BIG TRUCK - little budget

[apexcamper]

@Victorian That would be outstanding, I'll give him a call.

@shortbus4x4 Ya, with winter fast approaching, I think the "trailer on the bed" deal may work if we want to use it for anything this winter. We have also realized that, for a budget build, buying the trailer gets you things like sinks, stoves, faucets, wires, and such. Literally hundreds of items you would have to buy, all in one package. At the very least buying a trailer and stripping it is a good budget idea.

Spoke with a welder. We are working on the plans for the aluminum frame for the bottom of the box. It is going to be a simply box, mounted high enough to be above the wheel wells in the back. Cost wise, the basic flat frame is very easy on welding and materials, and when you get to building the box, not having to cut your panels to make them go around wheel arches makes things a lot easier.

I can already hear RoosterBoosters comments about my center of gravity
He is totally right. It does mean pushing things up a little more...BUT -
Our plans don't call for anything above the waistline in the box except some small overhear cabinets and a couple of solar panels. We don't have an elevated "over the cab" sleeper or any heavy or complex mechanizism to pop a top, and wont be mounting jerry cans and spare tires anywhere close to the roof. I think raising the floor 18" to avoid a wheel arch wont be an issue, and it also allows us MUCH more space under the box for heavy things (like spare tires, house batteries, spare fuel and water).

On a lighter note, met with a WONDERFUL German mechanic yesterday who used to drive trucks like mine, and we spent an hour going over some of the "need to know" of the Maggie. Cool stuff, like I have a brake alcohol reservoir and now know how to use it...who knew. We also identified the secondary air system and air tank, so that will be where the air bag suspension gets it's air from.

Work schedule has been rough on productivity this week...but next week I have the 4pm to midnight shift for 3 weeks...my days will be totally open to get stuff done.

 

[pairospam]

Apexcamper:

I like pretty much your enthousiasm and your project, but I am forced to say that the idea of using air bags for the box (or the camper) is quiet risky. It will simply not hold, no matter if you put six of them.
You need to use a torsion-free system, and for the lenght of your frame and to keep the off-road ability it needs to be a 4 point one. You need to firmly attach the mass of the box/camper to the frame.
There are many options of building them, cheaper or more expensive, but effective and SAFE.

Cheers.

Pairoa

 

[apexcamper]

@pairospam
I am very open to alternatives and NEED this sorted out before the welder starts doing his thing. It seems to me that the air bags will do the job simply because they can hold the weight and allow the frame to flex...BUT...I have no experience with the air bags at all. Could you be more specific about the possible fail points.

If I understand the 4 point torsion free system, the box is attached to the frame at the center, and then the front and rear of the box are mounted on pivot points allowing the frame to rotate around them. Definitely a "less to fail" system and very supportive.

For the air bag system, it would have the same number of frame mounts as the 4 point and the bags would more than be able to handle the weight along the vertical axis. I am assuming that when you say the air bags wont hold, you are referring the lateral forces, side to side shifting.
In truth you have brought up something I had not considered. For normal driving I think a pan-hard rod at the back and the front hinge would suffice, but the stresses off road, leaning the truck near it's max left or right and then driving a few hundred yards, are much higher. Would I have enough support since the air bags really only support weight, not control direction?

How do the trucks do it? The rear axle of a truck on air bags has to articulate somehow, and yet not slide out from under the truck left or right. The only thing that holds my rear axle in place is the leaf springs, I don't even have a pan-hard rod. There is definitely a lot going on aside from just the load support.

I know RoosterBooster has a LARGE airbag suspended cab on his truck, but I don't know how much off road driving he has done.

This is going to be a mostly road driven truck, but to off pavement destinations. When we get were we are going, I don't want to damage anything doing what the truck is intended to do in the first place. I really wanted a suspended camper box simply for the vibration absorption to allow the items inside it to last longer. I also wanted to try something different from everyone else.

In the end, I want functional and reliable, if that means 4 point instead of air bag...great...but I would like more understanding of why the air bags wont work before scrubbing that idea.

