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Sandy Munro talks about the teardown of the Model 3

Do you know why the fuel tanks in ICE vehicles are not stressed members of the chassis? Yep, because they don't want the tank to be breached in an accident. Tesla's early cars used the battery as a stressed member and they got roasted for a few battery fires. Now they fix the problem and they get roasted for wasting money.

It would be comical if it weren't so callous to the survivors of battery fires.

Gas tanks are protected by supporting them with flexible straps. Even if the frame structure is deformed the strapping holding the tank will not crush the tank. Why would you suggest the battery of a Model 3 doesn't deserve equal protection? This was obviously a conscious decision by Tesla, not an exercise in ignorance. I wonder how many EV's Munro has designed and manufactured? I would buy a Tesla over a "Munro". Especially if he used the highly flammable battery pack to absorb crash energy. Nobody wants to be in an accident but, if they are, they don't want the battery to burst into flames.

You seem to be conflating two arguments. On one hand, you talk about ICE gas tanks and draw parallels to how battery packs should be treated in BEVs, and on the other hand you accuse Munro about not having designed an EV (only ICE vehicles) which renders his points invalid. You could design the gas tank to be a stressed member and you would then design the chassis to allow that tank to add stiffness when installed. Whether or not its a good idea to make the gas tank a stressed member is an entirely different argument.

Based on what has been said by Munro about the testing that Siemens did, both the Model 3's pack and BIW seem to have been designed independently of each other for stiffness, when they should have been designed as a system. This would imply that if the BIW is stiff enough to handle the loads it may see on its own, then the battery pack would not also need to be designed as something to add stiffness to the chassis when installed - which, based on the design of the pack, seems to have been done.
 
Does the BMW i3 use the battery as a stressed member of the body? Your answer will be timed.

This paper is pretty good. It talks about mitigation strategies for battery damage when they are crashed. It does not indicate that the battery should be excluded as a stress bearing member in designing the vehicle chassis.

http://www.prba.org/wp-content/uploads/Elham-MIT-Presentation-17.pdf

Maybe he can answer if the Bolt EV's battery is a stressed member? ;)

Trickle Charged: GM Releases More Chevrolet Bolt EV Details – News – Car and Driver
 

JeffC

Member
May 15, 2016
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174
Silicon Valley
Companies (other than Tesla) have been using mixed high strength steels for awhile now. Front offset overlap protection essentially mandated their inclusion in designs to maintain occupant cell integrity during those impacts without adding significant weight. With that said, Sandy Munro and his team most certainly understand that as they've been benchmarking and pulling apart vehicles (specifically body in whites) for decades. They've most certainly done newer vehicles (like the BMW 3 Series he has data points for) during the discussion.
Fair enough, but I expect Tesla may have some novel arrangement of high strength steels in Model 3. Bottom line: it physically outperforms all other cars in crash tests, so it very well may be doing something different from them.

I do see that Volvo has been using mixes of high strength steels in their unibody for better crash performance for a few years. (That said Model 3 outpeforms all Volvos in crash tests.) P.S. Volvo is a Chinese owned company, in case anyone doesn't know.
 

ℬête Noire

Active Member
Jan 30, 2018
3,105
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TX
I found it very interesting that most of their concern was about puncture resistance of the pack as that is the highest risk of failure compared to say being squished or compressed in an accident.
You probably want to read it again....for the first time? There is a lot in there on full cylinder compression of cells.
I think if the battery pack being physically distorted in an accident where it was over-relied on as a load bearing member was an issue they would have mentioned it, but would have to ask them or read more of their work.
On what basis? Again, it doesn't address anything at the pack level much less the vehicle frame/body level. The closest it gets is providing a bunch of data elements for people working on the pack design and the body in white could feed in for simulating the cells contained there-in.
 

omgwtfbyobbq

Active Member
Aug 24, 2013
1,450
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Southern California
The problem is;

1. We don't know that treating the battery pack as a structural member in crash testing necessarily impacts battery survivability in a crash.
2. Tesla have never said that above and beyond protection of the battery pack was a design goal, that has merely been speculated.
I agree with 1. We don't know that treating the battery pack as a structural manager impacts survivability. We also don't know that it didn't impact survivability.

With respect to 2, my sense is that Tesla does prioritize protection of the battery pack based on how they handled the impact related thermal events in the Model S. It's likely less expensive to beef up the pack/body when they're designing everything than it is to retrofit an existing design.

Tesla Adds Titanium Underbody Shield and Aluminum Deflector Plates to Model S
 

ricohman

Member
Dec 31, 2018
470
403
Saskatchewan
Do you know why the fuel tanks in ICE vehicles are not stressed members of the chassis? Yep, because they don't want the tank to be breached in an accident. Tesla's early cars used the battery as a stressed member and they got roasted for a few battery fires. Now they fix the problem and they get roasted for wasting money.

