TerraLiner:12 m Globally Mobile Beach House/Class-A Crossover w 6x6 Hybrid Drivetrain


Dear potential thread participant,

The original title of this thread was "Fully Integrated MAN or TATRA 6x6 or 8x8 Expedition RV, w Rigid, Torsion-Free Frame", but it has since evolved into something rather different. Over the course of roughly 200 pages, it has become a thread developing the concept of the "TerraLiner": a large, globally capable motorhome roughly equivalent to an American Class-A, but one that can travel bad-roads and occasionally off-road, and camp on land rented from farmers. Maximal autonomy in terms of solar, water, and sewage have become leading priorities. And following the Class-A style of motor-homing as developed in the United States by retired, wealthy couples, the TerraLiner is now being conceived as more of a 'base camp". As per American Class-As, the TerraLiner will tow a "TOAD", a supplementary SUV for fetching groceries and exploring the surrounding countryside. Except that, because towing TOADS is not permitted in many countries, the TerraLiner's SUV will be housed in a towed trailer.

As a strong distinction emerged between the TerraLiner functioning as a base-camp for sojourning, versus the TOAD serving as the vehicle primarily used for exploring, size no longer seemed such a constraining issue. So the TerraLiner is now 12 m. Although the TerraLiner is being designed to travel bad roads, and do a bit of off-roading in order to access farmer's fields where it will camp, the TerraLiner is not intended to travel narrow fire roads, forest trails, and such like. And it is absolutely not designed to rock crawl. Instead, exploring is the mission-profile of the TerraLiner's TOAD SUV. Furthermore, as it became clear that maximal power autonomy would require somehow tripling the available area of solar coverage on the TerraLiner's roof, it also became apparent that drop-down decks with integral, very robust and wind-resistant pergola frames were the solution, pergola frames carrying awnings covered with thin-film flexible solar panels. So logistical and engineering considerations almost "naturally" propelled the TerraLiner in a design direction more reminiscent of a mobile beach house, one with expansive decks.

What is emerging is a crossover vehicle of sorts, a cross between an American luxury Class-A, a mobile beach house, and an expedition motorhome based on a 6x6 AWD chassis. The TerraLiner will have elements resembling all of these, but the combined sum total will resemble none of them. Hence "Expedition RV" has been removed from the title of the thread, because it is misleading, and tends to conjure up images of a mid-sized motorhome that strikes a compromise between sojourning and exploring. The TerraLiner strikes no such compromise, and instead deliberately separates sojourning (the TerraLiner) from exploring (the TOAD SUV).

Finally, for various reasons it has come to seem important that the TerraLiner should have a hybrid drivetrain, and this thread spends a great deal of time discussing hybrid technologies for larger vehicles like buses and trucks.

"MAN" and "Tatra" have been removed from the thread's title, because they no longer seem necessary. So too "Fully Integrated" has been omitted, because the debate on that is over. Most current regular participants now recognize the superiority of a fully integrated camper interior. Finally, "Rigid Torsion Free Frame" has also been omitted, because that debate on that is over too. The TerraLiner's rigid base-chassis, in concert with the tubular-space-frame of its camper body, will function together to provide maximum rigidity.

The new title is not perfect, but it more nearly captures where the thread is now headed, and current concerns.

Please note: although this thread explores "blue sky" design, and although it becomes highly speculative in places, the goal here is to conceive a vehicle that might be built circa 2020. In other words, a vehicle that is "innovative", but not Sci-Fi; a vehicle that might be built using technology that already exists, technology that is reasonably proven. The TerraLiner will be innovative primarily in how it combines existing technology to create a new kind of vehicle: a globally capable motorhome/mobile beach house that better meets the logistical needs, preferences, and priorities of active and adventurous retired couples who are wealthy, couples who want to "slow travel" the world.

Welcome, and I hope you participate!

All best wishes,


November 2015


Fully Integrated 6x6 or 8x8 Expedition Vehicle,

with Rigid Frame and Progressive Coil Suspension


1. The Purpose of this Thread

This thread explores the possibility of a different kind of very large, 6x6 or 8x8 off-road expedition vehicle: a “fully integrated” design in which the cab fuses seamlessly with the camper body.

For a rough idea of what this thread has in mind, see the following images, found on http://forum.bernard.debucquoi.com/viewtopic.php?f=11&t=4833&start=60 and http://www.offroad-forum.de/viewtopic.php?t=34729&sid=91a66bb976992decba7125d6f2458c30 :

Integrated Expedition RV on KAT Chassis 1.jpg Integrated Expedition RV on KAT Chassis 2.jpg Integrated Expedition RV on KAT Chassis 3.jpg

This is a vehicle that was first described by egn, in "pivoting frames and mounting campers" at http://www.expeditionportal.com/forum/threads/25494-pivoting-frames-and-mounting-campers?highlight=pivot+frame , as follows:

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…. The silhouette of the cab is just extended to the back.
-- see http://www.expeditionportal.com/forum/threads/25494-pivoting-frames-and-mounting-campers/page35?highlight=pivot+frame .

These very evocative images suggest at least one possible solution to the design and engineering problem that this thread wants to explore.


2. Fully Integrated Motorhomes

In the world of mainstream RV’s, most large motorhomes are either “semi-integrated” or “fully integrated”. For some excellent overviews of mainstream market possibilities, see http://en.wikipedia.org/wiki/Motorhome , http://www.motorcaravanning.com/vehicles/basics_types.htm , and http://www.camprest.com/en/caravanning-basics/motorhomes/types-of-motorhomes .

The last link provides a wealth of interior images that make it clear why fully integrated designs are highly desirable. Even very large motorhomes can benefit from space-saving designs that make “each fitting perform more than one task, like the dining area that turns into a bed.” In particular, even the largest, mainstream European motorhomes will be fully integrated designs in which the driver and passenger seat swivel around, in order to do double-duty as dinette seating:

rodzaje-kamperow-24_1.jpg rodzaje-kamperow-37_1.jpg
rodzaje-kamperow-38_1.jpg rodzaje-kamperow-40_1.jpg

It's also worth noting that high-end, bespoke American motorhomes made by luxury coach manufacturers such as Liberty, Marathon, Featherlite, and Millennium, could also be considered “fully integrated”, and are usually based on a Prevost bus chassis – see http://motorhome.prevostcar.com/section/product , http://motorhome.prevostcar.com/product/models , http://motorhome.prevostcar.com/where-buy , http://www.libertycoach.com , http://www.marathoncoach.com , http://www.millenniumluxurycoaches.com , and http://www.featherlitecoaches.com . The only exception is the American market-leader in bespoke luxury coaches, Newell, which custom-builds its own, bus-like chassis. But again, Newell’s design is fully integrated – see http://www.newellcoach.com/the-coaches/photo-gallery/ and http://www.newellcoach.com/newell-coaches/coach-1508/ .

So too, in the European market for high-end, bespoke luxury motorhomes, a fabricator like Ketterer will try as far as possible to integrate the truck cab of a Merecedes-Actros, MAN, or Scania chassis, with the overall camper body – see http://www.ketterer-trucks.de/en/models.html , http://www.ketterer-trucks.de/en/models/category/c/equestrian.html , http://www.ketterer-trucks.de/en/models/category/c/travel-motorhomes/model/continental-11250-2.html , http://www.ketterer-trucks.de/en/models/category/c/travel-motorhomes/model/continental-12000-2.html , http://www.ketterer-trucks.de/en/models/category/c/travel-motorhomes/model/continental-custom-line-2.html , http://www.ketterer-trucks.de/en/models/category/c/sports-business.html , and http://www.ketterer-trucks.de/en/trucks-in-stock/category/vehicle/ride.html . Like other large European motorhomes, two of the seats in Ketterer's cab will usually swivel, integrating with the camper seating area:

0d30de8178.jpg 2ddd495095.jpg

Notice how a pull-down bed is located in the cab. This bed pulls down over cab seats that fold, and it integrates beautifully with the rest of the motorhome.

Ketterer needs to come up with such "double duty" and "triple duty" solutions, because Ketter's RVs often combine a horse-box with a motorhome, with roughly half the available length allocated to the horses. So the remaining length available for human occupation has to be used very efficiently. Fully integrated designs make such space-efficient solutions much more feasible.

So the question that animates this thread is quite simple:

Why are high-end, 6x6 or 8x8 expedition vehicles almost never “fully integrated”?


3. Non-Integrated Expedition Motorhomes

Almost all of the designs provided by fabricators of expedition-class motorhomes such as ActionMobil, UniCat, and Armadillo, are best described as “non-integrated”, in so far as they typically involve placing a separate camper body on top of a previously existing truck chassis, with a flexible “tunnel” connecting the cab to the camper – see:

(1) ActionMobil, at http://actionmobil.com/en/ , http://actionmobil.com/en/3-axle , http://actionmobil.com/en/4-axle , http://actionmobil.com/en/4-axle/specials , http://www.youtube.com/watch?v=ceFF93HV974 , and https://www.youtube.com/watch?v=M7ljGd2DXUQ .

Some videos:

(2) UniCat, at http://www.unicat.com , http://www.unicat.com/ua-en/individual.php , http://www.unicat.com/ua-en/special.php , http://www.unicat.com/ua-en/info/MXXL24AH.php , http://www.unicat.com/ua-en/pics/MXXL24AH-2.php , http://www.unicat.com/ua-en/pics/MXXL24AH-3.php , http://www.unicat.com/ua-en/pics/MXXL24AH-4.php , http://www.unicat.com/pdf/UNICAT-MXXL24AH-MAN8x8-en-es.pdf , http://www.unicat.net/en/info/EX70HDQ-MANTGA6x6.php , http://www.unicat.net/en/pics/EX70HDQ-MANTGA6x6-2.php , http://www.unicat.net/en/info/EX63HDSC-MANTGA6x6.php , http://www.unicat.net/en/pics/EX63HDSC-MANTGA6x6-2.php , http://www.unicat.net/en/info/EX70HD2M-MANTGA6x6.php , http://www.unicat.net/en/pics/EX70HD2M-MANTGA6x6-2.php , http://www.unicat.net/en/info/EX63HDM-MANTGA6x6.php , http://www.unicat.net/en/pics/EX63HDM-MANTGA6x6-2.php , http://www.unicat.net/en/info/EX58HD-MANTGA4x4.php , http://www.unicat.net/en/info/EX58HD-MANTGA4x4.php , http://www.unicat.net/en/info/EX45HD-UnimogU5000.php , http://money.cnn.com/video/pf/2012/11/01/pf-extreme-rv-home.cnnmoney/ , and https://www.youtube.com/watch?v=45Km1ArLbdA&NR=1 .

