Yeah he probably should try a gearbox. He might get a better time with just 1 shift, maybe using 3rd & 4th. It would definitely be more fun!
Yeah he probably should try a gearbox. He might get a better time with just 1 shift, maybe using 3rd & 4th. It would definitely be more fun!
Very cool, reminds me of this, not so DIY but this thing looks fun.
OK reading that thread seriously makes my head hurt..... Is there a way to do something like this without an EE degree??
java230 wrote: OK reading that thread seriously makes my head hurt..... Is there a way to do something like this without an EE degree??
Yes, but doing a fast AC Motor/Controller based system for reasonable money right now is going to take learning a bit about the electrical and coding side. There are a few things in the works like being able to replace the "brain" portion of the motor controller from OEM stuff to make it easier to use in swaps but right now none of it is plug and play. Think of the early early days of megasquirt where a bunch of smart people are building cool stuff and talking to each other about it. Nothing like DIYAutotune has materialized up in that world yet.
There are multiple easier options for lower power AC systems or fast DC systems. The company that built the BMW a few posts up offers lots of cool stuff at fairly decent prices with the bulk of the learning curve taken care of.
In reply to java230:
Except that 850lbft at the wheels isn't that impressive. Even in 4th gear (1:1), a FDR of 3.5:1 would have the engine at 242lb-ft. And that's not all that special.
In reply to alfadriver:
That's true. Its a nicely sorted car overall though.
Im not up to date on all the electric car goodies these days....
alfadriver wrote: In reply to java230: Except that 850lbft at the wheels isn't that impressive. Even in 4th gear (1:1), a FDR of 3.5:1 would have the engine at 242lb-ft. And that's not all that special.
I think that's just typical dyno talk where they say 850lbft of torque measured at the wheels. The gearing calculation is already factored out. That meshes well with what you would expect with that motor/controller/battery setup.
MrJoshua wrote:alfadriver wrote: In reply to java230: Except that 850lbft at the wheels isn't that impressive. Even in 4th gear (1:1), a FDR of 3.5:1 would have the engine at 242lb-ft. And that's not all that special.I think that's just typical dyno talk where they say 850lbft of torque measured at the wheels. The gearing calculation is already factored out. That meshes well with what you would expect with that motor/controller/battery setup.
I saw the video, and the raw dyno measurement was 850 lb-ft. If that was 850 hp, that would be a very different answer, and a very impressive one at that. But 850lbft at the wheels is really, really easy. Heck, even a Miata is capable of doing that.
In reply to alfadriver:
It held the EV street class record at Pikes Peak for multiple years. One of those motors at 1000 amps should be roughly 300lbft of torque. They have two motors and a 3000 amp controller. If they are only pushing the torque of a turbo Miata in a 3800lb car none of that would be possible and they screwed up majorly on their build. So either they set final drive on the dynapack setup screen and it was calculating it out or something was seriously wrong with the car in that video.
In reply to MrJoshua:
Ok. Forgive me for not being impressed by 300lb-ft of torque. There are very many gas engines on the market that make more than that. I worked on one a decade ago.
Still, a Miata can make 800ft-lb at the wheels, very easily in first gear, and pretty darned easily in second.
The video clearly showed that the wheel torque was 800lb-ft. Which doesn't matter what the gear ratio is- it's just torque at the wheels. Doesn't even matter what the speed is.
I think you are missing the larger point- we should be talking in power, not torque, as power is the more important measure. Again, 800 hp would be very impressive at the wheels. 800lb-ft- not so much.
java230 wrote: Very cool, reminds me of this, not so DIY but this thing looks fun. https://www.youtube.com/embed/SVkJjt_Peg0
I just watched this again- this guy should have his enthusiast card taken away from him.
You don't need a dyno to know what 400kW is. It's 536 hp, if you can use it all. Apparently they can't, as it's only 342 hp at the wheels. It's not quite rocket science, but power is power- it's a matter of units to understand it.
