Exoskelton fake news?

[Jhodgesatmb]

Pretty sure that by having floor costing front, back or middle does not preclude the exoskeleton design. The truck would require some sort of floor. If the entire truck was a casting it would still be an exoskeleton...

https://insideevs.com/news/482658/musks-remarks-cybertruck-doubts-exoskeleton/

It is sad that anyone can write anything with no engineering knowledge whatsoever and a lot of people will believe them. I read the article, since you posted it, and the author is an idiot looking for clicks. Yes, the CT will have an interior cabin and an interior bed; you won’t be touching the exoskeleton. The doors won’t be a single sheet of metal either. After all, they have to contain the windows, a locking mechanism, etc. i could go on but it would just be more of the same.

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[Newton]

This internal frame does have all the curves and such, but it can't be 3mm there, and it sure as hell isn't cast. I'm pretty sure it's stamped stainless, but of a much thinner gauge. Just the exterior (exo) is 3mm. I'd love to see how it's welded/ spot welded

I think I heard something about friction stir welding, or adhesives. I hope that the internal frame is stainless and not aluminum, as I think their other cars have aluminum unibodies. But whatever works!

 

[Crissa]

I hope that the internal frame is stainless and not aluminum, as I think their other cars have aluminum unibodies. But whatever works!

Tesla makes no car out of a single material.

Tesla's megacasting parts are an aluminum alloy unique to them.

-Crissa

 

[Newton]

Tesla makes no car out of a single material.

Tesla's megacasting parts are an aluminum alloy unique to them.

-Crissa

I didn't say they did, but sure, sounds good.

 

[Crissa]

I didn't say they did, but sure, sounds good.

I can't find it outside his videos, but Munro had this great chart where he was tracking which pieces were aluminum, steel, composite; and which pieces were cast, stamped, extruded.

He said Tesla was always mixing materials, using what worked best for whatever part. Not wedded to aluminum just because it was lighter, or cast; or to steel. If a piece could be made cheaper or better with another material, they'd just do it.

He seemed to like that.

-Crissa

 

[rr6013]

It is going to be real interesting for those who get to take delivery of the first Tesla exo-skeleton/structural battery pack/frt+rr casting assembly.

Stiffness, compliance, acoustic signature, tar line tire snap through structure and tin can are going to be watch words on vehicle engineering.

No amount of annoyance dampens a 4x4 BEV at this price. Tesla success with its first ever exo casting structural battery will be judged by how well they get its beyond S3XY engineering tamed.

Going forward? Hope is, that Cybertruck is not only Tesla’s FORD F-150 success but a whole lineage of namesake vehicles that Tesla expands on its cyber function in keeping with its simple concept.

 

[ricinro]

A titanium Cybertruck would be epic. I would honestly be willing to pay >$100k for a titanium Cybertruck but that unfortunately won’t happen. Unless Tesla designed a Mars-spec Cybertruck. Then titanium starts to make more sense.


What on God’s earth are you talking about? Of course all cars are designed and built with unibody frames. Are me and BillyGee the only two people in this thread that realize the Cybertruck is a unibody frame design?


I’ll have to challenge you on this one, what exactly makes my statement outdated? Welding is always stronger than bolts or bonding in regards to metal. When the SpaceX Starship was first designed it was made of carbon fiber (one of the best composites available). But then SpaceX scrapped millions of dollars worth of engineering and research to abandoned the carbon fiber and go with welded stainless steel. What exactly are you talking about? I have to imagine you are comparing a few random spot welds to a completely bonded structure. The bonding is obviously stronger in this case. With the spot welding you are only fixing a few small points together whereas the bonding occurs along the entire seam. Also, spot welding is the absolute worst kind of welding you can do.

The fundamental material properties can not be changed. You can expand their envelopes with alloys but not by much. Anyone that has worked with cast or extruded aluminum knows these limitations very well. Let’s find a metallurgist to see what they have to say on the subject.


Never said my car has a megacasting. My comment was simply in regards to Tesla’s engineering and build quality. I thought I made that pretty clear?

https://www.engineersedge.com/aluminum_plate.htm

Aluminum alloys and their material properties vary widely

I am curious about the allow Tesla uses as it was designed to retain net shape after casting... that is cool!
but is it tough like 7075? or brittle like conventional aluminum cast alloys? metal fatigue?

 

[Crissa]

Elon said it's not brittle because of how they temper it, and their special alloy cools slower which allows them to make such a large pour.

But that's all I know.

-Crissa

 

[HaulingAss]

I am not sure I want Tesla getting engineering inspiration from a toy.

All joking aside, I think this approach is fine for a car that is intended to drive on smooth roads. I just don’t like the idea of a cast aluminum frame on an off-road truck. A truck frame gets twisted, stressed and abused if you use it like I intend to. And, regardless of how well it is engineered and built, cast aluminum does not respond well to this.

