ALL CyberTruck discussion

[Curt Renz]

Mexico News Daily: Mayor in San Luis Potosí puts down the cash for 15 Tesla Cybertrucks

 

[winfield100]

“Rolling rolling rolling, keep those tesla’s Rolling”

 

[Fred42]

Maybe everyone's seen this by now

 

[JRP3]

“Rolling rolling rolling, keep those tesla’s Rolling”

Not really Cybertruck related.

 

[mongo]

Not really Cybertruck related.

Since you made me go back and look
The pedestals on the end would work great for pull through when towing a camper. Especially if the tri-motor had dual charging ports (which I do not expect).

 

[JRP3]

That depends on how and where the flatbed was parked.

 

[LN1_Casey]

Worldwide Cybertruck reservation tracker

Self report doc for those of us who ordered a Cybrtrk.

 

[Doggydogworld]

Lower CD at higher speeds? That is counter-intuitive. Where can I read the science behind this?

It's very common for vehicle Cd to decrease as speed increases. This web page has a graph (scroll down) with some vehicle Cd data from both small scale and full scale wind tunnel tests. They helpfully show full scale vehicle speed in addition to the somewhat abstract Reynolds number. As you can see, Cd drops dramatically with speed until about 40 mph (64 kph). Above that the decrease is very gradual.

There are three basic types of flow - laminar, turbulent and separated. Laminar is when flow in the thin boundary layer, right next to the surface, is smooth and orderly. Flow within a turbulent boundary layer is unsteady, but still flows downstream.

Both types of boundary layers can separate from the surface, leaving a region of low-pressure vortices that include reversed flow. Separation most commonly occurs on the back part of your vehicle and downstream of bluff protuberances (e.g. side mirrors), and the low pressure regions create "suction" forces trying to pull you backward.

There's a bit of a paradox here - laminar flow has lower skin friction (viscous) drag than turbulent. So laminar is good, right? Not so fast. Laminar boundary layers are also more prone to separation. And separation is a much bigger deal than skin friction for cars and trucks. This Quora answer from Jeff Peterson explains the various flows better and includes a video with some good visualizations. It also explains why Cd drops so dramatically with increasing speed at very low Reynolds number where viscous drag dominates (viscous drag varies with velocity instead of velocity squared).

Lol, study some aerodynamics. That HP air in front of the bumper is a virtual plastic bumper, improving airflow...

Even though the region of high pressure air in front of the bumper improves upstream airflow, it's still high pressure air applying rearward force over a large part of that front bumper. It's far from ideal.

 

[lascavarian]

"Battery day"?

Did I phrase that poorly?

Come Marchish, there is to be a public event related to battery tech if I have it right. Chemistry and production implications if I understand it correctly. I perceive it as a unique event that will expand clarity.

We will hopefully learn how the packs for the Semi and Roadster 2 will be configured. I would expect trends to apply to the CT as well.

The date is not locked down yet.

 

[jebinc]

Did I phrase that poorly?

Come Marchish, there is to be a public event related to battery tech if I have it right. Chemistry and production implications if I understand it correctly. I perceive it as a unique event that will expand clarity.

We will hopefully learn how the packs for the Semi and Roadster 2 will be configured. I would expect trends to apply to the CT as well.

The date is not locked down yet.

Yes, I was looking for the date. I thought the last one (BD) was this past July; thought you implied there was another one scheduled in the near future and I got excited...

 

[Renew]

A great analytical video on exoskeleton, cold rolled 30x steel and its properties depicted from stress-strain curve.

This also explains that only the outside of the skin is hardened by cold rolling and inside is still somewhat malleable.

 

[AudubonB]

I placed the following on the "Unexpected technology" thread, but on reflection, I think it fits here better, so here it is. I found the preceding post's video to be a good description of the virtues of cold-rolling, although its presenter went too far off the rails discussing the shenanigans that Detroit has undertaken over the past decades. Anyway, here is the post I'm copying over:

On the "Main" thread, there is some moderately off-topic discussion regarding the potential of cast foam steel (or foam cast steel) as coming to Tesla vehicular production. Tying that in to the patent applications Tesla has introduced in order to create a 3-dimensional frame-molding machine, there develops something of a compelling story. I am happy to port over to here the appropriate posts if a discussion so warrants.

Perhaps.

As another poster points out, there are significant hurdles against using a cast product to create a vehicle's skin. It is - or, traditionally, has been - an inherently "crude" product, whose surface is inescapably rough. The same (?) poster states the benefits of cold-rolling a steel sheet are formidable.

My take on this:

• Yes - cold-rolling steel can be envisioned as analogous to kneading bread dough. You are imparting to the mixture both a uniformity of the ingredients so that they are in appropriate proximity to each other, and developing the protein molecules in the wheat's gluten a characteristic that creates both elasticity and strength. In steel, you are doing effectively the same: the crystalline chromium (mostly - but also nickel, manganese, cobalt and often vanadium, tungsten and a few other elements) is likewise kneaded throughout the iron matrix to endow the entire meld with remarkable resistance to oxidation (rust!), chemical corrosion, elasticity, strength and other desired characteristics.
• Now, foamed-steel is something of which I am lamentably ignorant, other than intrinsically the physical structure of a foam matrix being a staggeringly wondrous blend of light weight and both yield and tensile strength (I'm not sure about compressive nor impact strength; I suspect fatigue strength to be excellent). I also have not learned of foam steel being produceable in a combination of large sizes and volumes - woul be delighted to learn otherwise if anyone knows of same.

