University of California, Irvine's engineered schematic.
Sticking to the basics — Students at Murray State University are sticking to the basics with a simple hydraulic motor and pump. This system utilizes a hydraulic circuit, pump, accumulator, and gearing system. The rider will pedal the bike on the downhill, charging the accumulator for traveling uphill. This hydrostatic system will be fitted onto a three-wheel recumbent bike.
A pneumatic alternative — They're doing things a little differently at University of California, Irvine, where five students have opted to build a pneumatic-powered bike. Two 2-in. bore cylinders connected to the pedals generate pressure, while a 5-liter reinforced accumulator and 2.5 in. bore cylinder on the back turn the rear wheel. Solenoid valves, a microprocessor, and Hall-effect sensors were also included to time the air supply to the rear piston so the bike will move forward. A rear rack holds the bike's pistons, plumbing, and accumulator. The students chose a pneumatic system because it will keep the bike lighter than with a hydraulic systems, and it is environmentally friendly.