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Custom fit trunk cooler

Discussion in 'Model 3: Interior & Exterior' started by Butane, Aug 20, 2018.

  1. Butane

    Butane Member

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    Like others, I've tried to find a cooler that fits in the lower trunk as it's just such a convenient location for one. Since none of the ones I have fit and I haven't seen anything that makes optimal use of the volume, I decided the only reasonable choice was to build my own. :)

    This thread will be somewhat of a build thread. I'm learning lots of new things here, and with two little ones at home, I've learned to accept a more... leisurely pace with projects.

    In my head, this started out as just cutting and gluing some XPS foam boards together in the rough shape of the trunk. Test fitting wasn't all that great. I didn't like the boxiness of it and it just didn't look very good. Then I got some inspiration from folks who build custom fit subwoover enclosures out of fiberglass. I could do something similar. Nevermind my complete lack of fiberglass layup experience.

    OK, so several youtube videos and blogs later, I know I can put down a couple layers of tape in the trunk liner, some PVA release agent, and go to town. This will be the outer surface of the cooler.

    Since I'm going this far, might as well give the inner surface of the cooler the same shape as the outer surface. A true offset. Then it can be filled with expanding polyurethane foam for insulation.

    So what is the trunk shape? I decided to punt on trying to measure it manually and go with with photogrammetry to get the shape. Another new skill to learn!

    Here's my trunk with tape for contrast and an LED shop light above the vent:
    2018-08-14 19.48.12.jpg

    Here's the model in the rather excellent free version of 3DF Zephyr. Being completely new to this process, it was dead simple. The wizard produced great results on the first try, and it took very little tweaking to get something usable. I used my Canon 60D SLR with the 10-18mm EF-S and 28mm EF lens to take the photos. The software really wants you to use an SLR and common lenses as it pulls information from them to stitch the photos together.
    Trunk 3D.PNG

    I imported the mesh into Fusion 360, my CAD software of choice, and got to work fitting spline patches to the mesh. I've never done anything but relatively simple parametric modeling in F360, so this was a new experience. I had a lot of issues getting the patch surfaces to merge into a solid body. I kept getting random compute errors and the process failing.
    Tesla trunk mold fitting to mesh.png

    Finished mold body
    Tesla trunk mold finished.png

    The goal is to 3D print this and use it as a form to lay up fiberglass against. It will define the inner surface of the cooler, with the handles recessed into the sides.

    Sized to allow ~1.5" of foam to be poured between the fiberglass surfaces.
    Tesla trunk mold finished 3.png

    Breaking it up for 3D printing. My printer has a 210x210x250mm build volume, so I have to slice it up for printing. Also adding holes for dowels to align the pieces.
    Tesla trunk mold alignment pins.png
    Tesla trunk mold alignment pins 2.png

    First 1 of the 16 segments was finished just as I was leaving for work today, and I should have another done late tonight. Looks like it's going to be around 150 hours of printing and nearly 3kg of filament, even with a 5% infill. Pics to come when I get home!

    What do you guys think? Am I in for any major headaches as I move forward? It's not like I'm attempting to repair flood salvage Model S or anything...
     
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  2. Lasairfion

    Lasairfion Member

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    This looks like a great little project. Photogrammetry is something I hadn't heard of before but seems to be a really easy way to get a 3D model like that.

    Is there a reason for using the 3D print as a form and fibreglassing the sides rather than just 3D printing the whole thing in plastic and slotting it in?

    I assume once done that you'll add a lid with a cooling motor and 12V DC power; or will you just go for a thick insulated top?
     
  3. Butane

    Butane Member

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    Uh, I guess I kind of got fixated on using fiberglass. If I give it some thought, I see a couple issues with just printing. First the actual print would be huge, and take quite awhile. I'd have to print each section hollow and fill them individually with expanding foam and worry about the pressure on the thin plastic surface.

    I'd have surface finish quality issues too with the layers, but I'm mitigating that on the mold so that's a wash.

    Another is that the photogrammetry isn't perfect. There's a decent amount of noise in the image. Doing it again, I'd color the whole trunk in a light color and then use contrasting tape. The gaps in the tape showed up as height variances in the mesh model.

    If I can find a convenient source of 12V power in the back, I'll definitely look into a peltier cooler or similar. Otherwise just a thick top.
     
