# Researching building a racing car



## Duncan (Dec 8, 2008)

Hi Bill

Have a good read of the forum - everything you need is there
I am building a car I hope to use in some hillclimbs (and on a very small budget)

I am using an open source controller - look up OpenRevolt
a series of relays will not work at all well

http://www.diyelectriccar.com/forum...-dubious-device-44370p5.html?highlight=duncan


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## Qer (May 7, 2008)

Billzilla said:


> First post, be kind.


I'll try. At least I'll try to numb you down so you won't feel the killing blow when it comes. 



Billzilla said:


> but one idea was to use something like 20 lithium batteries


Lithium has extremely low internal impedance. This matters in a very big way since a small mistake will make them turn on their master in an instant. Not like lead-acid that tends to be very forgiving, at least compared to Lithium.



Billzilla said:


> and have a controller as simple as a potentiometer connected to the throttle pedal


There's nothing simple over that, trust me. We spent quite some time just fine tuning the function of a potentiometer controlling a motor, it's probably a lot more tricky than you expect.



Billzilla said:


> and as more throttle is applied it turns on solid-state relays in turn.


First problem: The Solid State Relays you've picked are made for AC. They won't work with DC. See? Already not so simple. 



Billzilla said:


> 20 steps of throttle is plenty enough for such a car.


Errr. No.

Don't expect an EV to behave as you want it to. The motor current will depend on RPM, motor voltage, temperature, what granny had for breakfast and the chaos butterflies on the other side of the world. Trying to control motor current with a bunch of relays will best case lead to seriously crappy performance and worst case a burning wreck.

There's been a bunch people here in the forum that apparently has thought "How hard can it be?" and gone DIY-frenzy on the controller building. A few has succeeded but in most cases there's either reports of "setbacks" or "catastrophes" if they bother at all to report back when the controller went 4:th of July on them.

Even those that HAS succeeded has found out the hard way that it IS hard (especially if you want more than mediocre commuting performance) and I don't remember how many transistors Paul blew up before he got Revolt running. Come to think of it, I don't even remember how many transistors we have blown up in the process but it took a while before we worked out all the kinks of the S1. 

Going for a relay layout might sound like it'd be simpler, but I doubt it. Long story short EVs didn't get useful performance until Lithium batteries and transistor based controllers. There has been people racing with relays but I doubt any of them used Lithium since you probably pretty much need the high input resistance of lead-acid to not blow the contactors up.



Billzilla said:


> The problem with that is we'd need a DC brushed motor and from what little I know they aren't as light or efficient as a brushless motor.


Um. I'd want a reference for that claim. 

AFAIK all drag racing nuts still run brushed DC because it's more power per kilo than anything else. Efficiency tends to be shot when you start to go for racing performane and I seriously doubt it should even be a design goal. At least not if you want to have a sporting chance...

I know there were several EVs in Pikes Peak that ran AC-motors, but they had a budget for it too. Ie, HUGE! Lots of sponsor money.



Billzilla said:


> I suspect such controllers for a much larger motor that we'd need for the racing car would cost a fair bit and the budget is tight on this one.


"Racing" and "Tight budget" is a bit mutually exclusive. At least if you don't enjoy finishing last...


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## major (Apr 4, 2008)

Qer said:


> I know there were several EVs in Pikes Peak that ran AC-motors, but they had a budget for it too. Ie, HUGE! Lots of sponsor money.


The Elias Anderson vehicle budget was on the same order or possibly less than your EVWest car. But yes, the Japanese entries appeared very high budget. I heard that Monster had a crew of 27 engineers with him 

Pikes Peak is more like a road race uphill (upmountain). 30 second hill climbs are more like uphill drag races, therefore probably better suited for DC. 

But Bill.....use a quality DC motor controller....for safety sake.

major


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## Billzilla (Sep 16, 2012)

Duncan said:


> Hi Bill
> 
> Have a good read of the forum - everything you need is there
> I am building a car I hope to use in some hillclimbs (and on a very small budget)
> ...


Thanks.
I have a car similar to yours though it uses a two litre petrol engine of about 185 kW.










I assumed there's all the information I need here, but a few pointers in the right direction to reduce the confusion of what to look for would be handy. 







Qer said:


> Lithium has extremely low internal impedance. This matters in a very big way since a small mistake will make them turn on their master in an instant. Not like lead-acid that tends to be very forgiving, at least compared to Lithium.


Has to be lithium for weight.






Qer said:


> There's nothing simple over that, trust me. We spent quite some time just fine tuning the function of a potentiometer controlling a motor, it's probably a lot more tricky than you expect.


Righto. It was just an idea I had that seemed to be the easiest way to do it, and something that we could build at home.






Qer said:


> First problem: The Solid State Relays you've picked are made for AC. They won't work with DC. See? Already not so simple.


I just picked that one as an example, I would have to work out the maximum current from each battery (or batteries) to see how big a DC relay I'd need. 







Qer said:


> Don't expect an EV to behave as you want it to. The motor current will depend on RPM, motor voltage, temperature, what granny had for breakfast and the chaos butterflies on the other side of the world. Trying to control motor current with a bunch of relays will best case lead to seriously crappy performance and worst case a burning wreck.


Okay more research needed in this area then. I only picked '20' again as an example as 20 steps of throttle would be plenty for such a car. You typically drive one with either full throttle or nothing and rarely anything in between that. I figured ten steps might be a bit rough but 20 would be good enough.
Anyway, more research ....






