A small brushless geared hub motor like the Cute 100 can run with the KU93 controller (
www.bmsbattery.com) at 48V, with one of its two shunt wires cut inside the controller case. That is a 48V controller, and is rated at 22 amps. I just tested one last week with one of its shunts removed, and it was bang on at 12 amps max output with my 48V15Ahr ping batttery. That is close to the optimum power for those small "250 watt" motors - 600 watts. With both shunts, the motor would eventually be damaged. Pulling 5 amps for an hour, at 52V, would be around 300 watts of power over that period. That is more than I generally use. Most of the time on the flats my bikes are maybe around 200 watts when I'm pedalling, and often lower. I do like the small motors, but they won't be very fast in a 16" wheel. The rpms per volt is not enough (typically around 350 rpm at 52V). I use 52 volts for reference as my 48V Ping packs are typically running around that voltage most of the time.