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  4. Butane

    Butane Member

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    Got a couple pieces printed now!
    IMG_20180820_183501.jpg
    IMG_20180820_222629.jpg

    I printed the piece with the handle the way because of printer dimensions. Rotating it so I don't need supports on the forming surface would require me to slice the mold on the long axis a 2nd time, creating another 6 pieces to print and more seams to smooth out later. The surface just has to be reasonably OK as I'll be sanding and smoothing with bondo anyway. Still, the flange has large texture patterns where the large gaps in support material created issues. Time to learn how to do variable infill densities in slic3r.

    Another issue that should have been obvious to me is that the handles are going to prevent me from cleanly pulling the fiberglass off the mold when cured. I guess I thought it would be flexible enough, but a friend at work disabused me of that thought. Especially since I may want to use the mold to ensure the fiberglass doesn't distort under the pressure of the foam as it exands. I came up with a plan to separate the handles, print them separately, and then secure them with bolts through the main body of mold. Then I can remove the bolts and pull out the mold from the fiberglass. If I put enough release agent on the seam, hopefully I can keep the resin from seeping in between.

    This turned out to be a pain in the ass in Fusion. Any F360 experts care to weigh in? The handles are formed on the body by lofting a sketch perpendicular to the face of the mold. I then combine the bodies together, and fillet the edges. To remove them, I tried creating a patch using the edges of the fillets against the main body and using that patch to slice the bodies apart. This gives me a compute failed error saying the cutting tool does not intersect the body to be cut. Variout efforts of extending the patch either roughly in plane or perpendicular failed the same way. However, if I go back in the timeline to before the fillets, this process works just fine. The problem then is I don't have a combined body to form the concave fillets against. Using a plane works fine, but I can't localize the cutting action to just the region of the handle; it cuts off the flange as well.

    Last issue is I should have bought a bigger nozzle. The default .4mm isn't really happy above 250um layer height and makes things slow.
     
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  5. PoitNarf

    PoitNarf The Clown Prince of Crime

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    Once you have a working prototype that fits well I’m sure you could find a manufacturer that could mass produce a bunch of these. I would definitely buy one if the price was right.
     
  6. Lake

    Lake Member

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    I would buy this
     
  7. PTinetti

    PTinetti Member

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    That is awesome
     
  8. Lasairfion

    Lasairfion Member

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    Just as a note, if you want to easily smooth your 3D prints, I did see a video on using an acetone vapour bath:

     
  9. Nocturnal

    Nocturnal Member

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    Nice idea!
     
  10. Butane

    Butane Member

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    Thanks, that's a good idea. Unfortunately that only works with abs, which I didn't have enough experience with to be sure I could keep it from warping. Either way I'll still have seams between each of the pieces, so I'll need to fill and sand those anyway.

    In the meantime, I'm getting serious surface quality issues on the flat parts and wall collaping due to low infill so I'm experimenting a bit. Slic3r has a cool new infill called gyroid that was my new default due to its equal strength in all directions but it turns out it delaminates easily at really low infill percentage (5%). I'm also getting a bigger nozzle to speed up printing and provide more wall strength. Turns out 3d printing large objects is a bit different than my usual trinkets and toys.
     
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  11. stonelance

    stonelance Member

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    This looks neat. I've never done anything like this before, but couldn't you just line the cavity in the trunk and fill it with some sort of expanding foam and then use that as the mold\template instead?
     
  12. Butane

    Butane Member

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    Possibly. The problem is how to control the depth of the foam. I brainstormed this with a composites engineer (who thinks I'm nuts) at work and he suggested adhering a bunch of small wooden dowels as depth gauges to fiberglass and then cutting/sanding the foam back until I find them. This could work, but would be labor intensive and tedious. However, the crucial problem with that approach is it doesn't give me an excuse to do the photogrammetry, learn how to work with surface patches in Fusion 360, 3D print obscenely large objects, or make fiberglass molds. Along with with failing at each step repeatedly. :D
     
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  13. stonelance

    stonelance Member

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    Yeah, I get it. I love learning opportunity projects as well. Unless they were projects I wasn't planning on being learning opportunities :)
     
  14. getto

    getto New Member

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    me too :cool:
     
  15. Jimmy 1

    Jimmy 1 Member

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    Curious, If this could be mass produced, what would be the cost?
     

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