Some videos:

[video=youtube;6xRyBC8I6q0]http://www.youtube.com/watch?v=6xRyBC8I6q0&list=PLN4B1KqrNKVR__gQdXUzU0Ty C9G1t5yQ3[/video]

(3) Armadillo, a newer Chinese company, at http://www.armadillo-rv.com , http://www.armadillo-rv.com/Product.aspx or http://translate.googleusercontent.com/translate_c?depth=1&hl=en&prev=/search?q=http://www.armadillo-rv.com&rurl=translate.google.co.uk&sl=zh-CN&u=http://www.armadillo-rv.com/Product.aspx&usg=ALkJrhggsDoN3MnNoJEUh-EIgFM01UIHFg , http://www.armadillo-rv.com/ProductDetail.aspx?ProductID=4 , http://www.armadillo-rv.com/ProductImageShow.aspx?ProductID=4&PhotoClassID=1 , http://www.armadillo-rv.com/ProductImageShow.aspx?ProductID=4&PhotoClassID=3 , http://www.armadillo-rv.com/ProductDetail.aspx?ProductID=7 , http://www.armadillo-rv.com/ProductImageShow.aspx?ProductID=7&PhotoClassID=1 , http://www.armadillo-rv.com/ProductImageShow.aspx?ProductID=7&PhotoClassID=3 , http://www.armadillo-rv.com/ProductDetail.aspx?ProductID=22 , http://www.armadillo-rv.com/ProductImageShow.aspx?ProductID=22&PhotoClassID=1 , http://www.armadillo-rv.com/ProductImageShow.aspx?ProductID=22&PhotoClassID=3 , http://www.armadillo-rv.com/ProductDetail.aspx?ProductID=18 , http://www.armadillo-rv.com/ProductImageShow.aspx?ProductID=18&PhotoClassID=1 , http://www.armadillo-rv.com/ProductImageShow.aspx?ProductID=18&PhotoClassID=3 or http://translate.googleusercontent.com/translate_c?depth=1&hl=en&prev=/search?q=http://www.armadillo-rv.com&rurl=translate.google.co.uk&sl=zh-CN&u=http://www.armadillo-rv.com/ProductDetail.aspx?ProductID=18&usg=ALkJrhidd0y_mOes-sMSggoNvbYNK-_Sww , http://www.armadillo-rv.com/Video.aspx?SmallClassID=13 , http://www.armadillo-rv.com/Video.aspx?SmallClassID=17 , and http://www.armadillo-rv.com/Multimedia.aspx .

Unfortunately, "youku" videos do not yet seem to embed on the Expedition Portal. But here are links to two Armadillo videos: http://v.youku.com/v_show/id_XMjc5MDg1MDUy.html and http://v.youku.com/v_show/id_XMjY5NTI4NjQ0.html .

There are many more expedition RV fabricators, but the above three seem to have the most experience creating very large, 6x6 and 8x8 expedition motorhomes. For a reasonably good list of European expedition-motorhome fabricators, see http://www.kctechnik.de/haendler.html -- KCT seems to be the window-manufacturer of choice, used by many such fabricators. And for a fairly comprehensive list of American fabricators (GXV, Tiger, Four Wheels, Earthroamer, etc.), see http://www.examiner.com/article/the-rving-examiner-guide-to-overlanding .

Now from a design point of view, the separation of cab from camper seems space-wasteful, because at a bare minimum, it duplicates seating. In large 6x6 and 8x8 expedition motorhomes, driver and passenger seats almost never swivel around in order to do “double-duty” as dinette seating. Instead, completely separate, additional dinette seating has to be provided in the camper box.


4. Expedition Motorhome Engineering Considerations

I first began exploring this question in the thread titled “pivoting frames and mounting campers”, because the answer to this question is partly a matter of engineering -- see http://www.expeditionportal.com/forum/threads/25494-pivoting-frames-and-mounting-campers/page33?highlight=pivot+frame , http://www.expeditionportal.com/forum/threads/25494-pivoting-frames-and-mounting-campers/page34?highlight=pivot+frame , http://www.expeditionportal.com/forum/threads/25494-pivoting-frames-and-mounting-campers/page35?highlight=pivot+frame , and http://www.expeditionportal.com/forum/threads/25494-pivoting-frames-and-mounting-campers/page36?highlight=pivot+frame .

When fully integrated, “mainstream” motorhomes try to travel in the Third World, over bad roads full of deep ruts and potholes, the stress created by such driving soon destroys their chassis frames and camper bodies.

Expedition motorhomes purpose-built for Third World travel overcome this problem, first, by choosing a chassis that is designed for bad-road or off-road travel. These are typically either:

(1) A Mercedes Unimog, a purpose-built off-road utility vehicle – see http://en.wikipedia.org/wiki/Unimog , http://www2.mercedes-benz.co.uk/content/unitedkingdom/mpc/mpc_unitedkingdom_website/en/home_mpc/Unimog/home/unimog_overview/models/u_300_-_u_500.flash.html , http://www2.mercedes-benz.co.uk/content/unitedkingdom/mpc/mpc_unitedkingdom_website/en/home_mpc/Unimog/home/unimog_overview/models/u_3000_-_u_5000.flash.html#chapter=1 , http://www2.mercedes-benz.co.uk/content/unitedkingdom/mpc/mpc_unitedkingdom_website/en/home_mpc/Unimog/home/unimog_overview/expertise.0002.html , http://www2.mercedes-benz.co.uk/content/unitedkingdom/mpc/mpc_unitedkingdom_website/en/home_mpc/Unimog/home/unimog_world/unimog_magazine.html , http://www2.mercedes-benz.co.uk/content/unitedkingdom/mpc/mpc_unitedkingdom_website/en/home_mpc/Unimog/home/unimog_world/unimog_history.html , and http://www2.mercedes-benz.co.uk/content/unitedkingdom/mpc/mpc_unitedkingdom_website/en/home_mpc/Unimog/home/unimog_overview/applications/construction.html .

(2) A Mercedes Zetros, a medium-size, purpose-built off-road truck – see http://en.wikipedia.org/wiki/Mercedes-Benz_Zetros , https://www.mercedes-benz-media.co.uk/commercial/model/144/Zetros , http://www.special-trucks.eu/webspecial_mercedes-benz_zetros/en/ , http://www.special-trucks.eu/webspecial_zetros/ , http://www2.mercedes-benz.co.uk/content/media_library/unitedkingdom/mpc_unitedkingdom/Unimog/pdfs/zetros/zetros_brochure.object.Single.File.tmp/Zetros 2011.pdf , http://www.pchristensen.dk/Files/Filer/pc/brochure/Zetros-Construction-Brochure.pdf , http://www.tradingeurope.at/Downloads/Zetros_engl.pdf , http://www.special-trucks.eu/webspecial_mercedes-benz_zetros/en/technische_daten_en.pdf , http://www.mb-military-vehicles.com/fileadmin/downloads/ZETROS Armoured.pdf .

(3) A MAN TGA (older) or MAN TGS (newer), a very large, purpose-built off-road construction truck – see http://www.mantruckandbus.hu/man/media/migrated/doc/mn_hu_1/TGS_broura.pdf , http://www.truck.man.eu/global/en/building-site-and-heavy-duty-transport/tgs-ww/overview/Overview.html , http://www.mantruckandbus.com/man/media/migrated/doc/master_1/Construction_site_vehicles__en_.pdf , http://www.man-bodybuilder.co.uk/specs/pdf/tgs/TGS 8x4 Heavy Duty Tipper.pdf , http://www.euro6ready.com/assets/pdf/TGS/TGS_8x4_Heavy Duty Tipper_Sept_2013.pdf , http://atstrucks.co.nz/uploads/specs/TGS_8x8Tipper.pdf , and http://www.man.com.au/truck-range/tgs-range/tgs-8x8-2 .

(4) A military off-road truck converted for civilian use, such as the MAN KAT A1, the Oshkosh ARFF (Aircraft Rescue and Fire-Fighting vehicle), the Oshkosh Hemtt, or even a Tatra 815 – see http://www.expeditionportal.com/forum/threads/11614-MAN-6x6-camper?highlight=man+kat+egn , http://www.rv.net/forum/index.cfm/fuseaction/thread/tid/20933867.cfm , http://www.actionmobil.com/4-achser/desert-challenger , http://www.examiner.com/article/action-mobil-desert-challenger-the-world-s-best-off-road-rv , http://en.wikipedia.org/wiki/MAN_KAT1 , http://www.military-today.com/trucks/man_kat1_8x8.htm , http://www.scribd.com/doc/17296072/The-Mobility-Elite , http://www.rheinmetall-defence.com/en/rheinmetall_defence/index.php , and http://www.rheinmetall-defence.com/en/rheinmetall_defence/systems_and_products/vehicle_systems/military_trucks/index.php ; http://www.expeditionportal.com/forum/threads/112015-8x8-HEMTT-Expedition-Vehicle-w-Garage , http://www.expeditionportal.com/forum/threads/48137-Hemtt-Define-America-Project?highlight=man+kat+egn , http://www.expeditionportal.com/forum/threads/11289-Oshkosh-Military-6x6-firetruck , http://www.gizmag.com/go/3708/ , http://www.oshkoshcorporation.com/brands/index.html , http://www.oshkoshairport.com/en/ARFFTrucks.aspx , http://oshkoshdefense.com , http://oshkoshdefense.com/vehicles/hemtt-a3-diesel-electric/ , http://oshkoshdefense.com/vehicles/hemtt-a4/ , http://oshkoshdefense.com/vehicles/p-19r/ , and http://www.oshkoshdefense.co.uk/wp-content/uploads/2013/09/EN-UK_OshDefOverview_Bro_6-3-2011.pdf ; http://www.theoverlander.org/my-wheels/trucks/tatra-815-2-6x6-expedition-truck.html , http://ergracing.com/tag/ctis/ , http://bangshift.com/general-news/craigslist-find-the-ultimate-off-road-rv-1985-tatra-t-815-czech-built-military-8x8/ , http://www.offroadexpress.co.nz/Forums/viewtopic.php?f=38&t=36480 , http://en.wikipedia.org/wiki/Tatra_(company) , http://www.tatratrucks.com , http://www.tatratrucks.com/trucks/customer-segment-catalog/defence/ , http://www.tatratrucks.com/trucks/customer-segment-catalog/defence/more-trucks/8x8-high-mobility-heavy-duty-universal-cargo-troop-carrier/ , and http://www.tatratrucks.com/trucks/customer-segment-catalog/defence/more-trucks/6x6-cargo-truck-troop-carrier/ .

Here too additional possibilities exist, for instance, some have used a Mercedes Actros chassis as the basis for an expedition motorhome. But in almost all cases, expedition fabricators simply mount a camper body on top of a pre-given chassis + cab.

