Exoskelton fake news?

[TheLastStarfighter]

I'm sorry to drag this thread even further though the gutter but here it goes...

I think the main disagreement is the interpretation of "exoskeleton". When Tesla announced this I immediately assumed that the 3mm flat exterior panels would be combined with thinner stamped and welded stainless panels on the inside (unibody or semi-monocoque construction). I have had lots of experience working with 1/8" 304L and 316L cold rolled sheet, just like what the Cybertruck uses. There is no decent way to make the visible 3mm flat skin exterior panels of the Cybertruck strong enough (torsionally) without internal structural members. It would be a flimsy mess. Heck, when you look at the picture of the Cybertruck "exoskeleton" on Tesla's website you can clearly see there are internal reinforcements (A/B/C pillars). And no, the pillars are not just there to bolt door hinges to. These are critical structural members of the frame (think of webs in a steel truss).

A good way to illustrate this is with a cardboard box. If all 6 sides of a box are securely taped in place then the box is very rigid. If you remove just one side of the box then it becomes extremely flimsy.

If the exoskeleton of the Cybertruck does not have a strong underbelly structurally fixed to the outer panels (either structural battery pack, cast aluminum or stainless welded floor pans and cross-members) then the frame would have very poor torsional rigidity.

And now back to the original topic of this thread... I am positive that the aluminum casting on the Cybertruck will be a major structural member of the frame in order to achieve the necessary torsional rigidity. It may be bolted, maybe bonded with resins, maybe even friction welded to the stainless panels. I would have just preferred that the underbelly part of the frame was stamped and welded stainless steel, like the prototype almost certainly is, instead of using a cast aluminum member.

The underbelly on the prototype looks like it's plastic.

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[Sonnus]

The underbelly on the prototype looks like it's plastic.

My Model 3 an Model Y have the same plastic on the bottom for aerodynamics. This is not structural, it is just for improving efficiency.

 

[VolklKatana]

Look at this article and find the Gif (from battery day) located somewhere in the middle of the article (takes a minute to load). This shows the structural pack with the front and rear castings being added. I'm sure there are weld, bonds, and rivets holding it all together but maybe this will help people visualize how this will all come together.

https://electrek.co/2021/01/19/tesla-structural-battery-pack-first-picture/

 

[Crissa]

And now back to the original topic of this thread... I am positive that the aluminum casting on the Cybertruck will be a major structural member of the frame in order to achieve the necessary torsional rigidity.

The battery pack and bottom plate create the torsion resistance. That's how it's structural.

The mega casting is to marry the parts together and carry the load of the motors and suspension.

I don't think anyone said the lighter pieces of the inside of the unibody were 'only' to mount the doors to. They do that, too, since the outer pieces wouldn't have the leverage alone. That's why you need that extra stiffness, so a point of applied force is spread evenly to the exoskeleton.

Just like the ribs in the inside edges of a crab's shell.

-Crissa

 

[TechOps]

I'm sorry to drag this thread even further though the gutter but here it goes...

I think the main disagreement is the interpretation of "exoskeleton". When Tesla announced this I immediately assumed that the 3mm flat exterior panels would be combined with thinner stamped and welded stainless panels on the inside (unibody or semi-monocoque construction). I have had lots of experience working with 1/8" 304L and 316L cold rolled sheet, just like what the Cybertruck uses. There is no decent way to make the visible 3mm flat skin exterior panels of the Cybertruck strong enough (torsionally) without internal structural members. It would be a flimsy mess. Heck, when you look at the picture of the Cybertruck "exoskeleton" on Tesla's website you can clearly see there are internal reinforcements (A/B/C pillars). And no, the pillars are not just there to bolt door hinges to. These are critical structural members of the frame (think of webs in a steel truss).

A good way to illustrate this is with a cardboard box. If all 6 sides of a box are securely taped in place then the box is very rigid. If you remove just one side of the box then it becomes extremely flimsy.

If the exoskeleton of the Cybertruck does not have a strong underbelly structurally fixed to the outer panels (either structural battery pack, cast aluminum or stainless welded floor pans and cross-members) then the frame would have very poor torsional rigidity.

And now back to the original topic of this thread... I am positive that the aluminum casting on the Cybertruck will be a major structural member of the frame in order to achieve the necessary torsional rigidity. It may be bolted, maybe bonded with resins, maybe even friction welded to the stainless panels. I would have just preferred that the underbelly part of the frame was stamped and welded stainless steel, like the prototype almost certainly is, instead of using a cast aluminum member.