 

[RoosterBooster]

yeah, my body is heavy ... but it is also riding fairly low on the frame and only very mild offroad;

but with a box sitting high on the frame (larger leverage) i could see problems ...
mainly side to side "wallowing" ; very sudden direction changes of the chassis in situations like diagonal crossing a washout.
the front pivot mounts are not very ideal for that (the subframe/box will see a lot of twisting force)

this is exactly why i plan to use a "diamond pattern" 4 point and not a 3 point;
flexible front and rear centered single mounts with two wide spread (and very beefy) rubber mid- mounts.
my mid- mount brackets will be sandwiched between the rear suspension mounts (i`m going to use a slightly modified Peterbilt "Air-Leaf" air suspension)
by jerking the box around at the center of its mass (instead of at one end) i greatly reduce twisting forces to the box.
i also reduce stress to the frame by basically bypassing the frame and placing the mid-mounts where the force is coming from (suspension mounts)

i hope my limited English makes any sense

 

[pairospam]

apexcamper:

Sorry for the delay. I did not want to throw cold water over your ideas and then just run away. I have had some trouble with my internet connection and also uploading the pictures that I thought will be helpful to show what I mean.
Roosterbooster is right. The lateral and bending and twisting forces observed even when riding on mild off-road terrain have a tremendous impact on the mass of your box or payload, and if not properly attached to the frame, via a subframe or not, things will surely start to brake from the moment you release the clutch.
The leaf springs are pretty strong and keep the axle in place without any helping rod, and you can mount an auxiliary air bag to "soften" the suspension , keep the height steady independently fron the loading stress, etc.
If you do not have leaf springs you, by force, need to have a pan-hard rod to avoid lateral displacement of the axle.
The air bags, convoluted or not, only work in the axial direction, and do not have any place in keeping the lateral stability of the suspension. Any.
The concept of the four points pivoting torsion-free system I think you know well, and you can apply it to a subframe over which you can install the box or the camper, like the one shown in the picture of the Mercedes 1017 torsion test, or you can incorporate it in the frame of the box itself. There is a lot of ways to do it, as I said, more or less complicated, more or less expensive.
The central pivots must also allow some torsion in the longitudinal sense, and they can be very elaborate, as shown in the picture. Some manufactures can charge you many hundreds of thousands euros for a super high quality box with such a system, but paying a lot is not necessarily the only way to get through.
These systems are less prone to fail, it is correct, they were designed for that purpose. And remember that you may drive a thousand kilometers on flat pavement, but if you need to pass only one time a slope your box will be damaged.
Please excuse me too because my english is very poor, specially at this time in the morning.
I hope this may help you to reconsider and give a second, a third and a fourth thought to the issue, crucial for your project.

Cheers.

Pairospam

 

[apexcamper]

OK, so all this makes sense and the "pivot at the front" idea on a box as long and high as I am planning would probably rip that out first try.

So I thought about plan "B", just using the current design to mount to. Figured I could test that easy enough, so just took the truck into a ditch by my house...I, apparently, have a very flexible frame.

Here it is in the ditch...the sides of the ditch get steeper as you move away from the front. It doesn't look it, but the front and rear axles are a fair amount of degrees apart.

Here you can see how much stuff the front tire has and how opposite the rear tire is...as well as the impressive amount of bed flex.

Another view showing the massive amount of bed flex

And for all that my bed only came off the sub-frame a half inch at the front

Another shot of the bed rolling up on the springs from the sub-frame

Even halfway down the bed, it came up about a quarter of an inch


I wish I had taken some pictures of the back axle (didn't think about it till writing this, will probably snap some this week) at the peak articulation...the anti-sway bar is HUGE and would probably give me a lot more flex by disconnecting it. I don't know how good an idea that is with a heavy camper box on, or if maybe just disconnecting the front ones would be enough help (do they make quick disconnects for trucks this size).


ANYWAY...I guess I have to go with a 4 point system. I was hoping to try something a little more innovative, everyone seems to run that...but don't want to cross a creek and rip open my camper either. I would assume everyone has a 4 point because it works so well.

SUGGESTIONS?

 

[RoosterBooster]

i think with some thinkering a air ride box would be possible but for the amount of work involved i personally would rather convert the chassis to airride suspension ;
very cheap to do (at least on a US truck) and less "harshness" as well as better riding comfort for the complete truck not just the box.

as i already posted i personally would not use the stock subframe ;
heavy, needless raised CofG and lost space (raising floor way too high over the truck frame), metal to metal contact that will transmit vibration/noise, loose/scuffing metal to metal parts (corrosion risks),...
it was obviously designed for the flexible flatbed.

i personally would also seriously consider to do wheel tubs and build the box as low as possible over the truck frame, regardless of how light you think the box will be.
for me a low profile is desirable not just for CofG;
better fuel mileage, reduced head- and cross-wind sensitivity, less restrictions of where you can go (or pass under), no need to bring a chainsaw when you go in the woods , ...

i also explored some different mounting ideas but always ended back at the 4 point.
however, i dont really like the pivot mounts in Pairospam`s pic links; they look impressive but IMHO too much wasted space and minimal noise isolation.
i`m not saying they dont work or are a bad design, "I" just dont like them (mainly how high the box rides over the chassis) ...
so i`m thinkering with something that has more rubber in the mounts (preferable in all 3 dimensions) as well as a very low profile.

