Will Tesla use the Cybertruck stressed-skin design on other products?

Discussion in 'Tesla' started by Domenick, Dec 8, 2019.

  1. Domenick

    Domenick Administrator Staff Member

    A rendering showed up the other day of a next-gen Tesla Roadster that incorporated the stressed-skin design of the Cybertruck. I don't typically write up these types of posts (renders) unless asked, but I thought this one offered an opportunity to ask a question: if manufacturing vehicles with this type of exoskeleton results in products that are cheaper, lighter and stronger, why not use it for other future vehicles?[​IMG]

    Ironically, the Roadster may be the least likely candidate for this treatment because (and I'm assuming here) you can't get the aerodynamic profile you want in a performance vehicle. However, it might be good for a future low-cost vehicle.

    With pretty much every traditional OEM introducing more EVs now, the challenge is now getting an EV into production that will push them (OEMs) to lower prices and make them more accessible. To do that, you need a super low-cost car with still a good amount of range and functionality. My suggestion is a hatchback that comes in under $20,000 (preferably $18k, really).

    It's hard to get a great aerodynamic profile with a shortish hatch, so I think that trade-off has less weight here, especially if the reduced weight -- which is more of an efficiency factor -- helps keep the energy needed per mile lowish.

    Of course, a low-cost car doesn't need to be bulletproof, so a lighter, cheaper metal would help out. I picture something like, say, a Chevy Spark or Toyota Yaris but a single plane hood/windshield (a la Cybertruck). Or, maybe, an-even-more-cubist 1st-gen Scion Xb (actually, now that I think about it, this design might could be my favorite because it has some much interior space for its footprint).
     
  2. interestedinEV

    interestedinEV Well-Known Member

    @Domenick very interesting question. You are wading into the form vs function debate, does form follow function or form lead function?

    The appeal with the Prius is not its form, but it is high mileage i.e. function as it has a very good aerodynamic profile which helps the mileage. The Cybertuck's single plane form may not satisfy what we consider a truck design but reduces manufacturing cost (function) as you are cutting sheet metal and welding it, rather than having to shape it using expensive dies (pressing).

    If you have a car platform, you do not need the rigidity of the cybertruck, you can use lighter and cheaper materials and you can also paint them while using single plane form.

    The question therefore is "Will a EV customer go for an better range and/or low cost to manufacture, but not attractive form over a more visually appealing car which may be a little costlier or have less range?" My wife for examples hates the Scion design, it is too boxy for her. But your point is that it might be cheaper and would that motivate EV buyers?
     
    Domenick likes this.
  3. Pushmi-Pullyu

    Pushmi-Pullyu Well-Known Member

    "Will Tesla use the Cybertruck stressed-skin design on other products?"

    I'd say that depends on whether or not it works well in production. I was hoping that BMW using a mass-produced carbon-fiber body for the i3 would be a new trend which would rapidly spread throughout the industry. Sadly, it proved to be "a bridge too far", with no other large production volume car using that sort of body. Not even another model from BMW.

    I regard Tesla using a "stressed skin" construction to be experimental, like BMW putting carbon-fiber into mass production. Obviously the stressed-skin approach works well for large airliners, but that doesn't mean it will prove economically competitive for ordinary passenger cars. But if it does, we can be sure that both Tesla and other auto makers will use that in other models!

    I always knew that the EV revolution would see a lot of experimenting with different designs and different construction methods. A disruptive tech revolution shakes up the industry and the market, and there are always a lot of experimental methods being tried until the market shakes out again.

    It's great to see Tesla once again being an industry leader rather than a follower!
    :cool:
     
  4. Pushmi-Pullyu

    Pushmi-Pullyu Well-Known Member

    I've always been a fan of the "form following function" school of design. I'm pretty neutral about the Cybertruck's angular shape; it's not pretty, but I'm far more interested in its functionality. Back when I bought a circa 1992 Toyota Truck pickup, it wasn't at all because of the style, rather because it had higher gas mileage than anything else on the market. But then, that was a compact pickup, not a full-sized one. If I was in the market for a full-sized pickup, I would definitely look at the Cybertruck due to its revolutionary approach to high energy efficiency.

