pivoting frames and mounting campers

[lehel1]

hey doug

here you go ; )

look forward to seeing you at the expo

cheers lehel and laura

[dhackney]

Lehel,

thanks!

I will attempt to copy as much discussion as I can find related to camper box mounting and pivot frames that is spread all over this forum into this thread. If anybody else has some time and wants to start, please do.

In the meantime, those desiring to learn a little bit about 3 point pivot frames can start here:
http://www.hackneys.com/mitsu/index-pivot-frame.htm

I'll try to add in the info on 4 point frames and other designs as soon as I can.

Doug

[FusoFG]

Charlie,

Would you be willing to post pictures of your U500 / Unicat 4 point mount?

Tom

[dhackney]

Thread goals:

• Consolidate all relevent posts about camper box suspension / pivot frame systems into one place.
• Engender and facilitate discussion about this topic.
• Provide an authoritative resource for people designing, building and using expedition campers who wish to learn more about this topic.

Thread realities:

• The majority of the initial posts in this thread will be copied from other threads. Quotes contained in these initial posts will refer to posts that may not exist in this thread.
• I do not follow, read or monitor threads or topics other than Mitsubishi Heavy Truck and a little bit on General Expedition Camper Discussion and Modifications. I will not be aware of those threads/topics and am unlikely to include those posts in this thread. There are undoubtedly threads in other areas that contain relevent discussion. I encourage others to copy those posts into this thread.
• There will be little to no attempt to maintain time or topic continuity when I copy and paste into this thread from other threads/topics.
• There will duplication and repitition between posts.

Thread assumptions:

• The Fuso FG has a very flexible frame. Unlike light duty trucks or standard road medium and heavy trucks, the frame is design to twist, somewhat like a Unimog's frame is designed to twist.
• The torsional twisting of the Fuso FG frame can introduce forces into any payload that is rigidly mounted to the FG frame.
• If a designer/builder/owner wishes to isolate their payload from the torsinoal forces of the Fuso FG frame, a payload (camper box) suspension or pivot frame system can be implemented.
• The purpose of a payload suspension or pivot frame system is to isolate the payload from the chassis frame, not to reinforce or strengthen the chassis frame.

Thread known facts:

• Information regarding mounting payloads onto the Fuso F series trucks, including the FG, is included in the Mitsubishi Fuso F series body builder's manuals available here: http://www.hackneys.com/mitsu/index-chassis-photos.htm
• Information regarding 3 point pivot frames is available here: http://www.hackneys.com/mitsu/index-pivot-frame.htm
• Mitsubishi Fuso North America engineering has provided engineering review and design support for successful 3 point pivot frame installations on FG and FM series trucks (Darren Fink / RUF http://www.ruf-inc.com/ )
• If not properly designed, implemented and loaded, a 3 point pivot frame can stress a stock FG frame beyond its design limits. http://www.expeditionportal.com/foru...ad.php?t=24225
• Unimogs successfully employ 3 and 4 point pivot mounting systems for vehicle components (engine, cab, etc.) and payload.
• Fuso FG expedition campers have been successfully designed, built and utilized without 3 or 4 point pivot systems. http://www.questconnect.org/
• Fuso FG expedition campers with 3 point pivot systems have circled the globe. (Carl & Mary Hunter)
• There are no known fact/science/engineering based publicly available reference sources for analysis of potential payload suspension / 3 or 4 point pivot systems for the Fuso FG.

[dhackney]

Threads dedicated to or containing significant content related to payload suspension systems / 3 or 4 point pivot frames include, but are not limited to:

Torsion-Free Sub-Frame http://www.expeditionportal.com/foru...ad.php?t=11709

Subframe Mounting & Suspension Mods
http://www.expeditionportal.com/foru...ad.php?t=22229

3 point pivot frame info
http://www.expeditionportal.com/foru...ead.php?t=6120

Broken frame
http://www.expeditionportal.com/foru...ad.php?t=24225

Camper Build (iandraz's build thread that was hijaacked by this topic and was the inspiration to try to move such discussion to this thread)
http://www.expeditionportal.com/foru...ad.php?t=25205


If you know of or find others, please post them in this thread.

[dhackney]

I will start the content portion of the thread by addressing the one known failure of a 3 point pivot system on an FG, which was on our truck. (Please note that Michel has also reported bending in his frame, but I don't know the extent of it and I'll let him, or possibly Ron, address that situation.)

On the Hackney truck, I think the 3 point mounting, frame extensions, and weight may have amplified the stresses in the frame significantly. With this 4 point mounting to distribute the forces, standard frame, and lighter weight, I think I should be good as-is.

