Critique my DIY plans!

[moroza]

Any armchair (or actual) engineers around here? Or anyone else with $.02 to share about my plans to DIY a motorhome?

I've got an '81 longbed 4x4. I want to build my own for several reasons, chiefly that I want it heavily insulated. Current plans are 3 inches of polyurethane or polyisocyanurate rigid boards all around, maybe more in the roof. Structural materials are mostly riveted aluminum, with some wood thrown in a few spots. For planning, I have it nominally as 2x1" beams, but actual pieces will depend on what I can find. It'd be great to come across a stash of broken aluminum ladders, and chop them up for beams.

The "stove" refers to either the smallest Ammocan stove, or something very similar of my own construction. I plan to use propane only for cooking, and diesel only for moving the vehicle.

Window shapes and positions are approximate; actual details will depend on what windows I salvage from something else. Really, that statement applies to everything in the design.

Walls materials and their thicknesses, inside to out:
3.2mm plywood (1/8) inside, except around stove, where it's cementboard and alu skinning
50.8mm alu and wood studs, insulation between them
25.4mm more insulation
0.6mm (0.019") alu skin on outside

floor:
15.9mm plywood (5/8)
50.8mm studs and insulation
25.4mm more insulation
0.6mm alu skin on outside (bottom)

roof:
3.2mm plywood (1/8) inside, except maybe around the stove
38.1mm insulation
50.8mm studs and more insulation
12.7mm (1/2) plywood
0.6mm or thicker alu skin on outside (top)

Here's my SketchUp model. I couldn't find a 1st gen cab, so I took a 3rd gen and fudged it to similar dimensions. The collection of stuff in front of the truck is a cutaway of the wall/floor joint, illustrating my positioning of the structural beams to avoid thermal bridging.

Er...how do I upload a .skp?

[linda s]

If you want lightest weight and super insulated look at this camper build

http://thesupercamper.blogspot.com/2006/09/super-camper-construction-begins-nida.html

Linda S

[Derek up North]

Don't use Sketchup. Can you save it as a jpeg?

[moroza]

I've seen and studied the Super Camper. Nidacore is too expensive and underinsulated.

I can take screenshots and upload them as JPEGS, of course, but you won't be able to fly around the model. I guess I'll try that.

Here we go:

Edited March 4, 2013 by moroza

[Maineah]

Weight, that's the key that is why the factory stuff uses thin studs etc Many use 1X1" aluminum studs.lighter and stronger. They get around the "R" factor issue with big heaters.

[Eve "n" Stephen]

Aluminum studs, brrrr... We used to have an old Airstream trailer, which was pretty much all aluminum. The thing wasn't well insulated, but with the heater way up, it was comfortable when the outside temp was in the 20's. The catch, it could be 70 inside, 20 outside and everwhere there was a stud, there would be FROST on the inside wall in a strip!

Steve

[zero]

As already aluded to - weight is the issue. I've redone many RVs and tried to "improve" with better materials. When done, they all had serious weight gains.

It's kind of amazing how things add up when you make just a "little bit" stronger.

I haven't seen them all - but from what I HAVE seen, the Toyota Sunrader and the Winnebago series of LeSharos-Phasars-Rialtas have the best engineering Ive seen in small RVs with a smart compromise between structural integrity, good insulation, and weight kept to a minimum. Note my reference is to the RV parts - and not the truck parts that were engineered by a non-RV company.

Your plan of an aluminum frame is certainly a good start. I was suprised to find my Chinook came with 1" square steel tubing and not aluminum.

[moroza]

Aluminum studs, brrrr... We used to have an old Airstream trailer, which was pretty much all aluminum. The thing wasn't well insulated, but with the heater way up, it was comfortable when the outside temp was in the 20's. The catch, it could be 70 inside, 20 outside and everwhere there was a stud, there would be FROST on the inside wall in a strip!

Steve

Thermal bridging. See the first pic for how I'm getting around it.

As already aluded to - weight is the issue. I've redone many RVs and tried to "improve" with better materials. When done, they all had serious weight gains.

It's kind of amazing how things add up when you make just a "little bit" stronger.