    I've never thought much of the Scion's very boxy shape. I have been a passenger in a lady friend's Scion several times, and the design hasn't grown on me a single bit. Of course I don't complain about it to her, but I'd never choose any car as ungainly and un-aerodynamic as that. The Cybertruck has practical reasons for its angular design. The Scion, not so much.

     
  5. interestedinEV

    interestedinEV Well-Known Member

    One of the arguments against "form follows function" is that all cars will start looking alike and that there will be little product differentiation. If all cars used the cybertruck stressed skin look, then cars would be plain looking and may not be aesthetically pleasing and drive away customers. (Again, not my view, I believe form should follow function).

    My wife for example thinks that the cybertruck form is hideous and does not want to have anything to do with it. She has been driving a Mini-Cooper for over 15 years but from a functionality point of view, it has many negatives. Yes, one can zoom in and out of tight parking spaces, but it has very little cargo room and is essentially a two seater (even with 4 doors, only a child can sit at the back). The Mini SE will have about 120 miles or so per charge, yet it already seems to have a fan following (form over function).

    So yes the stressed skin design could lower weight and costs, which will increase range (functionality). Are there people who will overlook the body style and buy an EV because it is inexpensive and has good range i.e. put function over form? Yes, I am sure there are?

    Are there going to be people put off by the spartan from and not consider such cars? Again I would say yes. The question are there sufficient people in the first category to motivate both Tesla and other manufacturers to rethink the design of cars. Elon, has taken a big bet with the Cybertruck. The initial response has been positive, but only time will tell if the enthusiasm can be sustained.
     
  6. Pushmi-Pullyu

    Pushmi-Pullyu Well-Known Member

    I've always thought that's been the case in car design, and in pickup design too. No doubt there are "car guys" who will disagree sharply because they can tell you the make and model of a car, and often the model year, just by glancing at it. But for the rest of us "unwashed masses", cars often look as alike as peas in a pod. I know it's not just me, because some people put some sort of flag, ribbon or other object at the top of the aerial on their car so they can spot it in a parking lot.

    Sure, if you drive a Mini Cooper or a Plymouth Prowler, then your car will stand out in a crowd. But that's very much the exception rather than the rule. (The Prowler is also one of the few cars which would be on my short list of modern cars if I was to choose on style alone.)

    [​IMG]

    I guess I'm in the minority who actually likes the styling of 1950's finned cars. That's back when auto designers weren't afraid to put sometimes large, bold add-ons to the basic design just to look different! Impractical as they were, I wish cars today would use such fins and other purely esthetic additions to the basic design.

    Of course, not all current styling trends are about practicality or wind-tunnel streamlining. The current trend in overly large, sometimes bloated pickups-on-steroids, all competing to look the most like a diesel semi tractor, some with front ends so ridiculously high that it's hard to see the road in front of the truck...

    [​IMG]
    Not a joke or a mere concept: The 2020 Chevrolet Silverado HD

    A lot of us EV fans find that sort of exaggerated pickup-on-steroids design even more ugly, or at least undesirable, than the Cybertruck's radical design. Personally I find such bloated pickups even more absurd than the huge tail fins on a 1959 Cadillac Eldorado!

    [​IMG]

    So altho I'm rather ambivalent about the actual style of the Cybertruck, I'm very glad and quite supportive of Tesla trying a bold new direction in pickup design! I hope even if it doesn't start a new trend, it will at least shake up the market enough to bring an end to the competition to build ever more absurdly high, grossly over-large or even bloated pickups which are cases of conspicuous consumption in wasting fuel and emitting pollution.

    [​IMG]

    Keep going Tesla!
     
    Last edited: Dec 9, 2019
  7. bwilson4web

    bwilson4web Well-Known Member Subscriber

    I prefer cars like in the 1930s ... like my wife, curves matter.

