Continued from Previous Post
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5. One or Two Rectangles?
grizzlyj, in effect, I am trying to redirect the thread back to where you and
egn left things on the second page, when you posted the video of the Tatra/Zetros comparison. At the end of your first post on the second page, you wrote:
And to remain on topic, if chassis twist means putting a flexy joint in the middle of a camper like bendy buses then how much of an issue is that? How ever the truck is suspended you could have a jack system to level out the camper floor, allowing a rigid, insulated and tastefully decorated sleeve to slide into place further sealing each half inside the bendybus bellows. Or a more normal crawl thru seal around a mid camper full size door, perhaps between sleeping and entertaining areas?
For me the big drawback with a Zetros is its nose, the big drawback with a flexy chassis is the height gained by the isolating camper mount, but I'd rather have what I perceive as the simplicity of a Zetros (and the theoretical Mercedes worldwide parts backup) to a Tatra at least. I would think its a few tons lighter than a MAN KAT too? And a U5000 type Mog is probably too short for what the OP has in mind. Goldilocks syndrome.
Now here I should provide a bit of narrative, and explain some of my additional design motivations.
The idea of a mid-camper, flexible-bellows, "bendy-bus" solution first occurred to me about 6 months ago, as I was doodling different layout concepts, and wondering how to create a more fully integrated interior space, in an expedition camper whose body had to be mounted on a 3-point or 4-point pivoting sub-frame, because the chassis frame was designed to flex. I was reading the latest Zetros literature, which mentions that the Zetros cab also mounts on a 3-point pivoting frame, and then the lightbulb went off. I thought,
“Hey, if the Zetros cab is 3-point mounted, and if the camper has to be 3-point mounted, then why can't they meet halfway? Why can't they split the overall length 50/50, instead of 30/70?”
However, I never much liked the idea, because it still entails a significant “break” or separation in the overall space. From a design point of view, there is so much more that one can do with a single, unified rectangle, than with two permanently fixed, separate, smaller rectangles. Just consider: many RV manufacturers will offer floor-plan variations, and often these entail significantly shifting elements and redefining room boundaries. But with a “two rectangle” 50/50 solution, that design flexibility vanishes.
So yes, this really
is an issue. It matters, a lot, both from design and marketing viewpoints.
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6. Pop-Up Choices
In addition, there is the not so small matter of Pop-up mechanics.
The UniCat can have a single, 4-side-hard pop-up, precisely
because the UniCat pop-up only mounts on the camper box, and the camper-box is structurally separate from the cab:
For the full range of UniCat pop-ups, see
http://www.unicat.net/en/individual.php .
Alternatively, the XP camper can also have a single, unified pop-up, because it is hard on just 3 sides, with the front section over the cab left soft:
But notice: the XP camper could
still have this,
even if the front of the pop-up and the roof of the truck cab were structurally fused. To be sure, in the pictures above the front of the XP pop-up cantilevers dramatically over the truck cab, and it does not attach. However, it does not attach mainly because the whole camper body is designed to easily dismount, leaving the truck-bed free for use during the week, when the owner is not camping....
There is probably nothing intrinsically
structural that requires that it cantilever, and not attach.
For further information about the XP camper, see
http://xpcamper.com . And here are a few videos:
[video=vimeo;18646984]http://vimeo.com/18646984[/video]
It's a brilliant design, and got me thinking:
"Couldn't a much larger pop-up function in much the same way? Hard on three sides, but soft in the front, above the cab? If the vehicle were a much larger, dedicated motorhome in any case (like the Unicat), then the front bit would not have to cantilever. There would be no need; the front bit could structurally fuse with the cab. Put another way, the Unicat-style vertical pop-up could remain hard on just three sides, with a long extension over the cab that has soft walls instead, just like the XP. But in order to do that, the cab and the camper body would have to remain aligned and fixed with respect to each other....."
It's hard to put all of this into words because it's a
visual idea, and it was only resident in my head and on paper as visual thinking. I do not want to post any of my sketches or detailed drawings yet, for various reasons. So I hope this verbal description, and the juxtaposed images of the UniCat and the XP above, should suffice.
Now I was a bit stumped, because I had come to accept the standard view that the chassis of an expedition vehicle
must flex. And therefore, the camper body
has to be mounted separately from the cab, on a pivoting sub-frame. And therefore, when driving over rough terrain, the camper body and cab simply won't and can't align. I then spent almost two months exploring the only spatial alternative, namely,
two separate pop-ups, one for each half of the 50/50, flexible bendy-bus solution. The first pop-up over the cab would open at an angle, like a Westfalia pop-up; and the second pop-up over the rear half would open vertically, "UniCat style", with 4 hard sides.
But I kept coming back to the obvious: I needed a completely
integrated cab/body, so that I could mount a
single, super-large, 3-sides-hard, 1-side-soft pop-up over the whole vehicle. Then, about 3 months ago, I just happened to be re-reading the SX-45 brochure, and for the first time actually understood the extraordinary nature of the claim that it was making: that the SX-45's box-frame would be so rigid, that either no or very little additional "mounting apparatus" would prove necessary.
In short, I first posted my query to the
"pivoting frames and mounting campers" thread because I wanted a single, unified pop-up. Sounds trivial, sure, but that was the immediate motivation. I read the SX-45 literature, and thought,
"Holy cow, if this is true, then I have my solution! I can design a single, fully integrated cab/body, to support a truck-camper-style, 3-sides-hard/1-side-soft pop-up. The resulting vehicle would have all the loft of a UniCat, combined with a fully integrated interior design.
But first I need to find out if this really is true."
In the beginning it seemed too good to be true. I had read almost all of the
"pivoting frames and mounting campers" thread, and had noticed the thinly veiled irritation of veterans who had little patience for newbies asking,
"Is a 3 or 4-point pivoting sub-frame really necessary?" But I needed to know the answer, because my design intentions would critically depend on it. So I phrased my question tentatively, and hung it off the MAN SX-45 brochure. After all, who knows, maybe the brochure was just hype. So too, in that first post I also indicated at least one motivation for my query: hoping for a fully integrated interior design. I wanted my question to seem at least
reasonable, the kind of question that a designer would naturally ask.
However, that was only half the story. The other half was hoping for a single, fully integrated, truck-camper-style pop-up....:coffeedrink:
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7. Torsion-Free Lite
So you see, I am strongly inclined to reject any design that splits the cab/body into two halves. As a designer, it's not just a single integrated space that I want. I also want the UniCat feeling of a New York loft. But a loft running the length of the
entire vehicle, from nose to rear bumper. And I know that I can only get
that, by mounting a completely unified cab/body on a stable chassis frame that does not twist.
Even still, your comments regarding weight and military "over-kill" are very well taken. That's why the Tatra intrigues me. If the
810 and the
Force are much lighter than the
815-7, but still provide a completely rigid chassis, because of Tatra's unique backbone tube, then Tatra is well worth considering. As far as I know, MAN does not make a "lite" version of the SX-45 that's torsion-free. The HX series is certainly not torsion-free. Whereas the
810 and the
Force do seem to be "lite" -- yet torsion-free -- versions of the
815-7.
But I am not certain about this;
egn will probably know.
So I've now laid my cards on the table; or at least a few more of them.....:sombrero:
I hope that helps. All best wishes,
Biotect