Qer said:


> Even those that HAS succeeded has found out the hard way that it IS hard (especially if you want more than mediocre commuting performance)


Not interested in commuting performance, regen braking or anything like that. Just maximum current to the motor when you plant your right foot and a bit less with less throttle.






Qer said:


> Going for a relay layout might sound like it'd be simpler, but I doubt it. Long story short EVs didn't get useful performance until Lithium batteries and transistor based controllers. There has been people racing with relays but I doubt any of them used Lithium since you probably pretty much need the high input resistance of lead-acid to not blow the contactors up.


I picked solid-state relays as they have no moving parts. They are commonly used in performance cars to control electric water pumps and other reasonably high-current devices that need to be controlled for speed by duty cycle. Though the ones they normally use are only about 30 amps or so.







Qer said:


> Um. I'd want a reference for that claim.


Another example of stuff I am finding out about. 






Qer said:


> AFAIK all drag racing nuts still run brushed DC because it's more power per kilo than anything else. Efficiency tends to be shot when you start to go for racing performane and I seriously doubt it should even be a design goal. At least not if you want to have a sporting chance...


That sounds reasonable then, a DC brushed motor would work for us okay.






Qer said:


> "Racing" and "Tight budget" is a bit mutually exclusive. At least if you don't enjoy finishing last...


Somewhat aware of that - I own four racing cars, two road cars, a rally car, etc. 





major said:


> The Elias Anderson vehicle budget was on the same order or possibly less than your EVWest car. But yes, the Japanese entries appeared very high budget. I heard that Monster had a crew of 27 engineers with him
> 
> Pikes Peak is more like a road race uphill (upmountain). 30 second hill climbs are more like uphill drag races, therefore probably better suited for DC.
> 
> ...


Had a quick look at a Zilla controller. (Hey, I like the name!!) and they aren't as expensive as I thought they'd be, so I'll have to do some sums and research to see how they would go for us. It's certainly seems to be the most effective and easiest way to go right now though.


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## Billzilla (Sep 16, 2012)

FWIW some photos of the car.
There's one of it running on a track. The sidepods are likely to go as they aren't needed. I'll be fitting it with a big ground-effects floor that works far better and weighs only a fraction as much.

And a couple of photos of how of looks with all the bodywork off the chassis. It's far from a brilliant chassis and I'm making a lot of little changes to drastically improve the stiffness of it. But anyway keeping it on-topic there's a fair bit of room for batteries in the back.


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## Tesseract (Sep 27, 2008)

Billzilla said:


> Had a quick look at a Zilla controller....


Qer - file under "No Good Deed Goes Unpunished"


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## Qer (May 7, 2008)

Tesseract said:


> Qer - file under "No Good Deed Goes Unpunished"


I sense the irony is strong with this one...


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## Billzilla (Sep 16, 2012)

Tesseract said:


> Qer - file under "No Good Deed Goes Unpunished"


They're NFG?


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## gdirwin (Apr 7, 2009)

Zilla and Evnetics controllers are both top-notch and are both well-respected.

What is happening is that Qer and Tesseract are the brains behind the Evnetics controllers, whereas you mentioned the use of their competitor (Zilla). This is all fair game - they are both very active in this forum, and have been very helpful to all (even if you don't use their product).

I would recommend looking at both the Zilla and Evnetics products if you are looking at a quality dc motor controller.


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## Billzilla (Sep 16, 2012)

gdirwin said:


> Zilla and Evnetics controllers are both top-notch and are both well-respected.
> 
> What is happening is that Qer and Tesseract are the brains behind the Evnetics controllers, whereas you mentioned the use of their competitor (Zilla). This is all fair game - they are both very active in this forum, and have been very helpful to all (even if you don't use their product).
> 
> I would recommend looking at both the Zilla and Evnetics products if you are looking at a quality dc motor controller.


Thanks.
I only picked that one because of the similarity to my name. There are many Billzilla's on the Net now, but I am the original.
Okay I'll have a look at the Evnetics one now.

We only need one that just pumps power out, no regen, no engine braking, etc. So I'm open to suggestions for something like that.


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## JRP3 (Mar 7, 2008)

With a high power series DC controller that's all you get, no regen.


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## Billzilla (Sep 16, 2012)

JRP3 said:


> With a high power series DC controller that's all you get, no regen.


Thanks for that.


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## MalcolmB (Jun 10, 2008)

Hi Bill,
You might be interested in this – a guy in the UK converting a similar hillclimb car: http://www.diyelectriccar.com/forums/showthread.php?t=75972


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## Billzilla (Sep 16, 2012)

Looks like lots of good info there, thanks.


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## Tesseract (Sep 27, 2008)

Billzilla said:


> ...Okay more research needed in this area then. I only picked '20' again as an example as 20 steps of throttle would be plenty for such a car. You typically drive one with either full throttle or nothing and rarely anything in between that. I figured ten steps might be a bit rough but 20 would be good enough.
> Anyway, more research ......


Your conception of the "throttle" is a little off for both ICE and electric motors.

The throttle in an ICE controls the cross-sectional area of the intake manifold, which only _indirectly_ controls the power output of the engine. Oversimplifying a bit, opening up the throttle in an ICE results in a faster rate of change in power output. It is important to emphasize that the throttle in an ICE does not directly control engine RPM, torque or power.

