# AC-15 Torque



## frodus (Apr 12, 2008)

How do you know the motor isn't being limited by the controller? 

How many amps are you running at 48V on the motor side?

battery side?

That graph only tells output HP and torque, but doesn't tell anything as far as motor amps, battery amps, battery voltage.


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## Formula_Jayhawk (Jul 19, 2011)

When the car was on the chassis dyno I watched the current display in the Curtis software. It was showing ~550 amps from 0-2000 RPMs. It drops off to ~200 Amps from that on up the RPM range. Unfortunately I don't have a way to record that data yet. I honestly haven't checked if the Curtis output is displaying motor amps or battery amps, and I don't have a way to check the current on my own yet.


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## Formula_Jayhawk (Jul 19, 2011)

Rereading the curtis manual says the current values I gave was the RMS current of the controller, taking into account all three phases. So i'm really not sure if that's battery side or motor side. I'll try to get an ammeter soon and measure both sides. I assume though that I have reached the current limit of the controller at ~500 Amps. The specs for torque output of an AC-15 on most websites state ~100 footpounds, and graphs show closer to 50 or 60 foot pounds. 
If voltage is independent from torque, why is my torque so low when pushing the same current that supposedly produces ~100 or ~50 foot pounds?

I was expecting something closer to the pdf on this site
http://www.electricmotorsport.com/store/ems_ev_parts_motors_ac15.php


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## frodus (Apr 12, 2008)

it's not 100ftlbs, it's been discussed over and over online, and none of the vendors will fix that info. It's closer to 60ftlbs at 550A.

The graph on the last page is correct, and it's for 550A.


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## Formula_Jayhawk (Jul 19, 2011)

So why does my graph not match their graph? Because my controller is limiting the current after ~2000 RPMs? Is this due to back-EMF, where raising the pack voltage would help allow more current further into the RPM range?


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## frodus (Apr 12, 2008)

I don't know. I think they need to redo their graphs and specs, because none of them make sense when you reference others. It'd be nice to get the excel spreadsheet.

higher voltage carries out the torque curve to a higher RPM, yes. 48V may not carry it out that far.

It looks like something is limiting the torque, or you're not loading the motor enough. What kind of dyno is it? Some don't work well with high torque at 0-RPM.


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## Formula_Jayhawk (Jul 19, 2011)

I looked for quite awhile to find dyno results for an HPEV setup, but i never came across one. Have you seen any others or just heard people's results? 

The dyno was a four-wheeler dyno. We aren't too confident it was tuned correctly because the engine we dynod showed incredibly high output by just changing the fuel mapping. I didn't think about it not dealing well with an initial high torque, that's a good point. 

Since the dyno we have changed quite a few things. Our battery packs had poorly designed terminals and the copper plate we used wasn't making much contact with the cell's terminals. Things got hot and the resistance in from a terminal through a contactor and fuse to the motor controller was way too high. It was welding the copper to the terminals. That's all fixed up now. We have also switched sprockets since the last dyno run, going from a 3.5 to 4.5 gear ratio. I'd like to take it to a good dyno and rerun all of the motor tuning tests to see if we can squeeze some more acceleration from it.

Even if the dyno isn't showing us the right results, the car really doesn't feel like it's accelerating with 60ft-lbs of torque. It's just plain slow to accelerate off the line. Our S car (with just a 600cc CBR rr engine) only makes 50 ft-lbs or so and it accelerates like a bat out of hell. I'm sure some of that's due to having a transmission though. 

I'm willing to accept that the motor may not be fast enough for what we want, but I dont want to throw money at a new motor until I'm convinced that I'm getting as much performance from it as I can, ya know?

Thanks for all the answers so far!


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## Dennis (Feb 25, 2008)

Sounds to me like the controller is dynamically changing the volts/hertz ratio in an effort to keep the battery voltage at the minimum limit that you have it set for. Maybe you fixed the severe voltage sag issue with the terminal repair you did which in turn should allow the controller to keep the volts/hertz ratio constant since the voltage sag cause by battery amp draw will not be bad now that you corrected the terminal issue. 

Also be sure to set the low voltage limit to about 38 volts to help account for voltage sag and possibly prevent the controller from limiting output current to keep the voltage within the minimum limit; and set the throttle up rate to maximum which makes the current slew rate very high, thereby giving you an abrupt take off rather than a smooth one.


