Investor Engineering Discussions

[GhostSkater]

But Tesla doesn't do that. I take a wild guess and state that Tesla's motor, what with a larger cross-sectional surface area to conductor area, doesn't have issues at high RPMs - and therefore doesn't need the extra expense, losses, and weight of a no-kidding gear shifting transmission.

A big part of that is that all permanent magnets (AFAIK) motors Tesla uses are a hybrid permanent magnets and reluctance motor, so at high torque it's a PM motors, but at low torque such as highway cruising, it operates as a reluctance motor

This doesn't chance much the losses on the windings, but changes a lot the core losses on the stator since the flux goes down and so does the Eddie and Hysteresis losses

 

[Tronguy]

Isn't that only relevant at high resistance or high torque combined with low inductance?
For continuous conduction and say 20% ripple of a low resistance stator winding, the current is closer to a triangle wave than exponential with I*R being dwarfed by pack voltage - BEMF. (Or have I been oversimplifying it when making switching converters?)

Yeah, like I said, I'm not a motor guy, so can get lost easily in the weeds here.

But the Obvious thing is your comment about it being triangle wave. Sure. Triangle wave. If memory serves, triangle waves vs. Fourier result in another infinite series of odd harmonics, but this time the odd harmonics aren't in phase, they're 180 degrees out of phase in each one.

Once again: Make resistive losses Much Bigger for higher frequencies, and that triangle wave (which one wants) turns into a sine wave, losing all the energy in the higher harmonics into heat, which one doesn't want.

Fun

 

[Artful Dodger]

A big part of that is that all permanent magnets (AFAIK) motors Tesla uses are a hybrid permanent magnets and reluctance motor

"Model 3 cars use a totally different motor called IPM-SynRM"

Tesla Model 3's motor - The Brilliant Engineering behind it | Learn Engineering (Dec 18, 2020)

 

[mongo]

It's been a while since I studied mechanical engineering, but iirc you have to include like 10% rotational energy in the wheels and similar to air and ground. This is what ChatGPT says:

Spoiler: ChatGPT

Assumptions for Simplification:​

1. Vehicle Parameters: Average passenger car with a drag coefficient (CdCd) around 0.3, frontal area (AA) approximately 2.2 square meters, and a mass (mm) of about 1500 kg. We'll assume typical values for the coefficient of rolling resistance (CrrCrr) around 0.015 and use standard air density (ρρ) of 1.225 kg/m³.
2. Speed and Acceleration: Acceleration to 60 mph (approximately 27 m/s) without specifying the time it takes allows us to ignore the specific dynamics of the acceleration curve.
3. Efficiency and Losses: We acknowledge that internal combustion engines and electric motors have different efficiencies and loss distributions, but we'll focus on the mechanical energy distribution.

Energy Distribution Estimation:​

• Translational (Kinetic) Energy: The bulk of the propulsive energy goes into accelerating the car's mass. For a rough approximation, we might allocate 70-80% of the energy to overcoming inertia and achieving the final speed.
• Rotational Energy: Energy needed to accelerate the rotating parts (wheels, driveshaft) is significant but much less than the translational energy. A rough estimate might be 5-10% of the total energy, depending on the vehicle's specific characteristics.
• Air Resistance Loss: The energy lost to air resistance increases with the cube of the speed, making it a significant factor at higher speeds. However, for the entire acceleration phase up to 60 mph, this might account for 10-15% of the total energy, with the percentage increasing at higher speeds.
• Rolling Resistance Loss: Energy lost to rolling resistance is relatively constant and depends more on the distance traveled than the speed. For acceleration to 60 mph, let's estimate this at 5-10%.

Summary of Approximate Energy Distribution:​

• Translational (Kinetic) Energy: 70-80%
• Rotational Energy: 5-10%
• Air Resistance Loss: 10-15%
• Rolling Resistance Loss: 5-10%

Yeah, it was a idealized spherical cow in a vacuum on zero loss high grip hooves.
That said, rotational inertia impacts net acceleration power but not tire friction (assuming AWD) as do drivetrain losses which may already be factored in depending on whether 1500hp is at the "flywheel" or at the tires.

