All aluminum hard sided popup toy hauler

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After building the ultra-lightweight floating popup camper out of foam and fiberglass 20 years ago, and building a wooden camper on a snowbear trailer 15 years ago, I've decided to go all out and build with aluminum.

The new build is from scratch, made from a thousand pounds of various aluminum angle/channel/sqare tube, a 3500# torsion axle and .032 aluminum skin.

The goal is to have one trailer that can do everything; its a rectangular box 16ft long by 7ft wide that collapses down to 6ft tall for towing behind a tesla model Y.

I chose the length and width to be the biggest possible thing that I could park in a standard parking spot, making it much easier to park in regular parking lots while traveling.

There's enough room on top for 1900 watts of solar panels, which will charge 12kwh of lithium iron phosphate batteries under the floor, and should be able to run a mini-split air conditioner, refrigerator, lights, microwave, and coffee pot.

It'll have a full bathroom with blackwater toilet and recirculating shower.

The back wall folds down into a ramp for loading a motorcycle, and will also allow me to use this as a utility trailer.

Step one in summer 2023 was laying out weight and balance during my down time at work.

Pictures of my build progress will come as soon as I learn how to upload them on the new forum.

 

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Here's one of the very basic weight and balance drawings I made while trying to determine where to mount the axle, and where to secure my heavier furnishings.
When I'm hauling toys, there will be between 600 and 900 pounds of motorcycle balanced squarely over the axle.

 

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Step two was learning how to tig Weld and welding up an aluminum frame from 1/4" thick 3x6 C channel and 1/8" thick 1.5x3 square aluminum tube.

After many sample pieces welded together and destructive tested with a 4 pound hand sledge, my Weld became consistent enough to trust with the not heavily stressed areas like this 1.5x1.5 inch L channel perimeter frame:

After that, I moved along to welding my 1.5x3" floor joists to that perimeter:

 

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Using my craptastic Harbor Freight chop saw, I cut my frame rails to length.

I leveled my 1/4 thick 3x6 frame rails on saw horses, laid the joists in their frame on top, and welded them all on.

I now have something that looks kinda' like a trailer frame with frame rails that stick way out past where a tongue should be.

 

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Oops, double posted

 

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Now it's time to take that pair of frame rails that are sticking out and turn them into a V tongue.

I used an 8" cutoff wheel to take v shaped chunks out of the top and bottom of the C-channel, then gently bent both rails together, and held them in place by bolting them to my hitch.

Once I did a bunch of warping and straightening of the frame/tongue area, I made what are probably going to be the most structurally stressed welds of the entire project: welding 1/4" aluminum plates to the top and bottom of where I cut out those notches to bend my frame to tongue transitions together.

I spent alot of time running at high current to make sure I had good penetration all the way through both pieces of 1/4" aluminum, and that's when I melted through the gas line on my welding cable.
$150 later I now have a heavier duty (and longer) welding cable and torch head.

Note the existence of large stainless steel bolts acting as a backup just in case those welds crack.

 

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To round the front corners of the perimeter frame, I cut notches into the 1.5" angle every inch, then bent it around a rounded plywood former.

Once I welded those to the frontmost floor joists, the curve stayed.

That's when I welded the ends of all those notches together, and realized that wind is not the friend of a TIG welder. My gas blanket kept getting blown away from the ark, and my tungsten electrode would burst into flame and contaminate the Weld area with big scorch marks and lots of burn through.
I'll eventually grind all that down and re-weld things before I install a floor.

 

[featherliteCT1]

WOW!

You have made a lot of progress.

I look forward to reading your future posts.

 

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Moving right along, time to mount the axles.

I have a 3,500 pound torsion axle which allows me low ground clearance for aerodynamics, as well as good bounce damping, but it does concentrate all the trailer's weight onto 2 tiny point loads on the frame rails.

I decided to spread those loads out a bit by using some scrap 1/4" C-channel pieces cut down into L profiles.

Those scrap pieces are about 3' long, so should seriously help with frame rigidity in that area.

Unseen in these pics is the fact that I put foam "sill seal" between the steel axle and aluminum frame to prevent any dielectric action from corroding the frame.

The hardware holding it all together is 5/8 stainless steel which is dielectrically compatible with aluminum.

 

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With the axle mounted, it's time for me to start into the comedy of errors which are my tire and rim selection.

Wanting to save a bunch of space, I decided to select a trailer wheel that allows me to use my car's spare tire as my trailer spare.
That's really good in theory, but really hard in practice.

I discovered that trailer rims have zero offset, which means that the face of the rim aligns with the center of the tire.
On my car (which has a 60mm offset) the face of the rim aligns with the face of the tire.