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## major (Apr 4, 2008)

Formula_Jayhawk said:


> My question: Why is the car slow, especially off the line and what can I do to fix it? Is the voltage or current too low? Is the motor undersized? Is the motor not programmed/tuned correctly?


Hi Jay,

I cant say definitely, but I would look at the drive ratio and parameter settings in the controller. I recently used the AC15 in a go kart at 48V and did not have the problems. Weight was less no doubt. Chain ratio about the same, but wheel diameter a lot smaller. The AC15 should be capable if set up correctly and geared right 

Regards,

major


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## Formula_Jayhawk (Jul 19, 2011)

My accel rate is already set to 0.1. I'll check the undervoltage settings, but i think they're already set pretty low. Since I've watched current sit at ~550 Amps from 0 to ~2000 RPMs, don't I already have as much torque as i'm going to get in that range? I mean, no matter how much I change the settings the acceleration isn't going to change considerably since I can't push more current?

We've already played around with the sprockets and drive ratio. We've seen the best performance at 4.5:1. Maybe I need to post a video of it accelerating, maybe my hopes are too high. It gets going, it's just nowhere near close to smoking the tires. 

Has anyone used a non curtis controller for an HPEV motor? I'm looking at the curtis model that can push 650 amps, and 210 continuous (1238-56), but I'd love to find something that could push considerably more. It's a race environment so I'm ok with pushing the motor to its limits.


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## major (Apr 4, 2008)

Formula_Jayhawk said:


> Since I've watched current sit at ~550 Amps from 0 to ~2000 RPMs, don't I already have as much torque as i'm going to get in that range?


Hi Jay,

Yep, if you're seeing 550A, that's maximum torque from this package unless you've somehow screwed up the motor tuning, which isn't likely.



> I'm looking at the curtis model that can push 650 amps, and 210 continuous (1238-56), but I'd love to find something that could push considerably more. It's a race environment so I'm ok with pushing the motor to its limits.


The ACIM is not like the DC motor. More current isn't more torque after a point, called breakdown torque, or BDT. This value is independent of the controller or voltage or frequency. I don't know what the value is for that HPEV motor, but it must be greater than torque at 650A. But I suspect that is getting close to the limit. And then there is the whole thing about current and heat 

What was the GVW when you were running electric only?

Regards,

major


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## Formula_Jayhawk (Jul 19, 2011)

major said:


> Hi Jay,
> 
> Yep, if you're seeing 550A, that's maximum torque from this package unless you've somehow screwed up the motor tuning, which isn't likely.


I did change the slip gain value. When we had it on our chassis dyno I saw better acceleration times for 0-3000rpms with a slipgain of 2.72 instead of 3.30. I'm questioning that now though, because our chassis dyno didn't apply any load. I'll try changing that back tonight. I also wonder about the field weakening setting. It warns about overheating in the manual, so i have it set to 75 or so. Could that be limiting torque?



major said:


> I don't know what the value is for that HPEV motor, but it must be greater than torque at 650A. But I suspect that is getting close to the limit. And then there is the whole thing about current and heat


So you're saying you think increasing current up to at least 650 will still be beneficial? I'm prepared to deal with heat. We can water cool the controller if necessary. And if we can get an extra 20 or 30 pounds of torque, we could probably make a water jacket for the motor.



major said:


> What was the GVW when you were running electric only?


After we removed the engine (as pictured in my first post) the car weighs 460 pounds. It was about 560 pounds with the engine and without wings, so dropping the engine was a nice 120 pound weight loss.

Thanks for the help Major!


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## frodus (Apr 12, 2008)

so the dyno didn't load the motor?

the motor only puts out what it's asked.


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## Formula_Jayhawk (Jul 19, 2011)

Sorry, this gets confusing. We have a chassis dyno in our shop. Right now it just rolls. There aren't any load cells hooked up to it or a good way to put load on it. The graph I gave came from a four wheeler dyno that donated their time. I'm sure it applied load, but like you said, i'm not sure it was able to properly apply enough load.

I've been using our dyno in the shop to minimize accel times. I figured, maybe incorrectly, that the parameters would carry over to the track. So I'm using the four wheeler dyno to get actual numbers for torque (~25ftlbs) and our dyno to tune the motor without gettin any torque figures. Maybe since there wasn't a load the slipgain is now significantly messed up.


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## frodus (Apr 12, 2008)

well, what kind of speeds and accelerations are you expecting? 

the AC15 is a good motor for a peppy motorcycle, but for heavier vehicles + rider, it seems to be a little small for the task.