Again, 850 lb-ft at the wheels is very, very far from a "Super Duty with a Tune". Like 1/3 of what a SD with a tune supposedly can really do at the wheels.
In reply to alfadriver:
Two Motors-300lbft Each, at 1000 Amps when they are running more like 1400 Amps each. None of that makes any sense to make 200-250lbft total at the motors if that displayed number includes the differential multiplication. If for some reason that is truly a raw number instead of a calculated one than it is not representative of the cars torque producing potential. The car should make somewhere close to 850lbft at the motors.
OK-Dug up published motor curves for WarP11's: One motor=135lbft at 450 Amps Doing the math means they need 1417 Amps per motor to produce 850lbft total at the motors. That is within the capabilities of the controller, within the short term tolerance of the motors, and up to around 600rpm or so within the ability of the battery.
I agree that power is a more meaningful metric, but they are of course highlighting its strengths which with brushed DC motors is torque. The CRX guy is going to be fun to watch because he isn't that far from catching the power output of 460lbs of DC motor with one 130lb AC motor.
In reply to MrJoshua:
Yea, but the measurement was a very ordinary 850lb-ft of torque and 342 hp at the wheels. All I'm trying to point out is that measure is very ordinary these days.
Not a comment about the CRX, just the BMW in that particular video, and the apparent lack of knowledge of what the numbers mean via the host.
And I am fully aware that there are more impressive EV's out there. I get it.
But that BMW is NOT one of them.
edit- BTW- raw current isn't that useful, either. 1400 A is very different for .1V, 1V, 10V, and 100V.
How do you rationalize your 250'ish torque with 342hp? With a redline below 5252 the torque would have to be higher than 342. If you use the 2364 RPM where it made its 340.4 max HP then you would get 756.25 lb-ft of torque. With over 750 lb-ft carried out to 2300 RPM I'm sticking with it making 850 lb ft at the motors at 600 RPM.
I'm not sure of your reason for dislike of that BMW. Even if you ignore our torque disagreement that car has 54 more horsepower than most readily available sporting OEM EV of its Era (the Tesla Roadster). It did it by using glorified forklift motors, a controller designed, coded, and built by a 2 employee company, and Chinese batteries designed more for energy storage than power delivery. It was assembled by a small EV company in California in a capable but outdated chassis. It then won the street EV class at Pikes Peak in 2012 where it set a record and held it the next year where the closest EV street car was a gutted and prepped Tesla model S that was 59 second slower. The EVWest M3 beat numbers of gas powered E36 M3's and was even 4th in the overall EV class despite many of the big names in Pikes Peak racing showing up that year in purpose built EV's.
Raw current is immensely useful for electric motors. It is your torque metric. Voltage changes the RPM where you can produce that torque, but the torque at a set number of amps stays fairly consistent.
In reply to MrJoshua:
WHEEL TORQUE. And gear ratios. Easy.
It's 850lb-ft WHEEL torque. Engine torque will be at least 1/3 of that, more likely lower.
It was 850lb-ft and 342hp at the wheel. Which is very ordinary.
Raw current is only really useful when you have voltage, so that you know what power you have to work with- which can be geared for different torque requirements.
It's just physics.
alfadriver wrote: In reply to MrJoshua: It's just physics.
On that we agree.
MrJoshua wrote:alfadriver wrote: In reply to MrJoshua: It's just physics.On that we agree.
So I'm confused by the confusion.
The video clearly pointed out that the data provided was wheel data. Not translated to engine data, or whatever, but wheel data. And since the car still has a rear axle, and the choices for that is limited to what the car can have fitted- it's likely to be in the 3.5:1 range.
And that gear increases the input torque to the axle by the ratio to get the output torque- and since output torque is wheel torque and input torque is from the engine- that means that 850/3.5 = 242lbft engine torque. That's peak torque. Peak power was 342 hp. And that range does make sense to me- if they happened to be at the same spot (which is rare) that would be at just under 7500 rpm. And that engine speed for an electric engine does not appear to be out of whack to me. Very reasonable.
