Isuzu npr 4wd

[rruff]

I suppose this might be too technical to discuss here.
This company takes this engineering solution more seriously https://www.rvglobetrekker.com/iso-habitat-corner-mounts

I don't think it's too technical... and people who put together that website have never impressed me with their engineering. Adding overkill in one spot while ignoring the weak link, isn't engineering.

Tell me what forces there would be on a habitat that 10 x 1/2" high strength steel bolts could not handle... or is it just the "foam" you are concerned about? It isn't really foam; pretty sure the fiberglass square tubes are bonded between the upper and lower skins of the composite panel.

Also note that the forces need to first overcome the weight of the habitat, since gravity tends to keep it where it is.

Also look at how huge slideins are mounted! Usually with 4 wimpy spring loaded rods that attach to the frame. And those campers are built like

 

[gator70]

I don't think it's too technical... and people who put together that website have never impressed me with their engineering. Adding overkill in one spot while ignoring the weak link, isn't engineering.

Tell me what forces there would be on a habitat that 10 x 1/2" high strength steel bolts could not handle... or is it just the "foam" you are concerned about? It isn't really foam; pretty sure the fiberglass square tubes are bonded between the upper and lower skins of the composite panel.

Also note that the forces need to first overcome the weight of the habitat, since gravity tends to keep it where it is.

Also look at how huge slideins are mounted! Usually with 4 wimpy spring loaded rods that attach to the frame. And those campers are built like

My initial view is under extreme conditions the composite panel foam core would give way and the panel sandwich would separate

I also am building a engineering for the floor and a connection to the subframe. Even though nothing is perfect, my choice for the engineering should be far superior. Is it overkill? Maybe, but that's assuring.

(12 brackets, six each side - 1/2 inch grade 8 bolts, and welds where they make sense - this is the connection from habitat frame to c-channel subframe) The habitat composite floor has a internal frame (sub floor) and external frame.

I'm not pointing fingers at anyone, just rationalizing my own engineering decisions.

 

[rruff]

Even though nothing is perfect, my choice for the engineering should be far superior. Is it overkill? Maybe, but that's assuring.

How will you do it?

Overkill isn't reassuring to me... it's the things not noticed, and workmanship issues that bite you.

My initial view is under extreme conditions the composite panel foam core would give way and the panel sandwich would separate

Yes, I gave an extreme (and ridiculous) condition that I think it would survive. You'd need to rip away all the fiberglass tube bonds as well as the foam core. I'd guesstimate that mounting is strong enough for at least 100,000 lbs of dynamic tensile load... and in this case you'd need something extreme to happen for there to be much of a load at all. I wonder what you are envisioning?

You mentioned wind loads. Determine the force needed to tip your rig over, assuming all of it is on the camper, and see what that gives you for bolt loading.

 

[gator70]

How will you do it?

Overkill isn't reassuring to me... it's the things not noticed, and workmanship issues that bite you.


Yes, I gave an extreme (and ridiculous) condition that I think it would survive. You'd need to rip away all the fiberglass tube bonds as well as the foam core. I'd guesstimate that mounting is strong enough for at least 100,000 lbs of dynamic tensile load... and in this case you'd need something extreme to happen for there to be much of a load at all. I wonder what you are envisioning?

You mentioned wind loads. Determine the force needed to tip your rig over, assuming all of it is on the camper, and see what that gives you for bolt loading.

I've seen this with crosswinds. Expedition vehicles are big sails.

 

[rruff]

I've seen this with crosswinds. Expedition vehicles are big sails.

Yes, that's why I asked you to determine the bolt loading if your rig was tipped over. "Overkill" would be designing in a 100x factor of safety for that condition. Make reasonable assumptions and it shouldn't take more than a few minutes.

 

[SkiFreak]

I've seen this with crosswinds. Expedition vehicles are big sails.

Be it a super strong or weak subframe mounting system, neither would negate the vehicle being tipped over by strong winds, as in your example picture.
If you are worried about this particular situation occurring, maybe reconsider the height of the vehicle, as that will have a more significant effect.
When traveling you can also choose not to drive your vehicle on very windy days, if you have concerns about it being blown over.

If over-engineering gives you a warm and fuzzy feeling inside, then you can choose to go down that path, but at some point you need to have a reality check about what engineering is beneficial and what isn't.

 

[gator70]

Lifting the habitat onto the truck frame

I've seen many methods on youtube. (1) Crane, (2) Forklift (3) Corner stands and drive under it

Has anyone done this and is there any good practice suggestions?

In any case moving a 3000lb object back and forth until you get it just in the perfect location is problematic.

Any guidance from the community?

 

[SkiFreak]

You keep asking generic questions for situations that are not generic.
How you lift your camper body will be specific to its design.

Case in point... I have built specific lifting frames for doing this particular task.