Now the chassis is usually designed to “flex”, to absorb extreme terrain irregularities by twisting in response. Of course, the suspension system (e.g. leaf spring or coil suspension) absorbs smaller irregularities, but the twisting chassis handles the really big ones. And in so doing, it allows the vehicle to keep all 6 or 8 wheels firmly in contact with the ground. One of the very best images illustrating this basic idea, can be found on Rob Gray's "Wothahellizat Mk 1" website at http://robgray.com/graynomad/wothahellizat/wot1/index.php :


This sort of structural solution then means that the camper body has to be mounted on a separate “sub-frame”, a sub-frame that “floats” or pivots above the main chassis, as pictured above. The camper body has to be rigid (obviously), and cannot twist like the underlying chassis frame. So the main purpose of the sub-frame is to structurally isolate the camper body from the twisting chassis frame, and needless to say, to also isolate it from the stress that the chassis frame absorbs when travelling over bad roads or off-road. Different ideas exist about how this might best be accomplished, for instance, whether a “4-point pivoting sub-frame” is superior to a “3-point pivoting sub-frame”. To my knowledge, by far the best web-discussion of the alternatives is the “pivoting frames and mounting campers” thread here on the Expedition Portal, already mentioned, at http://www.expeditionportal.com/forum/threads/25494-pivoting-frames-and-mounting-campers?highlight=pivot+frame .

If you check out the videos on the Armadillo and ActionMobil website, videos of big 6x6 or 8x8 expedition vehicles handling difficult terrain, you will see that the cab often goes in one direction, and the camper body in another -- see http://www.actionmobil.com/home/videos and http://www.armadillo-rv.com/Multimedia.aspx . Again, that’s because the underlying chassis frame has been deliberately designed to twist, with the camper body isolated from that stress by the pivoting sub-frame. For a good video playlist of "Expedition Trucks and Campers", also see http://shelf3d.com/Search/Expedition+Trucks+and+Campers+PlayListIDPLEDEADF4587B99C71 .

The overall consequence, from a design point of view, would seem to be that large expedition motorhomes cannot be fully integrated, because the cab and camper body have to be mounted on separate pivoting frames. The newest Zetros truck, for instance, comes with its cab mounted on a 3-point pivoting frame – see the technical literature at https://www.mercedes-benz-media.co.uk/commercial/model/144/Zetros .

So the answer to the design-question, “Why are high-end, 6x6 or 8x8 expedition vehicles almost never “fully integrated?”, seems to be the engineering response: “Because the cab and the camper have to be mounted on separate, pivoting sub-frames that structurally isolate them from each other, and from an underlying chassis that twists.”

I am not certain whether this is the whole story, however. In “pivoting frames and mounting campers”, Iain_U1250 posted some interesting pictures of a Unimog camper that has a single, unified, "fully integrated" body. Apparently lots of similar uni-body Unimog campers were built in the 1990's -- see http://www.expeditionportal.com/forum/threads/25494-pivoting-frames-and-mounting-campers/page33?highlight=pivot+frame. Now the Unimog chassis is deliberately designed to twist. So if a fully integrated design is possible with a Unimog chassis, then in theory at least, it should be possible with just about any chassis.

Still, this is just speculation on my part, and those with engineering backgrounds would be better able to asses the plausibility of this conjecture.


5. MAN and Tatra Trucks with Rigid, Torsion-Free Frames and Progressive Coil Suspensions

This thread, then, begins with the more conservative working assumption that, in order to successfully mount a fully integrated, unibody camper on top of an expedition-grade chassis, that chassis has to be completely rigid, and cannot twist.

Is such a thing possible? Does an off-road truck chassis have to twist?

Again, the chassis of a Unimog, the most extreme-terrain-capable vehicle in the world, which can handle rock-crawling (for instance), is deliberately designed to twist. So the answer to this question would seem to be , “Yes, an off-road truck chassis should twist.” And so pivoting sub-frames are necessary, and a fully integrated, large, off-road expedition vehicle is a design impossibility.

That’s the conventional wisdom, and it’s the perspective that seems to dominate discussion in the “pivoting frames and mounting campers” thread.

But what if it’s not true? What if there exist examples of off-road trucks that have completely rigid, torsion-free box-frames; trucks in which a progressive coil suspension absorbs all terrain irregularities?

In fact, Rheinmetall-MAN military does make such trucks, in its SX-series, as does Tatra, in its 815 series – see http://www.scribd.com/doc/17296072/The-Mobility-Elite , http://www.rheinmetall-defence.de/en/rheinmetall_defence/company/divisions_and_subsidiaries/rheinmetall_man_military_vehicles/index.php , http://www.tatratrucks.com/trucks/customer-segment-catalog/defence/more-trucks/8x8-high-mobility-heavy-duty-universal-cargo-troop-carrier/ . For an excellent video of such a truck in action, provided by egn, see the following, and notice how the cab and body remain completely fixed with respect to each other. Here the underlying chassis frame quite evidently does not twist:

I don't know whether other manufacturers of military-grade trucks, such as Mercedes and Oshkosh, also make "extreme mobility" trucks similar to the Rheinmetall-MAN SX-45, trucks that have rigid, torsion-free frames combined with progressive coil suspensions. Hopefully that's one of the questions that will be answered at some point, as this thread gets underway.

So the question of this thread becomes:

Can the military technology of torsion-free chassis frames coupled with progressive coil suspension, be adapted to civilian use, to serve as the engineering foundation for large, fully integrated, 6x6 or 8x8 expedition-style motorhomes? Can it be done cost-effectively?

That’s the main question that this thread will explore, at lest initially. But the overall design-goal is a fully integrated 6x6 or 8x8 expedition-style motorhome, and not any particular engineering solution.


6. Pivoting Frames and Mounting Campers

Now again, it needs to be emphasized that some of the key ideas and arguments that animate this thread were first posted elsewhere, namely, on pages 34, 35, 36, and 37 of “pivoting frames and mounting campers” – again, see http://www.expeditionportal.com/forum/threads/25494-pivoting-frames-and-mounting-campers/page33 , http://www.expeditionportal.com/forum/threads/25494-pivoting-frames-and-mounting-campers/page34 , http://www.expeditionportal.com/forum/threads/25494-pivoting-frames-and-mounting-campers/page35 , and http://www.expeditionportal.com/forum/threads/25494-pivoting-frames-and-mounting-campers/page36 .

So if you are a newcomer, to develop a full understanding of the issues it might be wise to read those pages first, before continuing here. However, in the next few posts I will try to re-post much of that material. And I would request that, if they have time available, egn, moe, Iain_U1250, and others might want to do likewise.

All best wishes,

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The following is the first entry that I posted in "pivoting frames and mounting campers”, on page 33, at http://www.expeditionportal.com/forum/threads/25494-pivoting-frames-and-mounting-campers/page33 . The issues were still a bit unclear to me, and perhaps because I was not clear enough, only a few people responded.


Perhaps the link has already been posted, but one possible interesting design variant was dubbed by its inventor the “two line pivot floating subframe” – see http://www.kookynet.net/220-cristo-3-ch04-subframe.html .


The following is a very long post, but I have some rather pressing design questions, questions that I was hoping those with some engineering knowledge and/or practical experience of frame/subframe systems, might be able to answer....:)


1) The MAN SX 45

A number of times in this thread, a question has arisen:

“Why not just build a chassis frame that is super-rigid, and 100 % torsion free, allowing just a suspension system with extremely long travel to handle the terrain?”

It does seem as if such a solution exists, in the form a very large military truck designed for extreme off-road use: the MAN SX 45, “extreme-mobility”, 8 x 8, all-wheel-drive military truck. See http://freundeskreis-videoclips.de/wordpress/wp-content/uploads/2009/01/the_mobility_elite.pdf , http://en.wikipedia.org/wiki/MAN_SX , http://www.military-today.com/trucks/man_sx45.htm , and http://snafu-solomon.blogspot.it/2013/12/rheinmetall-man-military-trucks-keep.html .

The first link is to a PDF that was once available on the “MAN Military Trucks” website. But it seems that MAN's military division went through a reshuffle, and is now owned / handled / operated by “Rheinmetall Defence” – see http://www.rheinmetall-defence.com/en/rheinmetall_defence/systems_and_products/vehicle_systems/military_trucks/index.php , http://www.rheinmetall.com/en/rheinmetall_ag/press/news/aktuell_1/news_details_2688.php , and http://www.rheinmetall.de/media/editor_media/rheinmetallag/group/publications_1/companymagazine/newsline/2010_2/Newsline_01_2010.pdf . Unfortunately, Rheinmetall Defence website is much less forthcoming with information, in contrast to the older, now-defunct MAN military division website. So the link just given for the PDF is to a third-party website; hope the link stays active for a while!

Now browsing through this PDF -- again, at http://freundeskreis-videoclips.de/wordpress/wp-content/uploads/2009/01/the_mobility_elite.pdf -- one sees that it describes the MAN SX 45 specifically as having an “extremely torsion resistant box frame” , one that provides “100 % torsional stiffness”. Instead, the MAN SX 45 absorbs all terrain irregularities through its progressive coil spring suspension. And the promised result is that “the body remains unaffected even during fast off-road driving!!”

Does this strike the contributors in this thread as plausible? Wouldn't such a truck still need some kind of pivoting sub-frame for mounting a body?

Or is it indeed possible to eliminate all torsional twisting with a chassis box frame, in a vehicle this large, about 10 m long….?


2) Brief Note

The SX 45 is basically a “souped up” version of the MAN TGA construction truck, a line of MAN trucks now supplanted by the TGS series -- see http://www.truck.man.eu/global/en/index.html , http://www.truck.man.eu/global/en/building-site-and-heavy-duty-transport/tgs/overview/Overview.html , http://www.truck.man.eu/man/media/en/content_medien/doc/business_website_truck_master_1/TGS.pdf , http://www.truck.man.eu/man/media/content_medien/doc/business_website_truck_master_1/Spezialfahrzeuge.pdf , http://www.man-bodybuilder.co.uk/drawings/euro5/ , and http://www.man-bodybuilder.co.uk/drawings/euro5/chassis/81.99126.0055.04.pdf .

In both the TGS and the SX 45 the two front axles are steerable, but the TGS is 8 x 4 instead of 8 x 8. And of course everything about the SX 45 has been “militarized”, including the ability to withstand outside temperatures from minus 32 to plus 49 degrees Celsius!


3) “Fully Integrated” Expedition Mobile Home?

My second question is more of a design query. Some of the largest expedition vehicles made by ActionMobil or Armadillo (a Chinese company), are based either on a Mercedes Benz Zetros chassis, or a MAN TGA chassis, or more recently on a MAN TGS chassis. For examples of ActionMobil vehicles, see http://www.actionmobil.at , http://www.actionmobil.at/page12/page12.html , and http://www.actionmobil.at/page16/page16.html . And for Armadillo vehicles, see http://www.armadillo-rv.com , http://www.armadillo-rv.com/Product.aspx , http://www.armadillo-rv.com/ProductDetail.aspx?ProductID=7 , http://www.armadillo-rv.com/ProductDetail.aspx?ProductID=18 , http://www.armadillo-rv.com/ProductDetail.aspx?ProductID=23 , and http://www.armadillo-rv.com/ProductDetail.aspx?ProductID=15 . Just click on the images on the Armadillo product-range page (the second link provided), and you'll be able to see copious photographs of all Armadillo vehicles.

