ajdelange

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If it really did make the traction control system less effective then Telsa would throttle it back automatically and you wouldn't have to.

In any case I am really excited to see how this will play out in the Rivian with it's 4 independent motors. Reason enough alone to order the truck.





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HaulingAss

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If it really did make the traction control system less effective then Telsa would throttle it back automatically and you wouldn't have to.
Tesla's do throttle back regen automatically in such conditions (as I described). But it throttles up again after a while of not detecting slippage. Tesla recommends turning it off in such conditions, probably to keep the driver experience consistent and so it doesn't have to throttle back regen in the middle of a potentially hairy experience when you are not expecting regen to fade and require the application of the brake pedal which the driver may not be expecting if they are accustomed to regen. It's different than anti-lock braking action, it's slower and "softer" feeling and it allows more slippage and more vehicle yaw. It feels more natural in that it's hard to tell it's intervening at all except that you can feel regen fade some.
 

ajdelange

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For the X they recommend using the Low setting but not turning it off. Perhaps it's different on the 3.
 

ajdelange

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Tonight's Plaid S delivery event revealed a couple of things that have been discussed in this thread. First off, he verified that the Plaid S has 3 identical PMSRMs. As it is widely supposed that the Plaid S drive train is a prototype for the CT drive train I think this puts to bed the question as to what the CT motor complement will be.

Second, he showed the power vs speed curve for these and the motors in earlier versions of the S. All my calculations have assumed that the motor would stay in the torque limited domain up to 60 mph and that is indeed the case with these motors. But the previous ones reached the power limited break point at appreciably lower speeds.

Although it has nothing to do with this thread how can I let a drag coefficient of 0.208 go without a comment. Wow!
 

Owner13669

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We all have seen the patent UI mock-ups - 610 miles of range! Shocking, surprising? Even unbelievable? Just a random number in a mockup? How does the CT get there in a package that weighs the same (or less) than a Ford ICE F-150 and cost $70k (or less)?

Elon had stated in the reveal that they didn't "cheat" with the Cybertruck - they stayed within the dimensions and weight of the F-150 which weighs 5700 lbs max. (8) If you take the F-150 body and frame as a reference, it weighs 5150 lbs (current F-150 weight + 700 lbs for steel and subtracting 1250 lbs of powertrain weight).(1) Elon has stated that the CT will be a stressed-skin design and use a three-piece casting process for the frame with a structural battery pack using the new 4680 cells. Switching a body and frame to a unibody build results in a typical weight savings of 25%.(2) I think we can expect a similar weight reduction for the stressed-skin design, which would bring the body/frame weight down to 3863 lbs. If we subtract that from the max weight allowed for the truck (5700 lbs) we get 1837 lbs left for batteries and drivetrain. Subtracting 70 lbs for the drivetrain leaves 1767 lbs for batteries.(3)

Unfortunately Tesla has not released weight info on the 4680 cell, but it has been estimated that 1416 2170 cells occupying a volume of 1.1*10^8 mm3 and weighing 1060 lbs can be replaced by 960 4680 cells with a similar volume of 1.28*10^8 mm3 and estimated to weigh as much as 40% less.(5) This is for the Model Y and the CT will be a wider and longer vehicle. So if we increase the battery volume by 100% we would end up with 1,920 4680 cells and still potentially be under 1767 lbs. The estimated kWh would go to 200 kWh. A 100 kWh in the Model X 100D provides a range of 325 miles with 2170 batteries.(6) Increasing the kWh to 200 (while still keeping the car weight the same 5700 lbs) could increase the range to 570 miles (200 kWh / 351 Wh per mile). Using 200 kWh of more efficient 4680 cells in a vehicle the same weight should increase the range by 16% or to 660 miles. (7)

The problem here seems not to be weight but the increased size of the battery. Can a battery volume of 2.56*10^8 mm3 be fit into the middle structural component of the CT? That volume would translate into dimensions that would be, for example, 60" L x 52" W x 5" H. It seems like that could be incorporated into the center casting of the CT but I can't say for sure.

The other problem seems like it would be the cost to produce as that is a lot of 4680 batteries. However, Elon and Sandy Munro have stated that switching to 4680 batteries can reduce production cost by 50% per kWh.(7) Sandy has also stated that switching to a three-piece casting process could cut production costs by 1/3.(9)

**UPDATE** I need to make a correction - in using the Model X as a surrogate for the CT I forgot to factor in the efficiency penalty that the CT would have over the Model X due to the difference in cd values. The Model X has a cd of .24 and the CT should have a cd of .30 (per Elon’s tweet). I don’t have a source, but as best as I can glean from different examples (10) this would equate to about a 15% penalty in efficiency. (This would not be the percentage difference between the two values but the measured effect.) So with a 200 kWh battery, all other things being the same, the range would be calculated as 495 miles (200 kWh / 404 Wh per mile) and with the 16% efficiency gain from the 4680 cells the calculated range would end up at 575 miles.

My math or interpretation of my source data could be wildly off here, so I am open to valid critical review. (No, I am not an engineer, but personal attacks based on my vocation I don’t believe are relevant. In fact, in these forums it would be appreciated if we just leave personal attacks and insults off the table.)

Sources:

(1) https://www.torquenews.com/106/ford-breaks-down-2015-f150-weight-savings
(2) https://link.springer.com/article/10.1007/s42452-019-0733-8
(3) https://chargedevs.com/newswire/elo...io-is-the-challenge-with-ac-induction-motors/
(4) https://enrg.io/tesla-battery-weight-overview-all-models/#:~:text=Model X – 1200 Pounds*
(5) https://techtricity.substack.com/p/the-4680-cell
(6) https://insideevs.com/news/355282/2019-tesla-model-x-epa-ratings-compared/
(7) https://www.teslarati.com/tesla-4680-cell-pack-breakdown-video/
(8) The Cybertruck has been registered as Class 2b (8501-10,000 lbs GVWR). This means the max weight of the truck has to be 10,000 minus it's max payload, which for the CT is 3500 lbs. So the Cybertruck cannot weigh more than 6500 lbs empty. https://electrek.co/2019/12/13/tesla-cybertruck-medium-duty-vehicle-carb/
(9) (10) https://aia.springeropen.com/articles/10.1186/s42774-020-00054-7/tables/2
There was a rumor going about at one point that testing (probably from the prototype) showed an actual range of 569 miles. Which is very close to your revised estimate.
 

ajdelange

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Common sense is a very powerful attribute for a man. Pity that it is so uncommon.
 

JBee

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I'm a bit confused why a PM motor needs a carbon wrap to hold the coils on the rotor together at high rpm centrifugal forces. Why have we got coils on a PM rotor?
 

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Why have we got coils on a PM rotor?
I completely missed that. Thanks for pointing it out. We don't know for sure what these motors are like but every PMSynRM motor I've seen or heard of does not have coils or copper in the rotor. The STATOR is coils of (typically) copper wire, but the rotor is typically made of ferrous metals and permanent magnets.

He spoke pretty vaguely about it. Here's what Electrek quoted him saying:

To the best of our knowledge, this is the first time that there has been a production electric motor with a carbon over-wrapped rotor. This is a super hard thing to do because carbon and copper have very different rates of thermal expansion. In order to have a carbon over-wrapped rotor, you have to wind it with extremely high tension and that’s an extremely hard thing to do.
Is the "super hard thing" he's referring to the ability to maintain an airgap between the carbon wrapped spinning rotor and the copper coils in the stationary stator?
 

ajdelange

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I'm a bit confused why a PM motor needs a carbon wrap to hold the coils on the rotor together at high rpm centrifugal forces. Why have we got coils on a PM rotor?
We don't but I too was confused at first and had to go back and listen again. Elon Musk may be a brilliant man but he is not an eloquent man. First he mentions that copper and carbon have very different coefficients of expansion (copper's is 2 - 4 times higher than graphite's) and then talks about how tightly things need to be wound leading the listener to conclude that the rotors have copper windings. Wha? Fixed frequeny PM synchronous motors may have amortisseur windings but these aren't fixed frequency. AFAIK you don't wrap the rotors of IM's but you do wrap the rotors of PMSRM's to keep the magnets from flying out. These new Tesla one's spin at 20,000 rpm. So why is he talking about winding copper in the rotors? He isn't. He is talking about winding the carbon fiber around the rotor and how tight that must be wound to the extent that they had to design a machine to do it. There is a picture somewhere of Tesla rotors and next to them spools of the fiber. I think overall he is trying to say that the carbon wrapping must be done precisely and at high tension in order to get the tolerances required to attain the small air gap they want even at 20 krpm. I think the earlier comments about expansion coefficients were supposed to lead to a statement that a carbon wound rotor can be built to tighter air gap tolerance becuase it won't expand as much as it heats up as the copper windings in an IM rotor would. That's a guess.
 
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HaulingAss

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For the X they recommend using the Low setting but not turning it off. Perhaps it's different on the 3.
The Model 3 has no "Off" setting, just "Standard" and "Low". Isn't the Model X the same way?

The "Low" setting is almost off but there is still a small tiny amount of motor braking going on.
 
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dtruckman

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1000km is 621 miles.

Anyhow, the range estimate is based upon driving history. If you only drive offroad, in residential streets, you're going to see massive range numbers.

-Crissa
Like no hills and no extreme temperatures too
 

ajdelange

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Tesla estimates range in a couple of ways. The battery status bar can be set for remaining SoC or remaining miles. The latter is obviously a range estimate. It is based on the rated consumption of the vehicle i.e. it has nothing to do with driving history. But as there are times when it would be useful to know what range may be given that driving conditions remain the same as they have been Tesla also shows range projections based on either the instantaneous current consumption or consumption history averaged over the last 5, 15 or 30 miles. You have to go to the energy screen to see this. The most useful display is available when a trip has been laid into the navigator. The screen that goes with this mode shows the consumption history up to the present time and then a projection of consumption for the rest of the trip based on the rated consumption adjusted for what the car knows about the elevation and speed limits along the route. The most valuable piece of information on this graph is estimated SoC at the end of the route.
 

ajdelange

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I certainly got a big surprise today looking at a Tweet from E. Musk. He is definitely talking about a copper rotor being contained with a carbon wrap. It looks as if PMSRMs are so yesterday!. The new thing (and they worked with manufacturers of them during the new Roadster design process) is the CRIM (Copper Rotor Induction Motor). At this point I have no idea how they are better than the standard induction motor nor how they differ in construction but as PWSRMs were more efficient than IM's and CRIMs are "better" than PMSRMs they must have ironed out a few kinks.

Now apparently Tesla, and other manufacturers, are turning away from PM motors because of the cost of the rare earth's required to make them. Perhaps the biggest component of "better" is cost.

So apparently as the Plaid has them the CT will have CRIMS.

Now as these are IM's at heart we are back to rotor hysteresis and copper losses. I wonder if these are responsible for the Plaids coming in at just under 400 mi and the cancellation of the Plaid plus.
 
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