It's an interesting discussion about structural design, but your posts seem to imply that you believe the design choices that Tesla's vehicle engineers are making are poor, and will lead to a weak or vulnerable design. And you prefer that they do things a different way.

I'm pretty sure Tesla engineers aren't taking design advice from this forum, so why worry and bother speculating about potential problems? It doesn't seem worth the mental energy. Wait and see what they come up with, and then decide whether you want it.

On the recent interview with Sandy Munro, Elon said that Tesla has some of the best materials science engineers in the world, and I tend to believe him. I feel confident that they'll make good metals and material choices; the CT isn't going to fall apart.

 

[TheLastStarfighter]

My Model 3 an Model Y have the same plastic on the bottom for aerodynamics. This is not structural, it is just for improving efficiency.

Yup. Are you assuming the 3 and Y are stainless steal on the bottom too?

 

[Sonnus]

I am very confident in the Tesla engineers and am sure that the Cybertruck will accomplish exactly what they want it to. I certainly hope they wouldn’t take advice from me.

My only concern is that it seems they are not designing the Cybertruck for my intended purpose. I realize I’m being wildly speculative but I’m just reading the tea leaves. It will be very good competition for the F-150 or 1500. I have no problem with this, Tesla is obviously making the right choice when it comes to the market they are targeting. It just wasn’t what I was expecting when I ordered the tri-motor based on the payload and towing specs.

If you have ever driven a 1/2 ton truck and then drive the comparable 3/4 or 1 ton truck you will know what I mean. They are completely different vehicles. Half ton trucks feel like a light passenger car after you’re driven to a 3/4 or 1 ton truck.

Of course it must still have b pillars. There has to be something to mount the door latch onto.

I don't think anyone said the lighter pieces of the inside of the unibody were 'only' to mount the doors to. They do that, too, since the outer pieces wouldn't have the leverage alone. That's why you need that extra stiffness, so a point of applied force is spread evenly to the exoskeleton.

Crissa, I was just referring to this post.

 

[Dids]

I am very confident in the Tesla engineers and am sure that the Cybertruck will accomplish exactly what they want it to. I certainly hope they wouldn’t take advice from me.

My only concern is that it seems they are not designing the Cybertruck for my intended purpose. I realize I’m being wildly speculative but I’m just reading the tea leaves. It will be very good competition for the F-150 or 1500. I have no problem with this, Tesla is obviously making the right choice when it comes to the market they are targeting. It just wasn’t what I was expecting when I ordered the tri-motor based on the payload and towing specs.

If you have ever driven a 1/2 ton truck and then drive the comparable 3/4 or 1 ton truck you will know what I mean. They are completely different vehicles. Half ton trucks feel like a light passenger car after you’re driven to a 3/4 or 1 ton truck.



Crissa, I was just referring to this post.

So when Tesla presented Cybertruck in comparison to F150 with better specs more in line with F250 you heard heavy duty and now because they are using a cast part you now think the duty cycle is lower. This is a valid concern but cast isn't necessarily weaker than machined and aluminum is stronger than some steel by weight.

 

[TechOps]

My only concern is that it seems they are not designing the Cybertruck for my intended purpose. I realize I’m being wildly speculative but I’m just reading the tea leaves. It will be very good competition for the F-150 or 1500. I have no problem with this, Tesla is obviously making the right choice when it comes to the market they are targeting. It just wasn’t what I was expecting when I ordered the tri-motor based on the payload and towing specs.

If you have ever driven a 1/2 ton truck and then drive the comparable 3/4 or 1 ton truck you will know what I mean. They are completely different vehicles. Half ton trucks feel like a light passenger car after you’re driven to a 3/4 or 1 ton truck.

Yes, I have driven both light and medium duty trucks, as well as a bit of heavy duty (although I don't drive a truck for a living or have expert-level experience). My expectation is that the CT will be a *completely* different vehicle than e.g. an F-150 or 1500.

If your intended purpose requires an extremely strong sub-frame, why not buy the CT and modify it to add reinforcement in the areas you think you're going to abuse? It's true that the first rev may have some weak points if you're using it for extreme duty, so you may just need to add in some budget for parts repair/replacement to your operational model.

 

[Sonnus]

So when Tesla presented Cybertruck in comparison to F150 with better specs more in line with F250 you heard heavy duty and now because they are using a cast part you now think the duty cycle is lower. This is a valid concern but cast isn't necessarily weaker than machined and aluminum is stronger than some steel by weight.