Putting these together, my thoughts are that at present Tesla likely is looking to create with CT a product that combines something like a traditional frame that also combines an exoskeleton body. I truly am incapable of envisioning a truck - pickup or larger - that can be a heavy hauler if its entirety is purely an exoskeleton. This may represent my knowledge weakness....if so, I plead guilty. Nevertheless, working with the assumption I am correct, I can see the staggering advantages of a frame that is foam cast combined with a body that is origami-folded cold-rolled stainless. All the right strengths exactly where they ought to be. How it is that Tesla would marry the two pieces? I do not know, and I admit this diminishes the smoothness and speed of the production process...but it also appears to me that both these portions individually could be created faster than by traditional methodology.

 

[lascavarian]

This may represent my knowledge weakness....if so, I plead guilty. Nevertheless, working with the assumption I am correct, I can see the staggering advantages of a frame that is foam cast combined with a body that is origami-folded cold-rolled stainless.

As I see it, (not a structural engineer) there is less advantage for the exoskeleton of 30x cold rolled SS if there is a frame. The SS is way too expensive/heavy and adds less if there is already a frame.

I could see a foam cast nose-cone (or other pieces) that could be more impact absorbing that could bolt onto an exoskeleton for crumple zones and/or helping with drag. But each of these adds expense and complexity if they could be reasonably duplicated by a few more folds of SS.

Also interesting will be the use of adhesives particularly if they can offer some form of thermal insulation. Fun to think about.

The frame concept is flawed in that it is primarily 2 dimensional and suffers from weakness (twisting). It also wastes space in the vertical plane by forcing the cab up. The exoskeleton is more like a 3-d pyramid and extremely stable and space efficient. An active adjustable suspension also helps.

Having a cast body/frame would be efficient but I don't know how fast it can be done and there are concerns related to cooling into a dimensionally predictable form. Folding holds the potential to be amazingly fast and accurate.

I am excited by both approaches and I think we will see both holding an important function down the road.

In the study of insects the advantages of an exoskeleton become apparent - integrated form, function and structure. If insects had evolved a way to use 30x cold rolled SS then we would probably not be here

 

[jerry33]

In the study of insects the advantages of an exoskeleton become apparent - integrated form, function and structure. If insects had evolved a way to use 30x cold rolled SS then we would probably not be here

And if they had lungs. The hard cases of some insects is likely stronger for the same size and thickness, but fortunately insect size is limited by the partial pressure of oxygen. That's why there were 1 m dragonflies in the Cambrian Period, oxygen content was much higher than today.

 

[AudubonB]

(replying to lascavarian's #673)
I understand that argument of frame/no frame. I will repeat that it may be an internal failing of my own, but I assert an inability of seeing how an exoskeleton - as mighty as it is in other ways - can properly withstand the strains of a heavy pull.

Changing the topic just a bit, you also mention how having an active adjustable suspension plays an important part. I utterly agree. I have not, however, written this before (errr...I did in some post but no longer remember where that was) but will take advantage of the moment to say that I am holding my breath in anticipation of learning the details of what Tesla has for us here. My modest understanding of the various forms of vehicular suspension has led me to propose that the only form through which Tesla can satisfy the extremely demanding and often counter-acting challenges of

• enabling very high and very low suspensions
• maintaining appropriate tire camber at all speeds
• being robust enough to stand up to the loads a pickup demands

is with a supremely cleverly designed multipoint suspension. And the complexity of such a beast in itself makes me shudder when I consider what it is I subject my own pickups to...and there are many who hit them far, far harder.

 

[jerry33]

• maintaining appropriate tire camber at all speeds
• enabling very high and very low suspensions

Citroen was doing both of these in 1955. The camber was maintained using centre point steering.
The hydropneumatic suspension delivered something like 9 inches of travel, maybe more (it's been a long time).
Suspension geometry pieces were pretty simple.
I'd be really surprised if Tesla Engineers couldn't come up with something.

 

[AudubonB]

That is true; it did. I was in one of those Citroens as a kid all over Holland, Belgium and northern France.
But a pickup is far more demanding.
Good point, though.

 

[jerry33]

That is true; it did. I was in one of those Citroens as a kid all over Holland, Belgium and northern France.
But a pickup is far more demanding.

Not too much more though based on the way I drove my DS-21. It worked pretty well off-road.

 

[bhtooefr]

Center-point steering wouldn't maintain camber through ride height variation, though - that would be related to other elements of the suspension geometry instead.

AFAIK, all of Tesla's suspension designs have the effect of having a shorter upper link than their lower link, meaning that they explicitly promote camber change as the suspension compresses. This is usually a desirable behavior to maximize cornering grip.

However, it definitely causes problems if you're adjusting suspension height...

You can have equal length control arms, and eliminate that effect, at the expense of grip. Or, you could use leading or trailing arm suspensions that are set up to not have camber variation with travel. Or, you could even use live axles (extremely unlikely for Cybertruck, although Semi uses them) or de Dion tubes - these have camber change in single-sided bump (and I believe they tend towards optimal camber in roll, too, as a result), but not with height changes that affect both sides, which actually makes their handling more tame than some primitive independent suspension designs (I've seen replicas of vintage Porsche race cars that had swing axles originally using de Dion tubes to make the handling better).

Edit: Looks like Motor Trend says it uses independent A-arm suspension. So, in that case, the only way camber change will be avoided is if the A-arms are equal length.

In that case... so with A-arms, wheel track shortens as the suspension travels away from neutral. With leading/trailing arm setups, wheelbase shortens as the suspension travels away from neutral. And, with live axles and de Dion tubes, wheelbase and track can stay the same.

 

[JusRelax]

Has anybody noticed that it seems like since about two days ago, the rate of CT orders is now increasing instead of decreasing?