pivoting frames and mounting campers



Many thanks. You've answered a lot of the questions that I had, and I've ordered Ocker's book from Amazon.de. I am just at the beginning of my research process, but your feedback has helped immensely. Just found the threads in which you discuss your own build and provide pictures, at http://www.expeditionportal.com/forum/threads/11614-MAN-6x6-camper and http://www.rv.net/forum/index.cfm/fuseaction/thread/tid/20933867.cfm . A terrific rig, and the blue exterior is great!


Casting about a bit using the Google pdf-search, I came across a document that includes a detailed diagram of a container loading system for a MAN KAT A1.1. See http://gulf.pexi.com/pdfs/Pexi_Surplus_MAN_Container_Chassis.pdf , and here's the diagram:



Also came across an “Army UK” page, for a surplus MAN KAT A1 8x8 Cargo Truck with HIAB crane, that seems to equivocate as to whether the box-frame is stiff or not -- see http://man.army-uk.com/equip.php?ID=346 .

It first claims that the box-frame does not pass along any torsion, even when driving at full speed in difficult terrain. Then in the middle it states that the frame is based on the TGA, and is “low torsion". And finally, a few paragraphs later, it claims that the KAT A1 frame is similar to the SX series, in so far as it is “100 % torsionally stiff”:

“No strategic vehicle is more reliable and long-lived.

The A1 series is probably the most mobile and reliable truck on earth.
It is primarily deployed as a carrier for sensitive weapons systems, since its
boxed frame structure does not pass on any torsion, even when driving at full
speed in difficult terrain. It is the only truck with a loading interface on which a
Patriot system can be mounted entirely without compromising mobility.
Vehicles in the A1 series are military trucks with strategic importance. Their rigid
axles and boxed frame construction give them an unsurpassed record of mobility
and reliability in any terrain.

It was scheduled for 30 years of use, making it the military vehicle with just about
the lowest lifecycle costs of any in existence……

A strong basis – the ladder frame.

The body-friendly, low torsion ladder frame of the MAN CAT A1 8x8 is based on
the tried and tested series frame of the civilian TGA range and is
designed for service with a large off road proportion – reliability
built-in. It is made of high-strength, fi ne grain steel and has riveted
and bolted cross members and a steel bumper. Due to the low
torsion frame, comfortable and gentle transport is guaranteed.
The lateral acceleration acting on the platform or body is low.

Comfortable and robust – the leaf suspension.

Like the frame the suspension has stood the test in many thousands
of MAN vehicles. The leaf suspension further developed for
the A1 & SX with long, wear-free, rubber mounted springs, large shock
absorbers and stabilisers absorb most ground irregularities.

100 % torsional stiffness – the box-type frame.

The extremely torsion resistant box frame with hollow longitudinal
members and welded tubular cross members put the A1 & SX in a
class of its own. With this design the suspension absorbs even
extreme terrain irregularities. The desired consequence: the body
remains unaffected even during fast off-road driving.”

So you would probably say that we should trust only the second claim in the middle, that the frame is "low torsion", and not "100 % torsion free", right?


Here are some additional pictures from the same website, for a MAN KAT A1 8x8 15t container carrier (also see http://man.army-uk.com/equip.php?ID=346 ):








On a vehicle of this type, how high off the ground do you think a full-width, 2.54 m wide payload would be? Where exactly would the container begin on the sides? At 1.5 m above grade? At 1.6 m? I know that this will depend partially on tire size and pressure, i.e. whether they're Michelin 14.00 R 20 (approx. 1.26 m in diameter), or Michelin 16.00 R20 (approx. 1.34 m in diameter). And so too, load weight.

The standard MAN KAT schematic gives H3 values for the two tire sizes, 1.249 m and 1.28 m respectively. But as the pictures of this vehicle make clear, a full-width payload has to mount well above that, and in particular, above the wheel arches:



Put another way, for design purposes, where should one realistically think of the payload (i.e. the camper) as beginning? At 1.5 m above grade? At 1.6 m?


You wrote:

I had once access to MANTED the MAN modell and construction database, but I cannot remember if it contained information about the SX series. But you may post your questions in the german KAT forum. There are a lot of knowlegable people around there that may know all the details you need.

