[ZX-E]

Well actually what I think it really tells us is that if you have a power vs rpm plot, you still have little or no idea how that would effect the vehicle's performance other than from peak power. A constant power vs rpm graph is a great example of that. Torque vs rpm on the other hand gives you important motor characteristics over the entire range of rpm. You almost need torque to interpret the power vs. rpm plot. Just my two cents.

[major]

Originally Posted by ZX-E

The constant power car actually hits its top speed right at the end of the quarter mile. The constant torque motor reaches 84 mph 3 seconds before the end of the quarter mile. I thought it was a fair comparison, but if you think there's something I can change to get more out of it, I wouldn't mind

Oh, I don't know. You can run these all day long and somebody will say it wasn't a fair comparison. I wasn't really saying that. But the loser wasn't using all his available power for the last 3 seconds. Gearing him to 6000 RPM at the 1/4 mile marker would increase his exit speed, but slow his acceleration, so I don't think it would get him a win. That monster torque blast off the line for the other guy would be tough to beat.

When it comes to electric motors, I hate the words "constant power". When you're talking peak power over the speed range, it is just a dream. Especially down to zero RPM. I notice you start him off at 1000 lb.ft. What's the matter? Won't your program handle infinite torque

Regards,

major

[IamIan]

ZX-E,

Thanks... you beat me to it... I had barely started coding and you are all done

I agree use what ever works for you and you find the easiest to work with and understand ... if that is torque ... fine ... if that is power fine ... In the end its your EV only you have to like your finished work.

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As for the two plots... I think it shows some rather nice examples of how both can be useful ... and have pros and cons.

It also clarifies I think a misunderstanding people had about the first one.

As long as the constant power graph is the same amount of power as the average power of the constant torque graph the net energy used should be the same between the two.

Despite this equal energy... the constant power graph clearly shows it is faster in the 1/4 mile and faster 0 to 60 MPH.

This is useful because the first graph I think gave people the opposite / backwards impression.

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I also 100% agree with the point that a major issue with a constant power curve is that the initial torque at low RPMs is so crazy high that it is just not possible in the real world.

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This brings us back to the sliding scale concept that I personally like to apply.

Depending on specifics of what you are trying to do and on what your preferences are... a good quality build can be had with either focus.

For myself I will focus more on one or the other depending on the specifics of what I am trying to accomplish ... Torque is often for many application very useful and sometimes very intuitive to use ... but I will admit sense so much of a EV is about energy flow , usage, etc ... kwh per mile ... usable kwh of battery capacity ... kw of heat generation / dissipation , etc... I do tend to lean a it more toward power most of the time.

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I think a big reason the harder initial acceleration tends to win whoever has it... is because the other forces acting against the acceleration keep getting bigger and bigger and occupy a larger and larger % of the system force or power.

Although I suspect that is not the only factor I would suspect it is a significant player.

[Duncan]

Hi Major
I didn't understand that either so I modeled it myself
I have ignored wind resistance - not relevant for a comparison

Dick Dastardly and Mutley have stolen Tesla's without the motors
Dick has the 300, 200, 100 lbft motor
Mutley has the 200 lbft motor

Because both motors are 6000 rpm the Tesla 8.28:1 ratio is changed to 4.1:1

http://www.diyelectriccar.com/forums...1&d=1257923457

My table should be in here!
As they start Dick is accelerating 50% faster than Mutley, at 2 seconds Dick has over twice the power
At 4 seconds Dick loses his extra torque but because his revs are higher he still has 50% more power and continues to pull away
At 6 and 8 seconds Dick is still pulling away
At 10 second Dick loses his power advantage but he is still going faster and continuing to pull away
At 12 seconds Dick is still faster
At 14 seconds Mutley is now faster but behind
At 16 seconds - all over

Mutley had more power for the last six seconds
Dick had more power for the first ten seconds

Mutley is going faster as Dick crosses the line - This represents more energy

[Duncan]

I will get the hang of these attachments - eventually

Lets try with a gearbox!
And the Tesla Gearing

see table

As they start Dick is accelerating 50% faster than Mutley
At 2 seconds they have dropped to the same acceleration, Dick is 4.6 m in front
At 4 seconds Dick loses his extra torque and Mutley is catching him
Mutley changes gear at 4 seconds, Dick at 5 seconds
At 6 seconds Mutley catches Dick and is 6 mph faster
At 8 seconds Mutley is 5 m past Dick and pulling away
At 13 seconds Mutley must back off to avoid blowing his motor but its all over!

