Hi Lawrence, Chris and All,
Motor eff is variable. Motor are not eff at low rpm, hub or
otherwise. Series like we use are about 82% peak, most PM's about 90% eff
peak. Specially made larger dia versions can be more eff but pricey.
Chris' comments on hub motors is correct especially in SF where their inability
to start up a hill is a deal breaker unless you want to put in 4x's needed
normal power and still have problems. I replaced my 3.5hp GE series from a
CitiCar in my E woody with a 9hp, 29hp peak Etek PM motor. The PM promptly
burned up trying to start up a mild driveway hill. It worked great at speed
but starting the 3.5hp series easily beats it. Now I just use field weakening,
higher voltage to get high end power. Hitting FW in the E woody at 45 mph gave
a nice kick, more than I expected.
Likely your best solution is like Chris said only use an oiled enclosed #41
chain from 2 of the larger PM AC MC motors sold by various sources if you keep
the EV light and not going over 65-70 mph so enough gearing to start up hills.
Your big problem is tires. MC tires both such rolling drag wise, 4x's car LRR
ones, and don't work on 3-4wheel vehicles as not designed for side loads. So
find out what the Stella, other solar cars use if going that way and let me
know.
Next is lightweight hubs, rims, brakes. Unsprung weight makes a very harsh
ride has been a big problem in my under 1000lb EV's. Air helper shocks I use as
my spring too helped soften the ride and could lower your EV for ;lower drag.
They only cost $30 each like Monroe HyJackers.
Having 16kw of battery , 250+ mile range is counter productive in a solar car
as raises drag, makes hill starting harder, and makes solar an afterthought
really. Better is save the special/high solar costs and plug into EV chargers
as most use just green power already. But is cool to show it can be done.
Jerry Dycus
On Sunday, October 5, 2014 8:24 AM, Chris Tromley via EV <[email protected]>
wrote:
On Sat, Oct 4, 2014 at 10:42 PM, Lawrence Rhodes via EV <[email protected]>
wrote:
> When I saw the Stella it made growling ticking noises that stopped after
> the vehicle made some speed. They said these motors were 98 % efficient.
> I thought the run of the mill ADC motor with a Curtis controller was 90 %
> and brushless were a bit more efficient. Are these motors worth the 10's
> of thousands they cost? Are there motorcycle/bicycle hub motors we can
> buy that are very efficient? Each of the Stella motors are 20kw. Some
> bicycle hub motors are very powerful. 10 or more kw. Is there a loss of
> efficiency with these new powerful motors? What do I need to compliment a
> very aerodynamic body/go freeway speeds & not suck the life out of my
> batteries?
I'm certainly no motor expert, but my understanding is that PM motors
only get that high efficiency at max power. The cogging effect (the field
is always there) hurts efficiency everywhere else, and a road vehicle
spends virtually all of its time NOT at max power. Other attractions of PM
motors are their relatively light weight and ease of implementing regen.
Those who have converted motorcycles have used these advantages, but some
have come to realize they come at a cost. Light weight also means a
greater tendency to overheat. Startup torque can be underwhelming. Series
motors solve these issues nicely, and also coast freely. I don't want to
re-start the coasting vs. regen debate, but coasting with no regen can be a
pretty effective range enhancement.
The other issue is hub motors. To my knowledge, no-one has made these work
on an everyday on-road vehicle. The main concern is unsprung weight, which
will be even more of an issue in a hyperlight car. If you want to give a
try anyway I'd suggest scooter hub motors, because they have presumably
been designed to survive the pounding an unsprung component gets. But the
ones I've seen have been designed more for cost than efficiency.
If it was me doing this, I'd probably go the Tropica route. Use small
series motors near the drive wheels. Use trailing arm suspension and mount
the motors at or near the trailing arm pivot, with belt or chain drive to
the wheels. That should get you a solution close to what you're looking
for with low risk. You're going to have your hands more than full with all
the other aspects of this vehicle. Getting hub motors to work well is a
whole 'nother project by itself.
Chris
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