I provided lots of Armadillo links, because if you can't read Chinese, you might find their website difficult to navigate. But Google "translate" renders the website reasonably accessible. For instance, check out some great videos of Armadillo vehicles negotiating sand dunes in (what must be) the Taklamakan desert, at http://translate.google.co.uk/translate?hl=en&sl=zh-CN&u=http://www.armadillo-rv.com/&prev=/search?q=armadillo+rv&biw=1885&bih=1 102 , and click on "Audio/Data". Or see http://www.armadillo-rv.com/Video.aspx?SmallClassID=13 , and http://www.armadillo-rv.com/Video.aspx?SmallClassID=17 , or on "youku" at [video]http://v.youku.com/v_show/id_XMjc5MDg1MDUy.html[/video] and [video]http://v.youku.com/v_show/id_XMjY5NTI4NjQ0.html[/video] .

From a design point of view, let's just say that the Chinese are “catching up”, and the interiors of many of these Armadillo vehicles are detailed to a level that might leave ActionMobil and UniCAT customers green with envy! My favorite is a really spectacular pop-up at http://www.armadillo-rv.com/ProductDetail.aspx?ProductID=18 .

Now all of these large expedition mobile homes follow a standard design format, in which a structurally separate, comparatively “short” cab (less than 3 m in length), is followed by a very long body (7 or 8 m in length), the latter mounted on a 3-point pivoting subframe. In the Zetros, however, the cab itself is also mounted on 3-points – see http://www2.mercedes-benz.co.uk/content/unitedkingdom/mpc/mpc_unitedkingdom_website/en/home_mpc/Unimog/home/unimog_overview/zetros/zetros/technical_data.html and http://www2.mercedes-benz.co.uk/content/media_library/unitedkingdom/mpc_unitedkingdom/Unimog/pdfs/zetros/zetros_brochure.object.Single.File.tmp/Zetros 2011.pdf . And earlier in this thread, a contributor wrote that in a UNIMOG, everything is mounted on separate 3 point subframes – the engine, the cab, the body, everything.

So I was wondering: Could it in principle be possible to change the size-ratios of Cab-to-body, in a very large expedition vehicle?

Imagine instead that in an Armadillo or ActionMobil motorhome (based on a MAN TGS chassis), the Cab were lengthened to 4 or 5 m, and that this "first half" of the vehicle were fully fused with living quarters, as in “fully integrated” motorhomes.

For a visual example of what I have in mind, see for instance The Hymer Starline, a large “fully integrated” German motorhome, in which the front seats can swivel around 180 degrees, and do “double duty” as chairs providing seating at a dining table: http://www.hymer.com/en/ , http://www.hymer.com/en/models/ , http://www.hymer.com/en/models/integrated/hymer-starline/overview.html#.UtE_6HmK05A , http://www.hymer.com/en/models/integrated/hymer-starline/hymer-starline-s/experience.html#.UtFAD3mK05A , http://www.hymer.com/assets/images/modell-2014/hymer-starline-s/impressionen/HY13_BM680S_I_Sitzgruppe_Leder_Kiesel_0.jpg , and
http://www.hymer.com/assets/images/modell-2014/hymer-starline-s/impressionen/HY13_BM680S_I_Sitzgruppe_Leder_Kiesel_1.jpg :



By way of contrast, most expedition motorhomes -- of the sort offered by ActionMobil, UniCAT, Armadillo, et al -- seem to be very space-wasteful, because the seating used for driving never does “double duty” as seating for dining. Instead, the cab remains a separate, short box at the front, and then a second set of seats has to be provided for the camper in the back, for dining.

However, if the cab were lengthened 3, 4, or 5 m, and became the “first half” of the vehicle; and if it were then connected to the second half, also 4 or 5 m long, by an accordion-type “tunnel” located in the middle of the vehicle, then a “fully integrated” design similar to the Hymer might become possible.

Sure, there would still have to be an accordion-type tunnel connecting the front half (4 or 5 m long) and the rear half (4 or 5 m Long) -- an accordion-type tunnel located in the middle of the vehicle. But from a space-usage point of view, these two, roughly equal-length halves would offer design possibilities that the traditional “semi-integrated” or “non-integrated” expedition motorhomes simply do not. In effect, almost all expedition motorhomes designed and sold thus far have been “semi-integrated” or “non-integrated”. The only exceptions might be some expedition-capable van conversions, which one could describe as “fully integrated”.

So the engineering questions here are::

A. Would it be possible to construct an expedition motorhome with a “Cab” and a “Body” of roughly equal length (both of them 4 - 5 m long), both mounted on separate, 3-point pivoting sub-frames, and connected by an accordion-type tunnel in the middle?

B. What would be the engineering challenges of such a design?

C. How big could the accordion-type tunnel located in the middle of the vehicle be? How tall? How wide?

D. And most critically, where would one locate the pivots for the two halves, front and back?

Presumably, if the underlying Chassis were a MAN TGS 8 x 4 (as per the biggest Armadillos), then the front half (call it the "cab") would mount on two points above the first pair of axles, and would have its third pivot located near the middle of the vehicle; while the back half (call it the "camper" or the "body") would mount on two points located above the second pair of axles, at the rear of the vehicle, but again would have its third pivot also located near the middle of the vehicle?

But I am not an engineer, so I really don't know the answer to this second subset of questions…..

For now, just "bracket" what happens to the engine, which in any case would probably mount separately at the very front, under a "nose" or "bonnet", as per the Zetros off-road truck. As Mercedes has realized, the cab-over-engine design of Euro-style trucks like the MAN TGS might be fine for highway driving, but for off-road driving, cab-over-engine is ergonomic hell (again, see the link to the Zetros PDF above).

So in the design that I am proposing, there might be at least three, separate, 3-point mounts:

(a) the engine, under a bonnet at the very front;
(b) the 4 - 5 m long "cab", or first half of the vehicle;
(c) the 4 - 5 m long "body", or second half of the vehicle.

For what it's worth, this also seems to be the mounting format of the Zetros, except that the "cab" of the Zetros is only about 2 m long.


A bit more about me: I am a student studying Transportation Design at an Art School in England, whose thesis project is -- you guessed it -- designing a very large, experimental, offroad-capable mobile home. So the questions above are really “design possibility” questions. I am curious about what might actually be structurally feasible, from an engineering point of view, in a very large, off-road, expedition-type motorhome.

Many thanks in advance for any and all responses!

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This is the second entry that I posted in "pivoting frames and mounting campers”, on page 34, at http://www.expeditionportal.com/forum/threads/25494-pivoting-frames-and-mounting-campers/page34 . I tried to rephrase the issues, and this time included jpgs from the critical MAN "Mobility Elite" brochure.

The response this second time around was much better.....


Ian and Victorian,

Many thanks for your replies to my query, now on the previous page, i.e. page 33. Sorry it has taken me so long to get back to you; other projects intervened.

I'd like to revisit the question of that the earlier post, and perhaps amplify it a bit. If you recall, that question was:

Is a 3-point pivoting sub-frame absolutely necessary? Could we design and construct a box-frame chassis that was torsionally stiff enough, such that it never twists, no matter how irregular the terrain?? Could the vehicle's progressive coil-spring suspension do all the "work" of handling rough terrain, instead?

Ian, you understood the question very well, and thanks again for your response. Thanks in particular for your explanation regarding the Unimogs, which have a chassis that is deliberately designed to twist, a lot. And Victorian, many thanks for your wise, prudent comments regarding the constraints motivating most buyers of expedition motorhomes. Experimentation costs money and time, and most buyers have neither in excess.

You both understood my question, but perhaps many on the forum did not? Even so, I really do want to know whether a "torsion free" chassis -- of the sort that MAN advertises for the SX 45 -- is realistically possible. So to make my question clear to others, below I provide some additional background information, in the first two sections.



Here is some background for those who might not be familiar with the very large, “8 x 8”, expedition motorhome market segment.

MAN Gmbh, a truck manufacturer based in Austria, makes most of the truck-chassis used by fabricators of the largest overland motorhomes, i.e. fabricators like Action-Mobil, UniCat, Armadillo, etc. Very large expedition motorhomes will typically be mounted on a MAN TGA or TGS chassis, of the kind used for off-road construction, in 4 x 4, 6 x 6, 8 x 4, and even 8 x 8 variants – see http://www.mantruckandbus.hu/man/media/migrated/doc/mn_hu_1/TGS_broura.pdf , http://www.truck.man.eu/global/en/building-site-and-heavy-duty-transport/tgs-ww/overview/Overview.html , http://www.mantruckandbus.com/man/media/migrated/doc/master_1/Construction_site_vehicles__en_.pdf , http://www.man-bodybuilder.co.uk/specs/pdf/tgs/TGS 8x4 Heavy Duty Tipper.pdf , http://www.euro6ready.com/assets/pdf/TGS/TGS_8x4_Heavy Duty Tipper_Sept_2013.pdf , http://atstrucks.co.nz/uploads/specs/TGS_8x8Tipper.pdf , and http://www.man.com.au/truck-range/tgs-range/tgs-8x8-2 /.

Over the last century MAN has built up a reputation for making rock-solid, very reliable trucks that can function well in off-road conditions like construction sites, or mining operations in the Third World..... And if MAN construction trucks can withstand the rigors of Third-World mining, then -- or so companies like ActionMobil, UniCat, and Armadillo reason -- such trucks can certainly withstand the rigors of off-road (or more like "bad-road") expedition travel.

