(USA) panel options Total Composites or GXV DIY Adventure Kits

[rruff]

You'll see sub frames incorporated into the floor. It reduces the OA height but there is allot more thermal transfer.

Use composites instead of metal.

My camper doesn't have a subframe. The bottom panel is 44oz carbon+epoxy skins on 2" 4lb PVC foam, with mounting areas reinforced with 3/8" epoxy cylinders on 2" centers. The reinforcement is probably not necessary (the foam is good for 150 psi), since I have large carbon mounting plates that are 20mm thick to spread the load.

 

[boogie944]

I thought the whole point of the subframe was to provide a stiff platform to mount the box to? The stiffest member is the one that takes the bulk of the load.

If the box is strong enough to take the load then you can remove the subframe and just provide reinforced mounting points between the frame and box. In your 3 point design, this means that 3 locations need reinforcement, and you can ditch the rest of the subframe. Seems like it would be more weight efficient.

The point of the sub frame is to provide a hinge and raise the box enough so it can move around (or the truck chassis torque freely underneath). It does eliminate all torsion intrduced by anything below the box (eg axles going over uneven terrain). But the box itself still needs to take up some torsion for let's say a person not standing in the centerline of the box but on one side. This is a small force, but if you would consider only the subframe the subframe itself would not be able to take up this torsional load. Try standing at a corner of the subframe.

You are right from structural analysis purpose the stiffest member is the one taking all the load and considering only subframe and box that is in all cases the box.

 

[Alloy]

The point of the sub frame is to provide a hinge and raise the box enough so it can move around (or the truck chassis torque freely underneath). It does eliminate all torsion intrduced by anything below the box (eg axles going over uneven terrain). But the box itself still needs to take up some torsion for let's say a person not standing in the centerline of the box but on one side. This is a small force, but if you would consider only the subframe the subframe itself would not be able to take up this torsional load. Try standing at a corner of the subframe.

You are right from structural analysis purpose the stiffest member is the one taking all the load and considering only subframe and box that is in all cases the box.

I disagree. If 150-200lbs can twist a subframe then it won't be strong engough. Once the subframe hits the stops it needs to be rigid enough to make the wheel(s) of the truck come off the ground.

 

[boogie944]

Use composites instead of metal.

My camper doesn't have a subframe. The bottom panel is 44oz carbon+epoxy skins on 2" 4lb PVC foam, with mounting areas reinforced with 3/8" epoxy cylinders on 2" centers. The reinforcement is probably not necessary (the foam is good for 150 psi), since I have large carbon mounting plates that are 20mm thick to spread the load.

Not all trucks need a subframe. Likely @Victorian does not have one either on his Transit. And I have an inbetween solution with spring mounts (Isuzu NPS 7t chassis). My truck is not behaving very well with a 3 point subframe as the chassis is relatively light.

All depends on weight of the truck and the terrain you like to go to. Looking at what others have done I noticed anything below 5t GVW most have no torsion free sub frame.

 

[rruff]

Looking at what others have done I noticed anything below 5t GVW most have no torsion free sub frame.

It depends on the frame stiffness. Newer 1 ton and under pickups (except for Tacomas and Tundras) have fully boxed stiff frames. 20 years ago I don't think any of them did. Over 1 ton the frames are flexible C channel, so the frame articulates rather than the suspension. When the frame is flexible you need to deal with it somehow, or your box will end up being the stiff part of the structure and take all the load.

Can you describe the "not behaving very well" of the 3 point?

 

[Alloy]

The foam has a crack. How long will it last when it is bolted to a sub-frame and people are walking on it. By the time the issue become serious the 1 year warranty would have expired.

 

[rruff]

The foam has a crack.

Their marketing is not giving me a warm feeling. If there was some actual engineering done, they wouldn't need dumb it down like this. The PUR vs PIR comparison is pure BS. PUR made for structural applications is rigid. I don't know where they got that stuff... maybe from a spray can?

The "standing on the panel" test is funny also. First... shaky cam and no actual measurement. I computed that a similar sized panel of the stuff I'm making should be able to hold 10x that weight... 2,500 lbs. Maybe I'll build a sample and make a video of my truck being supported on it...

 

[Alloy]

Their marketing is not giving me a warm feeling. If there was some actual engineering done, they wouldn't need dumb it down like this. The PUR vs PIR comparison is pure BS. PUR made for structural applications is rigid. I don't know where they got that stuff... maybe from a spray can?

The "standing on the panel" test is funny also. First... shaky cam and no actual measurement. I computed that a similar sized panel of the stuff I'm making should be able to hold 10x that weight... 2,500 lbs. Maybe I'll build a sample and make a video of my truck being supported on it...

I hate it because it's first time buyers that gets nailed by stuff like this.

I just watched the box assembly videos. At 3:49 the guy says "there is no shear point here in the panel"....that's wrong. The only thing carrying the load between the extrusion and the sub-frame is the floor panel.....so the floor panel is under shear. The flat bar in the floor does nothing to support the walls.

 

[boogie944]

It depends on the frame stiffness. Newer 1 ton and under pickups (except for Tacomas and Tundras) have fully boxed stiff frames. 20 years ago I don't think any of them did. Over 1 ton the frames are flexible C channel, so the frame articulates rather than the suspension. When the frame is flexible you need to deal with it somehow, or your box will end up being the stiff part of the structure and take all the load.

