Ultralight foam build

[R. W. Alexander]

Getting back into the build again. I sold my last tear drop, which was weighing around 550 lbs. If i remember correctly. With this build(based on the ultralight design) I"m aiming to take off 150 to 200 lbs. I'm going to do a Piccolo light type of A frame with some 500 lb torsion half axles that I have had lying around the shop. Since I need to remedy a problem with the axles moving of of alignment I will attach 2 pieces of 1/8" thick by 2" angles to the front and back of the torsion bars. I plan on a sandwich platform with 1/8" ply with a foam core and some wood strips placed in high load areas. The body will be 1" foam with cloth on the outside /inside and a 1/8" wood interior.

[KCStudly]

Looks like a good plan.

How do you plan to stabilize the angle steel? Will there be some kind of end plate or gusset plates joining them? Just saying, angle iron can be twisty if not laterally supported.

[rowerwet]

The frame plans for using angle iron shared by AngieB don't require any extra bracing.
I love this idea, but I take too many toys when camping, to get away with such a light frame

[angib]

How do you plan to stabilize the angle steel? Will there be some kind of end plate or gusset plates joining them? Just saying, angle iron can be twisty if not laterally supported.

Bolting the half-axle mounts to the angle iron will stabilise it fully - the mount will be a substantial casting.

Aligning half-axles seems to be a concern in the US and I think that is because they aren't common. It really isn't rocket science and does not need to be done with the same precision as car/truck wheel alignment. If you plan to do 20,000 miles of towing a year, there might be a benefit to aligning the half-axles carefully to minimise tire wear, but for normal trailers that isn't necessary.

[Mary C]

I want to suggest that you make a box put canvas on the outside and inside with TBII let it dry and paint it with a couple of coats of paint , then ask yourself why wood on the inside?.if you wantultra light why the wood? You can paint it with a faux wood if you just like the wood look. I like your idea and design.

Mary C.

[R. W. Alexander]

How do you plan to stabilize the angle steel? Will there be some kind of end plate or gusset plates joining them? Just saying, angle iron can be twisty if not laterally supported.

Bolting the half-axle mounts to the angle iron will stabilise it fully - the mount will be a substantial casting.

Aligning half-axles seems to be a concern in the US and I think that is because they aren't common. It really isn't rocket science and does not need to be done with the same precision as car/truck wheel alignment. If you plan to do 20,000 miles of towing a year, there might be a benefit to aligning the half-axles carefully to minimise tire wear, but for normal trailers that isn't necessary.

The biggest problem for using half axles would be overbuilding... and that adds weight. The 2 half axles are rated at 250 lbs each so this trailer will be a weight watchers special.

[R. W. Alexander]

I want to suggest that you make a box put canvas on the outside and inside with TBII let it dry and paint it with a couple of coats of paint , then ask yourself why wood on the inside?.if you wantultra light why the wood? You can paint it with a faux wood if you just like the wood look. I like your idea and design.

Mary C.

I'm looking at using a 2.5 to 4 oz. fiberglass covering at this time on the exterior. But that's not set in stone at this point yet. As for the interior I want to use fabric for the inside of the top and1/8" wood for the walls. The faux painting is possible, but that would involve painting the interior parts... walls shelves before assembly. I have done faux painting before. Here is a photo of a mdf magazine holder painted to look like exotic bocote wood.

[KCStudly]

Bolting the half-axle mounts to the angle iron will stabilise it fully

I appreciate the reply, and please recognize that I am making a few assumptions about the plan, not being familiar with it. I had assumed from the OP's description that the toes of the angles point toward each other and down with the axle halves connecting the two together at each end. Is it the fact that the angles are also fixed to the underside of the floor in several places that keeps the torque reaction from the trailing arm from twisting them?

The scenario I am picturing, if you can imaging one trailing arm clamped in a vice and you grab the other trailing arm and twist. With the angles attached to the floor at intervals along their lengths I can see that being okay for a light camper; but if the floor is lightly built, too, or the angles are only attached at the ends, I can imagine the angles becoming more like a torsion bar than a rigid body.

Reality check: In the real world it probably just doesn't matter that much. Analysis paralysis.

I guess I am forgetting the tongue members, too. Have to remember the mantra of the sum of the parts, not just single members.

[angib]

A trailer sits on only three points - 2 wheels and a coupler - so it is not like a car that can get big torsional loads from its two axles going in opposite directions.

But it may be that RW has left out the angle irons along the bottom of each sidewall, or just not drawn them. Those angles are pretty important since that is what transfers the main torsional load of the torsion axle into the sidewall.

[R. W. Alexander]

But it may be that RW has left out the angle irons along the bottom of each sidewall, or just not drawn them.

I did not draw them in on the first drawing. Too much clutter. Here is a more detailed drawing of the torsion axle. I will cut out part of the 2" angle and weld it to the mounting flange of the torsion axles. This will also save some weight since 1/8" by 2.00" angle is about 1.7 lbs per foot.

[R. W. Alexander]

I'm getting the design refined. I was going back and forth deciding on how thick I wanted the ply to be on the floor. After reading a few posts I will build a 1.00" thick foam floor with the 1/8" ply top and bottom and using 1/4"thick by 1.00" tall wood beams on 3.00" centers. Since I have a 4' by 10' C.N.C. it won't be too complicated. I will stand the side boards for the floor on edge and use a 1/4" end mill to notch into the wood for the beams. Also I have a few foam samples with Glidden gripper drying out with some fabric on them to get an idea of the laminating process for canvas. I want to compare it against some Tite bond that I did earlier in the week.

[pchast]

Interesting Ideas. I'll be watching to see how it works out.

thanks!

[R. W. Alexander]

CIMG2803.JPG (148.14 KiB) Viewed 1570 times

Well ya know how the best plans get changed?? I was surprized at how much some of the thinner plywood's cost. And me being the cheap person I am . I wanted to save some money on my foam build. So I got some 3/8" CDX plywood and routed out some of the material to save weight. The sheet weighed in at around 38 lbs. before routing, and by the time I got done I had it down to 20lbs. I put in 1/4" grooves for the 1.00" by 1/4" fir slats that are spaced 3.00" O.C. I then routed out some 2.50" holes to lighten up the frame. I still need to get some 1/2" foam to go in between the vertical slats. But the total weight at this point is 38 lbs. I could of something less complicated, but I like a challenge. Also since by floor panel is 54" wide I needed to so some splicing for the floor frame.

[KCStudly]

Although never intended to be a super light weight, my whole build has been based on a design concept of lighter and stronger thru unit construction. Sometimes taking many steps and extra effort to build it the way I picture it in my mind (or in my 3D model). It becomes a bit tedious sometimes maintaining the same ideology and stamina, plodding along toward that elusive 95/ct complete and campable stage.

What I am trying to say is you have certainly started off in a complex and labor intensive way, and I hope that you are able to maintain that same commitment to your vision throughout your project. I'm not sure that the extra effort is worth it from a weight and strength vs. cost and effort perspective (there are probably easier and more efficient ways to build), but it certainly is entertaining to watch.

For me the challenge of the build and developing the techniques needed is as much part of the challenge and journey as is the end goal of getting out there with the finished camper. I hope you are enjoying that same spirit!

[R. W. Alexander]

Added the foam board to the lower half of the floor panel. Then cut out the top half.