I have already done extensive downloading from the MANTED database for civilian trucks, at https://www.manted.de/manted/epl/einstieg.epl?sprache=us , http://www.manted.de/manted/aufbaurichtlinien/gb_all.html , and https://www.manted.de/manted/epl/einstieg.epl . But would you know the link for the military version? Is it accessible to the public?

Ever since Rheinmetall AG took over MAN military, public information about MAN military trucks seems less readily accessible.

Again, many thanks,

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I think the broschure mixes statement for HX and SX. The SX is based on the KAT frame and is nearly torsion free and th HX is based on the civil TGA frame.

The height at which a cabin on a KAT/SX will be located depends heavily on the weight. My cabin was originally about 2.48 m high and the total height at 18 t with 14.00R20 tyres was 3.90 m. An unloaded KAT has its plattform at about 1.70 m. I didn't keep the original distance between the rear tyres and the lower edge of the plattform, but reduced it about 5 cm to save height. This is no problem because we our motorhome is not indended to be used in the extrem situations, where this extra space is needed. It is designed as overlander and we wouldn't risk it by pushing it to very extreme terrian where crawling is necessary. The risk causing damage would be much to large. It is our home and not an offroad rallye vehicle. Other people installing 16.00R20 tyres on an old KAT will have the same problem with plattform distance.

As I added solar power in the meantime, the total height is now about 3.95 cm, when it is fully loaded with 1300 l fuel and about 650 l water and other supplies for a total weight of about 18 t. Even if I wanted I couldn't install 16.00R20 tyres.

There is still room between tyres and cabin when the suspension limiter is hit on both sides. But the tyres will hit the cabin when we would crawl through extreme terrain, where one side of the axle is going up and the other side is going down into extreme position. The cabin is protected against collision by a 4 mm thick aluminium plate at the lower side. With hydraulik suspenions of an SX the height can be kept constant independent from load. A friend, who is also one of the best KAT mechanics available, has installed a hydraulic suspension to his 4x4 and can control everything regarding suspension.

Regarding your project you will run into a serious problem with the SX - the placement of the engine. The engine of the KAT/SX is located behind the crew cab and not below like the TGA. The reason for this that the military versions have to be able to be transported on railway and concurrently the fording depth has to be kept to at least 1.20m. So the engine has been placed behind the crew cabin. Another reason for this placement was that originally the KAT was designed to be able to swim. But after first successful tests with the first 3 prototypes this concept has been dropped because of cost.

So to get everthing on even level you would have to move the living level to about 2 m height. The cockpit would alse have to be moved up considerably to get the advantage of an integreted layout. As you have seen in rv.net I had an integrated camper before the KAT. We liked this integrated arrangement very much and also had the idea to put a bus hull onto it. But because of all the effort we dropped this Idea very soon. Because of the watercooled engine of the SX it will be not as hard, but still a major rework will be necessary.

I see only two solutions to get this done. Both replace the standard engine and driveline:
1. Move the engine with conventional driveline to the back like with a bus
2. Use a diesel/electric/hybrid driveline

The first has been already done by a KAT II owner. He replaced the standard engine by a tank engine and put it to the end of the frame. He build everthing by himself and had documented it in the lkw-allrad from, which not available any more. But he is still active in the kat-forum.

The second solution has much more appeal to me, because I am electrical guy and have a lot of interest in electrical vehicles. If I would have about $300.000 to spend freely, I would convert my KAT to a serial hybrid vehicle with two smaller generator units, battery storage and 3 powerful electric motors for an electrical range of 100-200 mls. The outside would be covered fully with solar cells to get at least a small part of the energy from sun directly. But this is just a dream. :sombrero:

This all is now getting more and more off-topic and should be discussed in detail in a new thread.
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Today I looked through my large collection of truck images, especially the KAT ones, and found the build of an integrated camper. When you get the KAT book on page 118 you will see an image of it. It was build by Unicat based on the Austrian version of the KAT. It doesn't look very appealing. The silhouette of the cab is just extended to the back. I have two more images in my collection, but as I don't own the rights I cannot post them here.