For examples of some very large, expedition motorhomes based on a MAN chassis, see:

(1) ActionMobil, at http://www.actionmobil.com/en/4-axle/specials , http://www.actionmobil.com/en/4-axle/interior-design , http://www.actionmobil.com/en/3-axle/globecruiser , and http://www.actionmobil.com/en/3-axle/atacama ;

(2) UniCat, at http://www.unicat.net/en/info/MXXL24AH.php , http://www.unicat.net/pdf/UNICAT-MXXL24AH-MAN8x8-en-es.pdf , http://www.unicat.net/en/info/EX70HDQ-MANTGA6x6.php , http://www.unicat.net/en/pics/EX70HDQ-MANTGA6x6-2.php , http://www.unicat.net/en/info/EX63HDSC-MANTGA6x6.php , http://www.unicat.net/en/pics/EX63HDSC-MANTGA6x6-2.php , http://www.unicat.net/en/info/EX70HD2M-MANTGA6x6.php , http://www.unicat.net/en/pics/EX70HD2M-MANTGA6x6-2.php , http://www.unicat.net/en/info/EX63HDM-MANTGA6x6.php , http://www.unicat.net/en/pics/EX63HDM-MANTGA6x6-2.php , http://www.unicat.net/en/info/EX58HD-MANTGA4x4.php , http://www.unicat.net/en/info/EX58HD-MANTGA4x4.php , and http://www.unicat.net/en/info/EX45HD-UnimogU5000.php ;


(3) Armadillo, a newer Chinese company, at http://www.armadillo-rv.com , http://www.armadillo-rv.com/Product.aspx or http://translate.googleusercontent.com/translate_c?depth=1&hl=en&prev=/search?q=http://www.armadillo-rv.com&rurl=translate.google.co.uk&sl=zh-CN&u=http://www.armadillo-rv.com/Product.aspx&usg=ALkJrhggsDoN3MnNoJEUh-EIgFM01UIHFg ; http://www.armadillo-rv.com/ProductDetail.aspx?ProductID=4 , http://www.armadillo-rv.com/ProductImageShow.aspx?ProductID=4&PhotoClassID=1 , http://www.armadillo-rv.com/ProductImageShow.aspx?ProductID=4&PhotoClassID=3 , http://www.armadillo-rv.com/ProductDetail.aspx?ProductID=7 , http://www.armadillo-rv.com/ProductImageShow.aspx?ProductID=7&PhotoClassID=1 , http://www.armadillo-rv.com/ProductImageShow.aspx?ProductID=7&PhotoClassID=3 , http://www.armadillo-rv.com/ProductDetail.aspx?ProductID=22 , http://www.armadillo-rv.com/ProductImageShow.aspx?ProductID=22&PhotoClassID=1 , and http://www.armadillo-rv.com/ProductImageShow.aspx?ProductID=22&PhotoClassID=3 .

See in particular Armadillo's rendition of the UniCat-style pop-up, in a 6 x 6 TGA version, at http://www.armadillo-rv.com/ProductDetail.aspx?ProductID=18 , http://www.armadillo-rv.com/ProductImageShow.aspx?ProductID=18&PhotoClassID=1 , http://www.armadillo-rv.com/ProductImageShow.aspx?ProductID=18&PhotoClassID=3 , or http://translate.googleusercontent.com/translate_c?depth=1&hl=en&prev=/search?q=http://www.armadillo-rv.com&rurl=translate.google.co.uk&sl=zh-CN&u=http://www.armadillo-rv.com/ProductDetail.aspx?ProductID=18&usg=ALkJrhidd0y_mOes-sMSggoNvbYNK-_Sww . And for some multimedia videoclips of Armadillos in action in the Mongolian desert, see http://www.armadillo-rv.com/Multimedia.aspx .


2. MAN Military

Now as many regulars on the “Overland Portal” perhaps already know, MAN Gmbh has a military division, one that produces off-road military trucks that are widely used by NATO and other armed forces. This is a natural extension of MAN's experience fabricating off-road construction trucks for harsh conditions. As MAN has stated on its military-division website, the expertise it gains via the TGA and TGS line of construction trucks goes into its military vehicles, and so too vica-versa. So a MAN 8 x 8 military truck is, in a sense, a TGA or TGS "in disguise".

Years ago MAN's military trucks were known as the “KAT” series, and Actionmobil even converted a former KAT 8 x 8 into a motorhome for a sheikh – see http://www.military-today.com/trucks/man_kat1_8x8.htm and http://actionmobil.com/en/4-axle/desert-challenger .

However, at present, the line-up of MAN's off-road military trucks is known as the “HX” and “SX” series – see http://www.military-today.com/trucks/man_sx45.htm , http://www.military-today.com/trucks/man_sx44.htm , http://www.military-today.com/trucks/man_hx77.htm , and http://www.military-today.com/trucks/man_hx58.htm . These MAN military trucks now completely dominate the market in Europe, the UK, Australia, and New Zealand – see http://www.defenseindustrydaily.com/british-tactical-truck-order-rises-to-gbp-135b-02409/ , http://www.commercialmotor.com/latest-news/man-fleet-for-the-mod- , http://www.army.mod.uk/documents/general/285986_ARMY_VEHICLESEQUIPMENT_V12.PDF_web.pdf (page 39), http://www.armyvehicles.dk/man32430.htm , http://www.rheinmetall.com/en/rheinmetall_ag/press/news/archive_2013/news_details_6_2688.php , and http://www.armyrecognition.com/may_2013_news_defence_army_military_industry_uk/army_of_new_zealand_is_acquiring_200_military_trucks_from_rheinmetall_man_1605132.html .

The Mercedes Benz Zetros, by way of comparison, is sold mostly to the Bundesweher (the German military), and various armies in Arab countries – see http://www.battle-technology.com/exhibitions.asp?key=653 . As the last link just cited makes clear, over the last few years MAN has delivered literally thousands of new HX and SX vehicles to forces in Europe, the UK, Australia, and New Zealand.

It's then rather curious that, 3 years ago, it was very easy to find information about the HX and SX on-line, via MAN's military website, but now it's almost impossible. In the intervening years, MAN's military manufacturing operations have been taken over by “Reinmetall AG”, whose relationship to MAN is a bit unclear – see http://www.rheinmetall.com/en/rheinmetall_ag/group/index.php , http://en.wikipedia.org/wiki/Rheinmetall , and http://en.wikipedia.org/wiki/Rheinmetall_MAN_Military_Vehicles , and http://www.rheinmetall-defence.com/en/rheinmetall_defence/company/divisions_and_subsidiaries/rheinmetall_man_military_vehicles/ .

The bottom line is that, if you hope to find significant information about the HX o
r SX series of MAN military trucks on the current Rheinmetall website, you will be disappointed – see http://www.rheinmetall-defence.com/en/rheinmetall_defence/systems_and_products/vehicle_systems/military_trucks/index.php . Whereas when the company was still “MAN Military”, a PDF brochure detailing HX and SX capabilities – a brochure titled “The Mobility Elite” – was always available online. It's this particular brochure that I need to reference, in order to make my question clear.

In the previous post I gave a link to the brochure that was then still working, but that link has since expired. Here is another link, to SCRIBD, which I hope will last longer -- http://www.scribd.com/doc/17296072/The-Mobility-Elite .

But just in case this SCRIBD link also does not survive, below I've pasted jpg copies of the relevant pages in the PDF.


3. Is a 3-Point Pivoting Sub-Frame Necessary?

Is 3-point pivoting sub-frame absolutely necessary? That's the question I asked a few months ago.

According to MAN's “Mobility Elite” brochure, perhaps not. The following are snapshots from the first few pages of the PDF.










The text in the last snapshot is what got me thinking. Here MAN Military writes:


"100 % torsional stiffness – the box-type frame.

The extremely torsion resistant box frame with hollow longitudinal members and welded tubular cross members put the 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.

Coil-sprung high mobility – the suspension.

The secret of its high mobility is the progressive coil spring suspension for extremely long spring travel which permits rapid adjustment to the terrain. Additional shock absorbers with integrated dampers on the rear axle are available on request.

A special highlight is the optional hydro-pneumatic suspension with integrated, regulated load-dependent shock absorbers and extremely long spring travel for top driving stability under the toughest conditions. It is equipped with a height adjustment and can be locked in any position."


Should we take this description at face value? Is this just hype, or is it in fact possible to deliver what MAN Military promises here?

Does it strike those on this forum as feasible to build a frame that is so stiff, that it is 100 % torsion-free, as MAN promises? With a progressive coil-spring suspension that absorbs all “terrain irregularities”, even the most extreme ones? Such that any body placed on top will remain “unaffected, even during fast off-road drivi
ng”? If you compare the pictures of the HX and the SX vehicles above, for instance, it does seem that the box-frame in the SX is far more robust. And note that MAN only makes this claim only for the SX-45; it does not make this claim for the HX series.

Also note that MAN repeats this claim in the PDF. In the third-to-last page from the series posted above, MAN writes about the SX-45:

"With its unique off-road capabilities and torsional rigidity the SX sets the benchmark in mobility – high performance off-road. It can even get through where only tracked vehicles normally have the capability. The SX is the leader in its class, and either the 3- or 4-axle vehicle is predestined for the transport of high-class, complex and sensitive bodies, ideal as a system and weapon carrier for tactical missions......"

Now those who have been following this thread will realize just how significant a claim this is. MAN is saying that the SX 45 can carry "complex, sensitive bodies" without any need for a 3-point, pivoting sub-frame, precisely because its box-frame proves so torsionally rigid.


4. A Real Puzzle

But if this is true, then why hasn't this technology yet "spilled over" from the military side, towards the commercial end of things? Presumably MAN military and MAN commercial do talk to each other? And presumably someone might have seen the utility of a completely torsion-free, "high mobility" box-frame, for makers of very large, expedition-style motorhomes, like ActionMobil, UniCat, and Armadillo?

SX-45 technology has been around for a while: MAN started delivering the first vehicles, it seems, from roughly 2005 onwards. So why are ActionMobil, UniCat, and Armadillo still building their 6 x 6 and 8 x 8 "specials", on frames that twist? If you take a look at some of the videos of 6 x 6 and 8 x 8 vehicles on the ActionMobil and Armadillo websites, you'll see that when they go over rough terrain, as one might expect the cab goes one way, and the body another.... I don't know whether this potential to "twist" was already built into the TGA or TGS construction-vehicle chassis, as delivered from MAN's factory. However it arises, it is certainly a feature of even the largest 8 x 8 expedition motorhomes. It's also quite clear that all of them are still being mounted on 3-point pivoting sub-frames. But given the existence of a potential SX-45-style solution, why hasn't any fabricator yet adopted this as an alternative?

Something here does not quite "fit", and I am not sure what it is. I tried calling up Rheinmettal-MAN a number of times, but just got the run-around, and no-one I talked to seemed to understand my question, let alone provide a straight answer. So this thread seemed like the perfect place to post this puzzle.

Here's hoping that, this time around, many more will understand the query...:)

But again, Ian and Victorian, many thanks to you both for your responses.

All best wishes,


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by Aimé Tschiffely
From $10.99


This is a response to Moe, LukeH, and ntsqd, which explains why I am pursuing this research. Also from page 34 of "pivoting frames and mounting campers”, at http://www.expeditionportal.com/foru...campers/page34 .


Hi Moe, LukeH, ntsqd,

Thanks for the responses; very informative.


1. Moe:

This is a design "thesis project" that I will be working on, in earnest next fall, i.e. beginning in September. I've been anticipating a bit, trying to determine the engineering constraints. Please see my first post on page 33 of this thread, for a more thorough explanation.

