Which to me confirms that it's software dictating that. (not that this is being disputed)
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P3D horsepower?
- Thread starter 3LE-TRK
- Start date
It's software controlling most every aspect of the car (appart from the suspension). This applies both to the AWD and the P.
It's not like the P is completely un-corked, as in it lets let the possible energy to the motors in an uncontrolled way. (Not that it's actually possible to do this anyway)
Any modern car with an ECU will be running a map which restricts the performance of the car to a range which is within their safe for warrantee range.
Tesla is only different, in that they can change the map without having to plug in a diagnostic computer to do so.
If you look at an ICE car with multiple gears, and graph that across it's entire speed range, it will approximate that curve, the more the gears the closer it will be.
That would be the curve an ICE car designer will be trying to emulate. With a CVT, that's exactly what you would see.
So from a usability, pure design perspective, the AWD curve is 'better' than the P. Unless you are looking for ultimate performance, when you might be willing to trade off efficiency/drivability for raw performance.
Same happens in ICE cars/motorbikes different 'tunes' for different applications of the same power plant.
SammichLover
Banned
To have it spit out true at-the-wheel numbers you'd set it as lossless. The loss at 0.0% or the efficiency at 100.0%, whichever way the software wants that entered. I couldn't find where they gave the assumption, and they otherwise seemed to know what they were doing, so would know that that whatever assumption (guess) they used would be pertinent information to provide since so if they give any I'm assuming they didn't use any.
That's why I was asking if anyone could find a wheel-to-craftshaft fudge factor.
P.S. There is something of a way to estimate what kind of losses would be had. If you can get into maintenance mode to read the current from the battery to the motor and use reasonable fudge estimates of the power inverter and motor loses you'd get a decent idea of the crankshaft to wheel loses. But they are going to be small, the system is so simple and relatively small/light compared to most vehicles of this power.
WilliamG
Hinge Fanatic
Oh come on. Look, nobody is denying that it's possible Tesla is using rollout for some models and not for others. But you said Tesla EXPLICITLY said they are. Who cares about the P85D? That car hasn't been made for years. And as someone said (which I assume is true), that Tesla got sued for posting HP/TQ numbers and no longer include them. Maybe they no longer include rollout? All I'm saying is if you're not providing the full evidence of your claim. Historically? Yes. Now? No. Does that mean Tesla isn't ~"misleading"~ customers? No. But I need to see more data from current Tesla offerings.
AlanSubie4Life
Efficiency Obsessed Member
Yes, and it does not seem like they set it as lossless - or their dyno needs to be recalibrated. Otherwise, the data does not make sense, based on the real-world results, anyway.
I agree that to figure out the total efficiency fudge factor you could look at the kW from the battery during the run. But as you say, you still wouldn't know the output power & torque at the motor "crank" itself (which would be traditional). Just kind of have to estimate.
It doesn't really matter of course because all that matters (for this discussion) is what the actual 0-60 measured time is. Quoting HP/torque at the "crank" is not something Tesla would want to highlight because they get better drivetrain efficiency than ICE so those numbers make them look worse than they actually are, if everyone else is using their crank numbers for the member-measuring contest. Because Tesla's don't have to be as high to get the same acceleration. Very high motion of the ocean for Tesla, I guess.
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SammichLover
Banned
Dyno rollers trend to have extraordinary grip, to the point they'll eat tires. Plus no wind resistance, as you mention (although that's relatively low at these speeds).
AlanSubie4Life
Efficiency Obsessed Member
Wind resistance covered above - it's fantastically small for speeds below 40mph (200Wh/mi is 100 pounds of force, and 200Wh/mi drag is about what you get at 70mph - so say a maximum of 30 pounds at 40mph). We could just discuss the acceleration results at 10mph if you prefer, though (though the dyno data is invalid there, but I suppose we can just extrapolate a flat torque line from the dyno curve since we know that's how it actually works).
Grip: There's no evidence that acceleration times are limited by grip in the real world. Otherwise adding grippy tires would help. But it doesn't.
Since there really isn't a separate motor/gearbox/final drive, it's essentially direct drive as any gearing is internal to the drive unit, it really doesn't make sense to talk about at the crank, anyhow.
There is also more than one, with different designs, and they may not both have the same great ratio in theory. They also don't have the same output and curves at each end.
So really doesn't make sense to guestimate anything until it reaches the wheel hub. Better to look at at the wheel(s) and assume 100percent efficiency, unless you are Tesla and designing a new motor.
BUT that doesn't compare well to an ICE car, which build in a 15 to 20 percent loss.
But when you are up the numbers for your motors at the output shaft, you get sued!!!
AlanSubie4Life
Efficiency Obsessed Member
Absolutely. Unfortunately doesn't look like that is what the dyno plots are showing - all the evidence suggests they are building in a loss factor. And obviously they have been translated by the wheel diameter and drive ratio as well.