 

[mongo]

While I agree that 4 rear wheels makes no sense, tire friction is more complex than weight vs friction coefficient. What I mean is that friction coefficient isn't linear with contact patch area and usually increase with area

If you have the same weight and same tires on two wheels vs four wheels, the latter will have more grip

Yeah, that's what I (at least thought I) wrote:

That would not increase friction much because the downforce would be divided amongst the tires.
Only gain would be due to a shift in the rubber's coefficient of friction which is dependent on loading.

Shift in CoF, not force*CoF...
2x the tires doesn't yeild 2x the traction.

 

[Buckminster]

https://twitter.com/x/status/1763007612881355020

 

[MC3OZ]

There is an interesting concept reveal around 8:55 into this video.

two front seats and a central console are installed into the car in a single module and mounted in a fixed position.

Seats can move up and down or recline, but they don't move front and back.

While I like their solution, I think the Tesla solution of a yoke which slots into the dashboard is superior and is more likely to be robust over a long period of operation.

The remaining piece Tesla needs is the ability to move the pedals into a position which suits the driver.

Apart from cost savings, the additional advantage is that rear passengers can potentially have a larger screen or 2 separate screens,,

 

[MC3OZ]

I am seeing possible military applications for this drone...

 

[MC3OZ]

Worth watching, a software developers perspective on the unboxed process:-

I think this is right, designing the interfaces correctly then each of the boxes has more freedom the change without impacting on other boxes.

Adding weight to a box might impact on other boxes, I'm guessing that reducing the weight of a box generally doesn't impact on other boxes.

They also floated the idea of boxes moving around on "robot trolleys" and plugging into the trolley for testing.. I am keen on that idea also on the trolleys being intelligently routed. When a box has issues that need to be corrected that trolley should move out of the regular line and into a repair sequence line. re-joining the main line after the problem has been fully resolved.

 

[Artful Dodger]

Anti-Matter: The Future of Interstellar Journeys? | Sabine Hossenfelder (16 hrs ago)

SpaceX Roadster IV?

 

[Buckminster]

https://twitter.com/x/status/1764976308977594418

Elon pinned this tweet which seems out of character. Any chance he is truly hopeful on superconductivity? Could his materials team be looking into it?

 

[Artful Dodger]

https://twitter.com/x/status/1764752537150988338

 

[mongo]

34 by 8 cells on each module, 3 modules, extrapolating from 4680 energy content of 86 to 95 Wh per cell, each 4695 cell should be somewhere from 102 to 113 Wh

That ratio 95/80= 19% assumes the full length is active area.
With 5mm of non-active space, we get 90/75 or a 20% increase.
At 10mm, 85/70 = 21.5%
Only a Wh difference, but it adds up across 816 cells.
Also, Limiting Factor put the 4680 energy at around 98Wh.

 

[GhostSkater]

That ratio 95/80= 19% assumes the full length is active area.
With 5mm of non-active space, we get 90/75 or a 20% increase.
At 10mm, 85/70 = 21.5%
Only a Wh difference, but it adds up across 816 cells.
Also, Limiting Factor put the 4680 energy at around 98Wh.

Agreed, so likely efficiency will be worse

 

[mongo]

Agreed, so likely efficiency will be worse

Meaning Wh/mile?

 

[GhostSkater]

Meaning Wh/mile?

Yep, or bigger range, but the overall shape of all 3 vehicles are far from the most aero possible

 

[MC3OZ]

The part toward the end of the video on sodium solid state batteries is particularly interesting.

 

[ggies07]

The part toward the end of the video on sodium solid state batteries is particularly interesting.

I really perked up at the 23 minute mark when I heard Shirley say 5-6 minutes for charging - 15 to 20C. I mean, IMO, that's the last strawman argument to be knocked down.

 

[nativewolf]

It was a nice interview, very realistic. It's a multi decade marathon not a 3 year sprint.