The basic issue is this: from a purely design point of view, expedition motorhomes seem awfully space-wasteful. In the lingo of the wider RV industry, they are “non-integrated” designs in which a body is simply placed on a truck, whose cab remains separate. So the seating gets duplicated. This contrasts markedly with the most advanced European designs, for instance, Hymer motorhomes. In almost all Hymer RVs, the driver's seat and passenger seat swivel 180 degrees, and do “double-duty” as dinette seating. Again, please see my post on page 33 for pictures.

I still have to research the design-history of this innovation, but I suspect that it began with the VW Westfalia "camper van", back in the 1960's -- see http://en.wikipedia.org/wiki/Volkswagen_Westfalia_Campers . Almost all van-sized motorhomes employ double-duty swivel seats to save space, including “Sportsmobile”, which also makes vans that specifically target the expedition market – see http://www.sportsmobile.com/4_4x4sports.html , http://www.sportsmobile.com/4_maxim07.html , http://www.sportsmobile.com/sections/4x4/maxim/maxim07_spread.jpg :


Now the interesting thing is that top-of-the-line Hymers are big. Maybe not as big as Class A American motorhomes, but certainly as large as the biggest expedition motorhomes. So if double-duty swivel seating seems worthwhile in a big Hymer, you'd think it would be worthwhile in a UniCat or ActionMobil, too?

As near as I can tell, the main thing that prevents this, is the need to fix cab and body separately, because the latter has to be mounted on a 3-point pivoting frame. Class A American motorhomes and Hymers can be fully integrated designs, it seems, because they don't need 3-point pivoting frames. And they do not need 3-point pivoting frames, because “regular” RV's typically do not experience the same stresses as expedition motorhomes.

However, I then came across the SX-45 brochure, and began wondering why this technology had not yet “migrated” over to UniCat or ActionMobil. As stated in the post just above, ActionMobil has already built at least one 8 x 8 expedition motorhome on a MAN KAT military chassis. So perhaps ActionMobil has good enough relations with MAN military, to be able to request a SX-45 chassis? Would it really cost that much more? The engineering has already been done, and perhaps all that MAN needs to do, is combine the SX-45 chassis with the same engine and drive train used by the 8 x 8 TGS – which, by the way, is the chassis used by Unicat in the large build referenced in the previous post; and so too, the chassis used by Armadillo in one of its large builds.

I will be booking appointments with various companies in Germany and Austria, including ActionMobil and UniCat, to do some more direct, “on the shop-floor” research in June. I have two passports, German and Canadian, and speak German reasonably well, so it should be interesting. At present, I am still trying to establish who I should contact at Rheinmettal MAN, the company that has taken over production of the SX-45.

In the meantime, I figured it would be good to post the MAN brochure on the Expedition Portal, and see what the forum's response would be. Many thanks, Moe, for your enthusiastic reception!


2. Ntsqd:

You mentioned that the system you described has been used by the American military “since at least WWII and possibly earlier”. I f you have any links to websites that detail visually what you described above, would you be willing to pass them along?


All best wishes,


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This is a response specifically to Moe, in which I also address wider, aesthetic issues. It is the last entry from "pivoting frames and mounting campers” that I will repost. It comes from page 35, at http://www.expeditionportal.com/forum/threads/25494-pivoting-frames-and-mounting-campers/page35?highlight=pivot+frame.


Hi Moe,

Many thanks for the analysis, and I agree, it may be just a cost issue. But mine is not really a research project, in the sense of being just verbal and quantitative analysis. Rather, it's a design project. I am currently attending design school, so my project will be a concept vehicle, complete with models and illustrations.

Sure, in the end it's just the MFA-exercise of a student. But you might be surprised how much long-term effect some of these design exercises can have…. Often transportation designers do their best work – in the sense of most innovative – when completing their MFA's. Because once we begin working in the industry, there’s a tendency for creativity to ossify. There is a big market for independent industrial design studios, for instance, because companies often find that their own in-house designers simply lack the breadth and distance necessary to create truly innovative products.


1. Studio Syn and Christopher C. Deam

For instance, when Knaus Tabbert decided to shake up the trailer industry a bit, and create a conceptual "caravan-of-the-near-future" – a technology carrier that would test innovative design, materials, and products in concert – Knaus Tabbert did not go in-house. Rather, for their “Caraviso” concept-trailer, Knaus Tabbert turned to an independent design-studio called “Studio Syn” – see http://www.examiner.com/article/knaus-tabbert-caravisio-the-shape-of-caravans-to-come , http://www.studio-syn.de/en/studio/category/ueberblick , http://www.studio-syn.de/en/projects/category/alle_projekte , ttp://www.studio-syn.de/en/projects/article/caravisio1 , http://www.studio-syn.de/en/projects/article/caravisio , http://www.knaus.de/knaus/neuheiten-2014/caravisio-2014.html , http://www.knaus.de/en/knaus/novelties-2014/caravisio-2014.html , https://www.facebook.com/caravisio, http://www.gizmag.com/caravisio-camper-concept/28978/ , and http://www.carscoops.com/2013/09/caravisio-caravan-will-cruise-you-into.html :


Caravisio_Fotos_Prototype (27).jpg

Likewise, when Airstream began realizing that it’s customer base was significantly aging, and that it had to update its interiors or die, it turned to Christopher C. Deam, a wonderfully creative, outside, independent designer – see http://www.nytimes.com/2012/02/23/garden/christopher-deam-brings-airstreams-interior-up-to-date-qa.html?_r=0 , http://www.curbly.com/users/diy-maven/posts/1198-trailer-chic-the-vision-of-christopher-deam , http://www.cdeam.com/projects/discipline/airstream , http://www.cdeam.com/project/international , http://www.cdeam.com/project/international-signature-series, http://www.cdeam.com/project/sterling , http://www.designaddict.com/design_index/index.cfm/Christopher_C._Deam , and http://www.airstream.com/travel-trailers/intl-sterling/ :



Now to be sure, most American motorhome manufacturers seem forced to offer interiors that are best described as "colonial kitsch", with color choices ranging from plaid green to brown plaid, because that's what the American market demands. Just contrast the interior of the typical mid-market American motorhome with the interior of a German Hymer. Even a few Airstreams sold in the United States still offer colonial kitsch cabinetry – see http://www.airstream.com/travel-trailers/classic/photos-decor/ :


But this market-led mentality has limits, because often customers do not even know that they might like something different, until they actually see something different. And until Airstream hired Christopher C. Deam, Airstream interiors were not that different. Deam describes the situation in a NY Times article:

"What I found was, you had this great streamlined aerodynamic modern exterior, and then you opened the door and it was like grandma’s kitchen. There was a disconnect between the exterior and the interior. You approached the trailer and there was the magic promise of the future, and you walk in and it was like a log cabin on wheels. What we decided was, we had to do some kind of archaeology, stripping it down and getting rid of all the gewgaws and clunky interior, and taking it back to something really essential. I simplified it and emphasized the horizontal lines and put in a lot of fluid, curved laminates." - http://www.nytimes.com/2012/02/23/garden/christopher-deam-brings-airstreams-interior-up-to-date-qa.html?_r=0 .

Because of Deam, Airstream’s product line now feels more “European”, which Airstream signals by designating the trailers “International” in the American market – see http://www.airstream.com/travel-trailers/intl-signature/photos-decor/ , http://www.airstream.com/travel-trailers/intl-serenity/photos-decor/ , and http://www.airstream.com/travel-trailers/intl-sterling/photos-decor/ :


Also see http://www.airstream.com/travel-trailers/eddie-bauer/photos-decor/ , http://www.airstream.com/travel-trailers/land-yacht/photos-decor/ , http://www.airstream.com/travel-trailers/sport/photos-decor/ , and http://www.airstream.com/travel-trailers/flying-cloud/photos-decor/ . Many of the Airstream trailers spec’d for the European market also seem to have been designed by Deam – see http://www.airstream-germany.com/index.html and http://www.airstream-germany.de/download/Airstream2013de.pdf . The irony here, of course, is that these wonderful trailers were dreamt up by a superb American designer, and in that sense, there is really nothing "international" about them at all!

As you might appreciate, there is a potentially big economic payoff here, because Airstream has now achieved even more product differentiation vis-a-vis the saturated American market for caravans. Airstreams were already a rather unique product to begin with, because of their exteriors. Now (most of them) are also unique because of their interiors, too.


2. The 1990’s “haute-IKEA” aesthetic of German Expedition RV’s

The world of really big, off-road-capable RV’s is, for the most part, German – pace Earthroamer, GXV, Tiger, etc. As such, the interiors of UniCats and ActionMobils have not resembled grandma’s colonial-kitsch-kitchen for quite some time. But even still, in comparison to the wider German RV industry, UniCat and ActionMobil interiors do seem a bit dated.

One might charitably describe the interiors of many UniCats and ActionMobils as “haute-IKEA” , in the sense that a 90-degree, rectilinear, T-square aesthetic predominates, of the sort that characterized IKEA furniture back in the 1990’s and early 2000’s. Again, see http://www.actionmobil.com/en/4-axle/interior-design , http://www.actionmobil.com/en/3-axle/globecruiser , http://www.actionmobil.com/en/3-axle/atacama , http://www.unicat.net/en/info/MXXL24AH.php , http://www.unicat.net/pdf/UNICAT-MXXL24AH-MAN8x8-en-es.pdf , http://www.unicat.net/en/info/EX70HDQ-MANTGA6x6.php , http://www.unicat.net/en/pics/EX70HDQ-MANTGA6x6-2.php , http://www.unicat.net/en/info/EX70HDM-MBActros6x6.php , http://www.unicat.net/en/pics/EX70HDM-MBActros6x6-2.php , http://www.unicat.net/en/info/EX63HDSC-MANTGA6x6.php , http://www.unicat.net/en/pics/EX63HDSC-MANTGA6x6-2.php , http://www.unicat.net/en/info/EX70HD2M-MANTGA6x6.php , http://www.unicat.net/en/pics/EX70HD2M-MANTGA6x6-2.php , http://www.unicat.net/en/info/EX63HDM-MANTGA6x6.php , http://www.unicat.net/en/pics/EX63HDM-MANTGA6x6-2.php , http://www.unicat.net/en/info/EX63HD-MANM4x4CC.php , http://www.unicat.net/en/pics/EX63HD-MANM4x4CC-2.php , http://www.unicat.net/en/info/EX58HD-MANTGA4x4.php , http://www.unicat.net/en/info/EX58HD-MANTGA4x4.php , http://www.unicat.net/en/info/EX45HD-UnimogU5000.php , and http://www.unicat.net/en/pics/EX45HD-UnimogU5000-2.php .

Sure, I love the "New York loft" sense of space provided by the UniCat pop-ups, and this format has since been followed by other fabricators, for instance, GXV – see http://globalxvehicles.com , http://globalxvehicles.com/vehicles/ , http://globalxvehicles.com/global-expedition-vehicle-pangea-4x4-rv/ , http://globalxvehicles.com/gxv-pangea-gallery/ , and http://www.examiner.com/slideshow/gxv-launch-pangea-expedition-vehicle-with-vertical-slide#slide=1 . But, if anything, the GXV “Pangea” interior strikes me as even more doggedly utilitarian and lacking in contemporary design sophistication, than anything produced by UniCat.

