Retro-fit a bicycle indoor trainer with a generator, using a pair of low KV outrunner brushless motors.
Three phase output is to be rectified using Schottky diodes and fed into a DC-DC regulator. Actual power output has yet to be measured, but I'm aiming for around 45W.
Also included another version using a pair of (apparently) 36W DC generators made in TANWAN. The 30mm roller was a bit small and I easily exceeded the 35V limit of my DC-DC converter and blew a capacitor, it also required a bit of torque to get it cranking so I'd recommend the 60mm roller for that one.
Initial testing using a 20W USB cigarette lighter charger test load looks promising. Not surprisingly the purpose built DC generators performed as expected, able to supply 30V to the regulator with a good pace. The brushless motors did an acceptable job, although requiring a fairly high RPM and what felt like a bit more torque. Both setups were able to supply the required 20W to charge two iPads.