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Discussion Starter #1 (Edited)
Background:
I purchased my element with the sole purpose of the woman and I running away from adult life. The first big project was the 6-sp swap. With that out of the way, and knowing that my plan does include potentially sleeping in the back for periods of time (which is why I chose an E), I reviewed the existing designs in the sticky, and thought I’d do my own. I began by prioritizing my functional requirements. I wanted my shelf to be:

Comfortable (Full length mattress for 2 ppl)
Modular (ease of installation)
Dynamic (ability to change the configuration)
Lightweight (don’t need to explain this) EDIT: Final weight is less than one rear seat...
Reversible (no permanent mods to the car)
Stealth (no open hatch/tailgate, quick setup)

All existing designs (minus one) had one thing in common that I disagreed with: lots of floor supports. That is to say, some means of support that interfaces with the floorpan of the car. I want my shelf to float so the space underneath is universal storage. I would use the rear seat mount holes (custom fab mounts), the rear bins, and 2 legs (when extended) up at the front seats.

With that in mind (and the lightweight design), I drafted up a plan utilizing 80/20 HT series profiles:



Cont’d…
 

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Discussion Starter #2 (Edited)
The plan was to have the front 13” fold down for driving, and up for sleeping. The legs would interface with the metal pan of the car (for strength) and not the ‘carpet’ or plastic molding. Final top dimensions are 76”x54”. The rear section is cut for bin access and hinges up at the bins for floor access. The two center sections butterfly up for storage access. All hinges are lift-off style, so the sections just slip together without bolts.

For the top I felt that plywood was too heavy (no offense) so an internet search for corriboard led me to lightweight hurricane panels (Hurriguard®). They are a corrugated 3 layer polycarbonate (Lexan) 8’x4’ sheet that is about 0.65 thick and can withstand crazy impacts. The whole 8x4 panel weighed like 5 lbs. I would attach the panel to the structure with hook and loop tape because it is light and can be lifted off at any time.

Once I had the plan down, I prototyped with strips of cardboard. The design of the sections is such that I would utilize exactly ten 48” pieces of HT (with a few cuts) with only two 3” sections of scrap:


And purchased the necessary hardware:
 

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Man awesome bed build! Just curious what you think the weight limit it can take with no center leg support? Any flexing! Looks awesome and love all your design requirements. No legs, light weight and not perminate!
Nice work there
 

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Discussion Starter #5 (Edited)
Thanks!

Man awesome bed build! Just curious what you think the weight limit it can take with no center leg support? Any flexing!...
My calculations show that me and the woman will deflect that center beam ~0.171" downward and maintain a 52.4% safety margin!

Seriously though, this could go up to about 500# before you might think about breaking it. Aluminum extrusions are amazing. That beam weighs like 3.2# and can hold up to 500#...

-Karl
 

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KSE took the words out of my !mouth. What was the breakdown for each material? Will you provide the exact measurements, schematics, etc for duplication?

Thank you,
 

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Discussion Starter #7
KSE took the words out of my !mouth. What was the breakdown for each material? Will you provide the exact measurements, schematics, etc for duplication?

Thank you,
I'll try to put together a complete build list tonight, thanks!

-Karl
 

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This is really cool. I'm looking forward to seeing progress/revisions and your personal comments after some testing.
 

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I'll try to put together a complete build list tonight, thanks!

-Karl
Please add the cost of the materials too.

Thanks again,
 

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Discussion Starter #10 (Edited)
This is really cool. I'm looking forward to seeing progress/revisions and your personal comments after some testing.
I've had it installed since ~June. We've done 4-5 trips since and it has worked wonderfully. I did make a few minor changes. I used to have the panels bolted to the aluminum, but the hook and loop holds plenty well on its own. I also had to add the orange duct tape to the edges of the panel because they are seriously sharp. The next step is working on a rope system that will lower/raise the legs while the user sits atop.

-Karl
 

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From another Pittsburgh engineer (I live in Baltimore now), I say, nice work.

So did you get a custom cut mattress for this? What do you do with the part of the mattress that is unsupported when you fold the front part down for driving? Does it just fold down also? Do you roll it back?

Also, I like your deflection values, but for stress calcs did you account for...ahem...fatigue strength? Know what I mean....winkwink? :razz:
 

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Hello Karl,
Great build, description, and drawing. Did you do a drawing of your brackets? If you did, would you please post them?

Thanks
 

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Discussion Starter #14
...So did you get a custom cut mattress for this? What do you do with the part of the mattress that is unsupported when you fold the front part down for driving? Does it just fold down also? Do you roll it back?

Also, I like your deflection values, but for stress calcs did you account for...ahem...fatigue strength? Know what I mean....winkwink? :razz:
The mattress is a 'full' size 4" thick foam one from Ikea. The only cuts made were to allow access to the rear bins by the tailgate (two 4"x16" off the back corners), and to round it slightly to match the tailgate contour. We added a 1.5" thick cooling memory foam pad with matching cuts for comfort. And check out the full gallery linked in my original posts and a pic will show how the mattress folds down at the front. It's not the prettiest, but it works.

As for fatigue, I have outlined a rigorous test program!

-Karl
 

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Amazing! It looks so clean. Thanks for posting such detailed plans. I want this so bad! The only thing is, I don't know how I would go about fabbing the brackets. No welder... :twisted:
How did you do the lock in feet?
 

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Discussion Starter #17
...How did you do the lock in feet?
A 12mm deep socket resting on the rear outer bolt of the front seat mounting bracket (plastic had to be rounded out a bit). Then I put a 3/8" square headed bolt through a spacer into the bottom of the leg. The square acts just like a ratchet head and fits into the top of the socket. Load path is bomb proof, and when the legs are up, you just see a socket flush with the floor.

Leg up

Leg Down
 

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That looks great. How long does it take to remove the rear seat brackets and install your custom brackets. Did you try to make use of the stock brackets?
 
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