pivoting frames and mounting campers

[charlieaarons]

My Unicat's sytem is virtually identical to the top picture is Bob Lynch's post (#29). The members that are blue in the picture are bolted to some strong longitudinal steel stringers hidden inside the floor of the camper.

Charlie

 

[boblynch]

Charlie on your Unicat what's the approximate distance from top of frame rails to top of the "blue" members in the picture? One of the challenges is the flex gain vs. increased COG. It would be nice if this thread could start accumulating dimensions for others to consider in their build plans.

ExPo member UK4x4 posted this in another thread on articulation. If you look closely about half way into the video you'll see a setup similar to Charlie's. http://www.youtube.com/watch?v=YgmF8as2mFY&feature=related

Bob

 

[FusoFG]

My Unicat's sytem is virtually identical to the top picture is Bob Lynch's post (#29). The members that are blue in the picture are bolted to some strong longitudinal steel stringers hidden inside the floor of the camper.

Charlie

Charlie,

I hope the cell phone camera works out because a photo would be nicer than a stylized drawing.

Where is the center of the crosswise tube in center in relation to the pivots at either end?

In line with or lower than?

Is the center tube half way between the 2 pivots?

Tom

 

[Jacob7963]

This brings up one advantage to the design I'm using on my camper. By "cutting" and lowering the middle crossmember from the Unimog design, the floor is only about 50 mm above the frame rails - only what's needed to allow for deflection.

http://www.flickr.com/photos/iandraz/3387108542/

You can get to a higher resolution picture by clicking the link.

Advantages are lowered CG, easier entry, and better fuel economy (less frontal area for wind drag). Disadvantages are increased stresses (the frame becomes the middle third of the middle crossmember), more complex structure, less room for tanks/storage. And the part over the wheels still has to be raised to account for suspension travel.

Jacob

 

[kerry]

This brings up one advantage to the design I'm using on my camper. By "cutting" and lowering the middle crossmember from the Unimog design, the floor is only about 50 mm above the frame rails - only what's needed to allow for deflection.

Jacob

How did you arrive at the 50mm number?

 

[Jacob7963]

Here are some pictures of the 4 point pivot frame design. First a German made camper (not Unicat, can't remember who) on a MAN chassis:

Front pivot point:

http://www.flickr.com/photos/iandraz/2823913900/

Second is a Unimog (I think a U1300?) at NWMF:

Rear pivot point:

http://www.flickr.com/photos/iandraz/3406059854/

Front pivot point:

http://www.flickr.com/photos/iandraz/3406059706/

 

[Jacob7963]

The number is based on how much deflection angle I allow for in the pivoting crossmembers. The 50 mm is actually just a rough number, I need to do a bit more testing and CAD work before I finalize that. For now let's just say lower than Unicat!

 

[63tlf8]

Advantages are lowered CG, easier entry, and better fuel economy (less frontal area for wind drag). ...... And the part over the wheels still has to be raised to account for suspension travel.

Please remember that the height above ground of the UNIMOG torsion free subframe is a factor of compressible wheel travel and upper damper mounting location. With the substantially less wheel travel and smaller wheels of a Fuso, everything becomes closer to ground Zero. If you recess the wheel arches into the camper space as proposed by iandraz then the CofG will again be improved for the same design. Of course if CofG is a problem, a pop top or Alaskan style solution will yield much better results.

Tony

 

[kerry]

The number is based on how much deflection angle I allow for in the pivoting crossmembers. The 50 mm is actually just a rough number, I need to do a bit more testing and CAD work before I finalize that. For now let's just say lower than Unicat!

I ask because that linked piece on choosing an expedition camper van (by Stewart Stevenson?) states that some spring loaded u-bolts on expedition campers allow for 200mm of travel. (I think)

 

[longhaul]

Hi all, I have been following this thread and have a couple of points to make.Kerry asked

How do the australian rigs survive the stresses of flex.Now I'm know expert here but I think

you will find that they first,let the suspension do the work.There's a big clue in warriors

web site with the new spring pack. I personally would lengthen the springs, then drop one

spring off the pack, then add one coilspring above this.Secondly rigid mount the rear of

the box to the chassis and then add 3-4 retaining springs down the length of the chassis

rails, on both sides. This lets the chassis twist when needed.I am sure that I supplied some

photos of the spring mounts that warrior use, on the old expo site,Maybe Haven can dig them

up.They were scanned photos of the warrior in an Australian 4wd magazine and quite clearly

show there mounting system.This also explains how they can keep the height down.

 

[whatcharterboat]

and quite clearly
show there mounting system.

Are you sure?

 

[kerry]

Here are my latest thought about spring loaded front, (middle?) mounts. I have a clear picture in my mind but I'm not sure I can describe it.
Attached to the bed frame could be two brackets that drop down each side of the truck frame. This would keep the bed frame located over the truck frame. Attached to the truck frame would be another bracket on each side matching the location of the bed frame bracket. On top of this could be a rubber piece to absorb the shock of any movement. A bolt would pass through the upper and lower bracket, one on each side and would be spring loaded to allow for flex. This is similar to a u-bolt system except the parts of the system are attached to the bed and frame rails, stopping any motion back and forward that might occur with a spring loaded u-bolt and having a piece of rubber to absorb the shock of the frame and bed frame hitting each other.
Don't know if I can get this kind of system fabricated to retrofit to my service body

 

[whatcharterboat]

Kerry, not really sure what you're trying to describe there. I was simply thinking you could replace the u bolts you have with sprung ones. Should be quick and easy. Then weld some verticle channel to your bed that comes down along side the web of your chassis. Easy too.

You will need a type of wear pad on the bottom of the channel or when the frame twists, the channel will won't to dig in to the web. Maybe the wear pads could be nylon?? and rounded slightly. Remember they are only to keep the body centered over the chassis. The ubolts will do the rest.

Just my thoughts on the matter, as a simple conversion without any major fabrication considering your existing setup. Again>>>only if you are really worried about it and this type of mod can be done anytime (as a retrofit). Certainly if your ubolts are going to keep coming loose it would be worth doing.

BTW I intend to reply to GroupSe7en and Freds post over in Iandraz's thread on body mounting. Everything got a bit weird with the big hijak and the new thread, but I should have some spare time tonight.

Regards John.

 

[GroupSe7en]

:lurk:

 

[Octamog]

I got a couple of pics... Charlie may find some of them look familiar...