As far as I have heard the front and rear drive ratios on the Model 3 AWD are the same (on other Teslas not the case apparently), but I really don't know for sure.
EDIT: EPA document for Model 3 AWD, direct from Tesla, says the final drive ratio is 9.04. That's what I thought, I just could not remember the source until just now. Anyway, changes the numbers very little from the assumption of 9. I assume it is the same front and rear since they don't specify. I'm too lazy to look up an EPA submission from a Model S.
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SammichLover
Banned
¯\_(ツ)_/¯ It is possible they used a %5 fudge number to try get to a "crankshaft". That's nothing like you'd ever see in an ICE so not sure where they'd pull that from? Probably wouldn't be a bad guess, I suppose. I'd just be very surprised if they went through all that effort to do up a legit dyno, publish it out to the world, and didn't mention that a rather important fudge factor being applied.
AlanSubie4Life
Efficiency Obsessed Member
Well, as far as I know, they also didn't just cut off the plot and exclude data below ~3000-3500rpm either (as they should have, because the datapoints below that are obviously bogus), so they weren't all that interested in providing a clear picture of what they were showing...
I believe if you look at some of the MPP plots, they just cut it off at a fairly high RPM, probably to avoid showing this limitation of the equipment, but too lazy to go look right now.
Probably just going through the same procedure as they do with an ICE car. They don't start from 0mph for obvious reasons, and usually use 3rd gear or up to avoid traction control/loss. So probably have the car rolling before they start (and at different speeds on the different runs). Doesn't make much difference on an ICE if close to stall speed, but there is no stall speed on electric.
They may also have done a coast down test, put the car in neutral and see how fast the dyno decelerates. (which could be quite interesting, but not advisable.) Maybe the fudge factor, is what it takes to drive the whole assembly - including motors?
SammichLover
Banned
That data hole is inherent in how an ICE is dyno'd. With the multiple gear ratios provided by a transmission nobody really cares what an ICE engine does down at those low RPM, it isn't relevant in practical use because it is so sub-optimal that they work around ever operating there via use of the transmission shifting and also loading the transmission/dropping the clutch (or otherwise thrashing the drivetrain
) for the initial bit (also somewhat behind the historical use for the roll-out, I believe). Dynos just aren't designed to measure at that speed, they aren't designed for the Tesla's direct drivetrain. I'd be entirely unsurprised if the instrumentation didn't operate down there in an any meaningful way, and even if it did the software probably isn't set up to react and treat the info in that small window as relevant and likely throws out that data.
SammichLover
Banned
That's more inherent in the nature of an electric motor being able to do that. It is so efficient over such a wide range that all you need to do is feed it a constant amount of current at the battery's effectively stable voltage (at least stable in the moment) and you get a flat power (AKA HP) curve coming out.
ICE motors simply don't do anything like that, they have a sweet spot in their RPM with a pronounced curve falling off above and below that, and then patch together a smoother curve through a wider range with shifting.
AlanSubie4Life
Efficiency Obsessed Member
Exactly. That's why it is probably a better plan to just use accelerometer data in conjunction with the speedometer readout - which seems terribly primitive, but works surprisingly well and produces results that appear to be much more reasonable than the dyno measurements - of course, since they are based on a real world run. Or just use a VBOX (which is annoying since getting the data in usable format off the device takes work).
Of course, those results don't take into account various environmental factors (hills, winds, density of the air), but it appears they are still more predictive. Comparisons vs. prior software versions are also a lot less fraught with error sources.
Qualitatively, of course, the dyno measurements are interesting (as long as you exclude the data below 3300rpm).
Nit-picking alert. It's really not a very flat HP curve at all. It ramps linearly from 0 to maximum HP at 40-45mph, briefly stays sort of flat at the peak, and then decays from there. I guess it is all relative. Very flat torque (from 5mph up to 40-45mph) though!
My main nit-picky point is that power is 0 at 0mph, about half of maximum power at 20mph, and hits maximum at 40-45mph.
EDIT: I guess the original point was for the AWD - for the AWD it's pretty flat because it has been software limited. Not because of electric motors. It's actually an artificially flat power curve. See the Performance curve (ignoring below 3300rpm, instead replacing with a straight line between 0,0 and the point at 3300rpm for power) for a more typical electric motor power curve.
SammichLover
Banned
I think you mean "reading fail alert"?
We're talking about the flat-ish plateau part from roughy 50 to 100 (<edit> and unknown for how far after that).P.S. The other part suffers from wind, and whatever else, issues.
AlanSubie4Life
Efficiency Obsessed Member
Yes, I see that. As I clarified above - yes, that is flat for the AWD, but not related to electric motors - it's due to the AWD software limitation. The Performance power curve cannot be described as flat - thought it might well be described as "broad" relative to an ICE (in a fixed gear of course). As I said, it's all relative, and of course ICE usually have gears.
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