In the series DC motor, however, it is possible to directly control RPM or torque because torque is roughly proportional to current while RPM is roughly proportional to voltage. In on-road vehicle applications, the best driving feel generally results from having throttle control motor torque, as full throttle will then result in the fastest rate of change in motor speed, and therefore motor power.

For example, let's consider a motor controller rated for 1000A driving a 9" nominal diameter series DC motor which puts out 220 lb-ft of torque at 1000A and requires 50V for every 1000 RPM at that torque level. If you have a 200V battery pack (and neglecting the inevitable sag) then this 1000A motor controller will allow the motor to deliver a full 220 lb-ft of torque up to 4000 RPM. Power is the product of torque x RPM, so at low RPM (even at full throttle) the power output will be relatively low.

Your proposed scheme to divide the battery pack voltage up into 20 steps (or how ever many steps, as it doesn't matter) would be a total disaster. Full throttle will apply full battery pack voltage to the motor, and if the motor is at a dead stop then it will more or less look like a short circuit, drawing - potentially - many thousands of amps from the battery pack. Something will blow up, I assure you.

And that's why you need a good motor controller in an EV.


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## Billzilla (Sep 16, 2012)

Tesseract said:


> Your conception of the "throttle" is a little off for both ICE and electric motors.
> 
> The throttle in an ICE controls the cross-sectional area of the intake manifold, which only _indirectly_ controls the power output of the engine. Oversimplifying a bit, opening up the throttle in an ICE results in a faster rate of change in power output. It is important to emphasize that the throttle in an ICE does not directly control engine RPM, torque or power.


I'm very aware of pretty much everything to do with petrol engines. I've been racing for nearly thirty years with good success. I enjoy consistently beating every professional engine builder on the track, so I must be doing something right.







Tesseract said:


> In the series DC motor, however, it is possible to directly control RPM or torque because torque is roughly proportional to current while RPM is roughly proportional to voltage. In on-road vehicle applications, the best driving feel generally results from having throttle control motor torque, as full throttle will then result in the fastest rate of change in motor speed, and therefore motor power.
> 
> For example, let's consider a motor controller rated for 1000A driving a 9" nominal diameter series DC motor which puts out 220 lb-ft of torque at 1000A and requires 50V for every 1000 RPM at that torque level. If you have a 200V battery pack (and neglecting the inevitable sag) then this 1000A motor controller will allow the motor to deliver a full 220 lb-ft of torque up to 4000 RPM. Power is the product of torque x RPM, so at low RPM (even at full throttle) the power output will be relatively low.
> 
> ...


It was only an idea I had because I didn't know and it's already been mentioned that it probably wouldn't work earlier in this thread.
Anyway, you couldn't go directly to full power with the motor stopped as the throttle isn't a switch, it progresses from zero up to full power in a linear fashion. True it would depend on how quickly the driver presses the throttle but a few smacks to the head would teach him to take a second or so to do that from a standing start.

But never mind all that, it seems to be the universal consensus that we need a controller of some sort, so that's the way it will go. Been talking to the owner of the car and he wants a lot of power, quite a lot. I'm not sure if it's possible but I'd like to get as much as we reasonably can.
Things like forklift motors can be obtained here, what can be done to get more power from them? It's likely that we'd need two, is there a controller that can run two at the same time?


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## ruckus (Apr 15, 2009)

Hello,
Good to have another petrol-head joining in the EV fray. 

If you are interested in alternative drive systems there is a new brushless permanent magnet motor recently available. It is water cooled and has a peak output (30sec) of around 200kw with a 1hr rating of 60kw. I just imported the first one to this continent (it's currently clearing customs in Seattle) and will be testing and dynoing it to verify the output. It is about $7000 for the motor and controller which is about the same as you will pay for a decent brushed DC setup when you consider it comes with a contactor and 12v dc system. There is a thread on it in the motor section under 'Scott Drive' though the thread gets a bit off topic.

Also, if you are adventurous and on a budget then check ebay or other surplus sites for 'powertec' motors. They are air-cooled brushless dc motors running up to 720-800vdc and having very good power to weight ratios (because of the high voltage). Be aware that many are used in mining so they are non ventilated. These motors are greatly derated on the HP rating plate. With a blower attached that same motor will put out many times more power. 

Good luck!


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## JRP3 (Mar 7, 2008)

Billzilla said:


> Been talking to the owner of the car and he wants a lot of power, quite a lot.


Then there is only one choice 
http://www.evnetics.com/evnetics-products/soliton-shiva/


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## Billzilla (Sep 16, 2012)

Thanks again.
Too much information here!! 
I'll keep researching and post what I reckon is the way to go here.
(Then be shot down in flames, then we repeat the process several times until it's right lol)


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## winzeracer (Apr 3, 2012)

Billzilla said:


> Thanks again.
> Too much information here!!
> I'll keep researching and post what I reckon is the way to go here.
> (Then be shot down in flames, then we repeat the process several times until it's right lol)


HAHA yes this is how it goes. I thought I had a good plan, so I bought a motor controller and Batts, come to find out I had overlooked some important details. So, learn from my mistake and make sure to state your goals clearly and design an entire system that is matched well. Then post and repost....then repeat


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## ahab (Sep 17, 2012)

I might as well put my hand up and say, I'm the other party involved here.

I'm the one who will be footing the Bill and drive it, Billzilla is the brains of this outfit. For what it's worth, Billzilla can build racecars pretty well and isn't bad at driving them either.
I have a couple of quick cars I punt up hills pretty well, In my mind anyway.

