In the book there is also stated that all of the KATs converted by Action Mobil and Unicat at that time where prototypes and not the original military vehicles. This may be the reason why we don't see that many KAT campers from both manufacturers. Another reason may be that the technology is now more than 20 years old and the customers want modern trucks, even the modern engines will cause a lot more problems regrarding fuel and maintenance in 3rd world countries. It may be also that the export restrictions on modern military vehicles prevent the use for recreation purpose.
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Dear egn, moe, et al,

Again, I can't thank you enough for all the feedback.

As you suggested, I've started a new thread, titled "Fully Integrated MAN or TATRA 6x6 or 8x8 Expedition RV, w Rigid Torsion-Free Frame", at http://www.expeditionportal.com/forum/threads/124789-Fully-Integrated-MAN-or-TATRA-6x6-or-8x8-Expedition-RV-w-Rigid-Torsion-Free-Frame . The title is not poetic, and does have an “engineering” ring to it. But that's just as well, because the engineering constraints here are critical. Only if such a vehicle were cost-effectively possible from an engineering point of view (as moe suggests), does it have any kind of broad future in the market.

I am also still not certain that a rigid frame is absolutely necessary as a base-chassis for an integrated camper body, given Iain_U1250's pictures of a Unimog from the 1990's, with a fully integrated unibody, which he posted earlier in this thread – see http://www.expeditionportal.com/forum/threads/25494-pivoting-frames-and-mounting-campers/page33?highlight=pivot+frame . So I hope that the new thread continues to discuss such fundamental engineering issues, because they are clearly important.

Note that I had to cut the "i" and the "o" in "Suspension", because the title blocks have a character limit. I figured that "Suspension" was the best word to abbreviate, because the other words should be full-length and easily identifiable, for search purposes. So too, I had to compromise by using the phrase "Rigid Frame" instead of "Torsion-free Frame", because of the character limit.

If any of you can think of a better title for the thread, I am all ears.

Moe, I appreciate your feedback as regards the desirability of posting an "SOR - Statement of Requirements". As the engineering discussion evolves, I will definitely develop one. But initially at least, I want to leave things more open, because in the beginning I would like the thing to be driven by considerations of what is realistically possible, from an engineering point of view. However, I did label the new thread "6x6 or 8x8", to indicate the rough ball-park. And clearly, a 6x6 will be far more practical than an 8x8.

On the other hand I wonder, for instance, whether the "rigid frame + progressive coil suspension" concept works as well over rough terrain when the vehicle is 4x4 or 6x6, as opposed to 8x8? Watching the video that egn just posted, the 8x8 seems to have a great deal of grip or "traction", simply because it has 8 wheels, wheels that a 4x4 or 6x6 by definition won't have. But maybe I am mistaken in this speculation?

Egn, I've been following up your leads regarding “Tatra”, and will also post in the new thread with thoughts and questions about engine-location and type.

And so too I will repost this message, slightly modified, in the new thread. So if you want to respond to it, probably best to do so there, and not here.

All best wishes,

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New member
Thought you might find this interesting,

to be specific the rubber "strip" on the very left of frame is the a piece of conveyor belt I have glued on the front of my Aux fuel tank to fend off stones and rocks , check out how much it moves about, I was amazed when I saw this video I took today, just goes to show, you need to account for flex even on the short length of chassis that the tank is connected to. First pic below is original mounting, second pic shows spring to allow for flex (thanks to the poster earlier in this thread that gave me the idea) 25,000 km rough roads and the tank and mounts show no signs of stress (neither does the rear subframe and box body)

After seeing this I'll try to find somewhere to mount the camera to watch the subframe move as the chassis flexes !

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Wow. Over the last few days I have gone thru this WHOLE thread, reading most posts, skimming thru Biotect's (his stuff gets DEEP!), and come away AMAZED at the knowledge one can gain here about mounting camper bodies(or bodies of any sort). Somebody ought to sort, edit, and compile this stuff into a book! Many minds at work here!


Has spring rate been discussed? I am curious what springs to run on the frame mounts.
If it has, it will probably be in one of Biotect's posts. I kinda skimmed thru those as he gets pretty technical, figuring i would get to them when I had enough time to thoroughly digest it. But there is a lot of good stuff here.
On thing I noticed being mentioned more than once was the use of old valve springs for mount springs. Any engine machine shop will give away old valve springs, as they are scrap to them.


