pivoting frames and mounting campers

[dzzz]

I've come to wonder if beyond a certain weight if all wheel drive is necessary or all that helpful. Maybe a detroit locker on the back, the right tires, and true commercial winches are the way to go. The frame can then be oversized.
Perhaps the break point (ha) is dualies. Perhaps once there is no way to have single rear wheels it's best to get the right size truck. Truckers on market roads of the world aren't using 4wd. And once up to FG type truck, nobody is doing rock crawling.
The FG is pretty underpowered too. That's a way to get stuck in the mountains when the driver doesn't have the choice to carry momentum through a bad spot.

 

[dzzz]

Here is a short PDF om frame extension from the ford body builders guide. What I found interesting is the detailed approach in preventing frame stress.

https://www.fleet.ford.com/truckbbas/non-html/2009/bb_pdf/146-147.pdf

 

[762X39]

The FG is pretty underpowered too.

I don't think the problems have to do with power or lockers (or 4WD for that matter).
I often wondered during the course of this thread why everybody didn't just use the tried and proven 3 or 4 point mount. I now realize that if frame flex isn't designed in at the factory (and I am only familiar with Mann and Mercedes trucks) then perhaps a rigid mount and a rigid cabin (Like Jay has done with the ecoroamer) might be correct.
It seems obvious now that a constructor should consult with the factory and engineers familiar with a particular chassis before making assumptions and potentially expensive mistakes that may not become apparent until the chassis destroys itself.
It seems that there is no best way to build an Overland cabin but there is a right way.
I have often felt that the money spent on an Action Mobil or even an Earthroamer was well spent because it isn't just the quality of construction (which is high) but the engineering work and testing (and certainly, we have all read the stories about the early Earthroamers trying to destroy the chassis they were affixed to) that you are paying for so you don't have to learn these lessons for your self.
Finally, like the t shirt says, just because you can weld doesn't make you a fabricator!
Thanks all for contributing to our knowledge base, especially sharing your expensive knowledge (it is only a mistake if you didn't learn anything in the process!).

 

[dzzz]

I'm thinking about just mounting the camper like a truck cab with suspension.
Springs or airbags down each rail. Oppositional shear plates in four directions to allow rise and fall but no movement. The shear plate length would control the amount of movement to prevent over extending the airbags.
The system could even lower the camper down when the vehicle was stopped.
Repair would be easy. Lift the camper with the good airbags, block, and replace the airbag.
The system could be dual non-interconnected. Systems 1 and 2 in a zig zag pattern down the frame. Or using coil over bags to prevent a total system collapse on air loss.
The only part that concerns be is the jolt when the sheer plates read full extension (tension). On compression, the more force, the more the airbags push back. But tension is more linear.
I know an air spring can be made to progressively increase resistance in tension. But that solutions seems inelegant, and hard to calculate the real world force.
It would be fascinated to do a full camper suspension with instrumentation to measure the G forces.
What am I missing?

 

[kerry]

Would air bag on top, coil spring on bottom between sheer plate and bottom of the frame stop the shock problem? Or perhaps even dual air bags, above and below.

 

[ntsqd]

Considering the use it seems overly complicated to me. It sounds like the beginnings of how to go about carrying large shock sensitive gear while entered in the Baja 1000.

I am concerned about inertia of the box too. Dampers would be required.

 

[dzzz]

How about this for simpler:
Camper is hinged to the rails at one end. So no horizontal movements. Like a dump truck, but the hinges are 5" above the rails. All down the rail are progressive springs with a load height of 5 inches. Add four tension shock absorbers for upward inertia, although this may not be necessary if the hinges are at the end of the vehicle.
It's a 2+ pivot. Two hard two dimensional connections, but the rest of the frame can move away from the camper at different rates and have a soft return. Like a three point pivot with even frame loading and shock absorption.

 

[dzzz]

Would air bag on top, coil spring on bottom between sheer plate and bottom of the frame stop the shock problem? Or perhaps even dual air bags, above and below.

I think it would. The two practical issue I can think of for all these solutions are 1) Certainty that the box is securly attached and won't walk in any horizontal direction and 2) That the box suspension parts aren't too "fiddly".

Perhaps a high-end Ubolt spring system is all that's necessary. Could start with too soft springs. Then stiffen the springs up until they no longer completely compress. With a little thought a system could be devised that would make a mark when fully compressed. For a "soft landing", oak boards may be enough.

A durable tension suspension system. I'm sure there are of the shelf parts that can do this.

 

[ntsqd]

We're back to using die springs (or stacks of them possibly) on U-Bolts to clamp the box to the rails. Other than fatigue and rusting I'm wondering why this hasn't been used more. Perhaps it doesn't work as well as it seems like it should?

 

[dzzz]

We're back to using die springs (or stacks of them possibly) on U-Bolts to clamp the box to the rails. Other than fatigue and rusting I'm wondering why this hasn't been used more. Perhaps it doesn't work as well as it seems like it should?

What kinds of trucks? Die springs for durability? Thanks

 

[ntsqd]

One example:

I'm with you. My M109 has got some little springs under the hardware that bolts the box to the frame so that the box can pull away from the frame a little bit when the chassis flexes, but it's much more rigidly mounted than most of these pivoting setups that seem to be so popular. This particular M109 was made in 1963 and I'm sure it's seen it's fair share of use/abuse. It's held up GREAT. But the box itself weighs 4000lbs, so it's probably built a LITTLE bit stouter that most of the expedition rigs, but I'm curious to see how it the flexing will be an issue after it's all outfitted with all of the interior cabinets and whatnot. I'm guessing (hoping) it won't be a problem. If it is, I'll be re-reading this thread...

Die springs aren't the only option, just an easy one in the U.S.
http://www.mcmaster.com/#compression-and-die-springs/=220rr5

 

[haven]

Forum member Dontpanic42 has a Fuso FG with an air bag suspension attaching the front of the camper subframe to the truck chassis.

These photos originally appeared in this thread
http://www.expeditionportal.com/forum/showthread.php?t=5949&page=3

Bruce wrote,
"Instead of springs up front, we used 2 airbags from the cab of a Freightliner. Shocks are used to to restrict vertical movement and roll. I use another shock running at an angle from near the top of the curb side airbag to below the travel side bag. It limits the side to side travel. The rear has a traditional mounting. This setup gives me yaw, pitch, and some roll. So far since early spring of 2004, I have only had one failure. A broken shock which I was able to compensate for by adjusting air pressure.

I used a half inch piece of oak between the mainframe and subframe that attaches to the RV frame. That way there isn't metal on metal contact. The oak strips are flat pieces rescued from old pallets. They run the full length of the frame.

No cross-members except the original ones on the FUSO chassis and the RV frame. Tabs were welded on the subframe and then bolted to the FUSO frame. No new holes were made in the original frame. No welding either. Fenders, storage boxes, etc., are welded to the subframe with only bolts in the FUSO chassis."

Bruce's vehicle weighs about 11,000 lbs.

 

[kerry]

Anyone have any idea what kind of load rating the springs on a sprung u-bolt mount should have?

 

[kerry]

Bruce's subframe looks very substantial. In the picture it looks to be the full height of the dropped back section of the frame. He says that subframe is bolted to the original frame. It seems to me that a subframe of that magnitude would stiffen up the original FG frame to the point that a substantial part of the flexibility of the original frame would be gone, at least in the area of the chassis under the subframe.

 

[dzzz]

Forum member Dontpanic42 has a Fuso FG with an air bag suspension attaching the front of the camper subframe to the truck chassis............

I see Bruce is a Metallurgist.

He bolts and pads, doesn't weld or stiffen. Interesting.....