I ordered a sample of fiberglass angle and found it to be as heavy if not heavier than aluminum, but that was just one sample. The corners of the box will get the most transfer of energy, it seems to me that the aluminum would fair better in this type of construction. I'd be concerned that wet laying the corners may crack over time. The aluminum also serves as good mounting points.
DIY Composite Flatbed Camper Build
- Thread starter Terra Ops
- Start date
I ordered a sample of fiberglass angle and found it to be as heavy if not heavier than aluminum, but that was just one sample. The corners of the box will get the most transfer of energy, it seems to me that the aluminum would fair better in this type of construction. I'd be concerned that wet laying the corners may crack over time. The aluminum also serves as good mounting points.
@rruff that is a fantastic post. Very good info about the carpet roller vs woodpecker and sealed vs unsealed. Definitely peels up a layer of foam and not the other way around. I think he only used 15 psi xps though so I am interested to see how the 25 (sounds like you've already tested) and 40 psi do in a delamination. You can really feel a difference in the 40 vs 25 just by handling the raw sheets.
I took some clips while testing tonight. I will splice them together and throw a link in here shortly.
Video:
@Terra Ops thanks for even more insight into the pop-up vs static camper discussion. That's usually the first thing people ask me when I talk about my planned build. "Why not do a pop-up?" "Ohh could you build it with a slide out?" So hearing some confirmation is great
Just a few observations; The FRP looked pretty flimsy/bendable compared to what I used. Also noticed the side that is bonded, is not smooth. May or may not be a factor. Lastly, I tried to put as much weight on top of the FRP while drying. Also, be careful to not allow the wood to contact the epoxy while drying. It will destroy the panel when you try to detach. I learned that the hard way. Epoxy will not adhere to plastic.
I'm anxious to see your results!
Interesting that yours was stiffer. I think because it will have the foam core it is mostly in tension and compression and not bending but we will see. If it adheres well I'll do some 8" by 4' pieces and jump on them or something.
I was thinking about how to weight them last night. My parents bulk buy fireplace wood pellets that come in 40lb plastic bags so those might work. Or just go buy ~10 bags of the cheapest kitty litter I can find. No clue what I'd do with it after though. I'd be ready for an oil tanker spill lol
I think they definitely cost more and would have to be shipped. I could see doing 1" honeycomb followed by 1" xps and an inner skin to end up with around R 8 or 9. But then you're still laminating several layers together so why not just do foam with frp skins? Just my thoughts though, no real world experience. A foam filled honeycomb would be sweet also.
Watersmeet
New member
So here is another thought; if the honey comb panels are stronger "and available", why not construct then insulate the interior similar to a van conversion?
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I thought of that too, but if you use at least 1” honey comb and 1” foam (or even 1.5” or 2” foam) then you’re doubling the weight and the walls would also get pretty thick. Plus, you’d need a skin on the foam on the inside too. Total Composites likes the walls to be no thicker than 2” (floor and roof 3”) because over two inches you can have problems with windows and doors fitting correctly. That’s my understanding.
Does anyone have experience with this stuff? It’s honeycomb filled with foam:
I can’t find it right now but a guy made a camper similar to Everlanders and he used honey comb and I asked him some questions and the only disappointment was lack of insulation and they do get condensation inside on cold nights. Unlike any other material it seems with honeycomb it doesn’t matter if it’s 1/2” or 2” thick, each cell is nothing but air and the R value doesn’t increase much as thickness increases.
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I thought of that too, but if you use at least 1” honey comb and 1” foam (or even 1.5” or 2” foam) then you’re doubling the weight and the walls would also get pretty thick. Plus, you’d need a skin on the foam on the inside too. Total Composites likes the walls to be no thicker than 2” (floor and roof 3”) because over two inches you can have problems with windows and doors fitting correctly. That’s my understanding.
Does anyone have experience with this stuff? It’s honeycomb filled with foam:
Foam-Filled Structural Honeycombs - Carbon-Core Corporation
CarbonCore structural foam-filled plastic honeycomb has been specifically developed to optimize the relationship between honeycomb and structural foam.
www.carbon-core.com
I can’t find it right now but a guy made a camper similar to Everlanders and he used honey comb and I asked him some questions and the only disappointment was lack of insulation and they do get condensation inside on cold nights. Unlike any other material it seems with honeycomb it doesn’t matter if it’s 1/2” or 2” thick, each cell is nothing but air and the R value doesn’t increase much as thickness increases.
