The motor is built-in to the hub of a front or rear bicycle wheel 16"-27"/700C (3 speeds available).
Some folks think regenerative charging is needed: I don't - I think a great freewheel is better!
A choice of batteries (SLA, NiMh or Li-Po (LithiumPolmer)) is available for different range, budget and weight requirements. Speed control is by means of a handlbar twist or thumb 'throttle', and pedal sensing (Pedal Action Sensor or Pedal Force Sensor) is available.
Continuous output power of 250 watts and peak output of 425 Watts (600 Watts available with high voltage option) makes the nano system legal for use in UK and European countries, as well as Australia, USA and most other countries.
see www.nano-motor.co.uk and www.mr-motorvator.co.uk for details