Can you describe the "not behaving very well" of the 3 point?

At low/normal road driving speeds the suspension is not working well as it is too easy for the chassis to torque. Causing lot of movement of the driver cab which is not very comfortable.

 

[boogie944]

I disagree. If 150-200lbs can twist a subframe then it won't be strong engough. Once the subframe hits the stops it needs to be rigid enough to make the wheel(s) of the truck come off the ground.

Depends all on size of your truck. If the sub frame and/or box survives lifting an axle I would say you do not really need a 3 point suspension on yur sub frame/box. If you have something like LMTV size truck subframe and/or box is unlikely strong enough to lift an axle once you hit the end stops.

 

[rruff]

At low/normal road driving speeds the suspension is not working well as it is too easy for the chassis to torque. Causing lot of movement of the driver cab which is not very comfortable.

This is typical of HD trucks. The suspension is very stiff for load carrying, and frame articulates to keep the tires on the ground. A twisting frame is an undamped spring. It should help to upgrade your suspension with a greater number of thinner leaves and appropriate shocks.

Curious what your setup looks like exactly. You mentioned both a 3 point, and spring mount. The spring mounts typically have a subframe that is "clamped" to the main frame rails with springs. This will keep the two together until the frame twist reaches a certain threshold. These should work better on the street, but they will impart more torque to the box when offroad.

 

[simple]

This is an interesting discussion covering the subframe subject from various angles. Can someone move it to a new thread with appropriate title?

 

[Dave Anderson]

I don't think the foam is an issue at all, but rather the FRP skins. Fiberglass composites that are optimized for strength/weight have a low thermal expansion coefficient in the 7x10-6 range (deg F) vs Al which is ~13x10-6... but I looked up data for Filon and their skins are ~17x10-6... so it looks like a good match is possible if the right skins are chosen. Typical FRP skins have a lot more resin than a high strength layup, and the resin has high expansion, vs glass which is very little. What are you using for the skins?

What are specs on the PIR foam you use, and why was it chosen vs PVC or PU?

I really like the concept of the slotted rail edges... very versatile!

Globe Trekker uses a sheet of FRP inside and out, plus AZDEL as a sub-laminate, inside and out. A total of 1/2" of laminates in a 2.5" thick panel. Thicker AZDEL is on the walking surfaces (floor and roof) and outside walls for better gouge protection. PIR insulation is more dense, so you don't have to add a layer of plywood in the floor to manage the deformation from walking on it. PIR is also has a better R-value insulation, because it is dense. It is also fire resistant, and submergible without soaking up water, unlike PUR insulation. Different colors and body wraps are also not as much a problem, as the FRP laminates don't tend to delaminate since there are also sub-laminates supporting it as well. Check out this video... I did a bunch of testing from my garage... not scientific enough for nerds, but the proof is very apparent none the less. Many blessings!

 

[rruff]

Azdel should be good stuff; it's popular in RVs now. Oddly I can't find any tech specs on it though... like stiffness or strength.
PIR isn't "more dense" than other foams. You can spec pretty much any density you like for PU and PVC, but I think 4 or 5 lb/ft^3 would be most common in this application.
Higher density doesn't improve the R value of foam; rather it drops as you'd expect.

Do you know the density of the foam?
Do you know what the full panel weighs per area?

 

[Alloy]

Azdel should be good stuff; it's popular in RVs now. Oddly I can't find any tech specs on it though... like stiffness or strength.
PIR isn't "more dense" than other foams. You can spec pretty much any density you like for PU and PVC, but I think 4 or 5 lb/ft^3 would be most common in this application.
Higher density doesn't improve the R value of foam; rather it drops as you'd expect.

Do you know the density of the foam?
Do you know what the full panel weighs per area?

Hard to believe a company that has invested so much into the design of a product expects customers to be as idiotic as the videos are.


No way for water freeze in winter because it will be full of mud and road salt then in the summer on a FSR it will catch the pebbles tossed up by the tires.


Why not use a scale used for the water test? Maybe it is known that PolyIso absorbs water.......

Moisture Contamination of Polyisocyanurate Insulation - Canadian Roofing Contractors Association

Reports have been received of moisture contamination, or signs of moisture contamination of polyisocyanurate insulation on some construction job sites.

roofingcanada.com

Higher density does not produce a higher R Value. The foaming agent (which escapes over time) initially gives PolyIso a higher R Value. The foaming condense so the R Value of PolyIsO is reduced as the temperatures drop. Temp drop will be noticed the most where the slots are cut in the floor.


The AZDEL/FRP deforms but the PolyISO doesn't. Watch when the sample is broken the foam snaps with very little deformation. That's not good.


Fires testing the foam is bogus. Take a torch to the AZDEL/FRP and see what happens. You'd be dead from the smoke coming off the AZDEL/FRP long before the fire ever reaches the foam.


10 years ago AZDEL was going to replace LUAN wood paneling in the RV industry. Several companies tried it and went back to LUAN.


The 1/2" of laminate on the foam plus the heavy extrusions eats up to allot of weight that could be used for fuel, gear or water.