Guys,
Sorry for the delay in responding, I've been working on other projects since our return to the U.S. and haven't been on the forum much at all.
I will attempt to address the questions and comments related to our Fuso FG and our experiences in batch form.
Doug
Yes, a necropost...
I think it's pretty obvious what happened to Doug Hackney's frame. And since I just read this whole thread and didn't notice anyone else mention it, purely for the sake of getting as much into the archives as possible...I'll do it.
In the blue circle - no flex. Utterly stiff from both the frame extension/cross member and the (solidly bolted/unpadded/unsprung) forward mount of the 3-point (partially obscured by the camper jack).
In the green circle - flexible.
In the red circle - the interface between the two.
Basically the same effect as soldering a stranded wire - under flex (or vibration - same thing) it breaks at the interface.
There was the twisting due to the action of the suspension, and no doubt that contributed - but I think what really hurt it was the up and down bouncing due to the weight. I think that was also made worse by the long overhang rear of the axle, which increased the lever arm.
Beefing everything up and eliminating frame flex is one way. Floating above it and letting the frame twist all it wants is another...but mixing the two has to be done just right.
EDIT: Just remembered...
On the first version of Wotthehellizat, Gray had the frame lengthened - a LOT. I seem to recall, when I first read his build diary years ago, that he took it to some sort of welder who was a specialist in frames. Can't find it on his site now though. The point being that welding on a frame is not inherently bad - it just has to be done right.
I think frame changes need to be engineered. Did Hakney's frame break because it was strengthened? Or because it was overloaded? I expect both. That stiffening and/or supporting created a hot spot.
One thing for certain with the lightweight FG is that one needs to live within a weight budget when designing and using.
Comments from someone who actually knows the truck! Most interesting.
One could speculate that it might have been exactly this kind of stress that cracked M. Hackney's frame. Was not his motocycle garage rigidly mounted?
The Mitsubishi is appealing to U.S. buyers as it has factory 4x4. I would note however, based on limited observation around here that:
-- The Mitsubishi is really a rather light weight urban delivery truck, with relatively small tires (7.50x16)
-- Thus the Aussies do a lot of work with wheels and axles.
-- With such a light frame, reinforcement might thus be the first goal, whether your final element pivots or not. Thus a "rigid" camper (See Michael Groves) might be a valid approach.
More free hot air on a slow morning.
Generally speaking, on single axle trucks that have the frame fatigue and break due to load, they break over the rear axle, or close to the rear axle spring mounts.
The second place the frame will want to break, typically, is somewhere close to the midpoint between the front and rear axles.
And these are the two areas that failed on that truck, first the rear axle area, and then the midpoint area was beginning to show signs of failure. That's the gist I got of everything anyway.
Not initially as I recall. He used the original frame with some lengthening when he built but I don't recall any strengthening until he had some frame problems. Weight on the other hand. . .
The Unimog does have a stepped chassis. It's stepped in a different way from the Fuso though - down instead of up, and it comes back up at the front.
Even on the FG, if you look at the video I made of my frame flex, you can see that there is very little side to side deflection due to the step.
I don't think we can use the frame failures of the Hackney truck and the Fuso Szulc as examples of why the 4 point mounting leads to frame failure. These trucks were both 3 point mounting which is very different and increases frame stresses by a minimum of 1/3 over the 4 point mounting. On the Unimogs the 3 point pointing is only allowed on the shortest wheelbase trucks, and even then the 4 point mounting is preferred.
I know everyone says the Unimog is "designed" for a torsion free mounting. But comparing my Unimog to my FG, I don't see what is different about the frame which would exclude a torsion free mounting. To me the frames seem to have approximately the same construction. As they say on the Unicat website "do other laws of physics apply to the Unimog?"
I'm not saying the 4 point mounting is the only way to do it, and it's not ideal for all situations. But if I had to choose someone to design a mounting for trucks traveling rough terrain, my money would be on Mercedes Benz due to their great experience and engineering resources in this field.
gait,
Not sure if you saw this video, I had it posted in my camper build thread:
http://iandraz.com/post/175161730/
Might be helpful.
Personally, I don't feel the lateral motion due to twisting is significant enough to negatively affect the camper. The truck frame itself isn't 100% rigid laterally, so it will likely deflect some laterally as it twists. And the pivots should be on rubber bushings which give some more flex. The 9mm you calculated at 5 degrees isn't very much, and factoring these in it may be even less.
Regarding the 3 point design - I think the Hackney and Szulc truck problems mentioned in the forum seem to indicate the 3 point design does not sufficiently distribute the load, which leads to frame problems unless the frame is heavily reinforced (e.g. AATREC-FG). Although the 4 point (diamond) design does not 100% perfectly isolate the camper from the frame torsionally, the frame is not 100% rigid (otherwise it wouldn't be flexing!). So it really is more optimizing the interaction between the camper and the frame to reduce stresses, than completely isolating the box. In my opinion the 4 point design is a good compromise which both distributes the weight and frees the camper box from excessive deflection forces.
As often happens with a long forum thread, many of the answers provided in the early posts are lost to the mists of time in the later stages.
Many of the answers to the questions / theories / speculations / etc. in this thread are in the first few posts of this very same thread.
In particular, as mentioned in the first few posts, information on our frame bend / break can be found in this thread:
http://www.expeditionportal.com/forum/showthread.php?t=24225
and in our trip thread:
http://www.expeditionportal.com/forum/showthread.php?p=351745#post351745
Also in the first few posts of this thread you will find links to various Fuso documents, engineering drawings, etc. that provide info on the FG frame, our specific failure points, etc.