I agree with your assessment. Those considering a 3 point design need to make certain that the amount of weight they are proposing to load onto two widely separated points on the FG frame are within its design limits.

I encourage people to consult the Fuso body builder's manuals available here: http://www.hackneys.com/mitsu/index-chassis-photos.htm

For those interested in reinforcing the frame rails or the step down section, there are detailed instructions in the body builder's manuals. It's a lot easier to do before you build than after...

Also, Darrin at RUF has found Fuso North America very helpful with reviews of his sub-frame designs. The Fuso guys have the engineering horsepower to know if what you are proposing is within the design limits of the frame. Believe me, it's better to find out now that what you think will work will actually work. The alternative can be pretty ugly...



Believe me, you do not want to discover that in some remote corner of the planet.

The extremely important issue with the Fuso frame is that like nearly every truck in its class, the frame tapers down to a small cross section aft of the rear axle. Check the section modulus diagram of the stock frame to get an idea of how much weaker that section of the frame is than the area in front of the rear axle - 45.9 cm(3) / 2.8 in(3) vs. 72.3 cm(3) / 4.41(3) - nearly half as strong.

The issue with 3 and 4 point pivot frames is the load point aft of the rear axle. I have no way of knowing what load we were putting on our mounting point back there, but whatever it was, it was too much. Michel reports his FG frame also bent back there with a 3 point pivot design.

You may have no problem for a long time; we didn't for more than a year, and during that time we were on some very challenging roads and tracks at a higher weight than when it bent, cracked and broke. But all it takes is one winching, one unseen-in-time speed bump, one big rock in the dark, or one whatever and you could have a problem.

A four point design will help distribute the weight of your payload over three places on the frame instead of two. IMO, it is a good choice. If you are not going to reinforce it back there, be careful how much payload weight your design can possibly pivot towards the rear.

I plan to convert our payload to a system that distributes the load over the length of the entire frame.

[charlieaarons]

If someone at my house is skillful enough to take cellphone pictures and then post them I will do it.

Charlie

[dhackney]

If someone at my house is skillful enough to take cellphone pictures and then post them I will do it.

Charlie

Charlie,

If you need help posting them, email them to me and I'll put them on our server and post them for you.

Doug

[whatcharterboat]

Paging WhatCharterBoat
We need some comments by someone who does this for a living.

Fred Sorry mate. I'm in the middle of designing a medium scale wind turbine installation for a remote village in Alaska and addressing all the environment issues whatever they maybe. Just a uni assignment but it's Dday and I'm panicking a bit.

You've got a great handle on what happens under a truck in the real world anyway (going by what I read in your last big post) and I intend to add more to this discussion soon.

Back to it .

[ntsqd]

U.S. sourced urethane squeaks. If it doesn't squeak when new it will squeak when it needs to be replaced. Sort of a catch-22 there, it needs to be replaced because it squeaks; and it squeaks so it needs to be replaced as there is no long term remedy for the squeaking. Can grease it, but that's a whole new can of worms, and it is temporary at best.

For the wear/rub strips on top I would look into jobrock (sp?), one of the Acetal polymers (Delrin, Turcite, Celcon, etc.), or possibly UMHW Polyethylene. Avoid teflon in this application, it will cold flow. For the bottom bumpers I would use rubber. Tour the Asian pick-ups section of your local pick-n-pull as I know that there is a bumper shaped similar to that Prothane part, but made from rubber instead of urethane.

Have you ever had to replace one of those torque links on the truck? Seems like they would be unduly massive for locating the box. I'd look into using something like the truck's tie rod ends screwed into a threaded tube or simply a "johnnie joint" based link. You'll likely need a lateral link at each end of the box. Your phrasing is singular, so forgive if that is what you're thinking. I would probably make the lateral links and the fore/aft links all the same so that there is some interchangeability, but frankly I think that "interchangeability" is often carried too far for the real world. You end up compromising the design in directions it doesn't need to go just for the 1/10th of one percent chance that you'll need that ability. For the 99.9% rest of the time you're carrying around too much mass.

When the frame does twist the box sitting on top of it will need to be rigid enough to support itself with only 3 points of contact rather than having the whole length of contact. Point loads are always harder to manage than distributed loads. Since you won't know until it happens where those points will be you'll have to build such that those points can be anywhere along those contact rails. You'll also need to factor in that the bump-stops underneath will be working against your box's rigidity; it/they will be pulling down the hardest on the corner(s) most raised off of the frame rails.