[Brief aside: If memory serves, it seems that it was ActionMobil who first pioneered box-style pop-ups in expedition motorhomes. But please correct me if I am wrong about this.]

The pity here is that the interiors of Germany's non-expedition, “regular” motorhomes are usually very well-designed, and are decidedly more contemporary than most American mid-market models. The German designers who work for Ketterer, Hymer, Westfalia, EuraMobil, Knaus Tabbert, etc. all seem to handle curvilinear asymmetry with aplomb – see for instance http://www.ketterer-trucks.de/en/models/category/c/travel-motorhomes/model/continental-12000-2.html , http://www.hymer.com/en/ , http://www.hymer.com/en/models/integrated/hymer-starline/experience/ , http://www.hymer.com/assets/files/modell-2014/epaper/hymer-starline/epaper-STARLine_englisch/epaper/ausgabe.pdf , http://www.westfalia-mobil.net/en/ , http://www.westfalia-mobil.net/en/modelle/amundsen/amundsen-allgemein.php , http://www.euramobil.de/integraline_ls_galerie.html?&L=1&L=1 , and http://www.euramobil.de/integra_galerie.html?&L=1&L=1 :




But none of this German curvilinear design expertise seems to spill over into expedition motorhomes, even though UniCat and ActionMobil are just down the road, and both are German-speaking companies.

For what it’s worth, high-end American luxury coach manufacturers like Newell, Liberty, Marathon, Featherlite, and Millenium also try to deliver more contemporary, curvilinear interiors – see for instance http://www.newellcoach.com/the-coaches/photo-gallery/ and http://www.newellcoach.com/newell-coaches/coach-1508/ . But on my own view, Newell seems to handle curvilinear asymmetry less successfully than Hymer or Euromobil, and costs 3 or 4 times as much.

So cost is not the only constraint. Either you have the designers and craftsmen who can pull off a Hymer interior, or you don’t. I suspect that ActionMobil and UniCat could have more contemporary, curvilinear interiors too, if customers began demanding as much. But until customers do, their interiors will probably continue to seem driven mostly by engineering considerations.


3. Courageous Color, ARC, and Art Deco

My other quibble with the RV industry in general, is that it plays things rather “safe” when handling color. If one compares the interiors of almost all of the above brands – European and American, regular RV and expedition RV – to the new Airstream interiors, one huge, glaring difference becomes obvious: the color choices of most motorhome manufacturers tend to be muted, a restricted palette of whites, greys, browns, and blacks. Whereas Airstream, since it hired Deam, has developed the courage to handle strong, vibrant interior color, and a dramatic mixture of materials.

However, even the interiors of the newest Airstream trailers still seem a bit tame when compared to the interiors created by the bespoke conversion specialist, “American Retro Caravan”, or “ARC” – see http://www.arcairstreams.co.uk , http://www.arcairstreams.co.uk/refits/retro , http://www.arcairstreams.co.uk/blog/category/retro-airstreams/ , http://www.arcairstreams.co.uk/blog/2013/02/the-airstream-safari-with-the-egg-shaped-hole/ , http://www.arcairstreams.co.uk/blog/2013/02/a-closer-look-at-that-luxury-padded-bedroom/ , http://www.arcairstreams.co.uk/refits/luxury , http://www.arcairstreams.co.uk/blog/category/luxury-airstreams/ , http://www.arcairstreams.co.uk/refits/corporate , http://www.arcairstreams.co.uk/blog/category/corporate-airstreams/ , http://www.arcairstreams.co.uk/refits/catering-and-bars , http://www.arcairstreams.co.uk/blog/category/catering-airstreams/ , and http://www.arcairstreams.co.uk/blog/category/cafe-airstream/ :


What really impresses me about ARC is their courageous color choices (split-complementaries like red + blue-green, blue + yellow-orange); their mastery of curvilinear, aluminum-detailed cabinetry; their asymmetrical layouts; and the retro details throughout – port-hole windows, jet-engine spot-lamps, and circular-grilled air vents, for instance -- see http://www.ehow.com/facts_5649966_split-complementary-color-scheme_.html , http://www.incolororder.com/2011/11/art-of-choosing-split-complementary.html , and http://www.tigercolor.com/color-lab/color-theory/color-harmonies.htm . Sure, most people will not want over-the-top, vibrant color in a motorhome that they have to live in, day-in, day-out. And the more colorful ARC designs tend to be catering, café, and bar trailers. But check out some of the moderate ARC designs, where they still use color in strategic, calibrated ways to give interiors a sense of spaciousness and joy -- see http://www.arcairstreams.co.uk/refits/retro .

My strong design preference has always been for Art Deco and Streamline, although nowadays these tend to be rebranded as neo-Deco, diesel-punk, deco-punk, glam, retro, etc. I am an avid follower of "Lord K's Garage" diesel-punk blog, for instance – see http://www.dieselpunks.org and http://www.dieselpunks.org/profiles/blog/list?user=0n7d9yl571cmt . I partly grew up in South Florida, and fell in love with South Beach "Tropical Deco" as a kid. Many of ARC’s more colorful trailers – the Apollo 70 in particular – have interiors best described as “Miami Deco” – see http://www.amazon.com/Tropical-Deco-Architecture-Design-Miami/dp/0847803457 , http://www.pinterest.com/search/boards/?q=miami deco , http://www.pinterest.com/search/boards/?q=tropical deco , http://www.apollo70.co.uk , http://www.beautifullife.info/interior-design/apollo-70-airstream-bar/ , http://brosome.com/the-apollo-70-airstream-bar-is-the-perfect-place-to-have-a-drink/ and http://hiconsumption.com/2014/03/apollo-70-airstream-bar/ .

For me, Art Deco is the modernist design-aesthetic that should have dominated the 20th century. But for whatever reason, lots of people found the puritanical-minimalist, black-white-grey, Bauhaus rectilinearism of Mies-and-co ever so convincing, perhaps because it was so cheap on the details and color paint? Remember, I am German, so perhaps I am “allowed” to take a swing at Mies and the Bauhaus….:) The 1990’s/early 2000’s rectilinearism of IKEA is then the direct descendant of this Bauhaus aesthetic, as are most UniCat and ActionMobil interiors.

However things have changed dramatically in architecture and design since the 1990’s, and over the last 10 years “organic-tech” and "blobitecture" have displaced modernist rectilinearism. In effect, these are curvilinear, organic outgrowths of "hi-tech" architecture, made possible by CAD -- see http://www.kuriositas.com/2011/01/blobitecture-rise-of-organic.html , http://en.wikipedia.org/wiki/Nicholas_Grimshaw , http://en.wikipedia.org/wiki/Santiago_Calatrava , and http://fr.wikipedia.org/wiki/Architecture_high-tech .

And as demonstrated above, German RV manufacturers like Wesfalia, Hymer, Euramobil, etc. have been offering more curvilinear interiors for quite some time. One could even say that the Art Deco/Streamline aesthetic never really disappeared, persisting in certain design niches, transportation design in particular. If only because rectilinear, squared-edged vehicles are not very functional, i.e they're not aerodynamic.

So let’s just say that, even though UniCat and ActionMobil are not building grandma’s colonial kitchen, they are now roughly 2 decades behind the times, vis-à-vis wider design trends. Their engineering is no doubt top-notch, and Victorian quite rightly defended UniCat's careful engineering and craftsmanship in an earlier post. But just take a look at the links above, check out Wesfalia, Hymer, Euramobil, et al, compare for yourself, and everything that I have written here may seem somewhat self-evident.


4. Back to Engineering

Now don’t worry, I realize that the bulk of this post was very off-topic, because this is an engineering thread, about 3-point pivoting sub-frames. But just thought I should state all the above, so there’s no mystery as to where I am coming from. I am a designer, who wants to poke the expedition-RV industry a bit, with a concept vehicle that breaks a few unwritten rules.

It's easy enough to create wild designs that have no basis in engineering reality, and the world of transportation design is littered with concept vehicles that never got built, because they can't be built -- at least not cost-effectively. It's much harder to think through the incremental changes that are much less dramatic, but that, over time, can cumulatively revolutionize a given vehicle-type.

For instance, my suspicion is that companies like ActionMobil and UniCat are still mounting camper bodies on 3-point pivoting sub-frames mainly due to inertia, and not just cost. I may be wrong about this, and this needs investigation. But it's at least a possibility. A fully integrated off-road mobile home would be highly desirable, and perhaps not that much additional engineering is necessary to pull it off. This might be an "incremental" change, from an engineering point of view, but one that would change the game dramatically from a design point of view, with significant consequences for overall interior plans, layouts, the efficient use of limited space, etc. Similarly, I suspect that ActioMobil and UniCat are still doing 1990’s-style “haute-IKEA”, perhaps because customers have not demanded more. It sort of takes an outsider like me to come along and say, “Hey, why couldn’t you do x, y, or z instead?”

By far the best way to do that, in the world of design, is by presenting alternative imagery.

I’ll keep you posted, but in another thread….:)

All best wishes, and many thanks for your feedback,

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As I already wrote in the other thread, after fixing the problem of flex at 30+ ft vehicle length by using a stiff frame, the main obstacle for designing an off-road capable integrated vehicle will be the placement of the engine.

The KAT/SX line places the engine high behind the drivers cab in order to achieve a large fording depth of 4+ ft and concurrently keep the height low to allow train transport. This would allow a flat floor integrated cabin only if the floor is placed very high at 6+ ft. Moving the driver and passenger seats this high would give create view, but wouldn't be very comfortable off-road.

So the aim should be to keep the floor level directly above the frame without any sub-frame below. For this the engine has to be moved to the back or a totally different propulsion concept has to be used. With the SX frame this would allow to place the floor at about a height of 4 ft. Of course, the wheel houses then also have to be integrated into the hull and will use space inside the cabin. How slide-outs can be integrated here has to be seen.

But this would not only allow to keep the total height and center of gravity low, it will also move the engine noise away from driver and passengers. Nobody wants to be just one foot away from a truck engine when it provides 500+ hp. And the whole vehicle wouldn't look that obtrusive if it isn't that high. A total height below 12 ft would also avoid many restrictions.

Regarding exterior design I always liked something like the Panther CA7 from Rosenbauer. Of course, a camper would be considerably higher.


Tea pot tester

That is a lot of links!

