[Qer]

Originally Posted by CroDriver

I think that such a setup is almost impossible with DC motors (except for very short runs -> drag racers) because the motor would run at very low RPM most of the time and would probably overheat (and the efficiency would probably suck).

Yep, that's a limitation. But is that because of the RPM or the construction?

[CroDriver]

Originally Posted by Qer

Yep, that's a limitation. But is that because of the RPM or the construction?

I'm just thinking hypothetical. If I could trade 30% torque for 30% more RPM I would do it

The power would theoretically be the same, wouldn't it?

[Qer]

Originally Posted by CroDriver

I'm just thinking hypothetical. If I could trade 30% torque for 30% more RPM I would do it

The power would theoretically be the same, wouldn't it?

Yep. And there's a few advantages with rpm instead of torque, transaxles etc can be smaller. But then, balance is more critical instead so, well, it doesn't really matter. Or it does matter, but, well, hmm...

Apples and oranges, I guess. However, the torque I mainly talked about was the torque at the tire, that one won't change.

[paker]

Originally Posted by CroDriver

I'm just thinking hypothetical. If I could trade 30% torque for 30% more RPM I would do it

The power would theoretically be the same, wouldn't it?

How do you think Wayland's Datsun get's off the line faster than any other car he races? It ain't RPM that does it.

[Bowser330]

Originally Posted by paker

How do you think Wayland's Datsun get's off the line faster than any other car he races? It ain't RPM that does it.

Performance at launch is not the only form of performance...

[PhantomPholly]

If you had a perfect CVT, only HP would be relevant. The CVT would keep the motor right at it's optimum rpm while using all of the available power. However, there is no such thing as a perfect CVT today...

Electric motors often out-perform ICE motors of similar hp because of the range of rpms over which they will deliver full hp. ICE motors peak at a very narrow rpm range, usually right at or near max rpm with a sharp falloff. Electric motors typically increase hp linearly (and quickly) until they produce max hp, then produce that same hp all the way up to max rated rpm. Usually they can produce 100% rated hp over 50% or more of their rpm range.

That's probably the same thing someone else said and I just didn't understand their explanation...

[Abel]

i have to go with everyones opinion. I dont know any one here or there experances. The truth is EVERY spec counts. Here are some setup info that have help me with my gas,disel,and now electric cars/trucks. this is to biuld a well rounded set up. more iteams apply but this is for basic set up.

Low HP - High Torque - Light car -------- A wide ratio trany, mid range final gear.

Low HP - High Torque - heavy car--------Close ratio trany, low-mid rang final final gear

High HP - Low Torque - Light car --------a wide ratio trany, low final gears

High HP - Low Torque - heavy car -------Close ratio trany, super low final gear.

Low HP - Low Torque - Light car---------close ratio trany, low or mid-low final gear.

Low HP-Low Torque - heavy car---------- GET A BETTER MOTOR

High HP-High Torque - Light car-----------wide ratio trany,high to mid final gear

High HP-High Torque - Heavy car---------wide ratio trany, mid final gear

This is for a well rounded car. Drag racing you all ways use close ratio tranys and track cars mid to wide ratios. I have work with meny comeros, stengray vetts, and mustanges.

[bazou]

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[IamIan]

Interesting thread... sorry I came in late and took a while to read through it all.

I don't think it is a black and white either way.

but there are a few things that occurred to me that I didn't see mentioned I thought I would through out to get the point of view of others.

----------------
#1>
Equations represent relationships.

F=MA is just as correct as M=F/A... it is deceptive to say power comes from torque when that is only true in one form of an equation... the equation can be re-written still be 100% accurate and make torque come from power .... etc.

In short The whole equation is expressing a relationship ... pulling out pieces of it makes that piece meaningless on its own.

Keep in mind the context of the relationship the equation represents... M=F/A does not mean that your mass disappears when the force applied goes to zero... or becomes infinite as acceleration goes to zero.

---------------------------
#2>
There is power at 0 RPMs.

It is just not expressed in the simple power torque rpm formula.
Just like your mass doesn't become infinite at 0 acceleration or go to zero at zero applied force.
Given the power applied to the motor... V*A... and the Power being dissipated by the motor as its less than 100% efficient ... most of the dissipated power goes out as heat... a bit as light , radio waves, sound , etc... but the remainder of the power is applied at 0 RPMs...

The sum of the power losses from heat, sound, radio waves, etc... is less at 0RPMS than the total power applied to the electric motor... thus even at 0RPMs there is power.

-----------------------
#3>
While a a 1 HP or 1 kW motor with an ideal transmission can provide any amount of torque you want even over 2,000,000,000,000,000 Ft/Lb ... it is the real world limitations on parts, performance etc... thus power and torque can both be useful to varying amounts depending on the specifics of the application... specifics may effect priorities more toward one or the other but all of those things are still there in real world applications.

----------------

just my 2 bits / random thoughts.

Ian.!

[major]

Originally Posted by IamIan

Interesting thread... sorry I came in late and took a while to read through it all.

Hi Iam,

Thanks for your input and thoughts. So what is your vote? Torque is irrelevant of relevant?

There is power at 0 RPMs.

Gotta disagree with you here. On the shaft of a motor, even if there is torque, if it is stationary (zero RPM), the mechanical power is zero. Now there may be electrical power into the motor which produces torque, but the power output is zero. But there could also be a spring which produces that torque. Or a weight on a string around a pulley. Force (or torque) can exist without power.

Regards,

major