charlieaarons said:
A 3 or 4 point mounting system is not a "suspension". It doesn't matter if my camper weighs 20 or 100 tons, it wouldn't lean outwards on turns (relative to the frame) unless the frame rails flexed assymmetrically. It should merely allow the frame to flex without putting torsion or stress on the floor.
My advice: don't do what you mentioned in the last post, designing a true suspension for the camper. You will be asking for instability. Copy Unicat's system.
Charlie
Charlie, I hear what you are saying, but what I am proposing is no more a suspension than an engine mount is a suspension. An engine mount is more a shock absorber/vibration mount.
Anyhow, what I am designing is a 3-point system in which the three points are fail safe rubber engine mounts. The 3rd point center mount will pivot much like a pivot point on a Unicat, except it will absorb shock as well. Rob Gray in Oz took this same approach with his first big rig. Barry Controls makes these particular engine mounts and you can order them straight from McMaster Carr.
I agree with you that a strong enough box will not sway or twist on a 3-point frame, but that is because the walls of the box/or bulkheads are extremely strong in shear. I can't say for sure, but I'm guessing DougH doesn't have the shear strength necessary to control the flex on his subframe as much as he would like, so adding dampers stabilizes reduces flex when making sudden turns or hitting bumps.
There are two reasons I am probably adding airbags in addition to the 3point system.
First is I am building a convertible/modular camper system that enables the truck to be used as a flatbed or an expedition camper. While the camper is attached, it will be seamlessly and rigidly attached to the subframe/flatbed, adding all the shear strength a permanently built camper box would. But while the camper is off, it won't have nearly the shear strength (no walls) - Just like a rectangular tube is torsionally stiffer than a plate of the same wall thickness. Air springs placed on opposite sides of the pivot point will reduce the need for the subframe to be as strong in shear. While offroad the air pressure will can be reduced to allow the truck frame to flex without transferring stress to the subframe. A group of us ride the White Rim trail in Canyonlands NP on mtn bikes every year or so. I hope to have the subframe/flatbed finished so I can use it as the support vehicle and test the frame.
Second reason for adding air springs, I am buiding the entire subframe and camper frame out of 6061 aluminum. Aluminum is a great material, but considerations for cyclic loading -i.e. vibration, must be made. Using air springs to support and dampen the frame between the mounting points will greatly improve its resistance to fatigue and spread the load more evenly over the truck frame.
Like I mentioned, the design is ever evolving, so who knows . . .
I bet you have you the best built strongest camper box and subframe money can buy, but it too has limitations and with 100 tons, your subframe and box will twist.