What are the project requirements? are you limited to voltage?


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## Formula_Jayhawk (Jul 19, 2011)

Our max speed is probably under 60mph, usually staying around 45 or so. Preferably the acceleration is as fast as possible. The vehicle only weighs 460 pounds before driver, but I guess that's on the heavier side for a small motorcycle. 

We are limited to 300V. There's no power or current limit. Would an AC-20 be a significant improvement, or maybe the 1238-56 controller? We are looking to add front hub motors before we redesign the rear completely, but the adviser could probably be persuaded otherwise.


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## frodus (Apr 12, 2008)

the AC20 is more torque than the ac15, but if you want more power, torque, I'd opt for an AC31 or something along those lines. These motors are more for golf carts and motorcycles, although people HAVE used them on race bikes. 

Not sure if the dyno can measure high torque at a low RPM.

What rear wheel ftlbs of torque are you measuring? wheel diameter?


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## Formula_Jayhawk (Jul 19, 2011)

The wheel diameter is 13" and the tire diameter is 20". Since we ran the whole car on the chassis dyno I assumed the graph showed torque at the wheels. Someone may have given him a ratio to convert the wheel torque to torque at the "crank". In fact, they must have because 46 foot pounds of torque at the wheel probably wouldn't even move the thing. So i guess my answer for torque at the wheels is, I don't know. 

The only torque data I have is what's shown in the graph. 

I don't see an AC-31 from thunderstruck. Is it the same size as an AC-35? It gets frustrating to pick motors when their torque figures are so well known to be way off. Going by what's stated online, the AC-15 has a pretty good torque to weight ratio, but the AC-35 weighs 85 pounds and makes the same torque.


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## frodus (Apr 12, 2008)

HPEVS's torque figures aren't off, the distributors numbers are. Not sure where they're getting their peak numbers.

Just ask me direct (pm or email) and I can try to get the info. I work with them a lot. The AC31 is an older model I guess, the AC35 is the size of motor I'm talking about.


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## drgrieve (Apr 14, 2011)

Find the flattest bit of track you can and do some acceleration timings for every 10 mph up to your max. From that and the total weight you can determine how much kW you are actually using for each 10 mph acceleration. This might help to diagnose where the issue is.


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## major (Apr 4, 2008)

Formula_Jayhawk said:


> Our max speed is probably under 60mph, usually staying around 45 or so. Preferably the acceleration is as fast as possible. The vehicle only weighs 460 pounds before driver, but I guess that's on the heavier side for a small motorcycle.


Hi Jay,

That's not unusually heavy compared to a MC conversion. A lot of EV bikes get heavy with batteries.

I'd not buy new equipment until you figure your problem. I know the AC15 package works on 48V. I think you should go back to factory parameters and increase the drive ratio, maybe up to double what you have. Then get some solid data 

major


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## Formula_Jayhawk (Jul 19, 2011)

I think you're right Major. I want to figure out exactly why it's not performing like we expected before we spend too much money. I contacted Bill and he said the "motor type" parameter on the 1238 should be set to "2" for a AC-15. If I revert to default settings on the controller, and set the motor type to 2, should that be enough to start testing, or should I run through the whole motor tuning setup again?

Right now there isn't any clearance left to fit a bigger sprocket, and the sprocket on the motor is as small as we can find (10 or 11 tooth). Maybe changing the settings will fix it, but right it seems like gearing it more will bring down our top end power even further. 

I'll see what work I can get done on the car tonight.


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## frodus (Apr 12, 2008)

Good luck, keep us posted with things and let us know if you need anything.


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## Formula_Jayhawk (Jul 19, 2011)

Well I got it on the dyno but something strange is going on. I plugged in my computer to the controller and started running the car while changing my field weakening rate and base speed. For some reason though, even with no load applied, the motor doesn't want to spin above 1300 to 1500 rpms. Its the same in torque mode and speed mode, with the RPM limit set to 7500 RPMs. I'll give full throttle and it will accelerate up to 1300 and then climb around 1 rpm per second. The capacitor voltage is at 48.2 V. The "Battery current" will climb up to 400 Amps and then stay there while it's turning at 1300 rpms. If I change some settings around sometimes it will climb up to 1500 and then top out.

I reset the "motor parameter" to 2 and looked at one of my older .par files, trying to reset every parameter individually. I don't see anything different from a month ago at all. 

