[ausev] High torque or High RPM?

[Josh Handel]

Constraints.. (these I have a few, not many) of.

1) Range - 60+ mile Highway range (I have a 20 mile commute all hill
country).
2) Performance -
     A) Acceloration - sub 6 sec 0 - 60?
     B) Top Speed - 70+ (anything more and I'll just get a ticket anyways).
3) Budget - Undefined (I want to scope "ideal" then work backwards from
there :-P)

You mentioned a single speed transmission, and I had that thought.. If I
understand correctly Electric motors have 100% torque at 0 RPM. Too me, that
meant I should use a single gear that is a blance between not bogging down
my motor off the line and reaching my ideal topspeed when the motor reached
its max RPM. I talked it over with a friend and he seemed to think that
electric motors were more efficent at higher RPM so your better off using a
full blown transmission. He also seemd to think that the larger magnets of a
high Torque electric motor were performance prohibative over a higher RPM
motor that can run with smaller magnets. From a NON EV perspective that
makes since, but I don't know if those costs are real applicable to design
when you are talking about something that is already 1000lbs + in size...

So all that leads back to my first question. Which Electric motors are more
efficient, High RPM low torque or Lower RPM high torque?

Thanks
Josh

On 12/5/07, Ian Ward <ian.ward at gmail.com> wrote:
>
> Josh,
>
> You're going to get sick of hearing "it depends", but it is totally true.
>
> Define your expectations for performance in terms of:
> - top speed
> - range
> - acceleration
>
> Then put a cap on the price you're willing to spend (on just the drive
> components).
>
> Lastly, throw in any must-haves.  For me, this included regenerative
> braking and single-speed transmission.  Neither of these has a huge
> influence on the other constraints that I had for the vehicle, but they do
> constrain your choices of components.
>
> Weight will certainly play a major role in configuring your 7, but if
> you're willing to throw down some coin, there are some screaming batteries
> that you can put in it that will give you great weight, performance and
> life.
>
> At this point, there are no design constraints to make any decisions upon.
>
> - ian
>
>  On Dec 5, 2007 1:24 PM, Josh Handel <jhandel at ktomics.net > wrote:
>
> >  Howdy all,
> >    So I've been piecing togeather my "master plan" and I came to a
> > perverbial "fork" in the road.   The vehical I am building will be based on
> > a Lotus 7 Clone and is extremely light; so light that many builders of these
> > cars use Motorcycle engines & Transmissions in them AND still have a heck of
> > a fun car to drive.   This brings up a few questions.
> >
> > 1) Motorcycle transmissions are designed for higher RPM & Lower torque.
> > Given that I have the freedom to choose my transmission for my roadster, is
> > there any EV advantage to going with a transmission designed for RPM or a
> > traditional RWD Standard car transmission..
> >
> > 2) How much "extra" weight should I account for in an EV based car (yes
> > its all dependent on battery but a ball park).. Lotus 7's can be built ICE
> > and weight in at under 1200 pounds.. I am sure I get 2 ~ 300 of that "back"
> > for loosing the Gas engine, but how much MORE do I loose to batteries,
> > controllers, etc?
> >
> > Thanks
> > Josh
> >
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> > AusEV at austinev.org
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> >
> >
>
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