Re: Teardrop Camper -- Structural Thoughts
Thanks, guys!
The angle iron corner reinforcement may be 'strong enough'.
The hollow square tube is 'stronger'. Also heavier (approximately 2x for the same 'size' and thickness/gauge metal) and takes up some more interior space. (but you could tuck wiring inside the hollow tube, attach interior things to it and not blow through the skin to the outside unless you really-really used too long of a fastener, etc).
You have the tube roller, so that gives you a way to roll/bend the tube to your desired curve. Angle iron can be 'rolled', but you need different dies/supports and even then it can sometimes tend to warp in a different plane than the bend plane.
So for you and what I 'know' of your tools and talents (your patio arch cover, etc), I'd probably say use the hollow tube and move on.
It's true that I'd have to buy/make different dies to bend L-stock. And there is something to be said for running wires through the steel tubing. The only downside to square tubing is weight and that it nudges me toward slightly thicker walls (with 1" instead of 1/2" insulation (but then, that's better insulation).
Square tubing is the current front-runner.
Yes, the side panels could bend/move without some sort of framework and/or the 'roof' skin. But a thin 'skin' roof loaded from the side panels might wrinkle or buckle. So those side-to-side partitions/walls are what is mostly making the structure 'stronger' side-to-side. By a lot.
True. But the skin is composite panel, which is surprisingly rigid -- especially once it's curved. But your post has me thinking of adding an x-shaped brace to the largest interior side-to-side wall. Like a roll cage.
And regarding the floor and a frame support underneath it, I'd say a great big YES have a frame under the floor panel(s). Again, it is possible to make a floor 'skin' that is strong enough, but putting some sort of 'frame' underneath the floor gives much more support and you don't then have as much 'oil-canning' effect going on.
(yes, I
have been accused of 'overbuilding' things. More than once.
)
I'm thinking about adding a second floor, about 4" below the first -- for storage. I think some framing makes sense now -- and if it's a double-decker thing, it'll be even stronger.
I'll use steel down below, since it will resist cracking better. Of course, it'll have to be protected from moisture.
Oh, if you are thinking of doing aluminum skinned panels as your 'skin' of the trailer, I'd really-really suggest doing the frame tubes in aluminum as well (use aluminum or stainless steel fasteners too, no plain steel against aluminum!). That way you have similar metals in contact and minimize galvanic corrosion issues (remember, rust/corrosion never sleeps). Caulk all the joints/seams as you are doing the assembly (face to face lap seal with the sealant/caulk versus trying to just run a bead of sealant/caulk right on the joint seam) or have your adhesive possibly double as the 'sealant' (check the adhesive specs first) and thus minimize and reduce chances of water infiltration. IMHO.
That's my current plan. Aluminum square tubing up above. I'm going to use a combination of VHB tape, Dow 995 structural adhesive/sealant, and also 3M Scotch-Weld structural adhesive (and rivets) at the key juncture points.
Jack, everybody is over thinking this.
With the correct composite panel you will not need any diagonal braces.
The only weakness is cutouts like doors or windows that need framing
Using tubing as corner frames is a good way to run wiring [and to double skin the inside ]
With tubing you can use countersunk pop rivets to hold the panels until the adhesive cures [ unless you have a large clamp collection ]
The rivets wont show on the inside, and you cap the panels with angle on the outside to hide them later.
you can buy Aluminum Composite Sign board in the LA area up to 2m wide which will give you 1 piece sides.
http://www.aluminium-composite-panel.cn/products.htm?id=1
This Aluminum Composite Sign board can be put through a ring roller to get the roof profile.
Don't use 3M VHB , there is a Bostik product [Simson ISR 70-03] that is better.
and a flexible glue is advisable because it has better bonding properties.
The stiffness comes from the composite panels not the glue.
I'm looking into building my own roll bender for this, using steel pipe or stiffened PVC pipe. I was able to bend the stuff simply rolling it back and forth on a length of PVC pipe for a test model I made. But I'm hoping I can get a compound bend close to the shape of the profile with some patience and three rollers. We'll see how that goes.
This is the sample box. I bent 1" aluminum tubing for the roof juncture, and also used aluminum rivets at each end to prevent any kind of zipper-type failure. I used angle stock below with two layers of corrugated plastic. I will probably change that to square tubing.
But this thing is so strong I could jump up and down on it all day long.
With very little knowledge on the panels you plan to use, I only have one comment.
The floor at the door area takes a beating. You're likely to want the frame or reinforcements in that area.
That's actually very helpful. Thanks!
Another thing to think about is the expansion and contraction of the panels in the sun and cold. I have an open trailer that has a box that is 2ft wide 3ft tall and the width of the trailer on the front. Full doors on both sides. The box is covered with aluminum. The panels fit perfect when cold. As the sun hits it the panel, it will bow a 1/4 to 3/8 of an inch between the mounting bolts that are a foot apart. It has a steel frame with the aluminum bolted to it.
I would think that if the frame and panels were of similar materials this wouldn't be an issue.
Just something to keep in mind.
I've got two panel samples I made (aluminum composite panel/foam insulation/corrugated plastic) in the freezer right now. I'm going to cycle them from 0°F to 200°F a few times, and see if there's any change in the angle they sit at when they're set on their side. I also hope it will show me if there's going to be a problem with the adhesives I'm using.
Jack just wanted to report in after dragging the trailer with the axle less suspension around in the mountains on smooth roads (rare in CA), crappy roads ( I5/I80 to Truckee) , construction pavement ( I5/I80 to Truckee, dirt/gravel roads, and rocky roads.
Also high side, front and side winds with two kayaks on top
Pulled like a dream in all conditions. No sway in side winds. No bouncing off the ground when you hit a bridge or overpass.
Watched the trailer to see if it would Jump around at 65 mph when changing surfaces in construction zones and it did not.
Wife drove for three hours back and said she has to keep looking back to see if the trailer is there.
Did not weight it but I think maybe 1000-1200lbs loaded.
That's good to know. It looks like it's got plenty of tongue weight (relative to its overall weight), which should make it more stable. I'm hoping that a combination of tongue weight and torsion-type axles will give mine similar manners.
I have seen many versions on the internet from plain to awesome. They look fairy easy and cheap to construct. Good look on the build I will be watching. They have also peeked my interest but alas I really don't fit in them.
Mine will be bigger than the standard 4x4x8 trailer. It will by 5x5x10. But I'm only 5'11", so I should have better luck.
I may have missed it above but here's a good forum on tear drop trailers ...
Teardrops n Tiny Travel Trailers -
http://www.tnttt.com/
Thanks. I found it a short while ago. Very helpful. I've been subjecting them to my ongoing adhesives/materials tests.
I would use square tubing, maybe 1.5x1.5 ?
As I said before, cut hardwood stock to fir snugly inside the floor rails. Then you can through bolt to the frame without working about crushing the tube.
The top tube will be a pain. You will have to cut multiple little pie sections out of the sides of the tube to form the roof curve. I would weld the tube back together for maximum strength.
You are basically making a monocoque structure so the joint at the roof and floor are critical. Good adhesive and screws (into the bottom where there is wood) or blind rivets (along the top) are inperative.
I'm hoping I can get the complex curve worked out slowly and patiently with my roll bender and one piece of stock. We'll see how many tries it takes. If it doesn't work, I have a TIG welder.