Is there a way to set the controller back to default? 

I'm hoping I can go in tonight and see the obvious setting I missed and fix everything.


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## frodus (Apr 12, 2008)

Maybe ask HPEVS for the par file for the AC15.


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## major (Apr 4, 2008)

Formula_Jayhawk said:


> Well I got it on the dyno but something strange is going on. I plugged in my computer to the controller and started running the car while changing my field weakening rate and base speed.


Hi hawk,

Something sounds fishy. I do not think you can change those parameters while running. Maybe, IIRC, have to turn the unit off and then back on for parameters changes to set. And then speed control is locked out of the AC15 package from HPEVS as I understand it.

Where did you get your controller? Who set the initial software (or firmware)? It sounds like you may have to send it back to the vendor to get the program right.

Regards,

major

ps...I wonder why crusin isn't telling us how to fix this problem


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## Formula_Jayhawk (Jul 19, 2011)

I keep reading that torque is directly related to current. That makes sense, the amount of magnetic flux is directly related to current, which is directly related to torque. So if torque is only dependent on current, why do we care what voltage we run at? Well Power is v*i, or Motor current times motor voltage times some efficiency factor all divided by a constant. To quote someone from the elmoto thread:


> 1) HP = torque * RPM / 5252
> 
> or
> 
> ...


Solving for torque gives
torque = (I_motor * V_motor * efficiency * 7 ) / RPM

If you increase the voltage you decrease the current, but when you're running a motor controller that is always pushing max current up to a limit (550A), the current won't decrease will it? 

What am I missing? Increasing the voltage absolutely has to increase the power. Power is directly related to torque. So it seems increasing voltage has to increase torque.


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## Formula_Jayhawk (Jul 19, 2011)

major said:


> Hi hawk,
> 
> Something sounds fishy. I do not think you can change those parameters while running. Maybe, IIRC, have to turn the unit off and then back on for parameters changes to set. And then speed control is locked out of the AC15 package from HPEVS as I understand it.
> 
> ...


I know that before things went fishy I was able to change most values through the software without restarting. Unless it threw a parameter fault. Changing the max speed under Torque mode would definitely limit the motor speed immediately. I was able to limit it to 750 RPMs last night, but after bumping the limit up to 7500, the motor would still sit around 1500. 

What do you mean by speed control is locked out? When I'm in the programming software there is an option to run it as OEM, which is the default option. I believe I have access to change everything. 

Thunderstruck programmed the controller initially. I might ask them and/or HPEVs for the par file if i don't fix things tonight. 

I think I upset cruisin. I asked him for help programming the controller via PM. He just kept telling me to buy an AC-35 and to make sure I was in torque mode and using a 3 wire pot. After he repeatedly completely ignored my questions to tell me to buy an AC-35 I got fed up and told him if I do buy an AC-35 it will be from thunderstruck because they answer my questions. I probably shouldn't have upset someone who is such a perfect candidate for helping me in this case.


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## frodus (Apr 12, 2008)

because the higher voltage pulls the torque out to a higher RPM, and with higher voltage you can actually get that higher RPM.

So if you have higher RPM at the same torque as 100RPM, you get higher HP than you would if you ran at lower voltage.


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## frodus (Apr 12, 2008)

Formula_Jayhawk said:


> I think I upset cruisin. I asked him for help programming the controller via PM. He just kept telling me to buy an AC-35 and to make sure I was in torque mode and using a 3 wire pot. After he repeatedly completely ignored my questions to tell me to buy an AC-35 I got fed up and told him if I do buy an AC-35 it will be from thunderstruck because they answer my questions. I probably shouldn't have upset someone who is such a perfect candidate for helping me in this case.


Sometimes he's just overeager to sell you a new system, rather than help solve the problem. True, the AC35 would solve the problem by eliminating the AC15 system altogether, but it doesn't FIX anything, it ignores it. Don't worry about it, Just ask Brian at Thunderstruck, Todd at Electric Motorsport or Brian at HPEVS.

Now, I don't completely disagree with Cruisin on upgrading the motor, but it doesn't solve your issues. 

I don't think you're loading the motor right, you should really have a motor dyno, or something made for low RPM and high torque like an electric motor.


