Layering the foam
So, now that I had the EVA foam, it was time to assemble the 'base' of the pack. Basically, the bulk of the shape of the backpack portion.
Looking at how much foam came in the pack, and how it would all work layered, I realized I could do not only the base but many of the blockier bits protruding from the pack in EVA foam as well.
So I went ahead and used some poster board (available at pretty much any department store) and drew some shapes in with a Sharpie. For the round part at the base, I used the lid...er...cyclotron as a reference, making the shape about half an inch longer in radius. I figured three layers for the rounded bit, one layer for the absolute base, one layer for the thinner piece for the 'step' and about 4 layers per blocky bit. In the end, it would look something like this:
To glue all these together, I used high temperature, extra long sticks of good ol' hot glue stick and a glue gun. However, a small challenge presented itself. The length of the pack would be longer than the length of any of the EVA foam panels.
Fortunately, EVA foam panels are intended to be tiled together in a puzzle like fashion. I used a bit of poster board to stabilize the base layer and staggered the seams for both it and the 'thinner' layer (used for the stepping effect) so that they'd kind of reinforce each other, rather than have both interlocking seams be on top of each other and potentially act as a point of failure later on.
The end result of this glueing, however, is that the sides look kind of messy and have a strata I just knew would cause problems with painting and smoothing later on. So, what I did was cut that poster board into lengths about as wide as the sides are tall, drizzle some more hot glue and stick the paper to the sides.
I used tiny amounts of wall hole filler (the stuff you use to get your security deposit back if your toothpaste won't work....don't use toothpaste on this) to bridge any tiny gaps introduced. Be careful with this stuff though. It is extremely brittle and won't flex. Use it with that in mind. You can try to use some hot glue instead, but I find it's really hard to use that stuff in any way that would be smooth enough and, unlike the hole filler, it can't really be sanded down to shape.
So when all the foam was glue and set, I used a heat gun (available for cheap most places, you can get them for about $16 at Canadian Tire on a good day) on the surface of the foam. Closed cell foam means the cells are closed on the surface, as opposed to leaving holes and gaps, but not everything is perfectly sealed up and this can lead to it absorbing the primer or paint later on, and we don't want that. Heat treating the surface seals up lots of those tiny holes nicely, and also helps to set the shape (those doing cosplay armour know this trick well).
So with the base foam all glued and set, I remembered something important: where the electronics would fit. I cut a square hole where the cyclotron...er...lid, would be occluding it anyways. This hole would fit the Arduino, additional electronics, an amplifier, batteries and speaker.
I then started adding bits of things to make it look closer and closer to my reference pics. This was an additive process, wherein I would look through bins of junk, my trash, and a dollar store for anything that would have the same approximate shape as I wanted, and would get nicely covered up by primer and paint. It was all fastened via hot glue, with some small gaps filled via that hole filler compound.
This is very much a rough process. No detailed instructions here. I just, basically, added more and more crap to it until it filled out well.
I sadly have no surviving pictures of it all painted before adding everything else on. But just imagine all of the above in a uniform black colour.
To paint, what I did was use a paintbrush and some white 'school' glue (you can get jugs of it for under $10 at Canadian Tire) and coated the foam pieces multiple times. This is to 'seal' the foam and prevent it from being damaged or eaten into by the paint or primer. While EVA foam won't dissolve like styrofoam, it can still get damaged a tad and leads to some nasty artefacts on the final paint job. Also, it usually means additional coats.
After I got the thing fairly well sealed (the white glue takes a couple hours to dry, becoming rather invisible), I used a 'filler' primer coat of spray paint. You get this stuff in auto parts/auto detailing stores. I got mine at Canadian Tire (again). It's not the cheapest primer, by far, but helps smooth out any roughness. After that, I sanded where needed and just spray painted everything a nice flat black, except for the wooden dowel and some of the parts which, on the reference pic, were supposed to be metallic looking. For those, I masked them with masking tape when spraying the black then masked their surroundings with masking tape and paper before coating those pieces with stainless steel coloured metallic spray paint.
And that's it for the base for now! Stay tuned for part 4, where we'll tackle the cyclotron and wand!
"Inside every sane person there’s a madman struggling to get out."
Réal is a jackass of all trades, master of none, with interests in politics, human interface design, animation, video games, VR, technology, and making random stuff. Has a skill to have both too much time on his hands and nowhere near enough to get stuff done.