-How different is wheel travel in isolation between a MAN KAT, Zetros, Tatra, Unimog etc? If a rigid chassis Tatra can, purely from how the wheel is suspended, only achieve about the same wheel articulation as a Zetros, then the chassis articulation on the Zetros provides more real world traction by keeping all wheels on the ground at any given scenario by chassis twist? Having a really stiff chassis means you don't need the separate rail on rail or three point mount to isolate twist from the camper so you can save the maybe 100-150mm in height that takes up. But since train or Hercules transportation isn't often considered in camper design maybe the extra height isn't that big a deal compared to a military purchase? ;)

-Seats in a truck cab do a very specific supporting roll to the passengers. Swivelling them around in very compact campers is the only way you can seat four with seatbelts for driving and then the same four round the dining table in the evening. Adria Twin example layout attached. Very compact and efficient. But the seats are car seats, no good for snuggling the wife in the evening or relaxing with a book or dvd. Even worse, the rockandroll rear seat tries to be a bed as well which my back would not like for longer than a week. But at 5.99m long it exactly fits many Euro camping spaces, and is the same category as a car on many ferries.

-RVs with custom made cabs have enough room for comfy captains chairs for driving but you try that for comfort in a truck offroad all day. The seat and your spine may start complaining, especially in trucks with seats infront of the axle.

-I like driving with the window open. Do that in a sandy environment your evening shower becomes a bit irrelevant if I have to sit back in the days sweaty, dirty seat. Spent the day digging yourself out? Mud everywhere too?

-A big drawback to the Euro campers which keep the van cab is insulation. The walls and bulkhead may not be insulated against cold and heat at all, the glass won't be insulated meaning you'll lose a lot of heat at night and the windows will be coated in condensation in the morning. Add on covers can help but won't work as well as the camper bodies insulation. I know 8x8 hardly suggests efficiency, but adding a bigger heater and carrying more fuel so you can make use of inappropriate cab seating when parked isn't an ideal solution to me. The likes of Unicat seem to be so well insulated that a minimal degree of heating and cooling are required. The heat from a Tatra/MANKAT engine will try to get into a fully integrated camper too just because of where it is.

-Security while being shipped also suggests a separate cab is a good idea. In a fully integrated body you could create some sort of removable security wall between cab and camper as happens in most crawl thrus, but to maintain your poshly furnished interior it needs to disappear and be stored elsewhere and it won't be small.

My 2p :)



Dear egn, moe, et al,

OK, so this new thread is now up and running. Thanks for the suggestion. But gosh, that was a lot of work to get it going!

It seemed important to begin with a thorough explanation of the design problem and question, so that those new to the thread could get up to speed quickly. Also re-posted 4 of my entries from the other thread, for the same reason.

Grizzlyj, your excellent (and very relevant!) points suggest that this was wise, because you immediately understood the kinds of issues that this thread wants to explore. Yes, lots of links, but I figure that at the very worst, I am doing a bit of a “public service” here, providing a fairly comprehensive overview of the top end of the expedition-vehicle market, thereby empowering others who may be unfamiliar with that market to self-educate.

The title of the thread – "Fully Integrated 6x6 or 8x8 Expedition RV, w Rigid Frame & Progressive Coil Suspensn" – is not very poetic, and does have an “engineering” ring to it. But that’s just as well, because the engineering constraints are critical. Only if such a vehicle were cost-effectively possible from an engineering point of view (as moe suggested), 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 the “pivoting frames and mounting campers” thread at http://www.expeditionportal.com/forum/threads/25494-pivoting-frames-and-mounting-campers/page33?highlight=pivot+frame . So I hope that this 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", againbecause 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 this new thread "6x6 or 8x8", to indicate the rough ball-park. And clearly, a 6x6 would 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 from egn that appears in the very first post in this thread, 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 will not have. But maybe I am mistaken in this speculation?

Egn, I have been following up your leads as regards “Tatra”, and will post shortly in this thread with thoughts and questions about engine-location and type. In the meantime, thanks for the additional thoughts in your post above. And finally, Grizzlyj, once again, great points. But I need a bit of a breather from the Expedition Portal for a bit. Assembling all of the above, and getting this thread going, has seriously set me back in my other academic commitments. Rest assured, however, that I will respond.

All best wishes,



grizzlyi said:
How different is wheel travel in isolation between a MAN KAT, Zetros, Tatra, Unimog etc? If a rigid chassis Tatra can, purely from how the wheel is suspended, only achieve about the same wheel articulation as a Zetros, then the chassis articulation on the Zetros provides more real world traction by keeping all wheels on the ground at any given scenario by chassis twist?
This will be true with very soft ladder frames and at very low speed (crawling). Only then the frame can twist enough. Leaf springs normally don't have the same amount of wheel travel as coil springs. Tatra even adds independent air suspension.

biotect said:
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, ...
Of course, it isn't absolutely necessary, but it provides one tested solution to the problem of chassis twist in off-road situations. This isn't even a problem only in off-road environment. I have read about destroyed wind screens because someone has driven his large camper onto some uneven ground or a ramp small ramp. The other point is that this tour buses are only about have the size as a proposed vehicle on 8x8 platform. You can get away with such solutions if you turn around the pivoting 3-point fixture and let the back of the frame twist freely below the relatively stiff sub-frame of the cabin. But you will loose the stabilization against tipping in rough terrain caused by the counter movement of back and rear of the vehicle.

biotect said:
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?
Of course, there is lower traction with less number of wheels. In my opinion the combination "rigid frame + progressive coil suspension" wasn't chosen because of better traction, it was chosen because you can go much faster in rough terrain because of less mass involved in suspension. Without this combination a large part of the vehicle has to follow the bumps and dips of the surface. With the combination only the axles are moved. This gives a smoother ride when moving very fast. This doesn't translate automatically in best off-road performance in all situation, especially in terrain where you can only crawl. The example here is the Unimog, which has extraordinary off-road performance in such crawling environment. A SX or KAT may not be able to follow easily here, because the complete body moves to one side or the other.

So, here may be a first important question that has to be answered here:
Should it be an Overlander, that is moved comfortable and fast mainly on paved roads, but robust enough to be moved slower on unpaved roads and occasional use in light to medium off-road situations?
Should it be an Overlander, do be able to be moved comfortable and fast mainly on rough paved/unpaved roads with occasional movement in medium to heavy off-road environment?
Should it be an Overlander, to be able to be used in medium to very heavy off-road environment, with the cost of less comfort regarding travel on paved/unpaved roads?

When I defined the above vehicles I had specific vehicles/concepts in mind. Readers shouldn't be offended by this class building, because each of this classes has its own advantages and disadvantages:
The first would be matched fairly good by the typical MAN TGM/TGA with flex-frame, probably with air suspension. This is something build by Action Mil, Unicat and others.

The second class would match vehicles based on a stiff frame like KAT/SX/Tatra. They are designed to be moved fast through rough terrain. The military base gives high robustness and reliability.

The third class are the pure off-road vehicles, that are able to go into very heavy terrain. For this they give up comfort, but for the buyers this is of lesser priority.

In 2005/2006 my decision was between Kamaz, Tatra and MAN KAT. Therefore I have collected a lot of images and other information about this vehicles. I found the following image of an integrated Tatra 815 8x8 off-road vehicle. The construction was already started, but some time later the website disappeared.


At this time I also thought about of an integrated solution for the KAT and liked for potential builders. One of this builders was http://www.der-fehntjer.de . I looked for something like image 219. But I had to drop this idea after decision for MAN KAT, because of the engine placement.
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Expedition Leader
One option not mentioned here is the Pinzgauer series of vehicles - they are essentially the same suspension design as a Tarta but in a smaller package and with portal axles and 6x6. Torsion free cab mounting with minimal engine interference in the cab layout - but it can't be worked out to have the front seats swivel unfortunately.

The earlier gas power pinzgauers are underpowered for use as a camper but the later generation of diesel engined Pinzgauers are becoming available and legal in the US. Solid design with good parts support. Not as large as a Tatra or MAN chassis - but that can be good as well. Lots of good photos of fully intergrated cabin expo-camper Pinzgauers on the web.


I love the Pinzgauer, I want one as second vehicle for going onto old military roads here in the ALps. But the Pinzgauer is very small and come nowhere near the comfort of a camper based on a truck. Only the 6x6 Model is of interest, because it has a reasonable size.

The other point is, that not many used Pinzgauers are available in the market, and if you find one with a diesel engine you have to be very careful to look for rust. Most of them were used in coal mining areas and are not always in best condition.


Tea pot tester

Those vehicle classifications are nicely divided :)

Anything independently suspended will have a relatively short suspension arm (or whatever you may want to call it :)) compared with a beam axle which is why I was wondering what the actual axle droop is comparing an independently suspended Tatra to a leaf sprung Zetros for instance.

In the pic attached Merc quotes 30 degree rotation about the centre of the Mog axle, I can't imagine a Tatra can get close to that allowing for the fact the driveshafts must accommodate that, and its swinging down from the outside of the central chassis spine so a shorter radius than a beam rotating about its centre.

So ignoring chassis twist, since as said you would have to be going slowly to fully allow that, how much difference is there between the (really quite long leafed) travel on a Zetros compared to the coils on a Tatra? Do all Tatra 6x6 have coils on the front only and a walking beam at the back with leaves???

i.e. if the independence of a Tatra limits droop compared to a Mog, and the leaves of a Zetros limit it, does a Zetros and a Tatra come out about equal?

I hadn't realised until quite recently that having coils, and so how a Mog axle is held in place, plays a huge part in its short overhangs and so approach/departure angle. The nose of a Zetros stops at the leaf hanger, so its method of suspension is what seems to determine (in part at least) its approach angle.

If the advantage of independently suspended wheels is speed which I'm sure is important to the military, is it feasible to design champagne glass storage for those higher speed vibrations? ;)

The linked to video probably shows less vibration transmitted to the Tatra personnel vs Zetros if its unbiased (filmed at the Tatra factory I believe), but I don't think there's much wrong with slowing down and admiring the view :)


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 :)
Ex army diesel Pinz are becoming available in the UK but quite pricey.



The comparision between Tatra and Zetros isn't that fair. The Tatra is true military design, whereas the Zetros uses civil parts for export as lost military option to countries with low emission standards.

The linked to video probably shows less vibration transmitted to the Tatra personnel vs Zetros if its unbiased (filmed at the Tatra factory I believe), but I don't think there's much wrong with slowing down and admiring the view
If you have enough time and like 100s of miles feature less back country? :)

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Tea pot tester
The comparision between Tatra and Zetros isn't that fair
Of course it is, since we're only talking about putting a camper on the back of any of these lovely trucks, not how fast we can get how many troops how far away. :smiley_drive:
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Expedition Leader
Tatra does offer a truck similar to the MAT KAT trucks - the Tatra T-810-C


"Thanks to the excellent ladder frame design, high-quality original TATRA Rigid portal axles, their perfect suspension and axle attachment, including the front axle suspension by coil springs, the vehicle has unrivalled off-road as well as on-road vehicle performance. Two wheelbase lengths and a three-point superstructure mounting system can satisfy all customer requirements."