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## Formula_Jayhawk (Jul 19, 2011)

Perfect. That's what I had suspected. The higher voltage just allows higher RPMs which result in higher HP. I don't feel like that's talked about as often. I probably just missed that somehow. 
We're looking at new batteries because ours are 100 Ah and way oversize for racing. The new Haiyin batteries look pretty good. We could lose quite a bit of weight and double our voltage if we ran 30Ah. Then we could gear it even higher since torque would continue further down the RPM range.


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## frodus (Apr 12, 2008)

well, it increases RPM, but it also lets the torque at 550A ride out further on the curve. For example, if you have one motor that runs 48V and at 550A it does 50ftlbs up to 1500RPM, then maybe at 72V, 550A, it pulls that 50ftlbs out to 2250rpm before starting to decrease.


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## Formula_Jayhawk (Jul 19, 2011)

frodus said:


> well, it increases RPM, but it also lets the torque at 550A ride out further on the curve. For example, if you have one motor that runs 48V and at 550A it does 50ftlbs up to 1500RPM, then maybe at 72V, 550A, it pulls that 50ftlbs out to 2250rpm before starting to decrease.


Right. That's exactly how I understood your first comment. I just didn't restate it very well. 



frodus said:


> Now, I don't completely disagree with Cruisin on upgrading the motor, but it doesn't solve your issues.


Exactly. I'd like to figure out what's up with my motor now before I upgrade. Plus the 40 pound weight isn't something we really want to add to a 450 pound racecar if we can avoid it.



frodus said:


> I don't think you're loading the motor right, you should really have a motor dyno, or something made for low RPM and high torque like an electric motor.


I'll see if i can post some videos of acceleration. In the end I don't care what the numbers come out to. I just need the car to accelerate better. If some of you guys can watch the acceleration off the line and it looks terribly slow, or about right, i'll have a better idea whether we need to jump up to an AC35.


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## cruisin (Jun 3, 2009)

Formula_Jayhawk said:


> I know that before things went fishy I was able to change most values through the software without restarting. Unless it threw a parameter fault. Changing the max speed under Torque mode would definitely limit the motor speed immediately. I was able to limit it to 750 RPMs last night, but after bumping the limit up to 7500, the motor would still sit around 1500.
> 
> What do you mean by speed control is locked out? When I'm in the programming software there is an option to run it as OEM, which is the default option. I believe I have access to change everything.
> 
> ...


You are right, burn bridges and you cant cross the river. You said Thunderstruck is your favorite, why are you NOT asking them to help you with the problem instead of repeat posting here? If you bought it there, they have a responsibility to help you if it is a realistic problem. Your next post without exception should be what they did for you and the results there of. We will be waiting for that posting. Waiting!


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## Formula_Jayhawk (Jul 19, 2011)

I contacted thunderstruck 15 minutes ago. Brian promptly replied asking for my .par file. You might remember my email to you 

"Would it be beneficial to email you the settings file I downloaded off the curtis?"

to which you replied 
"We sell a lot of AC motors to the DIY forum members, but mostly the AC-35 and AC-50. Everybody now wants the 650a controller as well. If it were me I would use the AC-35 and the 650a controller with our water cooling on the controller. If possible I would also up the voltage to at least 96v. Use a 3 wire pot with parameter 2 and torque mode. I could help you with a lot of other recommendations as well."

I think thunderstruck has already helped me more than you did. I didn't ask for pricing on new parts, or for recommendations on how to build a new car. I just wanted help fixing mine. I came here first because I've ask thunderstruck hundreds of questions and I figured they could use a break. They have replied within minutes on a Sunday at 8PM. They are awesome, no doubt about that. 

I'm not asking for your help anymore. Please don't turn this thread into a flame war.


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## major (Apr 4, 2008)

Formula_Jayhawk said:


> What do you mean by speed control is locked out? When I'm in the programming software there is an option to run it as OEM, which is the default option. I believe I have access to change everything.
> 
> Thunderstruck programmed the controller initially. I might ask them and/or HPEVs for the par file if i don't fix things tonight.
> 
> I think I upset cruisin. I asked him for help programming the controller via PM. He just kept telling me to buy an AC-35 and to make sure I was in torque mode and using a 3 wire pot. After he repeatedly completely ignored my questions to tell me to buy an AC-35 I got fed up and told him if I do buy an AC-35 it will be from thunderstruck because they answer my questions. I probably shouldn't have upset someone who is such a perfect candidate for helping me in this case.


