Much Simpler ... but not terribly dignified ...

On the much simpler end of the scale, I'm very tempted to build a scooter around a Golden Motor Powered 12" wheel ... basically just that and a plank (and probably a pivoting front wheel on a T-bar). And a whole bunch of (30+, 9Ah) NiMH D-cells or a LiIon pack or something similar underneath. If built around a HSB-36, top speed would be about:
317mm * π * 333rpm = 6.00 m/s = 21.5 km/h
and max power with torque/speed:
17.68 Nm / .158m = 112 N = 11.4 kgf
317mm * π * 263rpm = 4.36 m/s = 15.7 km/h
At which point it'd be drawing something like 20A, so to make it useful the power pack would have to be biggish. Might make a nice "first EV" though ... and you could always carry it in the boot as a spare!

It's interesting to think about range: at max speed (21.5 km/h) it's drawing about 5A, so assuming a 10Ah supply would go about 43km. At max torque, it's drawing about 20A and only going 15 km/h, so its 10Ah supply would go about 7.5 km ... about 1/6 as far!

This 10Ah NiMH battery pack has 30 D-cells and is 162 * 97 * 45 mm and 5kg.

(If I put skateboard trucks or similar on the front, it'd technically be a leaning tadpole trike :-). Yes, I know there's already plenty of these kind of things on the market ... but it'd still suck less than a Segway.)

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