On 24/04/17 03:31, Johnny B Good wrote:
However, in order to maximise efficiency and power to weight performance
of electric traction motors, you get the best performance using a high rpm
motor[1] which basically precludes direct drive hub motor designs unless
you're prepared to sacrifice top end performance for improved battery
economy at more modest urban traffic speeds (you replace mechanical
transmission losses with much lower electric cabling losses).

[1] High rpm on account it uses less turns of heavier gauge copper in its
windings, meaning reduced I squared R losses.

But needs more current to achieve the same magnetic moment.

No, what counts is magnetic reversals per second, times the iron mass.

You can achieve that with a lot of poles, or a lot of RPM.

Copper losses turn out to be pretty much independent of the
configuration, and are a more a function of as you say RPM BUT its not
'RPM' that matters, its 'poles per second'.



--
"Anyone who believes that the laws of physics are mere social
conventions is invited to try transgressing those conventions from the
windows of my apartment. (I live on the twenty-first floor.) "

Alan Sokal