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Tesla, TSLA & the Investment World: the Perpetual Investors' Roundtable

Speedr117

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Supporting Member
Oct 12, 2017
589
3,517
Florida
Retrofit new cameras with existing connectors, is feasible. Additional cameras require a new wiring harness, which IMO is far less feasible.

My theory is this is why they hiked the price of FSD. So if/when they need to retrofit cars, they have the funds already.

In regards to needing a new wiring harness, I wouldn't be so sure. For example, the harness used for the headlights must already have some kind of data transfer capability, since they can play/show words, etc. via the headlights. So adding a camera to the headlight pod shouldn't be difficult. Of course, this is all speculation...
 
Why? I feel like the only thing these new ev companies copied from Tesla is how to hype. The real meat is how to make a profitable car which happens during the design phase AND the production line. I feel like both Lucid and Rivian skipped those classes when they were learning from Tesla. The Chinese however didn't sleep during those classes

-300% gross margin is a F - and should go back to the drawing board.
I always thought lucid was a scam but Rivian has no excuse. Neat suv but an f is generous, all they had to do is copy most of what Tesla did
 
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Dreadnought

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Nov 10, 2018
209
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Germany
Resistor banks are also used in some wind and hydro applications. But they are problematic. Hence my wondering what Tesla's plans for that situation are - beyond the obvious ones.
I can't imagine that Tesla engineers would not have either considered a case of limited regen or ensured that there's always spare capacity since this is safety critical and safety is always on top of Tesla's priorities.

The existing engine / battery / inverter / HVAC cooling system would be my first choice as it already has pumps, radiators, coolant etc. It may need scaling beyond what other use-cases require. If it's only a very rare last resort when everything else failed, just let the coolant boil off. Probably not good for the batteries but would still avoid a potentially catastrophic runaway situation. In any case, it's much easier to dissipate residual waste heat than with friction brakes.
 
I like the clutch implenentation, elegant.

I'm interested in how they will handle the use case where a fully laden and fully charged truck starts descending a long hill. Where will they put the regenned energy, or will they become brake-limited (primarily by thermal management constraints). Before anyone yells at me that such situations don't exist there are plenty of them around the world.

You keep the axles engaged and use the motors to brake. Multiple regimes, something like

* Normal Regen
* Normal Regen + friction brakes
* Inefficient Regen (starts producing more heat and less electricity)
* Inefficient Regen + friction brakes
* Inefficient Regen + friction brakes + thermal management (as the motors get hot you spend energy to cool them)
* Really inefficient Regen + friction brakes + thermal management (at this point your regen is not sending power to the main pack but it's not pulling from the main pack)
* Negative regen + friction brakes + thermal management (now you are pulling power from the pack and generating more heat)

You've got 3 motors so the amount of braking force they can provide is large. They don't have to put power back into the packs to brake. In fact they can brake harder if they pull power from a full pack.
 
I imagine you are keeping it simple (since you are an EE) but people here like the full story. Resistance for the wire sizes they use (and they are using fine strand so it is lower than what I have posted... less skinning effect) is PER 1000" of wire. The cable to vehicle is less than 20'. That means the resistance will be what... 50 times less than what's on the chart. I would imagine the high voltage lines up to the charge stand will be typical full size.

1000*1000* .08 / 50, or 1.6KW

I am going back in hiding now.
And just to finish the story: in a circuit, current flows into the vehicle on one conductor and back out of the vehicle on on the other conductor. So, if it’s 1.6 kW on one wire in the cable, it’s another 1.6 kW on the other wire.

Reminds of the three laws of thermodynamics: You can’t win, you can’t break even, and you’re stuck in the game 😁.
 
You keep the axles engaged and use the motors to brake. Multiple regimes, something like

* Normal Regen
* Normal Regen + friction brakes
* Inefficient Regen (starts producing more heat and less electricity)
* Inefficient Regen + friction brakes
* Inefficient Regen + friction brakes + thermal management (as the motors get hot you spend energy to cool them)
* Really inefficient Regen + friction brakes + thermal management (at this point your regen is not sending power to the main pack but it's not pulling from the main pack)
* Negative regen + friction brakes + thermal management (now you are pulling power from the pack and generating more heat)

You've got 3 motors so the amount of braking force they can provide is large. They don't have to put power back into the packs to brake. In fact they can brake harder if they pull power from a full pack.
When you get to your final bullet point you probably have a few seconds of useful braking life left, if that. The lighter and more efficient the motor - and the 3/Plaid is a doozy - the shorter the time, as the thermal mass reduces proportionately to the physical mass. This rapid termination is because the neos reach their Curie temperature. From then on you lose magnetic torque and the only route out then is:
  • Find emergency run-off ramp into loose gravel bed.
Hence my querying what Tesla have in mind for this use particular scenario, beyond the obvious ones that relate either to going more slowly downhill if at a high SoC, and/or not being at the high SoC in the first place when at the top of a hill.

I have seen this failure case many times over the years, which is why I am wondering if Tesla have figured out something new. (By the way debris from neos jammed into an air gap doesn't provide much braking torque either !)
 
When you get to your final bullet point you probably have a few seconds of useful braking life left, if that.

You are assuming the same amount of time in each regime / too long a time in the wrong regime.

The system can jump straight to the bottom of the list if needed. Mapping data, cameras, inertial sensors, motor speed, vehicle speed, etcetera is enough data for the vehicle to choose the right mode almost immediately.

