TURN8 - 20 September 2008 05:08 PM

Alright, an electric motor developes it's maximum tourque at at any rpm, meaning it theorticaly could produce infinte horspower. It is limited in a practical sense only by it's mechanicl rpm limit and the capacity of the windings to absorbe current without burning out. Correct?

Nope....... not even close. The typical electric motor develops zero torque at max rpm; therefore, zero HP. It develops maximum torque at zero RPM; therefore, zero HP. That may seem a bit odd and it's certainly different from an internal combustion engine, but that's the way it is, for most electric motors anyhow.

Here's a link that may help clear things up http://www.motortech.com/BULL_E-1.htm

Mozella - 20 September 2008 01:50 PM

hobbymanbill - 20 September 2008 01:25 PM

speedsense - 20 September 2008 01:17 PM

Mozella - 20 September 2008 11:20 AM

GreyWolf74 - 20 September 2008 09:57 AM

... snip....

Sorry SS, but electric's are also rated for HP as well as Torque. Horsepower is the amount of work, Torque is the push to get there. AA JMHO

Bill

Sorry Bill, but Horsepower is NOT the same as work. Power (or Horsepower) is Work divided by Time.

To put that in perspective, one "horse" is supposed to be able to move 33,000 pounds a distance of one foot in one minute. The work done is 33,000 ft•lbs. Someone like me, might be able to do the exact same work in ten minutes, but that is not the same as putting out one horsepower.

Actually, it's like putting out 1/10 HP. Or if I lift 3,300 pounds by one foot in one minute, that's also putting out 1/10 HP.

Since I don't like to work too long without a beer, I'd prefer to lift 330 pounds by one foot in 6 seconds (1/10 minute) and that's just about exactly what I do when I climb into my SUV. No wonder I'm tired all the time.

You're right of course, I was oversimplifing and forgot to add time. Mea culpa

Bill

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“REAL RACERS DO IT IN THE DIRT”
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Mozella - 20 September 2008 11:20 AM

GreyWolf74 - 20 September 2008 09:57 AM

...... snip........
As for power vs. force vs. all sorts of other things...I've had
a few arguments on this forum about the difference. Discussing
the difference between torque and horsepower, for
example, still gets me worked-up. ... snip.....

Yeah, me too and I don't understand why it's so difficult
for some to understand.

Power is simply equal to a force multiplied by a distance
in a certain amount of time.

Distance per time is what we know as speed; i.e. it's
something like "miles" per "hour" or "feet" per "second".

Of course, in the case of automobile engines we measure
speed rotationally by the familiar RPM.

The "force" is torque, measured in ft•Pounds (NOT ft per pound).

So, it should be easy to see that horse power is simply torque
multiplied by RPM; which said another way, is just a force
multiplied by a speed; i.e. the definition of power.
Simple......... no?

Perhaps what people seem to miss is that torque is a component
of HP, but I think some folks think of HP and Torque as two
entirely different things, like apples and oranges.
Could that be it?

I think that was the basis of the problem I had with that
gentleman. He'd heard the announcers talking about the immense
torque of the Audi R10 and couldn't understand why they were
making such a huge deal of it. He was of the opinion that
horsepower was the only important thing, and that torque was
just a meaningless number.

That's when the fight started.

In the course of the "discussion" (which got very ugly), I tried
to explain why torque was important to accelleration. I cited
sources, I mentioned similar cars (only the Porsche 917-30 can
rival the Audi in sheer numbers). I even "did the math" with the
horsepower vs. torque equation, solving for each component, thus
showing how and why torque was important. It was enormously
frustrating, and as I said, it got nasty. Finally, the monitors
had to get involved. I haven't seen the guy since. Thank goodness.

If nothing else, it's made me appreciate those like yourself who can cite their sources and explain things calmly and rationally.

Cheers!

-- GW74 --

TURN8 - 20 September 2008 05:08 PM

Alright, an electric motor developes it's maximum tourque at at any rpm, meaning it theorticaly could produce infinte horspower. It is limited in a practical sense only by it's mechanicl rpm limit and the capacity of the windings to absorbe current without burning out. Correct?

Don't have any idea, don't have enough experience with electric motors, even though I wound my own slot car motors when I was 18. Even after this dyno test, I still don't understand why the graphs came out like this...especially the torque... Hopefully at some point I will get to talk to the engineer that designed the motor. Boy do I have a lot of questions to ask, especially the fact it out performs the combustion engine it replaced by a considerable amount, yet is much smaller in physical size.

Mozella - 20 September 2008 05:27 PM

TURN8 - 20 September 2008 05:08 PM

Alright, an electric motor developes it's maximum tourque at at any rpm, meaning it theorticaly could produce infinte horspower. It is limited in a practical sense only by it's mechanicl rpm limit and the capacity of the windings to absorbe current without burning out. Correct?

Nope....... not even close. The typical electric motor develops zero torque at max rpm; therefore, zero HP. It develops maximum torque at zero RPM; therefore, zero HP. That may seem a bit odd and it's certainly different from an internal combustion engine, but that's the way it is, for most electric motors anyhow.

Here's a link that may help clear things up http://www.motortech.com/BULL_E-1.htm

Aha...Well, here's what I noticed: They are refering to max NO LOAD rpm. Well an internal cubustion engine produces no HP under no load conditions also. On the dyno, with a load applied, the motor will draw as much current as it can get to to maintain it's tourqe level, irregardless of rpm.

mick viper - 19 September 2008 05:07 PM

Great info...thanks. Some of things you're saying sound like the Reynolds number; is that correct or is that something else entirely.

One more thing I was wondering about. Why hasn't anyone in F1 tried wings that are forward swept, like the X-29A plane? Wouldn't that increase downforce without increasing drag?

They did in the 80s. Tyrrell in 83.

weight has inertia. downforce does not.

msaxman - 12 October 2008 01:02 PM

weight has inertia. downforce does not.

enlightening.

circles are round. squares are not.

DOF_power - 04 October 2008 04:41 PM

mick viper - 19 September 2008 05:07 PM

Great info...thanks. Some of things you're saying sound like the Reynolds number; is that correct or is that something else entirely.

One more thing I was wondering about. Why hasn't anyone in F1 tried wings that are forward swept, like the X-29A plane? Wouldn't that increase downforce without increasing drag?

They did in the 80s. Tyrrell in 83.

Let us not forget the dihedral winged Parnellis (flopped)...



Well, that didn't work...

jimclark - 13 October 2008 10:54 AM

DOF_power - 04 October 2008 04:41 PM

mick viper - 19 September 2008 05:07 PM

Great info...thanks. Some of things you're saying sound like the Reynolds number; is that correct or is that something else entirely.

One more thing I was wondering about. Why hasn't anyone in F1 tried wings that are forward swept, like the X-29A plane? Wouldn't that increase downforce without increasing drag?

They did in the 80s. Tyrrell in 83.

Let us not forget the dihedral winged Parnellis (flopped)...



Well, that didn't work...

Try this one



The "late 1972" Parnelli is on the left, with the normal wings.
It worked. The "early" Parnelli on the right has the infamous
"dihedral" wings that didn't do so well. They were supposed to
be both downforce and "aerodynamic anti-roll, but all they
ended up being was a "drag;" and a fair amount of drag, too.