Both cars are national record holders in their respective class

If I can't build a car that is a serious weapon I won't proceed with this, I'll just keep going along with what I'm doing now, I'm treating this as an interesting project to be built over a few years as funds allow.

And funds are not unlimited. I do understand there will be some considerable costs involved and depending how ridiculous they are will determine what direction I take.



JRP3 said:


> Then there is only one choice
> http://www.evnetics.com/evnetics-products/soliton-shiva/


I saw that the other day, as much as I like it it is outside my budget, It's little brother on the other hand looks like it could do the job pretty well.


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## Billzilla (Sep 16, 2012)

We've done a bit of research and it seems that we'll go one of two ways with the power system -
- Find a crashed Holden/Chevy Volt and use the motor from that as they're 111 kW so after we fiddle with it, it should be usefully more.
- A motor out of a UK milk float. Doesn't sound too exciting but check this out ...

http://www.youtube.com/watch?v=tay2jfHsfZo

That seems to have enough grunt!


The Volt uses a 4ET50 electric motor & gearbox unit.










It's an AC motor so we'd need to build or buy an AC electric controller for it. 

I've found a couple of Volts at the wreckers in the US and it might be possible to get one at a reasonable price.
The DC milk float motor should be too expensive but would need to be modified.

Any comments or suggestions?


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## Duncan (Dec 8, 2008)

Milk float - or forklift for your DC motor

Try to find who services and repairs forklifts in your nearest big town, then ask about motors from scrapped units

I got a recently rebuilt unit for scrap metal price - $100


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## Duncan (Dec 8, 2008)

Billzilla said:


> The DC milk float motor should be too expensive *but would need to be modified.*


As far as I can see the main modifications are;
A nice paint job
Some slightly better brushes
Advanced brush timing

_Possibly_ some better banding (for centrifugal force) to increase the blow up speed

I may be being a bit cynical here - Would any real experts like "Major" confirm/deny ???


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## Billzilla (Sep 16, 2012)

Duncan said:


> Milk float - or forklift for your DC motor
> 
> Try to find who services and repairs forklifts in your nearest big town, then ask about motors from scrapped units
> 
> I got a recently rebuilt unit for scrap metal price - $100





Duncan said:


> As far as I can see the main modifications are;
> A nice paint job
> Some slightly better brushes
> Advanced brush timing
> ...


That's good news, thanks gents. I could do all that in my garage no problems.
Had a quick look and there's a few forklift repair places not too far from me. I'll try to pop into one tomorrow to have a quick look.


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## JRP3 (Mar 7, 2008)

Check out the "Forklift Motor" thread for everything you ever wanted to know and more.


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## DIYguy (Sep 18, 2008)

Billzilla said:


> That's good news, thanks gents. I could do all that in my garage no problems.
> Had a quick look and there's a few forklift repair places not too far from me. I'll try to pop into one tomorrow to have a quick look.


With the exception of one or maybe two, all of the fastest 1/4 mile or 1/8 mile drag racers use lift truck motors modified for racing. Most are GE motors. Not sure of the brand Olly uses in BC. . but the milk float motors seem similar. Heck, even the Warp motors were a lift truck design in the beginning, IIRC. You can read the thread on lift truck motors here. It's long, but pretty helpful. Major is your best resource here. There are a few other tricks used for race mods, not all spoken of freely. . . but then again, when working with motors that have no published specs in most cases, it's hard to nail down some issues.


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## Billzilla (Sep 16, 2012)

JRP3 said:


> Check out the "Forklift Motor" thread for everything you ever wanted to know and more.





DIYguy said:


> With the exception of one or maybe two, all of the fastest 1/4 mile or 1/8 mile drag racers use lift truck motors modified for racing. Most are GE motors. Not sure of the brand Olly uses in BC. . but the milk float motors seem similar. Heck, even the Warp motors were a lift truck design in the beginning, IIRC. You can read the thread on lift truck motors here. It's long, but pretty helpful. Major is your best resource here. There are a few other tricks used for race mods, not all spoken of freely. . . but then again, when working with motors that have no published specs in most cases, it's hard to nail down some issues.


Thanks. Being a racer I'm used to having to re-invent pretty much everything all the time. 
It's still all quite overwhelming though, I don't know a lot of the terms you guys use. What's a 'lift truck' ?


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## JRP3 (Mar 7, 2008)

Forklift=lift truck


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## Billzilla (Sep 16, 2012)

I popped into the forklift shop today and had a good talk with the knowledgeable fellow there. He was quite adamant that the AC motors are by far better for power than the DC and that was the way we should go.
He said the Curtis AC controller that was in the forklifts would do the job just fine as you could adjust how it all worked with a laptop. 
But just in case ..... what other AC controllers are good to consider?


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## Billzilla (Sep 16, 2012)

FWIW this is a pretty typical sort of run that the car would be expected to do.
It's mostly full-throttle stuff with a little low & part-throttle stuff.


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## PStechPaul (May 1, 2012)

Hmmm. I was expecting much steeper hills, although maybe it's hard to tell what sort of slopes are being driven. So, what sort of grades and speeds and curve radius and such are involved? 

Personally, I would go with an AC system using three phase induction motors, but there have been some recent advances in switched (or variable) reluctance motors that promise much better performance. There are quite a few Aussies who regularly rewind motors for higher performance using higher frequency so you might have a look at their EV forum.

Good luck.