It's a list of options that are accessible at random (random access), not a list that has to be followed in order (ordered list).
 
You are assuming the same amount of time in each regime / too long a time in the wrong regime.

The system can jump straight to the bottom of the list if needed. Mapping data, cameras, inertial sensors, motor speed, vehicle speed, etcetera is enough data for the vehicle to choose the right mode almost immediately.
I wasn't assuming any particular length of time in any regime and my experience is that this can all happen much faster than people appreciate, but your point is a fair one. At any stage the truck can indeed say "I'm Sorry Dave, I'm Afraid I Can't Do That".

It'll be interesting to see if Tesla have found another way that hasn't previously been considered.
 
Not going to be positive ever. Tesla can make 2500 roadsters with a positive margin. The Model S had a positive margin during the ramping phase. It's grueling to hit profitability by having the gm high enough and operating leverage high enough to overcome operating expenses to have a positive operating margin. Lucid and Rivian are no where close.

The product must start with a positive margin in this car industry or else it's game over before you even started. Musk knew this, other companies seem to not understand.

Spot on. Design for cost is a lot harder up front but is significantly more executable in production than cost down efforts post design or later in the life cycle.

The results are significantly different as well. DFc wins. Always.
 
I wasn't assuming any particular length of time in any regime and my experience is that this can all happen much faster than people appreciate, but your point is a fair one. At any stage the truck can indeed say "I'm Sorry Dave, I'm Afraid I Can't Do That".

It'll be interesting to see if Tesla have found another way that hasn't previously been considered.
We already know that they can accelerate a full load going uphill with engines only and no friction brakes.

While regen for the purpose of recharging the pack is less than 100% efficient, braking and just converting it to heat is not.

So if they can use 3 motors to do more than counteract gravity going uphill on the steepest route they could find, then they can use 3 motors to counteract gravity going downhill. AND they have friction brakes on top of that.

I'm not sure what problem you think they need to solve.
 
And just to finish the story: in a circuit, current flows into the vehicle on one conductor and back out of the vehicle on on the other conductor. So, if it’s 1.6 kW on one wire in the cable, it’s another 1.6 kW on the other wire.

Reminds of the three laws of thermodynamics: You can’t win, you can’t break even, and you’re stuck in the game 😁.

Just don't wander off into discussing Hole flow vs Electron flow and we'll be okay. :rolleyes:
 

Oil4AsphaultOnly

Active Member
Supporting Member
Mar 14, 2015
2,426
6,817
Arcadia, CA
I wasn't assuming any particular length of time in any regime and my experience is that this can all happen much faster than people appreciate, but your point is a fair one. At any stage the truck can indeed say "I'm Sorry Dave, I'm Afraid I Can't Do That".

It'll be interesting to see if Tesla have found another way that hasn't previously been considered.
We already know that they can accelerate a full load going uphill with engines only and no friction brakes.

While regen for the purpose of recharging the pack is less than 100% efficient, braking and just converting it to heat is not.

So if they can use 3 motors to do more than counteract gravity going uphill on the steepest route they could find, then they can use 3 motors to counteract gravity going downhill. AND they have friction brakes on top of that.

I'm not sure what problem you think they need to solve.

I think petit_bateau's point is that reversing the motors to actively brake, instead of regen, would generate significantly more heat (and much more quickly) than anticipated.

So I think we should look at it this way:

How much power (in KW) does it take to go uphill at a constant speed? That should be the same power (in the form of heat) that you'd need to dissipate going downhill. As long as the motors + cooling system can convert that to heat and dissipate it out into the air, then there's plenty of "braking" capacity to go downhill, even without regen.

Edit: Relying on the friction brakes to "travel" downhill is a no-no. That's riding the brakes and is a sure way to deplete your available braking reserves.
 
Today I picked up my very first Tesla, Shanghai built, ordered in September. Invested since 2015 but now - at long last - I'll know what you guys are talking about.

20221203_181812.jpg
 

SmokyPeat

Active Member
Oct 27, 2021
1,070
6,791
Maine
Resistor banks are also used in some wind and hydro applications. But they are problematic. Hence my wondering what Tesla's plans for that situation are - beyond the obvious ones.
Resistor banks are also widely used in diesel-electric train locomotives with very few problems that I'm aware of. Seems like a good idea to me. I would think it much simpler and less taxing than putting large amounts of heat energy into the powertrain/heat pumps.
 
I think petit_bateau's point is that reversing the motors to actively brake, instead of regen, would generate significantly more heat (and much more quickly) than anticipated.

So I think we should look at it this way:

How much power (in KW) does it take to go uphill at a constant speed? That should be the same power (in the form of heat) that you'd need to dissipate going downhill. As long as the motors + cooling system can convert that to heat and dissipate it out into the air, then there's plenty of "braking" capacity to go downhill, even without regen.
If the aim is to bring the vehicle to a halt, and thereby eliminate the source of heat, then provided it is done early enough then @dhanson865 is quite correct.

The problem is if one is trying to make progress descending the hill in a controlled fashion, as opposed to simply stopping. That is the situation I pose for consideration.

But @dhanson865 is also quite correct that the Tesla control system will know how close to the limit it can drive before getting too close to an out-of-control situation.

My point is that things can go from 'tolerable' to 'disastrous' exceedingly quickly.

I suspect that @dhanson865 and I have both been exposed to some of the same prior industrial experience in this area, and that the pool of engineers facing this set of challenges has widened significantly in the last decade.
 

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