 

[rruff]

My son is PHD and did his thesis on Design and Analysis of Bolted Joints (DABJ). mostly for ocean bound wind electrical generation.
He warned me about this composite panel connection to the subframe.

I'll take a WAG on the forces. Assumptions: Truck and camper weighs 15,000 lbs, has a 80" track, the camper mounting points are 40" wide, the force is only on the camper itself not the cab, and is acting horizontally on a rigid box.

To tip the rig over, one side needs to be lifted off the ground, so a moment of 7,500 lbs x 80" or 15,000 lb x 40". If there are 10 bolts and half are compressed and the other half extended, then the force on each is 1,500 lbs. A 1/2" grade 8 bolt has a tensile strength of ~20,000 lbs, so the bolts should be fine, being ~13x what is needed.

But... you think the floor will rip apart.

TC used to provide more detailed info on their website, but as I recall the steel inserts fit inside square pultruded FG tubes of 3/16 or 1/4" wall that run the full width of the floor, and span between the upper and lower skins and are bonded to them. If there is a failure it will be in the bond between these tubes and the skins, since the foam will have a much lower modulus, and the tubes and the steel insert interface are quite strong.

In my estimation TC tends to be quite conservative. Your son was quite right that the mounting could be fragile if the steel insert was just bearing on the lower facesheet, but that is isn't the case.

 

[gator70]

You keep asking generic questions for situations that are not generic.
How you lift your camper body will be specific to its design.

Case in point... I have built specific lifting frames for doing this particular task.

I have posted a picture in this thread. It is a composite box with a attached metal frame on the bottom

I guess that is specific.

 

[gator70]

I'll take a WAG on the forces. Assumptions: Truck and camper weighs 15,000 lbs, has a 80" track, the camper mounting points are 40" wide, the force is only on the camper itself not the cab, and is acting horizontally on a rigid box.

To tip the rig over, one side needs to be lifted off the ground, so a moment of 7,500 lbs x 80" or 15,000 lb x 40". If there are 10 bolts and half are compressed and the other half extended, then the force on each is 1,500 lbs. A 1/2" grade 8 bolt has a tensile strength of ~20,000 lbs, so the bolts should be fine, being ~13x what is needed.

But... you think the floor will rip apart.

TC used to provide more detailed info on their website, but as I recall the steel inserts fit inside square pultruded FG tubes of 3/16 or 1/4" wall that run the full width of the floor, and span between the upper and lower skins and are bonded to them. If there is a failure it will be in the bond between these tubes and the skins, since the foam will have a much lower modulus, and the tubes and the steel insert interface are quite strong.

In my estimation TC tends to be quite conservative. Your son was quite right that the mounting could be fragile if the steel insert was just bearing on the lower facesheet, but that is isn't the case.

Thanks for the detail explanation. We all have opinions. Yet this thread gave me some reinforcement that the engineering I designed and is now complete is a bit overkill but assures me I did enough to feel good about the finished product. And on a borderline windy ride down the freeway, I will not be so concerned. We do get 70 mph crosswinds on hwy 10.

And I did not stress the composite floor at all in my design. In fact the 1/2 grade 8 bolts do not touch the composite material, and I have 24 over a span distance of 3700mm by 2200mm.

The TC design used 10.

 

[rruff]

Just to give you a bit more piece of mind, I'll tell you how mine is made... 🤪

It's a flatbed style but I figured... "why not make the floor structural?" rather than have a separate flatbed, so that is what I did. I was planning on using full span FG tubes in the panel similar to TC, but the cost of freight shipping and the time it would take annoyed me, so I just drilled holes in the foam at the mounting locations and bridged the gap with columns of strengthened epoxy. The mounts (about 5ft^2 in total?) which attach to the frame via aluminum tubes and poly isolators, are epoxy bonded to the lower skin. Each side of the base/floor is 4 layers of 11oz carbon/epoxy over 2" PVC foam. The mounts are 3 layers each side of carbon/epoxy over 6mm expanded PVC.

It's only been on the truck about 14 months, but I've put it through some pretty tough "tests" and it's showing no issues... it's flat as a pancake and very stiff like it was when new.

 

[SkiFreak]

I have posted a picture in this thread.

In fact you have posted numerous pictures of habitats, but I am unsure which, if any, are actually yours.
As they say... the devil is in the detail.

 

[gator70]

In fact you have posted numerous pictures of habitats, but I am unsure which, if any, are actually yours.
As they say... the devil is in the detail.

Still in production, but you can understand, size and shape.

 

[SkiFreak]

Given that you are getting the habitat manufactured by someone (not a DIY build) I would take the simple option... ask the company as to how they recommend you lift the unit.
They should know better than anyone else.

On a side note... I see that this specific unit (which I assume is yours) is being built to LHD specifications, not Australian specifications, as you had mentioned previously.
That should definitely be seen as a positive.