Now, trailer tires can be mounted on car rims with no difficulty, but it turns out that car rims cannot be bolted to trailer axles without a ton of difficulty.

This right here is about $1,000 of tire and rim, since they were one of only 2 designs which had the appropriate offset as well as the size that allows me to mount my chosen tires.

 

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On automotive axles, the bearings are set inboard of where the wheel mounts, on trailer axles, the bearings are centered in the middle of the rim.

This means that the rim has to have a large hole in the center for the bearing housing to pass through it.

My automotive rims had center holes that are too small for that (and there are small plastic center caps in these rims).

 

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Well, it's time to take a hole saw to my $1,000 rims.

Fortunately there was enough space for me to shave off 1/8" all around that center hole, allowing the bearing housing from the axle to slide right through.
WHEW!

Unfortunately there's another difference between a trailer torsion axle and a car axle: the axles lever arm is set very close to the face of the brake drum, which is no problem for a rim with zero offset, but rubs hard against a rim with 60mm offset.

My temporary solution was a stack of washers on each wheel stud that spaces the rim far enough out not to rub on the axle.

Eventually, those were replaced with some wheel spacers from Amazon

 

[OP827]

Just saw your new build and subscribed.
I do not want to fear monger nor discourage you in any way and hope you did your research and know what you are doing with this aluminum tongue frame, especially tongue welds near the main frame platform. Welds are normally the stress concentrators(weakest points) where a fatigue crack could start.

The difference between steel and aluminum alloys is that steel has this so-called fatigue/endurance limit where it does not develop fatigue crack while Aluminum will eventually develop the fatigue crack no matter how low the load is. The main question is how long (cycling loads) will it take under the dynamic loads.
Aluminum fatigue limit.

There are very few trailer companies who sell aluminum frames and then possibly even fewer that are doing it right.
https://youtu.be/Yg55GXksEnY?si=39DtluMK34-8M7sO

Good luck with the build

 

[coal_burner]

Yeah, I stressed out about aluminum fatigue for quite awhile, and was finally convinced to go this route after crawling under a lot of aluminum utility trailers of a similar size to what I'm building.

3" x 3" x 3/16 square tube seems to be most common framing material (even for a twin axle 4,000 gvw unit).

I figured if I doubled the frame height and stepped up to a quarter inch thickness, I'd have cyclical loading / stress crack issue covered by gross overbuilding.

Hopefully this can make up for any deficiency in my welds.

I ran the numbers through an online stiffness calculator, and it showed that my bending at gross weight even on a hard impact with speed bumps would be measured in the low thousandths.

I ran the same calculator on the 3x3x3/16 tubular frame, and it came up with flexing numbers in the low hundredths.

So, theoretically, I'm an order of magnitude stronger than a factory built unit.

 

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Here's a couple angles of the tongue to frame welds.

I practiced these exact welds for a few days before putting arc to trailer.
I was eventually able to get good enough penetratio that I could crumple the samples up with a sledge hammer without cracking the welds.

 

[OP827]

That is good to know, thanks for sharing and happy building!

 

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A couple additions
Mud flaps made from cheap .125" rubber sheet from Amazon, and held on by a zillion stainless steel screws.

And a wheeled tongue jack

 

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Next up is the trailer lights and wiring.
Since I've had to troubleshoot and/or replace so much trailer wiring in the past, I went all out and bought a high end junction box and PVC coated wire to go along with it.

The lights are all mounted on temporary aluminum brackets that will be removed when I get walls on the camper.

Wow, the round plug that has wires for trailer brakes is HUGE (and much sturdier) compared to the common 4 pin flat plug all my other trailers had.

After I got it looking street legal, I hooked it up and towed it to the nearest scrap yard to get an official weight slip for it.

With the weight slip and a bunch of receipts in hand, I went to the Secretary Of State, paid my taxes, and received my license plate.

Now I have a trailer that's capable of picking up all of the 24 ft long aluminum stock I'll need to build the rest of the trailer.

Having the first batch of aluminum delivered cost me $75, and I had to take the day off of work to make sure I'd be home to help unload when the delivery guy got there.

 

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Well, I ran out of parts at the same time my car went to the shop, so there was a month long pause in work.
(It's not cheap to hit a concrete block)

Now that I have the car back, the trailer has been on a freeway road trip to pick up more material.

Those are 24ft sticks of square tube and angle.

(And a pair of boxer shorts flagging the overhang)

 

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Time to build some walls!

I started by cutting all of my verticals, and getting them to match down to less than 1/32".

I welded them all to the top rails laying flat, using my floor beams as alignment jigs.
(Worked like a charm).

Here's the first wall section temporarily clamped in position: