Investor Engineering Discussions

[mongo]

Well, at 60K lbs that's 22K for each Semi and 15K for the trailer. I think we knew that already.

What we did hear new is that Tesla Semi has up to 1,500 hp AND is configured for each customer Note that's at least 375 hp for EACH MOTOR in a quad motor setup! We haven't heard that before! Paging @mongo

Tesla Semi also senses the load attached and matches its power to maintain consistent performance. Nice!

BTW, extremely unlikely the plaid carbon-wrapped motors put out 500hp each for a tri-motor 1,500 hp Semi - the Quebec software-uncorked Plaid S shows the tri-motor has a max power right around 1175 hp.

We also learned Truck Director: "Tesla has made 60-70 Semis on the pilot production line as of Sep 2023"

Cheers!

Yeah, though the individual configuration is all in software.

Power can be limited by a few things:
Motor (pack) current
Motor (pack) voltage
Motor speed
Max torque

Even with racing tires, Plaid is going to spin tires at a lot lower torque level than a semi with 17 thousand pounds on the axle. 1,500 HP (1,100kW) comes into play if accelerating up a steep grade.
80k pounds up a 6% grade at 60 MPH takes 540kW
1.8kWh/mile for driving losses is 108kW
That's >500HP on their own.

 

[mongo]

There is a really good reason for the clutch and why the Semi has but the passenger vehicles don't

The two climb motors have a significantly higher gear ratio, close to double the cruising motor, there is a whole another stage to them. The climb motors are likely reaching 20k rpm under 100 mph, we can calculate that, been meaning to do that for a while, just need to find a bit of time

View attachment 979237

On a Model S/X, you will only get to 20k rpm at over 200 mph. The problem is that rpm related losses (core losses) grows somewhere between to the square to the cube of rpm, so if your motor is off but running at close to 20k rpm with you just cruising it can be a significant power hog, on top of you also having to spend energy to cool it

Here is an example from some real data from real motors, these are palm sized ones weighting around 1 kg and capable of 3 to 5 hp, so power density is comparable to the motors Tesla makes, but the principle is the same, it becomes a heater just by being off and spun fast

View attachment 979240

Another way to look at it is that when you need the power, you need to spin a motor really fast because that is where it's most efficient and can make the most power, but spinning it really fast when little power is needed, such as cruising on flat, it's really inefficient

A Semi needs around 80 kW for cruising of flat road fully loaded, a single motor spinning at half of the 20k rpm limit can easily do that all day long and efficiently

A few more plots of one of the motors from the graph above, first one is an efficiency map and second is a power output map, ignore all the white labels and lines, not relevant

Let's say we need low power for cruising at just 640 W, if we spin the motor at 11000 rpm, we will operate at 75% efficiency and have 160 W of waste heat, or we can operate at 2500 rpm at 90%+ efficiency and have just 64 W of waste heat

Now for the other scenario, climbing a big hill and we need 2.5 kW of power, at 2500 rpm this would be 80% efficiency and 500 W of waste heat, that motor would cook in no time, but at 11000 rpm we operate at 92% efficiency and just 200 W of waste heat, way more manageable

View attachment 979241
View attachment 979242

Now circling back to why the passenger cars doesn't need the axle clutch, the motor are always operating at slow rpm at normal driving speeds, such as the power lost is so low that it doesn't warrant the complexity added

The Semi is pushing the motors to it's limit, from the above about needing high rpm for high power, in my opinion the two acceleration motors are putting significantly more power each than the cruise motor, if we go from the gear ratios and 1500 hp Dan gave us, I would say each climb motor does close to 600 hp while the cruise motor are on the high 300s hp

Semi clutch feasibility is also helped by low acceleration of the wheels, there is a lot of inertia and likely low turning dynamics during engagement. Passenger cars have higher rates of change.

Clutched motors have half the traction of the cruise motor and their steeper gearing means more back-EMF so I'm not sure they are running much, if any, higher in power output individually than the cruise motor. They do add a lot of torque per stator amp.

Your power numbers in the middle, are those actually Wh per mile?

 

[GhostSkater]

Semi clutch feasibility is also helped by low acceleration of the wheels, there is a lot of inertia and likely low turning dynamics during engagement. Passenger cars have higher rates of change.

Clutched motors have half the traction of the cruise motor and their steeper gearing means more back-EMF so I'm not sure they are running much, if any, higher in power output individually than the cruise motor. They do add a lot of torque per stator amp.

Your power numbers in the middle, are those actually Wh per mile?

Yes, also that

On the back-EMF part, keep in mind the motor operate into the field weakening region at least in part of the rpm range, so back EMF limits aren't that much of an issue if you really need the power

You mean the 80 kW one? 1.7 kWh/mi at 55 mph is 93 kW average power, but that includes hills where the acceleration motors are active, so I took it down a bit just as an example of how little power it needs into steady state cruise

 

[mongo]

You mean the 80 kW one? 1.7 kWh/mi at 55 mph is 93 kW average power, but that includes hills where the acceleration motors are active, so I took it down a bit just as an example of how little power it needs into steady state cruise

Nah, that made sense, it was the 640 watt and 2.5 kW part.

On the back-EMF part, keep in mind the motor operate into the field weakening region at least in part of the rpm range, so back EMF limits aren't that much of an issue if you really need the power

Explains the really straight Plaid power curve.

 

[GhostSkater]

Nah, that made sense, it was the 640 watt and 2.5 kW part.

Ah just was for the example and to line up with the curves on my plot

Explains the really straight Plaid power curve.