It would be comical if it weren't so callous to the survivors of battery fires.

Gas tanks are protected by supporting them with flexible straps. Even if the frame structure is deformed the strapping holding the tank will not crush the tank. Why would you suggest the battery of a Model 3 doesn't deserve equal protection? This was obviously a conscious decision by Tesla, not an exercise in ignorance. I wonder how many EV's Munro has designed and manufactured? I would buy a Tesla over a "Munro". Especially if he used the highly flammable battery pack to absorb crash energy. Nobody wants to be in an accident but, if they are, they don't want the battery to burst into flames.

Wrong.
The straps will crush the tank. Both poly and steel tanks.
I've worked on vehicles that had the straps slice right through the tanks as result of collisions. Unit or frame construction.
Seen this many times. It's probably the most common cause of a fuel tank rupture is a collision.
 

voip-ninja

Give me some sugar baby
Mar 15, 2012
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Colorado
You probably want to read it again....for the first time? There is a lot in there on full cylinder compression of cells.

Be nice... because I did read it.

In the "summery of cell testing" slide they discuss the difference types of objects used on cells to test them, including hemispherical dies, flat plates, etc... and of course they tested compression as well as strain/stretch and combinations of the two (stretching and compressing in two different axis as well as adjusting the force levels in one axis to be double in the other to see what effect that has).

There's also an entire section on pack protection structures, which interestingly, seems to focus heavily (exclusively) on impact protection of the bottom of the battery pack.

I would have liked to see more detail, this slide deck is more than likely just a high level overview of the full research that was published, but I didn't find their full paper.
 
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voip-ninja

Give me some sugar baby
Mar 15, 2012
4,124
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I agree with 1. We don't know that treating the battery pack as a structural manager impacts survivability. We also don't know that it didn't impact survivability.

With respect to 2, my sense is that Tesla does prioritize protection of the battery pack based on how they handled the impact related thermal events in the Model S. It's likely less expensive to beef up the pack/body when they're designing everything than it is to retrofit an existing design.

Tesla Adds Titanium Underbody Shield and Aluminum Deflector Plates to Model S

The MIT paper quoted earlier has several slides that specifically discuss puncture of the battery pack and includes some simulated impacts that give some basic information on how the "armor" of the battery pack functions with regard to underside intrusion from foreign objects. It's not clear though that they in any way provided guidance on other areas of the pack needing protection during crashes.
 

StealthP3D

Well-Known Member
Dec 12, 2018
10,590
92,196
Maple Falls, WA
Wrong.
The straps will crush the tank. Both poly and steel tanks.
I've worked on vehicles that had the straps slice right through the tanks as result of collisions. Unit or frame construction.
Seen this many times. It's probably the most common cause of a fuel tank rupture is a collision.

Of course, in a severe enough impact the fuel tank will be breached. The reason it doesn't get crushed in medium impacts is because it's protected by the structure of the chassis and hung with straps. But no one in their right mind would design the fuel tank as a stressed member of the chassis so it's baffling why anyone would argue that a battery MUST be integrated into the structure as a load bearing member. It's silly to argue that and yet that's exactly what you are doing.
 

ricohman

Member
Dec 31, 2018
470
403
Saskatchewan
Of course, in a severe enough impact the fuel tank will be breached. The reason it doesn't get crushed in medium impacts is because it's protected by the structure of the chassis and hung with straps. But no one in their right mind would design the fuel tank as a stressed member of the chassis so it's baffling why anyone would argue that a battery MUST be integrated into the structure as a load bearing member. It's silly to argue that and yet that's exactly what you are doing.

You said. the strapping holding the tank will not crush the tank
I’m merely pointing out this statement is false. Feel free to edit your post.
Fuel tanks need to float as they expand and contract. Sometimes a large amount.
And I never once said the battery needs to be a stressed member. I’m a mechanic, not an engineer.
That said, many components of vehicles are stressed members. Engines for example. And many companies (Honda for example) have found that to much stiffness in a chassis increases lap times. So they built more compliance into the chassis and had faster lap times as a result. I believe this was first noticed in bikes and then progressed to 4 wheeled vehicles.
I am not suggesting the Model 3 is to rigid. I will have to wait months until I can even drive one.
I prefer a stiff chassis regardless.
 

StealthP3D

Well-Known Member
Dec 12, 2018
10,590
92,196
Maple Falls, WA
You said. the strapping holding the tank will not crush the tank
I’m merely pointing out this statement is false. Feel free to edit your post.

No, I will leave my comment as originally stated. I trust that most people understand if the crash is severe enough anything can be ruptured but the goal with strapping the tank between stressed members of the chassis is to protect it in the event of a crash..

I am not suggesting the Model 3 is to rigid. I will have to wait months until I can even drive one.
I prefer a stiff chassis regardless.

