used for starting again. A small electric motor could easily be added to the system.
Hydrostatic transmissions are used when high torques, power and control are needed. The efficiency of these drives use to be smaller compared to gears or chains. But the efficiency can be improved a lot. Innas has developed machines with pump efficiencies up to 97%. I think a hydrostatic transmission developed for the velomobile may compete with the derailleur en planetary gear systems.
Imagine two pedal cranks that are swinging about 120º. Each connected to a hydraulic cylinder. Both front wheels of the velomoble are fitted with a small hydro motor. The scheme shows the basic system. Questions left: How to make it a variable transmission? How to realize a rear driving option?