5x10 Rigid Pop-Up with Foam

[kipa]

As discussed in my design thread, I am building a popup trailer to tow behind my EV. The primary goal is to minimize aerodynamic drag while keeping weight reasonably low.

This model is a rough idea of what I am going for, though I am likely to change the top design as I get the base completed. It is being built on the Harbor Freight 5x10 trailer, giving me up to 76" of interior width and pushing the walls and fairings out to the fender edges.

The popup portion will end up with rigid walls.

I thought I might try to form a foam tongue box using 2-part polyurethane, but the logistics of making that work and turn out well seemed more trouble than it is worth, as it is largely within the turbulent portion of the vehicle wake anyway, so flat sides would be unlikely to hinder aerodynamics while going together far more quickly. (The top cover was temporary for some road testing and will be replaced by a better fitting piece.)

I've decided to use prefab FRP panels to line the interior of the tongue box and will likely PMF the exterior. Same for the rest of the lower body.

 

[kipa]

Current build status:

As I mentioned in my design thread, I have decided to go full fiberglass layup for the base structure.

The decking isn't trimmed fully for the intended side tapers front and rear. It is 2" foam completely on top of all framing, laminated to another 1" layer of foam between the rails, with another layer of 1" foam underneath the frame to clean up turbulence. I will likely revise how that aero layer is done, but it proved the concept for me, though I have not done further road testing at this point and really can't until I get the upper structure completely formed out.

I think that the combination of fiberglass and upper structure will provide all of the support I need for the lateral extension of the decking beyond the frame, but that is the primary reason I abandoned the idea of PMF completely, as I would have had to source other reinforcing materials (aluminum angle or tubular extrusion most likely) that would have cost more to use than simply going FRP will. I intend to use absolutely no wood in the structure of this build.

 

[Pmullen503]

You are going to need something that you can bolt to. The foam will compress, even with fiberglass on both sides. You can drill a larger hole and line in with a wooden dowel or thick PVC pipe and use more fasteners that you would with a more solid floor material.

 

[kipa]

You are going to need something that you can bolt to. The foam will compress, even with fiberglass on both sides. You can drill a larger hole and line in with a wooden dowel or thick PVC pipe and use more fasteners that you would with a more solid floor material.

Thanks, and yeah, that is all in my mind as I build out the form. Not planning to glass much of anything until I get a lot of that figured out.

Not much progress in the last couple days, but got a couple more panels setting up over the wheel wells. (Using a combo of clear Gorilla Glue spots for quicker setup and PL300 for that.)

I am really enjoying how easy it is to work with the foam in any case. So long as all of my cuts are just a little bit oversized, shaping everything to fit together tightly is quick and easy.

 

[Pmullen503]

Cool shape, should be more aerodynamic. That large tongue box should help quite a bit.

 

[kipa]

I just realized yesterday that it has basically morphed into the shape of the Lightship EV camper.

I don't plan to create an upper half of the same shape, opting for the more simple rectangular popup portion as afforded by the hard shell tonneau cover I have for it instead. That way I get the aero advantage on the road when collapsed without the build headaches of making a matching shape to fit and seal with tight tolerances. I also get to skip using complicated lift mechanisms, though I am now thinking it would be just as easy for the entire top section to move vertically vs. the tilt as originally planned.

 

[kipa]

I have decided at this point to use steel unistrut as internal framing. That will provide some needed strength, and if I just do an 8'x 5' x 2' box, open at the rear with some bracing, it only adds about 40 lbs to the build and will be more than adequate as a structural support for the popup section as well as stabilize the walls when tied in.

(It's just sitting on top of panels as clamping weight in these photos.)

 

[pchast]

I found it simple to route out the location for inserted wood blocks.... I used western red cedar for light blocks, poplar for lock set hard points.

 

[kipa]

Got the sizing and placement of the unistrut frame figured out to match up with the tonneau cover. It is currently just resting on top of the foam, and the rear support walls are temporarily oversized to aid in stability. I am planning to extend metal legs down from the upper frame to tie in more rigidly with the decking.

When lined up with the rubber seals, it leaves about 1/4" gap around the drip edges of the cover, which I intend to fit into aluminum u-channel for water drainage. Also worth noting that the tonneau seal is not square, but tapers 1-1/2" toward the rear, so had to build the frame to match.

Obviously, the current design somewhat forgoes the vertical taper of my original idea, but I am thinking a custom build of a new cover could provide a more aerodynamic taper. For now, it's all about making it solid and functional. Aerodynamic tweaks will come later.

 

[kipa]

For anybody wondering about my choice with the tonneau, it comes down to cost and strength. To build ACM panels as strong would have cost me as much as grabbing the used cover was off of a local sale, and the ASA cover is more than strong enough for a person to jump up and down on it without damage.

 

[Pmullen503]

So, are you still thinking of hinging it in the front? Hard walls or tent?

 

[kipa]

I've convinced myself to do a fully vertical design with hard walls. It won't make a lot of difference on cost, but it would allow me to stand fully upright inside.

Thinking horizontal bifolding sides and a single front wall that swings down from the cover, and likely the same at the rear with whatever door I figure out.

Just did a test fitting of the cover and I apparently measured right for my support frame, as it fits exactly as I was expecting. Will need to trim the corners off the cover and enclose them with gussets later on, but that is not a surprise.

 

[kipa]

First layer of glass not a total disaster.

This is the bottom and I only intend to lay up one layer for rodent protection and to add a little stiffness to the floor. (But I will likely install a wood floor inside regardless.)

I wasn't really too sure about using this epoxy, as it is sold as a casting epoxy with no reviews by anybody doing layups. So far, I can't discern any problems with it. It is also very low odor in my attached enclosed garage, though I did the layup with the doors open.

 

[kipa]

Continuing with the underside glassing. Finished the underside of the wheel wells, but also put together my budget disc wheel covers.

Honestly, it's not like legit Moon Eyes are that expensive (roughly 2x what I paid), but I won't feel the least bit bad about painting a couple of pizza pans later on.

 

[KCStudly]

Moon discs usually screw into the perimeter of the rim, into the tire bead, using 3 or 4 tek screws. I like your resourcefulness, but would be concerned about using just one small fastener at the center of the wheel. The mass at the rim of the pizza tray has the most momentum and leverage to act on the center fastener. By putting multiple screws out at the rim this is mitigated.

 

[KCStudly]

Also, not seeing how sturdy the adapter is, I would question how good the center mount can keep the tray centered (and therefore not an eccentric balance issue).

 

[kipa]

Valid concerns that I will be watching. The pans aren't just bolted onto the covers. They are glued at the rim in a few spots as well. Possibly not well enough, but the covers themselves will likely come off of the wheels before the pans come loose from the covers.

 

[kipa]

Valid concerns that I will be watching. The pans aren't just bolted onto the covers. They are glued at the rim in a few spots as well. Possibly not well enough, but the covers themselves will likely come off of the wheels before the pans come loose from the covers.

Just realized I failed to include the back side pic.

 

[kipa]

Worth noting that one of the reasons I built my own was because I am not convinced it will make a measurable impact either way. May invest in MoonEyes later . .

 

[KCStudly]

Oh, I see now. You attached the pans to a hub cap (wheel cover) that attaches to the wheel conventionally. That's better than what I had been picturing in my head.