pivoting frames and mounting campers

[Iain_U1250]

The chassis on my Unimog is very flexible, and the mounting point system has to match - the jacking up one of the rear wheels was enough to flex the chassis quite a bit as shown in this photo.


My camper box is on the OEM 4 point bed - the centre mount is rubber mounted to the cross member between the axle mounts, the front and rear pivoting mounts allow for about 25 degrees of flex each way. The cab is fixed on the cross member between the front axle mounts, and the rear pivoting mount is mounted off the chassis.

If I stand on top of the camper, I can rock the box so that I get about 50mm of differential movement between the cab and the camper. I'm thinking of adding some shock absorbers to stop the wobble, but still allow it to flex. The OEM U1700 bed has a large shock on the bed to limit the movement, and there are OEM cab shock available as well.

A friend did some basic finite element analysis on my camper box - and it is incredibly stiff - if you don't mount it properly, either the box or the chassis will be destroyed eventually - my guess would be the chassis is a lot weaker than most camper boxes - just due to the relative section modulus - massive box verses relatively tiny chassis.

 

[canals1164]

after a technical fork lift test we decided to go for a three point monting!

 

[westyss]

after a technical fork lift test we decided to go for a three point monting!View attachment 86737

Keep in mind that once more weight is on the truck the suspension will do more than it does in that pic and less frame flex. I cant tell but to me it looks like the suspension isnt giving at all?

 

[Iain_U1250]

Check out the flex in this Unimog - articulation between cab and camper scales off at around 400mm.

We are currently making the "sock" for the seal between the cab and camper, and need to cater for the 400mm of differential movement.

Regarding the pivoting mount - standard MB Unimog - 3 point mount on the cab, and 2x 3 point mount on the camper. Lateral fixed ( on 12mm rubber bushes) is on the cross member on the spring mounts, and lateral pivoting mounts.

 

[Sigurður Ingi Jónsson]

This seems to be where the greatest brains gather to discuss better mounting of campers. I've just posted my woes in the hard camper section. I would appreciate any input from those in the know on this thread.
The post is here: http://www.expeditionportal.com/for...mper-mounting-system-Torsion-free-three-point

 

[Alastair D(Aus)]

There is a separate thread that has been started regarding spring mounts that would benefit with comments by the learned members here.

http://www.expeditionportal.com/forum/threads/83283-Camper-mounting-help

 

[kookynet]

Two line pivot subframe on a Canter FG

Hi,
Just adding my two cents.

I have been driving for two years on often bad Baja tracks a FG with a custom Two Line Pivot subframe without any issue.
The building was quite easy and quick.

here are some details http://kookynet.net/220-cristo-3-intro.html



Safe threading to all !

 

[HowardH]

Another approach

Why not completely separate the camper and its frame from the cab and its frame. Similar to a 5th wheel trailer with all the stress and articulation on the hitch pin. Or like an articulating loader or transit bus?

Each frame could be stiff wouldn't have to flex yet the pivot point would give you all the movement you need.

 

[RoosterBooster]

i guess i update this thread with the pivoting body mount solution i ended up with

however, after stumbling over a vintage 1952 "Diamond T" cab my medium duty truck project went a different direction then originally intended
(less expedition, more vintage looking long distance travel truck)

but i think the basic principles and goals stayed the same;
i still wanted (almost) un-restricted frame twist for off the pavement traction (by design the typical H/MDT rear air suspensions do not articulate well)
i also wanted a complete solid cab to camper connection (no movement between the two and no rubber bellow)
so after some thinkering i ended up building a front pivot sub-frame with rear air bag setup again ( i did the same thing when i extended the sleeper on my previous Peterbilt truck)

here are a couple pics (click on them for a larger view );

donor International truck chassis (i picked it for the HSS low profile frame rails and the nice Z-leaf/ torque arm rear air suspension)





fabricated front pivots;



to keep frame webbing flex/stress to a minimum i located them direct opposite of the SAE bell mounts and very close to the front spring shackles
(in place of the stock cab mounts)



the rear of the sub-frame is located with this forget steel panhard bar (a OEM Peterbilt part that is used on integral sleeper cab trucks)