I haven't seen them all - but from what I HAVE seen, the Toyota Sunrader and the Winnebago series of LeSharos-Phasars-Rialtas have the best engineering Ive seen in small RVs with a smart compromise between structural integrity, good insulation, and weight kept to a minimum. Note my reference is to the RV parts - and not the truck parts that were engineered by a non-RV company.

Your plan of an aluminum frame is certainly a good start. I was suprised to find my Chinook came with 1" square steel tubing and not aluminum.

Well, I'm not using any fiberglass. The only heavy plywood is on the floor and a bit on the roof. The wood studs could probably be thinner; all they're for is supporting the windows, and keeping the thin wall skins from flexing too much. The alu studs might get thinner, too.

Weight is the reason I redesigned the whole thing to use alu instead of steel. My previous scheme involved steel tubing of various shapes and sizes, plus the same skinning materials as this. I estimated 280kg before interior fixtures and whatnot. With this, I'm hoping for more like 230kg.

I've yet to run weight calculations. For now, I'm looking for feedback on structural design. Like does it look adequately triangulated? Is part of it overbuilt? Underbuilt?

[moroza]

I played with a few different configurations of skin material and thickness vs. stud material and thickness, and came to the conclusion that triangulation with studs is much lighter than with skin. At least, that's how it was with wood/plywood.

I would think that triangulation is a lot more important in a structure that sees frequent side to side loading, rather than buildings.

[Mikesta]

Those are some great photo's of your Ideas... I really don't have anything to contribute other than to find out what you want to utilize this for. Expedition?

If buiding my own camper from scratch.... I'd put a ton of time into utilization.

1. I would build within the frame, so a center strip of flooring that would have a hinged door and could store stuff between the frame rails where the GAS TANK isn't.

2. I would bring the outside of the camper down and angle it into the frame rails giving you more storage area and utilization. Believe it or not, more weight near the frame rails will bring your center of gravity down a tad too and this will also make it look better.

Your departure angle looks great!

[moroza]

I would change one thing on the framing, you have an upright member bearing down on the point of the triangle over the wheel well. I would clip off the point of the triangle and put in a cross member that ties over to the uprights that bear down on the floor. It will be much easier to construct and the downward load will be better shared to supporting.members. You are creating yourself a lot more work by having too many joins at one single point of intersection. Plus it won't be as strong as it could be.

Wouldn't that be weaker than the triangle structure I have now? Anyway, that upright member is for keeping the walls from flexing too much, and supporting a window. I don't see it supporting much other weight.

Duly noted, anyway. More comments like this, please!

Those are some great photo's of your Ideas... I really don't have anything to contribute other than to find out what you want to utilize this for. Expedition?

If buiding my own camper from scratch.... I'd put a ton of time into utilization.

1. I would build within the frame, so a center strip of flooring that would have a hinged door and could store stuff between the frame rails where the GAS TANK isn't.

2. I would bring the outside of the camper down and angle it into the frame rails giving you more storage area and utilization. Believe it or not, more weight near the frame rails will bring your center of gravity down a tad too and this will also make it look better.

Your departure angle looks great!

1. Good idea, and I will do something similar temporarily, but I plan on adding a second tank opposite the first, so other than little cubbies there won't be much room down there.

I plan to keep at least some of my drinking water and all of my batteries inside the insulation layer, for function in extreme cold. I am considering making space for temporary mounts for the batteries as low and centered as possible, in case I ever really need to squeeze out an extra couple degrees of traverse angle.

2. There'll be exterior storage bins at least in front, if not also behind, the rear wheels. I did not include them in the drawings because they are outside the structural and insulation layer.

The departure angle looks so good because I completely redesigned my project to maximize it. I can't get any better without getting real creative with the rear springs (not shown, but they are the drag point right after the full-sized spare). Right now, the spare sticks out a good bit, and I'm not sure if that's a very good thing (hang a steel plate under it and it's a very good bumper) or if I should relocate it to maximize the angle.

I lived in my car for about a year, got hooked on that lifestyle, but decided that an old BMW wagon just wasn't appropriate for it. Carving corners at 200kph doesn't mean much when I get stuck on my way to a campsite, then spend all night freezing in the back of the car because there's no heat or insulation. I call this project a "tinyhouse", but it's not a house scaled down, it's a car scaled up.

Edited March 19, 2013 by moroza