Hi Jay,

With the AC15 system I got from Thunderstruck, I could not get it to accept the change to speed control. Thunderstruck was very helpful and explained that the system is "tuned and programmed (as in firmware)" by HPEVS for basically motorcycles and therefore cannot be put into speed control. You can change the parameter, but as soon as you navigate elsewhere and return you'll see it has reverted back to torque control.

I still say that the AC15 at 48V will give you decent performance on that size vehicle up to 40 or 50 if properly tuned and geared. Maybe not breakneck accelerations, but much better than you describe.

{comment deleted}

But I do agree that you should get back to the starting point by using Thunderstruck 

Regards,

major


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## cruisin (Jun 3, 2009)

Formula_Jayhawk said:


> I contacted thunderstruck 15 minutes ago. Brian promptly replied asking for my .par file. You might remember my email to you
> 
> "Would it be beneficial to email you the settings file I downloaded off the curtis?"
> 
> ...


 I guess you wanted the last word. Thread should be closed. Do what Thunderstruck tells you to do since they are your dealer. You say they have helped you, quit your belly aching.


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## frodus (Apr 12, 2008)

cruisin said:


> burn bridges and you cant cross the river.


Exactly. Burning bridges really hurts *you* in the end 

FJ,

I'm always here to help (along with others like Major). Brian Hall is a great guy and should be able to help. I own of three of their systems (and sell them) and am a paid consultant for Manzanita Micro and Elithion, Inc if you need anything else for the vehicle.

Good luck!


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## EVfun (Mar 14, 2010)

cruisin said:


> Thread should be closed.


I don't see any reason this thread should be closed. FJ is still working on a suitable solution.


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## Formula_Jayhawk (Jul 19, 2011)

I wasn't thinking too clearly last night. The only new factor in the equation was the dyno. We recently setup a waterbrake on the dyno to apply some load for further testing. I incorrectly assumed that with no water flowing into the waterbrake that it wouldn't apply a load. And the way the car stopped so abruptly at 1500 rpms I assumed it was a controller setting. Well I unbolted the waterbrake and everything spins up again. Then I realized although the inlet didn't have water flowing in, the outlet was still closed so there was still water in the waterbrake. 

I'm still going to send my .par file to brian to take a look at. I realized my fw base speed has probably never been set correctly. It has been set at 5000 rpms. And i'm not sure what min field current is, but it's set to 0. I'll let you guys know once I get some answers back from brian. 





major said:


> I still say that the AC15 at 48V will give you decent performance on that size vehicle up to 40 or 50 if properly tuned and geared. Maybe not breakneck accelerations, but much better than you describe.



I hope so. We will probably end up increasing our pack voltage soon, so if the results aren't good enough we can see how it performs at a higher voltage . A long term goal for the car is to add some sort of front wheel motors. I think running at 72 or 96 V would be better for most other motors we might add. And with our current kokam setup we can only discharge 500A continuous, so 3 motors will probably need different batteries anyways.


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## Dennis (Feb 25, 2008)

> Perfect. That's what I had suspected. The higher voltage just allows higher RPMs which result in higher HP. I don't feel like that's talked about as often. I probably just missed that somehow.
> We're looking at new batteries because ours are 100 Ah and way oversize for racing. The new Haiyin batteries look pretty good. We could lose quite a bit of weight and double our voltage if we ran 30Ah. Then we could gear it even higher since torque would continue further down the RPM range.


Unfortunately, this is not the case with AC induction motors. Frequency is what determines the speed of AC motors, but you need the voltage to increase such that you over come inductive reactance which changes with frequency so that you maintain torque. If just the frequency increases then you would get more speed on the motor shaft, but as soon as you load it down it will drop significantly in speed due to lack of torque and thus this is why you have what is called volts per hertz ratio. So for AC motors it is frequency, amps, and volts that you must change where as DC motors all you need to deal with is volts for speed and amps for torque.


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## jkf (Feb 22, 2011)

FJ, I just finished restoring/converting a 1980 Kawasaki KZ750E with 72V of Li batteries and an AC-15 + Curtis 1238 controller. In place of dynamometer measurements I simply performed roll-down tests to determine the total drag plus rolling resistance for the bike. Now whenever I want to determine my torque I record a run with a GPS that records a track file and, using the drag+rolling resistance data along with the current track’s elevation and acceleration data, derive the torque with some basic physics. 
A search will give you several discussions of roll-down testing. I generate a GPS track file (a measurement every second) while the vehicle is coasting down from its top speed. I kill the traction system (drop Ksi) to avoid regen. The deceleration, from numerical differentiations of the position data, gives you the forces slowing down the vehicle. Correct for hills with the track elevation data. I don’t bother separating the retarding forces into drag and rolling resistance since I always use the sum. I just fit a curve to the data.
I have not tuned the Curtis so I can’t tell you what the AC-15 is capable of with my 460-pound bike. HPEV does limit the low-rpm torque to keep their typical customers out of trouble. The Curtis software is just too expensive for my single unit.
Good luck and Rock Chalk from a fellow Jayhawk.