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## EVfun (Mar 14, 2010)

Billzilla said:


> I popped into the forklift shop today and had a good talk with the knowledgeable fellow there. He was quite adamant that the AC motors are by far better for power than the DC and that was the way we should go.
> He said the Curtis AC controller that was in the forklifts would do the job just fine as you could adjust how it all worked with a laptop.
> But just in case ..... what other AC controllers are good to consider?


If you want to build a race car you might want to talk to them again. Explain that you want about a half a megawatt of power (500,000 watts!!) I suspect that their recommendations will change.

The Curtis AC systems go up to a little less than 100 kW. Fine for a daily driver, but I wouldn't call that racing unless you stick it in a gocart.


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## Duncan (Dec 8, 2008)

Billzilla said:


> I popped into the forklift shop today and had a good talk with the knowledgeable fellow there. He was quite adamant that the AC motors are by far better for power than the DC and that was the way we should go.
> He said the Curtis AC controller that was in the forklifts would do the job just fine as you could adjust how it all worked with a laptop.
> But just in case ..... what other AC controllers are good to consider?


Hi Bill
He is correct AC is the way to go - if you have very deep pockets!

It's like saying the best engine to tune up is a Ferrari V12

But that is NOT the most cost effective way to useful power!

My 100Hp setup cost
$100 - motor
$600 - controller 
Less than 400 Pounds

I lusted after an AC propulsion system -
http://www.acpropulsion.com/products.html

$25,000 + and 200Kw

A more normal setup for 200Kw
Warp 9/11 - $3000
Soliton - $3000


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## Billzilla (Sep 16, 2012)

PStechPaul said:


> Hmmm. I was expecting much steeper hills, although maybe it's hard to tell what sort of slopes are being driven. So, what sort of grades and speeds and curve radius and such are involved?


That's a flat track, most have decent hills involved. But the overall time isn't too far off that ~30 second or so run.





EVfun said:


> If you want to build a race car you might want to talk to them again. Explain that you want about a half a megawatt of power (500,000 watts!!) I suspect that their recommendations will change.
> 
> The Curtis AC systems go up to a little less than 100 kW. Fine for a daily driver, but I wouldn't call that racing unless you stick it in a gocart.


We don't need (or can use) 500 kW but 200 kW - 300 kW would be nice.






Duncan said:


> Hi Bill
> He is correct AC is the way to go - if you have very deep pockets!
> 
> It's like saying the best engine to tune up is a Ferrari V12
> ...


Fair enough.
Thanks again everyone.
I'll do some more reading and try yet again.


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## Tesseract (Sep 27, 2008)

PStechPaul said:


> ...
> Personally, I would go with an AC system using three phase induction motors...





PStechPaul said:


> Not having driven an electric car I can't say from experience....


So you have no experience with EVs but still feel qualified to offer an opinion on which drive technology the OP should consider? Hmmm...


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## JRP3 (Mar 7, 2008)

In a power to dollar ratio series DC wins over AC, period, end of story, do not pass go. Compare the price and max potential power from an AC50 HPEVS system to a Soliton Jr. and a Warp9.
AC 50 120V x 650 amps = 78 kw around $4500
Warp/Jr 340V x 600 amps = 200 kw around $4000


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## PStechPaul (May 1, 2012)

Tesseract said:


> So you have no experience with EVs but still feel qualified to offer an opinion on which drive technology the OP should consider? Hmmm...


I just said it was the way I, personally, would go. I base my *opinion* on many years of experience with high current AC systems and (mostly AC) motors, as well as several motor control seminars provided by Microchip. I have rewound AC induction motors and I've built controllers for them. It is true that I have not driven an electric car, but I have built a small electric vehicle using three phase AC.

There are probably many people here who have never driven an electric car, and probably most have only experienced one particular technology: brushed series wound DC motors. Most of the serious problems that I've seen reported have been with this type of motor as well as PM DC motors and BLDCs. There may be very few who use AC motors, so the sample size is smaller, but I have not seen reports of any serious problems with them. And those who use the technology overwhelmingly seem to endorse it over the older BDC systems. 

I'm only adding my own perspective from my background as an engineer with a fairly good understanding of electric motor technology, particularly the driver hardware and microcontroller code. In this case, the OP has little experience with electric motors and controllers and I'm just trying to provide my own knowledge and experience from a technical aspect, and I think it is important to "push" the consideration of AC motors and drives because they seem to be generally not as well understood by the DIY EV community.


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## DIYguy (Sep 18, 2008)

I don't think there is much disagreement in any of the posts. AC has some great advantages. The biggest disadvantages (for higher performance systems) are cost and raw power. JRP is correct about that. 1/8 and 1/4 mile applications are dead easy decisions. As soon as the duration starts to get longer, heat management (continuous power management) becomes a bigger issue. From the duration of the run I saw on your video, i'd say, you will have a hard time beating the performance of DC. If you have very deep pockets, you can look at AC systems and maybe you can find a suitable one since your car is not really big/heavy. One thing is for sure, it will cost you. 

As an example. .. . just today, I pushed 3000 amps through a DC motor I made in my basement. I got it for $100 (actually less as that $100 included a few other things.)


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## Billzilla (Sep 16, 2012)

Gotta make a decision at some point, gents, to progress and I've decided that something close to this is what's going to happen.



JRP3 said:


> Warp/Jr 340V x 600 amps = 200 kw around $4000


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## Batterypoweredtoad (Feb 5, 2008)

Billzilla said:


> Gotta make a decision at some point, gents, to progress and I've decided that something close to this is what's going to happen.