West slope, N. Ser. Nev.
jefe here. This is the second time in 3 years I've been forced into reading this entire thread. It is, and remains awe-inspiring. I've seen, firsthand enough of the 3-and-4 point diamond pivoting mounts for camper boxes and have a pretty good handle on all the derivations and 'covert' mounting styles. So, the following could be considered point-counterpoint.
I have taken a much more laid back approach to my XTC (extreme truck camper) using much of the physics of metal I learned from building quite a few off-road vehicles including rock crawlers. Pretty good articulation for a leaf spring CJ8: This is in the Little Sluice on the Rubicon,

1. I have a 2001 Dodge 2 series HO Cummins 4x4 short bed that I bought new as I had a feeling it would outlive me. So far, so good. It has the factory stamped and spot welded metal bed held to the frame tabs with FOUR, 3/8's inch bolts. Beats me. Must be the shear factor of the thin stamped bed. It sure has no torsional resistance. I have found that a short bed frame twists less than a long bed. I have found the Dodge Hydo-formed frame of that era, although not as good as the current frames, twisted a lot less than the frames of similar era trucks built by Ford. Subsequently, I beefed up the front and rear suspension by adding 3" lift coils in front and put together a homemade rear spring arrangement with 5 leaves on the main pack and 3 leaves up on the secondaries (overloads) giving me a pretty good ride while empty but a lot of load carrying suspension when fully loaded and or towing. It's good to note that I get a lot more flex out of the front coil springs than I do with the rear 8 leaf packs, loaded.
2. I bought a used 1998 Lance Lite, 165-s, hardside, wooden frame truck camper in 2001 and have camped, mostly boondocking for over 200 nights from Mexico to above the Arctic Circle. It weighs 1845 pounds, wet. Right away I was cognizant of the fact that if the four tie-downs were too tight, bad things would happen to the camper's wooden frame. Further, if too tight and on undulating roadways or trails, things would go south quickly. So, it was time to improvise, make do, overcome. The very first thing i did was to do what i could do to prevent the camper box from shifting in the truck bed. This is a no-no as it puts extreme tension on the tie-downs if the camper is skating around. Enter a quartet of Lance camper guides. I have seen much better versions of this recently, but at the time these were it.

I started to 'play' with the tie-down tension, loosening the rear pair to very loose when the axles started to twist up, and loosening the front pair to slightly loose. It's almost a Zen thing. You 'feel' the roadway and instinctively want to loosen the tension. Why that scenario? While using my four mechanical/manual jacks to jack the box up off my camper stands I found a lot more weight was on the front jacks and not so much on the rears. Hmm? If the truck frame twists, as it is want to do, if not tied down, which end of the camper would want to lift compared to an undulating frame and bed? The rears, of course as there is less weight. I have seen this action and am truly amazed at how unyieling the Lance wooden frame actually is. I can crank one jack all the way up, standing on 3 legs, and get no visible deflection out of the Lance frame. So, how has this constant twiddling worked out? So far, so good. On a recent XTC trip over some pretty rough jeep trails, I did my loosening but found the bottom of the frame had some concussion damage from pressing into the guides on one side. You can see a slight frame twist by comparing the camper box to the cab in this photo but that's about as bad as it gets. Also, the low side in this pic is the side that received the most concussion damage:

My fix was affix some long extruded aluminum L bars to the side/bottom of the camper box. This should spread the concussion out along the bar. Time will tell. Im also going to put rubber strips on the camper guides to mitigate any shock loading. I have the thinnest rubber bed mat I could find and it takes a lot to move the box at all, even if not tied down.

I know this is so damned low tech for many of you pivot junkies, but I'm pedaling as fast as i can to stay ahead of the dredded camper pull-apart.
In the end I try to avoid twisting up the axles as much as i can, and while I go looking for the off-road edge, I'm still sane enough to not go looking for trouble.
I live about a mile from the guy that owns XPCamper and have had some good talks with him. It was very difficult not to drool over the units he had 'in build' at his new giant facility in Grass Valley, CA. I could be swayed. And he uses pivoting frames.
regards, as always, jefe