the rear air bags are Firestone 2600 lbs units. my goal was to build the sub-frame as low profile as possible, so i located them outside of the frame in fabricated "shelves"



again, to keep frame webbing stress to a minimum i mounted the bag shelves very close to the rear suspension mounting points and frame crossmember
here is a pic of the almost finished sub-frame including the cab and mockup seats



with the aluminum body in place;



the shocks are adjustable Rancho 9000 series (the King sticker is a joke to mess with diesel ricers )
they are set as wide as possible to give them a good leverage to fight body sway.
not visible are the bumpstops (to protect the sub-frame from bottoming out as well as over-extension)
the airbag supply is plumbed with a Peterbilt auto-leveling valve as well as a dash mounted "dump" valve
(to lower the camper for easy entry/exit as well as to drop it onto extendable legs to keep it from rocking when camping)



...

 

[pappawheely]

wow! Impressive build.

 

[haven]

Before leaving for a multi-month drive around Europe and Asia, Gary and Monika Wescott did some preventive maintenance on their iconic Turtle 5 camper. It turns out that their torque-free camper mount was designed and built 10 years ago by Midwest Four Wheel Drive, the company that builds the Bigfoot monster trucks. Gary and Monika paid them a visit to inspect and lubricate the camper mount.

The mount attaches the camper to the F550 frame in three places: two behind the truck cab, and a third on a crossmember behind the differential. The rear mount is pivoting, allowing the rear axle to tilt without a affecting the camper. Read a little bit about this feature and see a photo of the pivot pin in Gary's blog post.
http://turtleexpedition.com/across-the-usa-2013-3/

Putting the pivot at the rear of the truck chassis is unusual. Most three point designs put the pivoting mount at the front of the camper, and mount the camper to the frame in two locations close to the axle.

 

[westyss]

Before leaving for a multi-month drive around Europe and Asia, Gary and Monika Wescott did some preventive maintenance on their iconic Turtle 5 camper. It turns out that their torque-free camper mount was designed and built 10 years ago by Midwest Four Wheel Drive, the company that builds the Bigfoot monster trucks. Gary and Monika paid them a visit to inspect and lubricate the camper mount.

The mount attaches the camper to the F550 frame in three places: two behind the truck cab, and a third on a crossmember behind the differential. The rear mount is pivoting, allowing the rear axle to tilt without a affecting the camper. Read a little bit about this feature and see a photo of the pivot pin in Gary's blog post.
http://turtleexpedition.com/across-the-usa-2013-3/

Putting the pivot at the rear of the truck chassis is unusual. Most three point designs put the pivoting mount at the front of the camper, and mount the camper to the frame in two locations close to the axle.

I am not sure where I saw it on their blog but they did have a frame failure of some sort not too long ago, just wondering if anyone knows the reason and the result of it all, was it mount issue or some other issue??

 

[haven]

I think most pivoting designs follow the Unimog model, which puts a pivot point at the front, two stationary mounts at the rear axle, and a pivot behind the axle if the frame and box extend much beyond the axle.

That's fine if you have a Unimog, maybe not so fine for other trucks. A couple of well documented Fuso fg140 frame failures seem to recommend a camper subframe that distributes the weight along the full length of the truck frame, rather than at a few mounting points.

 

[westyss]

Here it is, along with a few other failures. It doesnt elaborate on what they think caused the cracked frame and is a little vague in general.


http://turtleexpedition.com/adventu...e-turtle-v-visiting-whales-caves-old-ranches/

 

[Goingbush]

Thanks everyone,
I joined the forum to read this thread. Lots of good ideas.

I recently bought a new Iveco Daily 4x4 and am about to start building a subframe (tray) to mount a box module on the back.

I'm going the 3 point mount, using a pair of Landrover Trailing arm bushes NTC9027 to mount the front of the subframe to the chassis and a Toyota SV21 engine mount as the single flexy mount on the rear. Well thats the plan.

building the 1950 x 2000 x 1500 box from coolroom sandwich panels. (like a uhaul trailer) hope to be all done in the next week or 2

now I must check out the rest of the forum.
cheers Don