What I do find odd is that they have a 400kw system that can only deliver 342hp to the wheels. That's a rather massive drop off- it's only 64% of the rated output of 400kw.
Still- 850lb-ft at the wheels and 342 hp is not extraordinary at all these days. Let alone for a performance car.
Cool car, huh?? 
alfadriver wrote: In reply to MrJoshua: Yea, but the measurement was a very ordinary 850lb-ft of torque and 342 hp at the wheels. All I'm trying to point out is that measure is very ordinary these days. Not a comment about the CRX, just the BMW in that particular video, and the apparent lack of knowledge of what the numbers mean via the host. And I am fully aware that there are more impressive EV's out there. I get it. But that BMW is NOT one of them. edit- BTW- raw current isn't that useful, either. 1400 A is very different for .1V, 1V, 10V, and 100V.
The CRX measured 2xx ft lb at the wheels in its dyno video. Dyno programmer corrects for gear ratio prior to the runs. So the numbers the screen spits out are accurate wheel numbers in a 1:1 situation, not being multiplied by gearing changes between engine output and wheel.
I don't have time for the video right now but that's how it works. When people quote wheel HP and torque numbers they're already corrected in the program prior to even making a pull.
MrJoshua wrote:alfadriver wrote: In reply to MrJoshua: It's just physics.On that we agree.
I'm not always the biggest Alfadriver fan, but he's right. The guy build a decently functioning piece, but he's measuring his output all wrong. I'm sure it performs well, but it seems pretty inefficient, and definitely isn't as good as he's touting. He made a good thing out of other things, but he doesn't understand gear ratios and physics.
In reply to alfadriver:
It redlines sub 5000 rpm not 7500. Torque falls off just after 2000 RPM. The motor dyno would have a fairly flat horizontal torque curve that then falls off after you run out of voltage to keep the controller at its amp limit. From there you basically have a dead short from the batteries to the motors and you get a fairly flat/horizontal hp curve until you stop the run. So this motor peaked at 850 ft lbs around 600rpm and then fell to 750 ish (im guessing at the current limit set in the controller). It held that until 2200 rpm and then started to fall off. So from 2200RPM until the end of the run in the low 4000RPM range they probably maintained around 300hp.
Efficiency-they lost voltage due to sag, a few percent at the controller, quite a few more at the motors, some in the driveline, etc.. Still better than the sub 40% ICE's can manage at peak efficiency.
In reply to Patrick:
I think you missed an x, it was 23xxx torque from reading the build thread.
Keep the discussion up. I'm learning. And if CRX dude comes out with his controller as a non DIY I'd be all Over it.
MrJoshua wrote: In reply to alfadriver: It redlines sub 5000 rpm not 7500. Torque falls off just after 2000 RPM. The motor dyno would have a fairly flat horizontal torque curve that then falls off after you run out of voltage to keep the controller at its amp limit. From there you basically have a dead short from the batteries to the motors and you get a fairly flat/horizontal hp curve until you stop the run. So this motor peaked at 850 ft lbs around 600rpm and then fell to 750 ish (im guessing at the current limit set in the controller). It held that until 2200 rpm and then started to fall off. So from 2200RPM until the end of the run in the low 4000RPM range they probably maintained around 300hp. Efficiency-they lost voltage due to sag, a few percent at the controller, quite a few more at the motors, some in the driveline, etc.. Still better than the sub 40% ICE's can manage at peak efficiency.
The wheel torque peaked at 850lb-ft, not the engine torque. At least that is what they are claiming.
And while I realize that 64% is better than ICE's, I was under the impression that EV systems are far more efficient than that.
Plus the presenter apparently has no idea that 400kW means something in HP, since they are both power.
In reply to alfadriver:
You accept their hp reading. Just do the math for tq at the RPM where it displayed peak hp.
java230 wrote: In reply to Patrick: I think you missed an x, it was 23xxx torque from reading the build thread. Keep the discussion up. I'm learning. And if CRX dude comes out with his controller as a non DIY I'd be all Over it.
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