You are going to be beyond the voltage limit of that Warp9 quite a bit with a Soliton Jr. The Kostov 220v 9" is more of an appropriate match for the amp and volt limits of the Jr. If you were designing a system like the AC systems on the market (matching controllers that cant ever hurt your motor) a K11 Alpha would be perfect and handle everything the Soliton Jr could throw at it.


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## JRP3 (Mar 7, 2008)

Good point if he intends on running near the higher end voltage potential of the Jr.


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## DIYguy (Sep 18, 2008)

Billzilla said:


> Gotta make a decision at some point, gents, to progress and I've decided that something close to this is what's going to happen.


Do your self a favour and go with the Soliton1, not the Jr. U will end up buying it anyways. . . may as well do it first, then u won't have to buy both.


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## DIYguy (Sep 18, 2008)

JRP3 said:


> Warp/Jr 340V x 600 amps = 200 kw


The problem here is. . . this is not what u end up getting. Take your 340 volt pack, sag it to 200 (which coincidentally is all the commutator will handle anyways . . with Helwigs even). Now u have 120 kw. 
Of course sag depends on battery type/brand etc etc.

Buy the Soliton1. Even that may be light on current.  Maybe Zilla might need a Zilla. . .


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## JRP3 (Mar 7, 2008)

True but I was just doing a comparison to the AC system, which I also did not calculate losses. But yes you are correct for actual power output. I do agree that the Soliton is a better choice than Jr if he can afford it.


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## DIYguy (Sep 18, 2008)

JRP3 said:


> True but I was just doing a comparison to the AC system, which I also did not calculate losses. But yes you are correct for actual power output. I do agree that the Soliton is a better choice than Jr if he can afford it.


Yes, I understand you were comparing specs. . . I just wanted op to understand what he would end up getting.

Regarding the Kostov option. . . personally, I'm not a big fan of using these where higher (especially sustained) current levels are involved. Again, looks good on paper, but for racing type applications, they just don't seem to be the practical choice due to current carrying capability. Interpoles and winding for higher voltage, tends to preclude high current capabilities. . .


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## Batterypoweredtoad (Feb 5, 2008)

DIYguy said:


> Yes, I understand you were comparing specs. . . I just wanted op to understand what he would end up getting.
> 
> Regarding the Kostov option. . . personally, I'm not a big fan of using these where higher (especially sustained) current levels are involved. Again, looks good on paper, but for racing type applications, they just don't seem to be the practical choice due to current carrying capability. Interpoles and winding for higher voltage, tends to preclude high current capabilities. . .


Buuut-they handle higher voltages so a K9 220V can have higher voltages thrown at it _and_ produces more torque per amp. Even comparing running the 220V rated Kostov spec to the "push it to the limit" specs you are giving for the Warp9 you are 12kw ahead when using the K9 220v and SolitonJr. Jack up the volts on the K9 220V and you gain even more. The Junior is fully utilized by the K9 220V. The Soliton1 is a better match to the amp capacity of the Warp9 or even better the amp _and_ volt capacity K11 Alpha or the Warp11HV. 

This car is going to be lightweight and have a gearbox right?


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## DIYguy (Sep 18, 2008)

Batterypoweredtoad said:


> Buuut-they handle higher voltages so a K9 220V can have higher voltages thrown at it _and_ produces more torque per amp. Even comparing running the 220V rated Kostov spec to the "push it to the limit" specs you are giving for the Warp9 you are 12kw ahead when using the K9 220v and SolitonJr. Jack up the volts on the K9 220V and you gain even more. The Junior is fully utilized by the K9 220V. The Soliton1 is a better match to the amp capacity of the Warp9 or even better the amp _and_ volt capacity K11 Alpha or the Warp11HV.
> 
> This car is going to be lightweight and have a gearbox right?


There is a reason the race tracks are not full of Kostov's. Don't get me wrong, I like the motors. 
Check the motor voltage during hard acceleration and see what it is. . . regardless of the battery voltage or controller specs. . . it comes down mostly to current. Sure voltage matters for higher rpm. It will depend a lot on gearing for sure.


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## Batterypoweredtoad (Feb 5, 2008)

I really wish more logs were available. There are really not that many motors on racetracks at all and very few of the people are producing or sharing good data. It does seem like batteries are finally improving to the point where a high voltage pack remains a high voltage pack under load. I think most serious racers have chased amps because the commonly used batteries and motors favored that.


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## Billzilla (Sep 16, 2012)

Batterypoweredtoad said:


> Buuut-they handle higher voltages so a K9 220V can have higher voltages thrown at it _and_ produces more torque per amp. Even comparing running the 220V rated Kostov spec to the "push it to the limit" specs you are giving for the Warp9 you are 12kw ahead when using the K9 220v and SolitonJr. Jack up the volts on the K9 220V and you gain even more. The Junior is fully utilized by the K9 220V. The Soliton1 is a better match to the amp capacity of the Warp9 or even better the amp _and_ volt capacity K11 Alpha or the Warp11HV.
> 
> This car is going to be lightweight and have a gearbox right?


It should still end up pretty light, under 500 kg or so I hope. No gearbox, just a diff and we'll pick the sprockets we need (it'll be chain-drive) to get the overall top speed we want. It'll only need to top out at about 160 km/h or so, so not that fast.

So from what you guys have been saying, we need to look at a Soliton 1 controller and a Warp 9 or 11 motor?