The specs of the tri-motor are similar to my 2012 2500HD so I was expecting something comparable. HD pickups have jumped up a lot recently with their specs but realistically, the capabilities are still close to my 2012.

I agree, aluminum is stronger than mild steel pound for pound. But there are other characteristics of aluminum that make it less than ideal in certain situations.

If your intended purpose requires an extremely strong sub-frame, why not buy the CT and modify it to add reinforcement in the areas you think you're going to abuse? It's true that the first rev may have some weak points if you're using it for extreme duty, so you may just need to add in some budget for parts repair/replacement to your operational model.

Modifying the truck is definitely an option and I have no doubt the aftermarket suppliers will offer products to improve the Cybertruck's capabilities.

I also agree that the early Cybertruck runs will likely have issues that later revisions will address. If my current truck wasn't so long in the tooth I would happily wait a few years to order a 2024 or 2025 Cybertruck. Unfortunately my truck is past its due and I'll likely keep my ealry reservation number on the Cybertruck. Tesla has a decent warranty on their cars. I'm sure if I have an issue with the Cybertruck it will show up in the first few years of use.

 

[FutureBoy]

I also agree that the early Cybertruck runs will likely have issues that later revisions will address. If my current truck wasn't so long in the tooth I would happily wait a few years to order a 2024 or 2025 Cybertruck. Unfortunately my truck is past its due and I'll likely keep my ealry reservation number on the Cybertruck. Tesla has a decent warranty on their cars. I'm sure if I have an issue with the Cybertruck it will show up in the first few years of use.

Given that people ordering now are supposedly getting order numbers out past 1 million, you might put down a second $100 for a new order now. That way, when your early order comes up you can buy that one if you want to try it out. Then when your second order comes available (in all probability in the 2024 to 2025 time range) you could trade "up" to the newer one. Or get your $100 back if you are satisfied with your initial purchase.

Or if the CTs produced are not meeting your satisfaction at the time, get your refund on the early order and wait for the later one with further improvements.

Basically, $100 is a cheap hedge of a bet. And the $100 is refundable anyway.

 

[Sonnus]

Given that people ordering now are supposedly getting order numbers out past 1 million, you might put down a second $100 for a new order now. That way, when your early order comes up you can buy that one if you want to try it out. Then when your second order comes available (in all probability in the 2024 to 2025 time range) you could trade "up" to the newer one. Or get your $100 back if you are satisfied with your initial purchase.

Or if the CTs produced are not meeting your satisfaction at the time, get your refund on the early order and wait for the later one with further improvements.

Basically, $100 is a cheap hedge of a bet. And the $100 is refundable anyway.

Good idea!

 

[Bill906]

Given that people ordering now are supposedly getting order numbers out past 1 million, you might put down a second $100 for a new order now.

I actually did this. My original reservation was Dec 2019, (I didn't know about the CT until then). Then, just before FSD jumped to $10k I placed another reservation. My reasoning, if something happened where I totaled my first CT I didn't want to wait years to get its replacement. Otherwise if my dad or someone I know decided they liked mine I'd have the $8k locked in. Either sell them my original and I buy the new one, or buy the new one for them with their money. I didn't work out all the details, and hopefully I won't NEED the second order, but refundable $100 seemed a cheap insurance from being without a CT. It will be my only vehicle.

 

[rr6013]

Stainless Steel bends before it breaks. It also is reparable. Cast breaks. CT you don’t want to break. That’s a tall specification.

Aluminum casting has to be one-trick pony that’s able to bear strain in 180 degree plane, stress diffusion without deformation, sheer point loads and then collapse, crumple and not puncture wet ware in the passenger compartment. Whew, genius indeed as Elon commends. That is how magnesium found its way into trucks in place of alum. until they found out that a mere fire fighter can’t extinguish magnesium once it catches on fire.

Engineers are going to unitize to gain force transfer through .S.S. that would otherwise fail a casting and add mass at points to strengthen the combined assembly. The assembly combined will need to absorb/defect force away from the aluminum castings.

At the end of the day, SpaceX rocket scientists will bow in respect to Tesla engineers with the metalurgy engineering and innovation brought to solve the exoskeleton application and casting assemblies.

@Sonnus’ CT will definitely have its greatest test at the point it meets terra-firma, even a sand pile is an immovable object.