I think you have a misuderstanding of the materials properties of the type of castings Tesla is using and how they are using the alloy under-chassis.

These are not the low quality gravity castings of cheap parts such as you might find on typical consumer goods. They are pressure cast using a recirculating liquid thermal management system to control the cooling of the metal and using huge hydraulic presses to apply enormous pressure on the molds as the aluminum is changing from liquid to solid. This mimics the benefits realized by forged parts by preventing small voids and aligning the structure of the metal alloy using 8,000 tons of pressure at the critical time and rapid cooling of the metal using the recirculating cooling system. The resulting part is incredibly strong and light.

A legacy truck uses I-beams and excessive frame flexure to handle large loads and better distribute the weight to the wheels. The frame is only strong in the direction of the load and the wheels have limited travel with which to absorb terrain irregularities so it's going to flex excessively. The Cybertruck will have the strength and rigidity and additional wheel travel to use the superior method of keeping the chassis rigid and using the suspension to "float" the load while the suspension absorbs more of the terrain irregularities. When the suspension is fully compressed on some wheels and fully extended on other(s), the chassis is designed to handle the rated load without excessive flexure. Through triangulation, the incredibly strong roll-hardened, high-strength stainless steel attached firmly to the lower pressure cast alloy lower chassis, becomes incredibly strong and able to resist tremendous loads.

For extreme off-roading in low traction situations the lack of chassis flex will reduce the available traction once the wheel travel is used up but this is minimized in normal work-type situations by the long-travel suspension. Extreme rock crawlers want a lot of chassis flex to conform to the ground better.

However, the rigid chassis has numerous and dramatic benefits when it comes to towing heavy loads and for general handling characteristics. It will steer very precisely and trailer sway, generally the limiting factor when towing heavy trailers, will basically be eliminated, at least when towing any reasonable tow setup. It will corner flatter at high speeds and resist roll-over like no other truck on the market (including the GM Hummer EV and the Rivian). It will also handle better when doing normal off-roading on rough and pot-holed fire roads and the like.

As to durability, no, I wouldn't worry, it's going to be a tough truck. Like any completely new vehicle platform, there will be some teething issues, hopefully all minor but more serious issues cannot be ruled out. For that reason, anyone with an early reservation (defined as a lower reservation number than mine) might be wise to cancel their order now and wait for the first few months of production to prove itself. The truck will only get better as Tesla always makes numerous small improvements early in a new vehicles production. This will have the added advantage of helping me get mine sooner.

 

[HaulingAss]

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

Good analogy with the crab shell!

Also, it seems some people on this thread don't understand how roll-hardening completely transforms the characteristics of whatever 300 series stainless steel Tesla is using. Cold-rolling, under hardened steel rollers and many tons of pressure, displaces the metal and aligns the atoms more tightly making the material much stronger and more rigid. Both the inner and outer layers of the 3mm stainless are hardened. It can be thought of as turning the sheet product into a big, thin I-beam. It doesn't resemble the pre-cold-rolled product at all. This is how it is able to deflect 9mm handgun rounds that would go right through the same material before it is roll-hardened. Cold-rolled SS also doesn't resemble the "flimsy mess" some are envisioning. Remember, Tesla has some of the best materials scientists and engineers in the world. Are they perfect? Of course not (no engineer is). But they look at vehicle engineering right down to the atomic level. They are thinking outside the box when they design the load paths on the Cybertruck and how they can use their materials expertise to craft a superior vehicle that will not fail when repeatedly loaded. In comparison, a conventional 1 ton truck is not engineered for anything but low cost and not having to excercise the engineers brain too hard.

To worry about aluminum fatigue without even knowing or understanding the design specifics is silly beyond belief. Do you really think Tesla engineers were told to ignore how the product would perform over time when regularly loaded to it's limit and driven on challenging terrain? Tesla is not making a structure that's going to fail when used as a truck. Do you really think no one on the design team has expertise in aluminum fatigue?

 

[Mr.Dee]

A truck frame gets twisted, stressed and abused if you use it like I intend to. And, regardless of how well it is engineered and built, cast aluminum does not respond well to this.

Your statement assumes that the geometry would be the same between a steel part and a cast aluminum part. If that was true then so would be your statement.

But that's not how engineering works. They know what the material properties are and they know where the fatigue limits are. Applied loads are easily calculated and the cast aluminum part is designed to keep stresses and deformations below a standardized level to increase expected cycles to any number they see fit.

It's not as if they designed a perfectly good steel part and then randomly decided to switch to cast aluminum without changing the design. In reality, they could make the mega casting out of paper, or cotton candy and still make it work just fine.

 

[Crissa]

Very technically, carbon fiber is like paper. ^-^

-Crissa

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