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## Duncan (Dec 8, 2008)

Hi Bill

My take on (DC) motors and voltages

The controller is a power in - power out device

200v and 500amps IN = 100v and 1000amps OUT(motor)

The motor has back EMF - proportional to rpm

At zero rpm - zero back EMF it only takes ~20v to push 1000amps
So with a 200v battery 
200v x 100amps = 20v x 1000amps

The only way you can have 200v and 1000amps is when the back EMF = 180v

(20v + 180v ) x 1000amps = 200v x 1000amps - which will be at a certain rpm

Higher voltage reduces the battery current and enables higher revs to be used
BUT once you can reach MAX rpm extra volts don't help

If I had a free choice of a DC system I would use a Soliton 1 and a 9inch motor
because the 9 inch has a higher burst Rpm

What I actually have is an 11 inch motor ($100 - Did I say I'm a Scotsman?)
and a 500amp controller

I calculate that I should be able to break traction at 400amps and that 4000rpm will be 110Kph and safe
5000rpm will be 137Kph and "probably OK"

With better tires the 400 amps goes up - 
A 9 inch will need ~20% more current for the same torque 
A Soliton 1 has 250% more current - 

the 9 inch motor may be OK at 7000rpm AND weight half as much - 50Kg rather than 100Kg


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## Qer (May 7, 2008)

Duncan said:


> The controller is a power in - power out device
> 
> 200v and 500amps IN = 100v and 1000amps OUT(motor)


Finally! Finally I'm not alone preaching this!


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## DIYguy (Sep 18, 2008)

Duncan said:


> Hi Bill
> 
> My take on (DC) motors and voltages
> 
> ...


Thanks Duncan. This was my point. . . you described it more in detail. I did have this combination before with a Soliton1 and a 9" motor. I used this combination to push around a 4200 lb truck. . with a 5 speed though. It worked just fine. Was no race car but it would go over 160 kph with a 211 volt nominal pack. My 9" is a GE motor from a lift truck with a few of my own mods. I'm not sure I would be comfortable with the 7000 rpm though. . .without some additional mods. Also, my 9" came in closer to 70 kilo.
Here is what mine looked like before and after....


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## DIYguy (Sep 18, 2008)

Batterypoweredtoad said:


> I really wish more logs were available. There are really not that many motors on racetracks at all and very few of the people are producing or sharing good data. It does seem like batteries are finally improving to the point where a high voltage pack remains a high voltage pack under load. I think most serious racers have chased amps because the commonly used batteries and motors favored that.


There is probably some truth to that point. That said, and again, at lower rpm and high current, motor voltage is relatively low. 

as for log files. . . here is one for you. Have u ever seen one hit 3000 motor amps? This was one of my first attempts and was having trouble with my throttle signal. Thanks to Qer for turning this log file into a graph.


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## Qer (May 7, 2008)

DIYguy said:


> as for log files. . . here is one for you. Have u ever seen one hit 3000 motor amps? This was one of my first attempts and was having trouble with my throttle signal. Thanks to Qer for turning this log file into a graph.


Ah. I was pondering if you'd be ok with me posting it here. 

That graph shows one thing exceptionally well too; when you start to draw some serious current from the pack the pack voltage drops badly. In this case I guess it's a good thing 'cause I'm amazed your motor can handle 3000 Amps at all. Handle 3000 Amps AND a few hundred volts, however... 

Nice data though. I bet you can scare a few people at the red lights!


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## Ace_bridger (Nov 22, 2011)

Simple is key here, I feel, and you're going to learn a lot.

I think you'll end up with a Warp and a Soliton 1 matched with some suitable lithium.

You might consider starting with an Open Revolt to get everything running and, if you need to up-grade later, then go for the Soliton 1. The Open Revolt will give you something inexpensive to break your teeth on...and may just do the job.

Your going to need a reasonable sized lithium pack. To get the voltage you need you'll need to keep adding 3.2V cells in series until you get to your desired voltage (e.g. 144V is 45 cells, 192V is 60, etc). The size (Ah) you need will not really be based on the range you need but more based on what current you'd like to draw from them. Let's say you go for the new CALB cells which can give 20C (20 x the Ah rating)...if your controller would like to deliver 2000A then, based on 20C max, you could go for 100Ah batteries. This combo means you'll need to carry 45 off 100Ah cells in the car. Should you go for a battery which is only capable of 10C then you'd have to double the AH rating for the same 2000A....

If I was doing a hill climb I would go for Soliton 1, DC motor (Warp or fork lift) and the new CALB cells.

I'm sure people will comment but that's what I'd do.


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## Billzilla (Sep 16, 2012)

Ace_bridger said:


> Simple is key here, I feel, and you're going to learn a lot.
> 
> I think you'll end up with a Warp and a Soliton 1 matched with some suitable lithium.
> 
> ...


I'm thinking much the same, though going straight for the Soliton controller first. It will same time and money overall.
I can get a forklift motor without too much trouble (I think ....) so when that happens I'll either add to this thread or maybe start another in the motor sub-forum on how to hot it up.
I'll no doubt also have to start another thread on the batteries when the time comes.
Thanks again gents.


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## Billzilla (Sep 16, 2012)

Another thought ....
I was wondering about using a slightly smaller motor and revving it harder. We can run pretty much whatever gearing we need to, and a motor doing lots of revs is a bit of an advantage in some ways.
More volts and fewer amps?