    Bob Wilson
     
  8. You know, that Cybertruck wouldn't look so bad, if it didn't have all those sharp edges and pointy corners. I don't mind a bit of a sculpted look, but not one that looks like it was done by a giant cheese slicer. I honestly don't get it... Could have been a real hit, if they didn't turn off 90% of current truck owners.

    Will have to see what Ford and others come out with. At least Tesla has set a benchmark, not the least of which is price (for an EV), for the competition to match or beat.
     
  9. I might add that what the made the S, and later the 3, so popular is not just the functionality, but also the looks (exterior that is). Why wouldn't he build on that success with the Cybertruck?
     
  10. Pushmi-Pullyu

    Pushmi-Pullyu Well-Known Member

    The reason Elon and/or Tesla gave was that bending 3mm thick stainless sheet metal into a car body was difficult to do with regular stamping methods and would quickly wear out the dies. So they went with a design where they could just fold the sheet metal into the right shape, presumably with the fewest number of bends.

    The result is suppose to be what Elon described as a "stressed skin" approach to vehicle bodies, like large airplanes use, rather than the body-and-bed-on-frame build of most pickups, or even the "unibody" vehicle design used by many or most auto makers, including Tesla with its previous models. Tesla, or Elon, claims that's a cost-savings method of manufacture and also a way to make the vehicle significantly lighter.

    I don't know how true those claims are or are not; certainly there are other vehicle bodes made of stamped, curved stainless steel body panels. Of course, those generally aren't 3 mm thick.

    As I said above, I regard this approach to building passenger vehicle bodies as experimental. Only time will tell if it's successful or not.

     
  11. A cockroach has an exoskeleton but doesn't have doors. A stressed skin can't work unless the doors were rigidly fastened all around to the surrounding structure and that doesn't appear to be the case, judging by the photos. And then if you opened a door the whole thing would collapse. Am I wrong?
    My feeling is that this talk is just Elon marketing spin and it's simply a stamped steel welded unibody with steel doors that have a SST outer panel.
     
    interestedinEV likes this.
  12. He is probably going to fool the heck out of all of us, incl the competitors, and the final product will actually end up looking completely different, and not unlike his other cars. That Cybertruck concept was just a trial balloon. The outside skin and looks is the easiest thing to change on a car. I think he is maybe smarter (crafty) than than we think.
     
    bwilson4web and interestedinEV like this.
  13. interestedinEV

    interestedinEV Well-Known Member

    I agree with you, except that he has a much stronger outer panel to give it more rigidity against torsion or twisting effects, then is normally needed.

    Stressed skin, Unibody are all variants of the semi-monocoque system as opposed to the moncoque design which is really the exoskelton design. ( The word monocoque is a French term for "single shell" or (of boats) "single hull".[1] First used in boats,[2] a true monocoque carries both tensile and compressive forces within the skin and can be recognized by the absence of a load-carrying internal frame. https://en.wikipedia.org/wiki/Monocoque).

    The very need to hang a door implies that there needs to rib or frame for mounting. So it cannot be a monocoque structure, it has to be semi-monocoque in design.

    So it seems to me that Elon has made some modifications to the car design (which are unibody) to suit a truck. So it is nice sounding name, but may not really mean much at the end, time will tell.


    By contrast, a semi-monocoque is a hybrid combining a tensile stressed skin and a compressive structure made up of longerons and ribs or frames.[3]

    Other semi-monocoques, not to be confused with true monocoques, include vehicle unibodies, which tend to be composites, and inflatable shells or balloon tanks, both of which are pressure stabilised. The term is frequently misused, particularly as a marketing term for structures built up from hollow components
     
  14. Pushmi-Pullyu

    Pushmi-Pullyu Well-Known Member

    Some types of beetles have exoskeletons, but also retractable wing covers. So your analogy here is rather flawed.