[Duncan]

Mutley Verses a real Tesla


The Tesla is off like a scalded rat
At 2 seconds the Tesla is 9 m in front and 13 mph faster
At about 9.5 seconds the Tesla is maxed out 100 m in front of Mutley and 30 mph faster
At just over 11 seconds its all over


I enjoyed doing these simple models

The Tesla's huge rev range makes it simple,
At up about 60 mph it has constant torque, so much torque that it must be close to breaking traction
I am not sure if more torque could be used off a race track!

Above 60 mph it is power limited, with more power it could continue to accelerate that hard to a higher speed

Sticking a motor with more torque in a standard geared /tyred Tesla would probably not make it go faster as you would be tyre limited
A motor with more power would allow it to accelerate harder where the current Tesla is power limited

More power is always more important

But I would love something that delivered like a Tesla!

[ZX-E]

Originally Posted by Duncan

Mutley Verses a real Tesla


The Tesla is off like a scalded rat
At 2 seconds the Tesla is 9 m in front and 13 mph faster
At about 9.5 seconds the Tesla is maxed out 100 m in front of Mutley and 30 mph faster
At just over 11 seconds its all over


I enjoyed doing these simple models

The Tesla's huge rev range makes it simple,
At up about 60 mph it has constant torque, so much torque that it must be close to breaking traction
I am not sure if more torque could be used off a race track!

Above 60 mph it is power limited, with more power it could continue to accelerate that hard to a higher speed

Sticking a motor with more torque in a standard geared /tyred Tesla would probably not make it go faster as you would be tyre limited
A motor with more power would allow it to accelerate harder where the current Tesla is power limited

More power is always more important

But I would love something that delivered like a Tesla!

Yea the Tesla really is a beast.

[Duncan]

I got carried away with the Tesla!

What I intended to show was

In the single gear example the "more powerful"car (Mutleys) actually had less power for most of the run
And Lost!

With two gears Mutleys car had more power than Dick for most of the run
And Won!

It is all about power BUT if you have not got a Tesla type huge power band then you need gears

[electrabishi]

Originally Posted by Duncan

I got carried away with the Tesla!

What I intended to show was

In the single gear example the "more powerful"car (Mutleys) actually had less power for most of the run
And Lost!

With two gears Mutleys car had more power than Dick for most of the run
And Won!

It is all about power BUT if you have not got a Tesla type huge power band then you need gears

I don't have the Huge Power Band like the Tesla. But the Pinto with a single gear ratio will beat the Tesla in the 1/4 mile. Because I have so much more "torque" and can get 2 car lengths out in front at the start he has to use that extra power just to catch up. Like was mentioned earlier, by then its all over ;-)

I just read through this thread and will say without elaborating much that the person who said Torque is irrelevant must have never tried to drive his car around in 5th gear all the time with a little 4 cyl engine. Even with a hi power twin turbo 4 banger, taking off in 5th gear all the time really sucks. So torque IS relevant. Not much more to say on that except that there are several trade offs to consider when designing your car. Torque, Power, Dynamic Range, Gearing, Speed, Acceleration etc etc are all aspects....and Torque is one of those real aspects.

[gor]

Originally Posted by electrabishi

...

I just read through this thread and will say without elaborating much that the person who said Torque is irrelevant must have never tried to drive his car around in 5th gear all the time with a little 4 cyl engine. Even with a hi power twin turbo 4 banger, taking off in 5th gear all the time really sucks. So torque IS relevant. Not much more to say on that except that there are several trade offs to consider when designing your car. Torque, Power, Dynamic Range, Gearing, Speed, Acceleration etc etc are all aspects....and Torque is one of those real aspects.

this is been answered several times in this thread:
for calculations "this person" made, he needed :
1. torque and rpm together, combined, torque*RPM (power); from here:
2. his next step - to find out particular values of torque and rpm for each gear ratio, depending on power and torque curves;
- so for his task, he needed only kilowatts, and for him it was irrelevant what are separate values of torque and rpm - exact numbers of each was yet to find out and will be relevant on next stage

depending on what you need to accomplish - you have several ways and same math. equation: power=torque*rpm/9549
- choose whatever approach you like and what works for you

p.s. the only relevant - is formula, irrelevantly to what we might call it, what really irrelevant - is semantics : ))))