This is my bike it has been through various incarnations in the past 6 months.
This is the second bike I've built the last bike used a 24 Volt wheel chair motor and was a total scratch build.
Specs:
Motor 350 Watt hub drive
Battery 4 X 7 Ah SLA's in series for 48 Volts. I have 40 X 6 Ah Nimh D cells but not to sure whether to change over to them. Definitely lighter, I may not notice any difference in range as I mainly do short trips. I live in a small country town.
Top speed on the flat 38 KPH (GPS used to check speed) I only weigh 60 Kg.
Range unknown my controller is limited to 17 Amps and after returning home from my 8K round trip my Watt's up meter tells me I'm putting about 1Ah back into the batteries.
Biggest weakness needs better brakes.
I ride it everyday.
