The motor

This is the kind of motor I would like to use in the velomobile wheels. It is a cam drive. The pistons make multiple strokes per revolution. This is ideal because the velomobile wheel rotates at low speeds (~ 500 rpm). The Hagglunds has to be scaled down a little. The smallest type weighs ~800 kg has a displacement of 15100 cc (15.1 liter) and produces 530 kW.

The Hagglunds Compact hydraulic motor

Efficiency of this machine is high but should be improved for the velomobile. Options for improving the efficiency may be found in reducing leakage, friction and optimizing the commutation. The velomobile motor may have a cam with 3 or 4 waves, 4 or 5 pistons and a total displacement of ~2 cc per revolution. The transmission ratio may be controlled by switching on and off the pistons with valves (see Artemis intelligent Power and this video). See also this page