Re: Wheel motors - too good to be true?

dagmargoodboat@xxxxxxxxx wrote:
Paul E. Schoen wrote:

The following is from a "Voltage Forum":
http://tinyurl.com/ogvr7

I checked the company website:
http://pmlflightlink.com/motors/wheelmotors.html

and found specs for their wheelmotors which seem reasonable enough
http://pmlflightlink.com/pdfs/eWheel.pdf


[hybrid car specs snipped]

Refreshing to see a car maker touting actual performance advantages,
rather than the fact that they'll pay for part of the gas their vehicle
will guzzle.


(Much of the data above is predicted and is dependent upon the terrain,
weather conditions, driving style etc. PML has used its best endeavours to
present accurate information, but accepts no liability for any errors
and/or omissions).


Okay, so it's not *actual* performance yet, but on the right track.
Present "weak" hybrids are little more than a conventional drivetrain
with an electric booster. Direct-drive would let one drop the tranny,
clutch, differential, and weight and mechanical losses of same. Also,
with per-wheel drive the tiny on-board internal combustion engine,
de-coupled from the road, can then be run at optimum rpm and
torque...much more efficient.

The 21KWH LiPoly battery looks like a nasty wear item -- last time I
looked, LiIon cells were about $0.50 / WH.

Cheers,
James Arthur


Motors tend to have torque proportional to their volume. There's a maximum feasible value of the B field, around 1 tesla. As you increase the diameter, you win linearly because the torque is force X distance, and linearly again because you can pack more wires into the circumference of the rotor. In addition, you win torque linearly by increasing the length. Multiplying out, you get torque proportional to volume.

That means that the only way to get high torque out of a small motor is to run it at high speed and gear it down. Disadvantage #1 for wheel motors. Disadvantage #2 is that they have terribly high unsprung mass, which makes for very poor handling, especially over bumps.

We'll have transmissions quite awhile longer, I think.

Cheers,

Phil Hobbs
.

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