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## DIYguy (Sep 18, 2008)

Billzilla said:


> , and a motor doing lots of revs is a bit of an advantage in some ways.


This may be a bit of ICE thinking though. . as you are use to peak torque further up the rpm scale. With electric motors, the torque is all at the bottom end. There isn't so much inertia either, especially with direct drive and no flywheel... 
It's been said a few times that in an electric drivetrain, the motor is more like an ICE transmission and the battery is the engine. There is a lot of truth to this however, there are a few caveats. Gearing and need for multiple gears is one. So, for example, you could get the same torque out of a 8 inch motor as a 9 inch, but you would need lower gearing.. . and maybe more of them (gears). So with direct drive, you need to make sure the torque curve will match your application (weight, acceleration etc). The other is heat. Smaller motors tend to have lower continuous power ratings and may overheat prior to finishing the race. Adding a centrifugal blower to cool the motor is a good thing regardless.
Finally, bear in mind the weight and space requirements of any kind of transmission WRT larger motor-only options must be considered.


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## Billzilla (Sep 16, 2012)

DIYguy said:


> This may be a bit of ICE thinking though. . as you are use to peak torque further up the rpm scale. With electric motors, the torque is all at the bottom end. There isn't so much inertia either, especially with direct drive and no flywheel...
> It's been said a few times that in an electric drivetrain, the motor is more like an ICE transmission and the battery is the engine. There is a lot of truth to this however, there are a few caveats. Gearing and need for multiple gears is one. So, for example, you could get the same torque out of a 8 inch motor as a 9 inch, but you would need lower gearing.. . and maybe more of them (gears). So with direct drive, you need to make sure the torque curve will match your application (weight, acceleration etc). The other is heat. Smaller motors tend to have lower continuous power ratings and may overheat prior to finishing the race. Adding a centrifugal blower to cool the motor is a good thing regardless.
> Finally, bear in mind the weight and space requirements of any kind of transmission WRT larger motor-only options must be considered.


All noted, but if I could get, say, 50% more revs from, say, an 8" motor* than a 9" then even with a little less torque because of the smaller motor and higher revs I'd more than pick that up from the gearing.
And thoughts on doing that with more volts and fewer amps ....? (Again, not sure so I have to ask)


* Does this refer to the diameter of the motor casing?


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## winzeracer (Apr 3, 2012)

Billzilla said:


> All noted, but if I could get, say, 50% more revs from, say, an 8" motor* than a 9" then even with a little less torque because of the smaller motor and higher revs I'd more than pick that up from the gearing.
> And thoughts on doing that with more volts and fewer amps ....? (Again, not sure so I have to ask)
> 
> 
> * Does this refer to the diameter of the motor casing?


I have been folowing your thread all the way through so I am up to speed.
Yes, * is the casing Diameter. The only value in going with higher voltage/RPM is if you were needing higher top speeds, thus sacrificing amps/torque. In order to evaluate if gearing will make up for this sacrifice you would have to get into the specifics of the gearing ratio and do some physics to see if it makes sense in your case. 
In general ( and with your background in racing this needs not be stated) go with the largest setup with the most torque you can afford in all areas (weight, cost, and space) for the best results. Obviously there is a "tipping point" where the weight of the motor becomes a problem, however it does not sound like you have hit that point with a 9" motor.

In my Kart I decided to up the cost so that I could go PMDC motor ( instead of DC series) to bring the overall weight down, and I did sacrifice a little torque, however power to wieght ratio went up. If you are in the same power but just swaping volts for amps, you do not improve this ratio.


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## Duncan (Dec 8, 2008)

Hi Bill

Motor size 
Big motors tend to be restricted in max RPM
so small is good!

BUT
You are going to be overloading your motor - running well above the continuous power rating.

A bigger motor will allow you to produce more power for longer than a small one will

I have an 11 inch - I expect to kill it by overspeed when I start playing on the track

If I had a 9 inch I would probably kill it by overload-overheat

In your shoes if I had an 8 inch I would try it - but not be surprised when I toasted it

Batteries
I am using Headway - my pack is 44series 2 parallel 16Ah
These are rated at 10C continuous and 15C burst
140v and 320A continuous - 480Amps burst
This should give 30Km range and weighs 44Kg

I think the Headway 8Ah have higher C ratings

CALB are for range - not for playing silly buggers on the track


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## JRP3 (Mar 7, 2008)

The new CALB CA's have tested to 12C. EV West did their Pikes Peak run with CALB's, I think the older SE series. The new ones are stiffer.


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## DIYguy (Sep 18, 2008)

Ya, all good advise. As motor size (diameter) goes up, safe rpm goes down (assuming no mods) and torque per amp goes up. Check the specs of some of the stock motors available from ADC and Warp. The difference between an 8" and 9" is not 50%. . more like 15%. . or maybe 20%.
My gut feel for your application would be a 9". . . or MAYBE even a very short stack 11". The 11" may sound a bit crazy, but it is worth to mention that not only diameter is relevant to torque. If you are shopping for fork lift motors, you can find different lengths also. The longer armature motors will develop higher torque also. I have a very short 11" motor with a high bar count (good for higher voltage) that I think would be an interesting combination with a Soliton1. I'm not looking to sell it. . . but something like that might be good.


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## Billzilla (Sep 16, 2012)

Thanks again gents.
I'm think that perhaps a 9" motor, the longest length I can find one, might be the way to go. 
What mods need to be done to keep them intact at high revs? And what sort of revs do people get out of them?


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