    [​IMG]

    I'd say it's not so much that you're wrong, as that you're oversimplifying the matter. A large airplane uses stressed-skin construction, but that doesn't stop it from having doors and hatches which open, nor prevent it from having functional landing gear attached to interior structural members. Obviously the plane doesn't collapse when it's supported at only three places by the landing gear, even when the landing is somewhat rougher than normal.

     
  15. Almost all small aluminum aircraft are semi-monocoque structures (wings, fuselage and tail) utilizing bulkheads (with flanges), ribs and stringers to position the skins at strategic locations and for support around doors, wing/tail attachment points and the firewall area. What makes the very thin aluminum skin (typically .016 - .040") super strong in compression is the curved edges. Creases are also used, but more to reduce vibration and noise. It makes for an extremely light, but strong structure which of course is very important in airplanes. Cars/trucks also use this design/engineering with their curved and sculpted structures for the same reasons.
     
  16. Pushmi-Pullyu

    Pushmi-Pullyu Well-Known Member

    Tesla has also given us this image, which despite the description of a "stressed skin" structure, clearly shows some internal reinforcement around the door frames:

    [​IMG]

    I confess I'm having a hard time seeing how any vehicle supported by wheels can be a fully "monocoque structure"... that is, to have the framework fully integrated into the "skin". In fact, thinking about it, the only vehicles I can think of with strictly monocoque structures would be certain types of boats, including dugouts and lightweight plastic or fiberglass rowboats without a motor mount. But no doubt there are others I can't think of at the moment.

    I thank "interestedinEV" for his explanation of the term "semi-monocoque"; from that, I think I understand what it means.

    Anyway, I thought the above image was interesting, so I posted it because it relates to the discussion, not as evidence that any of my comments on this subject are either right or wrong. I note that, from appearances only, it seems to indicate (at least to me) that the Cybertruck's structure isn't entirely supported by the "skin" alone. But then, I never thought it was, despite Elon's description. (For example, how could the suspension support the weight of the entire car if it was just attached to "the skin" at a few points?) The image seems -- at least to me -- to support the assertion from "interestedinEVs" that it's a semi-monocoque structure.

    Another unanswered question which has been raised in discussions in comments to InsideEVs articles: What about the front crumple zone, designed to absorb the force of an impact in a frontal collision? How does an auto maker create a proper crumple zone in a "stressed skin" construction of sheet metal which is substantially stiffer than ordinary body panels used in cars today?
     
    Last edited: Dec 12, 2019
  17. interestedinEV

    interestedinEV Well-Known Member

    Actually I will go one step further, most modern aircraft are semi-moncoque design, the monocoque design cannot be used beyond small aircraft as the entire load is borne by the skin. Smaller rockets and missiles can be moncoque design if they have internal pressure to keep the structure in place.

    Stressed skin is to make it a load bearing surface. That does not mean that you cannot attach anything outside or inside. A pure exo-skeleton or what is a moncoque design means that the entire load bearing surface is on the skin and there are no ribs and stingers. So beettle can have attachments inside and outside. You could have a opening in monocoque design or even a door, but it would need to attached to the skin but cannot be very big (picture below). Clearly, the cyber truck is a semi-moncoque design, the unknown question is how much of the skin is load bearing

    Here is the net of it

    Cybertruck is an innovation in terms of how trucks are designed and one of the design considerations is ease and cost of manufacture. It borrows concepts from both car (sedan and so on) design and rocket design (Space X). However, there have been some compromises. The form has to be unconventional and the shell has to be much thicker, as the usage conditions for truck are different from that of a car.

    As my long experience tells me, what looks good on paper often fails when it gets to the factory floor. It is easy to make an hand crafted prototype, but mass producing the same thing is a different ball game. Elon should know this better than most. I am with @R P in that what actually comes out 2 or 3 or 4 years from now is going to be different from what it looks today. However Elon has achieved a small victory, he has media and the users buzzing, created a small publicity sensation and put his competitors on watch.

    [​IMG]
    Zeppelin D.I, the first production all-metal monocoque aircraft
     

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