Watersmeet
New member
Sad news: Carbon-Core is only capable of producing small amounts of that foam filled honeycomb and all of what they will be making is pre-sold, and they’re not taking any new orders for now.
rruff
Explorer
Both the glass and resin are lighter than aluminum, so it has to be lighter with the same dimensions. ~72% of the weight according to these guys: https://www.creativepultrusions.com...e-product-vs-traditional-products-comparison/
I was concerned about differences in thermal expansion rates (something Victorian mentioned) but the truth is that FG products are all over the place depending on the resin they use and the glass content, so aluminum is probably a decent match for light skins that are mostly resin.
One thing you could do to save a lot of "corner weight" is cut your foam (panel) edge on an angle. If you have a 90deg joint then cut each one at a 45 so they match up. Then you'd only need a 1-1.5" angle... if that is sufficient bonding area. 1" would be ~12x your skin thickness, which seems like it should be enough.
1/8" 6061 angle should be plenty. That is ~5 times stronger than your skins and very stiff.
If you hand lay the edges you'd need to create a rounded outer and inner first. It would be plenty strong if it's done well.
Doesn't appear to be available, but looks like good stuff. There is a company called Rhinocore that makes something similar... but I don't know if they sell in small amounts. It isn't cheap.
For a camper I think the PVC foam should be more than sufficient; it's several times stronger than XPS. Note that CarbonCore doesn't have some of the stuff that's on their site. C19 issues in some cases. They were out of PE foam and the Coosa board clone when I ordered mine.
The flex of a single sheet will vary depending on its thickness. If you compare two sheets of the same thickness then their stiffness relationship will be about the same as in the panel. In other words if one is 2x stiffer in sheet, then the panel (of same thickness) will be ~2x stiffer. Sheets like that vary a lot depending glass content and how it's arranged, but the company should have specs on it. Terra Ops sheet specs are here:https://expeditionportal.com/forum/...r-build.184366/page-2#lg=post-2393389&slide=0
Watersmeet
New member
Don't be nervous about the cab-over, just don't over do it. My interior height is 6'. The point where the cab over starts is half way meaning 3 feet of height to sleep in. I tried to minimize with the current design, but just a little more for comfort won't make that much difference. My goal is stay as compact as possible on a 7' flat bed. My Tiger was on a longer wheel base and found backing up on the white rim trail to make sharp turns was skittish to say the least. Current truck has the shortest wheel base with the crew cab. Turning radius sometimes makes a difference. Just some random thoughts
Thank you for saying don’t be nervous, that’s what I needed to hear! Of all the builds I’ve seen yours is definitely checking the most boxes. When you say "a little more for comfort" are you talking about increasing the height at the very front of the cab-over? Like rather than coming to a virtual point at the very front it could be 8" tall which would increase the space inside the bed area a noticeable amount?
It sounds like all the concern about 25psi foam is delamination. Drilling through to make those epoxy plugs sounds like a good idea. Or, sacrificing aesthetics somewhat, what about a 12" grid of rivets to help hold everything together? To avoid cracking the FRP they would likely need washers of some kind on both sides to disperse the pressure. It seems like the weakest link by far is the foam and it's ability to avoid failing. The 25psi foam seems like it gets an A for light weight, cost and R value but gets between a C and an F for strength to hold a lamination together, so perhaps the cost of getting all those benefits it offers is to add physical fasteners that will eliminate that weak link?
@Watersmeet Thanks for checking that out. Sad to hear it's not available. Looks like a cool product. I wonder if honeycomb could be sourced and then have a pour foam poured into it and trimmed flush. Could end up being a tedious process though.
@rruff those pultrusions are really cool! I wish they came in non 90* angles though. I'm planning to go with 3/16 custom bent alu on mine (like everlanders). Maybe if there is a significant cost difference I would try 1/8" but I'm betting the largest driver of cost is gonna be the bending.
I linked my sheet's datasheet earlier (VR2 from US Liner Co.). Seems like it has slightly higher tensile stiffness and much higher strength than what Terra Ops used. Mine are 1.6mm thick vs his at 2mm thick though.
G60/30: 110 MPa Tensile Strength, 8.4 GPa Tensile Modulus
VR2: 230 MPa Tensile Strength, 10.34 GPa Tensile Modulus
I had always thought it was the exterior sheet's tensile stiffness (modulus) that mainly determined the stiffness of the panel so I googled for an article to cite and came across this interesting one disproving me. I'll admit to skimming the math completely but I think the points made in the article are good.
www.mayahtt.com
"Increasing the facesheets’ thickness is the least effective method of achieving a rigid sandwich (not the mention the cost involved, especially when dealing with composites). In practicality, the optimal sandwich structure will be a judicious combination of core thickness and core stiffness."