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## Formula_Jayhawk (Jul 19, 2011)

jkf said:


> FJ, I just finished restoring/converting a 1980 Kawasaki KZ750E with 72V of Li batteries and an AC-15 + Curtis 1238 controller. In place of dynamometer measurements I simply performed roll-down tests to determine the total drag plus rolling resistance for the bike. Now whenever I want to determine my torque I record a run with a GPS that records a track file and, using the drag+rolling resistance data along with the current track’s elevation and acceleration data, derive the torque with some basic physics.
> A search will give you several discussions of roll-down testing. I generate a GPS track file (a measurement every second) while the vehicle is coasting down from its top speed. I kill the traction system (drop Ksi) to avoid regen. The deceleration, from numerical differentiations of the position data, gives you the forces slowing down the vehicle. Correct for hills with the track elevation data. I don’t bother separating the retarding forces into drag and rolling resistance since I always use the sum. I just fit a curve to the data.
> I have not tuned the Curtis so I can’t tell you what the AC-15 is capable of with my 460-pound bike. HPEV does limit the low-rpm torque to keep their typical customers out of trouble. The Curtis software is just too expensive for my single unit.
> Good luck and Rock Chalk from a fellow Jayhawk.


jkf,
Thanks for the idea. Our adviser actually recommended we do this awhile ago. Instead of GPS data though, we should be able to do all the tests on our dyno as long as we keep the load the same. The curtis software has a Time to Speed function, so we should be able to record acceleration times fairly accurately. 

Do you know what kind of acceleration times you were getting for low speed acceleration, like 0-10mph or 0-20mph? That's where we feel it's the slowest.

I got some values back from Brian the other day. I'll go to the shop tonight and try them out.

And ROCK CHALK!


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## frodus (Apr 12, 2008)

Here's a question for ya......

have you checked the encoder to make sure it's on tight? Almost every one I've seen out there comes loose at some point. You should notch the motor shaft and make sure the set screw is loctited.


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## jkf (Feb 22, 2011)

I'll make some new runs this weekend and get back to you.

And do pay attention to Travis--my encoder failed twice due to a loose encoder disk grinding the reader. I since found that a bead of RTV keeps it fixed to the shaft. The encoder is located behind the fan after you remove the dust cover.
Good luck.


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## Formula_Jayhawk (Jul 19, 2011)

Dennis said:


> Unfortunately, this is not the case with AC induction motors. Frequency is what determines the speed of AC motors, but you need the voltage to increase such that you over come inductive reactance which changes with frequency so that you maintain torque. If just the frequency increases then you would get more speed on the motor shaft, but as soon as you load it down it will drop significantly in speed due to lack of torque and thus this is why you have what is called volts per hertz ratio. So for AC motors it is frequency, amps, and volts that you must change where as DC motors all you need to deal with is volts for speed and amps for torque.


Thanks Dennis! That makes sense. Essentially it comes back to jwL or 2*pi*f*L, and we definitely have some inductance L. I guess the frequency in this case is the rotor frequency. The inductive reactance is low when rotor frequency is low and increases as motor RPM goes up, making jwL go up. Since the frequency has to increase, the inductive reactance has to increase. Current is I=v/2pi*f. So if i increase my voltage the current can increase without having to reduce the frequency.

Essentially it means the same thing. If I increase voltage, I can extend the max current aka torque further down the RPM range.


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## Formula_Jayhawk (Jul 19, 2011)

Awesome, thanks!

I'll definite check the encoder now. I didn't realize that was an issue. That's something we probably wouldn't have caught for awhile if it did come loose, so thanks for bringing it up!


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## frodus (Apr 12, 2008)

Yeah, it's one of the last things you'd think of. Several TTXGP teams had this issue last year. I had this issue once. 

I did this:
Take the cover off, take the fan off, take the cover of the encoder off. Remove the set screw of the encoder. Put some black greese pen, or ink on it, put it back in and align to the shaft. Remove again. Then file a little "notch" in the shaft for the set screw. Reassemble, but put loctite on the set screw, or put another set screw behind it.


