Two- or three-speed gearbox?

Do you own or use a EV. Then this is a good place to discuss things.
bobc
Posts: 107
Joined: Thu Dec 20, 2007 1:11 pm
Location: Knutsford

Postby bobc » Tue May 20, 2008 9:21 am

Peter,
you're squaring/cubing the power
no no no no no - it's the speed you have to square/cube (cube actually) to get the power ;^)
The 6x2x2x2 in my email above was because the speed has doubled.
bob

MalcolmB
Posts: 423
Joined: Sat Jun 23, 2007 8:07 pm

Postby MalcolmB » Tue May 20, 2008 9:53 am

Like Bob says. Double the speed and you need to increase the power by a factor of eight (2 cubed).

If you increase the speed by fifty per cent (i.e. a factor of 1.5), you need to increase the power by a factor of 1.5 cubed = 3.37

Obviously this only holds true at higher speeds and there are other factors to consider, such as rolling resistance. Once you get above 20 mph or so air resistance becomes the dominant factor though.

bobc
Posts: 107
Joined: Thu Dec 20, 2007 1:11 pm
Location: Knutsford

Postby bobc » Tue May 20, 2008 12:08 pm

Your efficiency figures for the motor look so good I wonder if you'll really need liquid cooling?

the reason for liquid cooling is mainly so I can use the original heater matrix for demisting, also it should make the inverter design a bit easier.
The motor efficiency figures neglect core losses and bearing losses (it's just the steinmetz equivalent circuit) so it will be a few percent worse than that. Also it is now a rewound motor, they're never quite as good as new
cheers
Bob


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