Zcd1
Active Member
It’s really interesting that the P3D is only 0.68 mph slower at the 1/4 mile mark.
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P3D+ Acceleration
- Thread starter kbecks13
- Start date
It’s really interesting that the P3D is only 0.68 mph slower at the 1/4 mile mark.
All this of course underscores the old drag racing Maxum that ET is more about traction and torque while trap speed is about horsepower to weight ratio. The model 3 Performance has about the same horsepower to weight ratio but because of its switched reluctance motor at the rear it probably has current and therefore torque restrictions until it hits a minimum RPM. And those initial torque restrictions act like a traction restriction on elapsed time, and as everyone has commented, the model 3 lacks that initial violent surge of the Model S. One would hope that the model 3 can get further tuning and some degree of additional optimization in software but I suspect there's a physical limit here in terms of how much torque the motor can generate at low RPM without torque ripples / instability. You have to assume that those limits simply don't apply to older induction style electric motors, suggesting that the model 3 will not have a ludicrous mode or at least it's hampered in that launch operation by the intrinsic nature of Switched reluctance Motors.
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12Pack
Member
Moving from a non-P MS to a P, I've always felt the biggest difference that that immediate hit which I understood to come from uprated motors and inverters. Never driven a M3 P, but that certainly sounds like what is being described here.
It's possible with additional fine-grained placement of rare earth magnets on the rotor that you might reduce the torque Ripple interval so that you can have full torque at a lower RPM than the current system. Outside my pay grade and I'm just speculating but I have to suspect that there's a way to reduce this from incremental design refinements.
AlanSubie4Life
Efficiency Obsessed Member
Torque ripple and cogging torque are real, but I think probably with modern fast motor controllers it’s not that huge an issue except at very low speed. And even there they may be able to manage it with careful rotor position sensing and compensation. I really don’t know, but a brief review of the literature suggests it might not be a huge (unsolved) issue. Anyway, at 5mph (which is about 1 foot into the run at full tilt) the motor is already at nearly 500rpm and my understanding is at that speed, motor and drivetrain inertia is really helping out the situation to smooth the ripples.
So as you said, it’s possible that torque ripple does have some impact on the onset of torque (and the amount of jerk the P3D can produce). But in terms of 0-60 times and useful acceleration, we really need Elon to answer the question “What is the maximum motor torque the P3D can produce? And what is it currently producing (471lb-ft?)? And what is the front/rear split?” If we could get 10% more torque from 5-45mph, that would get us close to breaking 3 seconds.
EDIT: this would just result in hitting HP limit sooner though. So if 10% more torque were possible, probably could only get that 10% more torque up to about 40-42mph or so.
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Don't get your hopes up. It's not like Tesla didn't try to engineer the thing to squeeze every last drop of acceleration out of the drivetrain that they could. Perhaps with further optimization and reductions in torque ripple and perhaps some inverter tuning they might chop two-tenths of a second off 0 to 60. I wouldn't expect much more than that being possible without fundamental changes to either the battery, the inverter, or the motor or all three.
I had a non Luda P85D and I think I was getting 3.5 out of it. I may have seen a 3.3 every now and then but it really depends on traction. My P3D+ feels like it's just as fast 0-60, it just hits you differently. Also with the latest 5% bump my P3D feels faster to 100.
In my P3D+? I dont have a way to measure 0-60. When I use my phone's stopwatch I consistently get 3.5 which means nothing since I'm sure there's some variance in me starting and stoping. All I can tell you is that it feels faster and in some areas where I traditionally floor it I'm now hitting a higher max speed before I get off the pedal than before.
AlanSubie4Life
Efficiency Obsessed Member
I find that VBOX produces more believable plots. All the Dragy plots I have seen show velocity time plots that show faster acceleration at the beginning (which contradict their own acceleration data, and everybody’s understanding/perception of the actual behavior).
Furthermore, the acceleration data is pretty noisy.
The VBOX problem is that it does not seem to allow producing acceleration vs. time in the app (possibly because it would look noisy), but it is relatively easy to emulate this (and derive after the fact) by capturing every 5mph interval split. It also sucks to connect to on an iPhone, for some reason. It is really inexcusable.
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AlanSubie4Life
Efficiency Obsessed Member
I have not ever used it, I have only looked at results, so I can’t comment on that aspect of the accuracy in the real world relative to VBOX. To speculate: Dragy seems in general to have some issue with determining the starting point of the run based on the velocity vs. time plots, and based on those v vs. t plots I’d actually expect the 0-60 times reported to be faster than reality since the initial v vs. t slope is higher than reality. But that may be a derived plot and not used for the timing. I have no idea.
Anyway, that is just speculation. It’s hard to compare runs of other people’s cars to mine. Really would need a VBOX and Dragy compared on the same run.
I have vbox and dragy. Dragy is much easier to use. I never compared them though and stopped using xbox because dragy is much easier and social. You can see what everyone's time is on dragy. Maybe throw out out liers and it is good data on times, at least comparable to other entries in dragy. It is in line with my time slips at track -- although a tiny little bit slower which I attribute to temperature (my fastest time slip was on a very hot day) and age of battery, and fact of slight uphill but I haven't taken to the strip yet. I'm sure someone in the world has.
Dragy is great.
Dragy is great.
AlanSubie4Life
Efficiency Obsessed Member
Based on my VBOX experience, that is not hard to believe. Just think the Dragy data is pretty suspect. a vs. t might be fine (all the issues with the v vs. t plots may be simply plotting issues). The integral of a with respect over time should equal v vs. t. But it does not, in any of the Dragy plots I have seen...the noise on the a vs. t data is to some extent expected, but that wouldn't have much effect on the final 0-60 results as it would be averaged out.
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