This just brings me back to really wanting to try some 40 or 70 psi pour urethane foam.
Ok, ok I have to get some work done today lol. Really enjoying discussing this.
-Derek
@rruff those pultrusions are really cool! I wish they came in non 90* angles though. I'm planning to go with 3/16 custom bent alu on mine (like everlanders). Maybe if there is a significant cost difference I would try 1/8" but I'm betting the largest driver of cost is gonna be the bending.
I linked my sheet's datasheet earlier (VR2 from US Liner Co.). Seems like it has slightly higher tensile stiffness and much higher strength than what Terra Ops used. Mine are 1.6mm thick vs his at 2mm thick though.
G60/30: 110 MPa Tensile Strength, 8.4 GPa Tensile Modulus
VR2: 230 MPa Tensile Strength, 10.34 GPa Tensile Modulus
I had always thought it was the exterior sheet's tensile stiffness (modulus) that mainly determined the stiffness of the panel so I googled for an article to cite and came across this interesting one disproving me. I'll admit to skimming the math completely
but I think the points made in the article are good.
Optimal stiffness of sandwich structures | Maya HTT
Understanding the true behavior of sandwich structures related to stiffness under in-plane and out-of-plane loading | An example of estimated deflection and core shear stiffness
www.mayahtt.com
"Increasing the facesheets’ thickness is the least effective method of achieving a rigid sandwich (not the mention the cost involved, especially when dealing with composites). In practicality, the optimal sandwich structure will be a judicious combination of core thickness and core stiffness."
This just brings me back to really wanting to try some 40 or 70 psi pour urethane foam.
Ok, ok I have to get some work done today lol. Really enjoying discussing this.
-Derek
rruff
Explorer
How would the rivets help? You need to structurally connect the two faces with something stronger than foam. The epoxy plugs would do that, but I tried it and had trouble... way too much for it to be viable for panel joining. I even rejected it for hard points. I'm going to just add some layers of FG for point loads. The PVC foam is strong enough.
If you want to reinforce the XPS I'd use wood. Get some 1x or plywood and cut it into strips that are the thickness of your panels. Then cut your foam into 1 foot wide vertical strips, and glue the wood in between each piece of foam. I'd probably use PLPremium for that. Then you'll have a foam panel with a wood stringer every foot that bridges the two sides of the panel.
You could also use the lightest luan (2.7mm) on the interior walls... would be pretty and save money to boot. Believe it or not the stiffness is better than the composite sheet. You could even use that for the exterior too and put a layer of wet FG on it. I've done this, I know it works well.
Mine was at 2mm thickness might make the difference. Also glass content. If yours does not adhere, its most likely the VR2.Interesting that yours was stiffer. I think because it will have the foam core it is mostly in tension and compression and not bending but we will see. If it adheres well I'll do some 8" by 4' pieces and jump on them or something.
I was thinking about how to weight them last night. My parents bulk buy fireplace wood pellets that come in 40lb plastic bags so those might work. Or just go buy ~10 bags of the cheapest kitty litter I can find. No clue what I'd do with it after though. I'd be ready for an oil tanker spill lol
Try buckets of water for weight.
If I do another build, the cabover will become the main bunk for my wife and I. Instead of a point, I would raise it 6-12". The roof would extend out around 2' before sloping to the front.
There really is no concern about delamination with the lower psi. When I first started thinking about it, how to improve strength, cut cost, I was thinking in terms of density. Also by joining the skins, you no longer have a sandwich. Instead the panel is more connected which I would think adds strength. Derek's link to stiffness of panels is what I had in mind. Also Ruff's comment about a wood stringer is very similar. I had the thought of using 2x2's. All this may be overkill, I don't know.
Page 24 has much of this same discussion and interesting links----- https://www.expeditionportal.com/forum/threads/diy-composite-flatbed-camper-build.184366/page-24
rruff
Explorer
I really like the exoskeleton they did... is that your plan? You good with CAD? I'd be curious to know what that would cost. I guess they also got the panels CNC cut?
If you only have the aluminum on the outside and no inner reinforcement it makes sense to use thicker material. 3/16 seems about right.
If this is representative, it's quite weak compared to the PVC foam. https://www.carbon-core.com/pdfs/pds-carbonfoam-pu-pir.pdf