 

[naterry]

Nice, as I suspected! Just saying.

 

[pairospam]

apexcamper:

I could not download some of your last pictures but I was wondering if you measured the twisting of the bed itself when making the frame twist. This happens; the subframe can twist and the bed also. But your camper or box can not.
RoosterBooster is right, again, about the highness of the majority of the rigs that use 4 point torsion-free pivots, but it is only one of many compromises you have to deal with when building your off-road capable motorhome.
Converting to air-suspension will be good for your kidneys and for the whole truck and payload, but it does not change anything about the twisting of the frame and the necessity of having a torsion free system for the box, one with break-springs or pivots.
The anti-sway bar is a necessity, not a switch-on, switch-off item. It keeps you safe and stable when riding and when getting into or getting off the ditch. If you want more flex-ability you must free your frame, not your suspension, and that is why almost every 4x4 and 6x6 big camper trucks use 3 or 4 point systems.
I know you want to make things as simple as possible, but it is better sometimes not to oversimplify. Yours is a beautiful truck and you must keep your family safe and entertained and go all around without trouble, and now is the time to care of.
If it is of help for you I leave the link to the site where I show my own project: http://www.allrad-lkw-gemeinschaft.de/phpBB3/viewtopic.php?f=33&t=26452

Cheers.

Pairoa

 

[pairospam]

Any updates?

Cheers.

Pairoa

 

[westyss]

If you havent checked out this thread on mounting you should, its all been talked about before and some different ideas are addressed.
http://www.expeditionportal.com/forum/threads/25494-pivoting-frames-and-mounting-campers

Also, something that never seems to come up, in some of these pictures of your frame flex with the spring mounts, the springs shown are supposed to be for compression! yet the available amount of compression is extremely limited. If you look at the springs, they have a space between each coil of say 1/8", that is a liberal estimate, multiply that by 8, which is the total number of wraps of the coil and you have 1 inch of compression available! That is not much at all, even pointless with the amount of frame flex you show. What should be on there is a compression spring like you would see on coil overs, where there is an inch+ on each coil wrap, allowing actual compression of the spring.

 

[dzzz]

........ What should be on there is a compression spring like you would see on coil overs, where there is an inch+ on each coil wrap, allowing actual compression of the spring.

The springs are designed to manage how stress is loaded to the frame/subframe, not necessarily to meaningfully reduce frame flex. A body builder may have put the back on that truck, but that was likely installed to the manufacturer's spec.

I think it's difficult to know the correct choice on a truck like this. There may be a body building document on this truck that show engineered mounts. Plenty of novel three point mounts have initial problems, which should be a disincentive to one time builds.

You can break a frame with a three point mount. Allowing the frame to flex beyond its design limit is not necessarily a good thing. Placing the four point loads from a three point mount on a lighter weight frame needs to be done with some skill.

 

[westyss]

The springs are designed to manage how stress is loaded to the frame/subframe, not necessarily to meaningfully reduce frame flex. A body builder may have put the back on that truck, but that was likely installed to the manufacturer's spec. "

Not sure what you mean by "manage how stress is loaded to the frame /subframe" I'm under the impression that its there to accommodate frame flex if needed while still keeping the body on the frame, the body frame sits on the truck frame so the load is distributed evenly that way.
The way I see it is whatever is required to accommodate vertical movement, ie. allow the truck frame to flex beneath the rigid body frame, will need to be done by using springs with enough compression or there will be no difference between truck and body movement. I see many of these spring mounts being used but some I really see no use for them because they will not provide any separation between the two and both will need to flex and bend. If a vertical movement of 2" is needed to accommodate the required flex, then get a spring that has a difference of two inches between free length and solid length, allowing the spring to compress to the solid length unhindred.

 

[pairospam]

apexcamper:

I hope that all the discussion raised on the body mounts will in no way discourage you.
Please, let us know what are you thinking or planning to make your project move on.

Cheers.

Pairoa

 

[Steinbruchsoldat]

Awesome build. If you need some help with the german TÜV and stuff feel free to contact me, I'd be glad to help you...

Greetings from the guy that lives where the Iveco testtrack is and all the Magirus-Deutz and Iveco are produced...

Julian