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## jkf (Feb 22, 2011)

Formula Jayhawk,
I made a series of acceleration and roll down tests this weekend and just finished working the data.
My 460-pound motorcycle is powered by an AC-15 + Curtis 1238 fed by ~72V from 21 LiFePO4 Thundersky 60AHr cells. I have a 5:1 chain ratio and a 25-inch-diameter rear tire. I am running with the original Curtis parameters loaded by HPEV.
Here is what I found:
1. I achieve the motor’s peak torque above 1800 rpm, 55-60 ft-lb which is within 10% of the 72V torque curve published by HPEV. The motor torque then rolls off around 3300 rpm, just like the published curve. It takes me about 6-7 seconds to hit the peak. 
2.	The starting torque from 0 to about 1500 RPM is a curve that increases fairly linearly over time from 0. It then gradually curves up to the peak torque, around 1800 rpm.
3.	The motor current, as best as I can tell from the Curtis Spyglass display, is increasing along that same trend as expected since the controller is managing the torque.
4.	It is not a pure time delay. I tried accelerating in time steps looking for more torque over time. The full-throttle torque slopes are the same, just shifted in time.
5.	I also tried building up current using the brake to hold the bike back while I cranked up some (stall) current. Again, once I let go, the torque curve vs. rpm was exactly the same. 
6.	I made 10 runs and the torque curves plotted right on top of each other. The controller is very consistent.
Have you asked Bill at HPEV about which parameters manage that start-up torque curve? I have found him and the company very accommodating and a pleasure to work with.
Good luck,
--kevin fullerton


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## Formula_Jayhawk (Jul 19, 2011)

jkf said:


> Formula Jayhawk,
> I made a series of acceleration and roll down tests this weekend and just finished working the data.
> My 460-pound motorcycle is powered by an AC-15 + Curtis 1238 fed by ~72V from 21 LiFePO4 Thundersky 60AHr cells. I have a 5:1 chain ratio and a 25-inch-diameter rear tire. I am running with the original Curtis parameters loaded by HPEV.
> Here is what I found:
> ...


Kevin,
Thanks so much for the data! That's exactly what i've been looking for. I've been pretty busy the last week with work and job hunting but we should be taking the car to an autocross event this weekend so hopefully I can look into some things.

We're looking into getting new batteries to increase our voltage and current capability. I noticed under full load that the battery voltage sags from 48V to 38V. Also while talking to Brian at Thunderstruck he mentioned his 48V system on a 450 pound motorcycle with 20" tires (all identical to our setup) ran pretty well,but they're using a 7:1 ratio, where we're only using 4.45:1.

I'll give an update once we make some more progress. Thanks everyone!


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## cruisin (Jun 3, 2009)

Formula_Jayhawk said:


> Kevin,
> Thanks so much for the data! That's exactly what i've been looking for. I've been pretty busy the last week with work and job hunting but we should be taking the car to an autocross event this weekend so hopefully I can look into some things.
> 
> We're looking into getting new batteries to increase our voltage and current capability. I noticed under full load that the battery voltage sags from 48V to 38V. Also while talking to Brian at Thunderstruck he mentioned his 48V system on a 450 pound motorcycle with 20" tires (all identical to our setup) ran pretty well,but they're using a 7:1 ratio, where we're only using 4.45:1.
> ...


When programming the 1238, you may want to set the Response Accel Rate to .1 in the Torque Mode for max low RPM amps to the motor. I dont believe that was the factory default.


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## jkf (Feb 22, 2011)

Cruisin,
any thoughts on how to set the Curtis parameters without a several hundred dollar investment for their handheld programmer or their software? I can make cables but I never read a description of the Curtis protocols. 
I hope the Formula Jayhawk folks are in torque mode. Could explain how they change a parameter but nothing changes.


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## cruisin (Jun 3, 2009)

jkf said:


> Cruisin,
> any thoughts on how to set the Curtis parameters without a several hundred dollar investment for their handheld programmer or their software? I can make cables but I never read a description of the Curtis protocols.
> I hope the Formula Jayhawk folks are in torque mode. Could explain how they change a parameter but nothing changes.


I can help you, but it would be very difficult to do it on the forum and I am forbidden to provide you with my email. Why dont you PM me with your questions, where you are at and your email so I can help you.


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