You are in for a treat. In my opinion, the limited flexibility of the Model 3 chassis contributes significantly to the crisp and precise handling it exhibits as well as it's safety.
 

apsen

Member
Nov 15, 2018
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164
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After reading this I realize you have zero experience racing anything.
BTW, if you are doing it right every single run is traction limited. When you have the power to smoke the tires at 100 mph you bet less weight is a good thing. The skinny pedal is a rheostat, not a switch.
Unless you are racing 40 hp cars of some sort.

'Traction limited' is too broad a term actually. What kind of traction limitation? Is it rubber burning or slipping? In first case the mass will make a difference because it is not related to friction but to how much stress the rubber will be able to handle before tearing apart and that number has a limit and therefore mass times acceleration is limited by that number. If the friction is below what will cause rubber to tear the mass mostly* doesn't matter as it will cancel out.

*mostly because there may be some lower order of magnitude effects that theoretically could matter but probably nothing that could be reliably exploited, in any case it is easier to play the game of the friction/strength of the rubber trade off.
 

apsen

Member
Nov 15, 2018
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164
somewhere
On particular items, most, however he has explicitly changed his overall opinion of the car over that time. His own turn of phrase for it is "eat crow". He has even come to the realization that things like the "gap fit" don't actually matter as much for the product as they do for his own personal ideals.

What he hasn't quite grasped yet is why the things he doesn't like look the way they do. He's so close, it's right there mixed into his words but I don't think he's quite grokked it yet.

He did say about crow though I think this is mostly about his overall impression. And that is very understandable as the fit and finish flaws are very obvious and that doesn't suggest that there could be anything significantly better with the harder parts. Once he got to look at those his impression has changed. I actually do not remember single factual statement that he needed to go back on. He also at some point states that this is what he could say at that point as the analysis of the car has not been completed.

And it completely baffles me how some people are misrepresenting his 'I don't know' statements... I could only recommend to anyone who has not seen those videos to not rely on those misguided assessments of Munro's abilities and just watch the videos and decide for themselves.
 

apsen

Member
Nov 15, 2018
222
164
somewhere
Now You Know
Best review and summary of OP [original post of this thread]

This is indeed very good overview. The only thing thing I have a reservation about is 'overbuilding doesn't matter'. It doesn't matter in a sense that the car is so much better than anything else out there that it will not change the choice of a vehicle but it generally does matter as it comes at a price (not necessary monetary one though that probably too) and if that trade off were known I may have preferred different solution of that trade off. If that would just make car a couple of hundreds cheaper then I wouldn't be interested but if that would give us extra 10 miles of range I wouldn't be so sure.
 

JeffC

Member
May 15, 2016
209
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Silicon Valley
This is indeed very good overview. The only thing thing I have a reservation about is 'overbuilding doesn't matter'. It doesn't matter in a sense that the car is so much better than anything else out there that it will not change the choice of a vehicle but it generally does matter as it comes at a price (not necessary monetary one though that probably too) and if that trade off were known I may have preferred different solution of that trade off. If that would just make car a couple of hundreds cheaper then I wouldn't be interested but if that would give us extra 10 miles of range I wouldn't be so sure.
Sandy says the car is overbuilt. Crash testing shows Model 3 is probably the safest car ever built. My hypothesis is that Tesla designed the body the way it did for very specific reasons and Sandy may not fully understand those reasons.

I do wish we would stop perpetuating and spreading his possibly unfounded opinion as fact, particularly when the facts of crash test results and also real world crashes say something else.
 
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JeffC

Member
May 15, 2016
209
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Silicon Valley
He did say about crow though I think this is mostly about his overall impression. And that is very understandable as the fit and finish flaws are very obvious and that doesn't suggest that there could be anything significantly better with the harder parts. Once he got to look at those his impression has changed. I actually do not remember single factual statement that he needed to go back on. He also at some point states that this is what he could say at that point as the analysis of the car has not been completed.
If he were more interested in facts, he would check the gaps and finish on recent cars. His very early car probably was not as good as recent cars.

My own inspection of dozens of Model 3s had horrible gaps on the first dozen early employee cars, major improvements in the first few thousand, and almost as good as BMW in the recent cars, with continual improvement between them. I'd wager that Tesla's internal metrology department has similar results.

Paint has been good to very good with recent cars comparable to some German cars. Tesla uses the same paint booths, etc., as Audi, BMW, etc. In fairness, Tesla's paint process may not be quite as good as the best European mass market luxury cars, but it's not too far off.
 
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Garlan Garner

Banned
Mar 31, 2016
11,351
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Chicagoland
I wonder if Sandy wrote this article.

Tesla Model 3 recognized as the United States' best-selling luxury car in 2018

Wait.....did they say United States "Best Luxury Car" or did they say "Best Track Car"? Isn't it amazing that we can even discuss the track performance of the best Luxury car in the United States?

Or....did they say "Car with the most useless rivets"?

( He should have stopped them )
 

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