Upon our return to the U.S., I was asked by Michel and Ron to inspect Michel's FG frame and I did so. Michel subsequently requested that I not post the detailed results of my inspection. I can share that due to Michel's duplication of our 3 point design, he suffered the same types of frame bending, cracking, etc. that we did. He did not suffer the catastrophic frame rail break we did, but IMO, it would have happened eventually had he not had his payload suspension system redesigned and replaced.
As I stated in the first few posts of this thread, in the frame break thread, in our trip thread, etc., these FG frame failures were caused by placing too heavy of a load on only two widely longitudinally separated points on the stock FG frame.
The reason Carl and Mary Hunter's FG 3 point system worked is a) they had a much lighter load, b) the load points were closer together longitudinally on the frame and c) they pivoted at the front.
As pointed out in the first few posts of this thread:
- Fuso FG expedition campers have been successfully designed, built and utilized without 3 or 4 point pivot systems (Don and Kim Green). http://www.questconnect.org/
- Fuso FG expedition campers with 3 point pivot systems have circled the globe. (Carl & Mary Hunter)
I appreciate the curiosity and effort that everyone has put into analyzing our frame failure, including red, green and blue circles. However, the circumstances and series of events that led up to the break were a progression of events and not an isolated "take a pencil and..." type scenario. In addition, however well intentioned, red/green/blue "obvious" analysis is misleading when not fully informed, and our chassis had other factors at play beyond those mentioned in these snapshot / timeslice observations.
From the beginning, I have attempted to make our FG a completely open source project (
www.hackneys.com/mitsu), and in that vein, I have endeavored to openly share any and all factors that contributed to our frame failures. Unfortunately, due to the nature of forums, where info is spread out across multiple posts in multiple threads, it can be very challenging to have a coherent, cohesive, encompassing understanding of something, including this chassis and this series of events.
I believe all the information regarding our vehicle, its features, foibles and failures, is available in the sources mentioned here. If you have any further or detailed questions, I answer emails every week about expedition vehicles and our travels, so don't hesitate to email me.
The short version is:
1. For FGs, listen to what whatcharterboat is trying to (repeatedly) tell you: suspend the load along the longitudinal length of the frame.
2. Listen to what people who are out there or who have been out there overlanding full time tell you. There is no equivalent in observational time to actual experience time, meaning no amount of speculation/shopping/web surfing/etc. equals even a month of real-world full-time overlanding experience.
3. Read the
Overlander Interviews and listen to what their lessons have to teach you.
How many FGs have they done? Or at least the question should be > how many trucks have they done with a stepped chassis?
Jacob, the number of FGs we've built is well into triple figures. We never see frame failures as a result of body mounting. Some of these trucks are still in operation after 10 years or more and most of the trucks are absolutely pounded day after day in some of the worst conditions imaginable. These conditions are why most truck manufacturers come out here to do their initial testing of new models. Doesn't it even make you wonder just a little why we would never use a pivot mount on an FG?
The two recent frame failures (on Expo) using pivot mounts should not have happened . The owners in both cases went to extremes in terms of research, quality workmanship, materials, effort, attention to detail, etc, etc. First class construction, both of them and they should be praised for what they put together. There was just one fundamental flaw for which they can't really be blamed. They both appear to have had the same view of "If the Europeans do it with so much success on other trucks then it must be the best option for my FG too." Only thing is the Europeans aren't having successes with FGs yet.
I've probably repeated myself over and over on this. Apologies if I've offended anyone. Not my intention.
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I think Doug Hackney has posted in the past that MAN expedition campers have had problems with frame failures. If I'm right in remembering that, I wonder if these failures are related to pivot mounts in the same way that the recent FG failures are related to pivot mounts.
If my memory serves me correctly, I think Doug Hackney reported that some Man expedition trucks (in South America?) had experienced frame breaking problems.
The references to MAN are from an Overlander Interview here:
http://www.expeditionportal.com/forum/showthread.php?t=11983
MAN – Very good quality heavy trucks (class 7/8) (require special driver's license in Germany). Medium duty 4x4 MAN trucks sold to overlanding market have lightweight frames. Wolf has seen multiple examples of frame failures on MAN overlanding rigs. He strongly advocates a minimum frame size of 6mm.
BTW, I interviewed Wolf about a month after we started our South America trip, our first travel by expedition vehicle (most other travel was/is by motorcycle). He was such a great guy, and brought up this whole frame thickness dimension several times, but in such a gentle, circumspect way. He could see, with clarity, what was destined to happen to the FG's 4.5mm frame, but didn't want to rub it in my still bursting-with-enthusiasm-rookie-overlander face. In retrospect, it was such invaluable wisdom delivered in a way only someone with 12 continuous years of overlanding could do it.
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James,
No - we never thought about that kind of an arrangement. When we first tried out the air bag setup, the the camper bounced around like a crazed bobble head doll. That is why we added the shocks to control the amount of movement. I am not sure that we could do what you suggest because of the way the plumbing is located. A camper like Oliver, Bigfoot ( if they reopen), or custom box with enclosed plumbing might work for that kind of arrangement.
As an aside, did Doug or Michel save the pieces containing the fractures? There is considerable information in those fracture surfaces.
I did save the pieces containing the fractures. There is an FG overland expedition vehicle attached to them. I'll sell you the fractures and you can have the FG overland expedition vehicle, and the two Honda 150s in the FG's garage, for free!
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