Yeah, that is one of the key things that allow it to maintain the flat power curve

 

[mongo]

Ah just was for the example and to line up with the curves on my plot

I thought it was something like that, I'm going 500W? That's not a lot of heat at all...

 

[GhostSkater]

I thought it was something like that, I'm going 500W? That's not a lot of heat at all...

Keep in mind this is for the hand sized 1 kg motor that I measured to make these plots, this would be way more on a EV motor

For that motor, it would last less than 3 minutes at those waste heat power levels, might even burn immediately due to the windings heating up

 

[mongo]

Keep in mind this is for the hand sized 1 kg motor that I measured to make these plots, this would be way more on a EV motor

For that motor, it would last less than 3 minutes at those waste heat power levels, might even burn immediately due to the windings heating up

Right, but if you are still thinking of a Plaid motor, 500W is 3 degrees F at 1 gpm coolant flow. Then you needle scratch and go, that number is not right...

 

[GhostSkater]

Right, but if you are still thinking of a Plaid motor, 500W is 3 degrees F at 1 gpm coolant flow. Then you needle scratch and go, that number is not right...

Your mistake is thinking on the Plaid it will be 500 W, my motor is less efficient on than the Plaid, let's say the Plaid has 1/2 the losses for the same rpm, and let's scale with weight, and Plaid weights 45 kg, so we are talking about 11 kW of heat per motor

This number is nowhere near correct, but one way to sanity check, according to Bjorn Nyland tests, the Plaid has around 18 kW of battery heating power by using the motors as heaters, 1 kW comes from the heat pump losses, so 3 motors can generate 17 kW of heat while stationary, so it's fair to assume that each motor has at least 5.5 kW or more

We don't even need speculate, here is the Model 3 motor efficiency map, it won't be the same for Plaid, but we can speculate that at peak power it might be 90% efficient, each motor doing 340 hp or 250 kW, so 25 kW peak losses

https://motorxp.com/wp-content/uploads/mxp_analysis_TeslaModel3.pdf

 

[mongo]

Your mistake is thinking on the Plaid it will be 500 W, my motor is less efficient on than the Plaid, let's say the Plaid has 1/2 the losses for the same rpm, and let's scale with weight, and Plaid weights 45 kg, so we are talking about 11 kW of heat per motor

This number is nowhere near correct, but one way to sanity check, according to Bjorn Nyland tests, the Plaid has around 18 kW of battery heating power by using the motors as heaters, 1 kW comes from the heat pump losses, so 3 motors can generate 17 kW of heat while stationary, so it's fair to assume that each motor has at least 5.5 kW or more

We don't even need speculate, here is the Model 3 motor efficiency map, it won't be the same for Plaid, but we can speculate that at peak power it might be 90% efficient, each motor doing 340 hp or 250 kW, so 25 kW peak losses

View attachment 979417

https://motorxp.com/wp-content/uploads/mxp_analysis_TeslaModel3.pdf

That's my point, I'm not thinking the Plaid losses will be 500W. Hence me asking what those numbers signified.

You jumped from semi to motor plots and then into other motor hypotheticals, not semi hypotheticals, then back to semi. That was where I got tripped up on your post, that the intermediate numbers were just for discussing motors in general, not the semi as a scaled version of the graphs.

 

[GhostSkater]

That's my point, I'm not thinking the Plaid losses will be 500W. Hence me asking what those numbers signified.

You jumped from semi to motor plots and then into other motor hypotheticals, not semi hypotheticals, then back to semi. That was where I got tripped up on your post, that the intermediate numbers were just for discussing motors in general, not the semi as a scaled version of the graphs.

My bad

I should have been more clearer, I'm using a smaller motor that I actually have on hand, measured all the data myself and used it in many products to make a comparisson to a bigger one

 

[MC3OZ]

Some amazing engineering and design in this video:-

 

[MC3OZ]

What exactly that 3d printing process would look like IDK.

I know 3D printing of sand molds exists...

Sand casting - Wikipedia

en.wikipedia.org

Additive manufacturing (AM) can be used in the sand mold preparation, so that instead of the sand mold being formed via packing sand around a pattern, it is 3D-printed. This can reduce lead times for casting by obviating patternmaking.[3] Besides replacing older methods, additive can also complement them in hybrid models, such as making a variety of AM-printed cores for a cavity derived from a traditional pattern.[3]

I suspect we could track down a YouTube video on this topic, if we really tried hard to find one.

 

[Buckminster]

https://twitter.com/x/status/1712141320410607677

 

[mongo]

That is what a higher aspect ratio tire will do.

Along with a narrower rim.

 

[mongo]

Cybertruck - confirmed 800V architecture (slide deck page 8). There were rumors of 1000V, but this puts that to bed.

Huh?
1,000 has always been a voltage limit, not a pack nominal. The only uncertainty I know of was current voltage of ~400 (V3 Superchargers) or higher (Semi) voltage ~800 (V4).
800 is the higher voltage architecture.

 

[Buckminster]

https://twitter.com/x/status/1715723286695346605

 

[mongo]

@GhostSkater @scaesare
I don't think the drive shafts can be centered on the motor since that is where the mounts are.

 

[scaesare]

@GhostSkater @scaesare
I don't think the drive shafts can be centered on the motor since that is where the mounts are.
View attachment 984634

I said the drive shafts were not centered on the motor in my post:

...the shafts would not be aligned with the center of the engine, or motor in the case of an EV.

 

[mongo]

I said the drive shafts were not centered on the motr in my post:

Yeah, I wasn't trying to imply you were saying they were centered. I posted here to give my thought in support and tagged you both since you were the main discussors.