This year I decided to be Tony Stark for Halloween. Not Iron Man, just Robert Downey Jr with an arc reactor in my chest.
This is about how I made that arc reactor. I started with a ring of 24 NeoPixels from Adafruit, because color and animation are fun.
Modeling
I figured I could 3D-print the form of a reactor to go around it. I used OpenSCAD for modeling a cylindrical ring with a circular channel cut into the back that exactly fits the LED ring, and ten notches on the sides.
Brackets to hold the wiring fit onto the notches:
I realized the arc reactor glows in the middle too, not just around the edge, so I got a little 7-element NeoPixel "jewel" (also from Adafruit) and made a cylinder to hold it. Like the outer ring, it has a channel on the back that's cut to exactly fit the jewel (the edge of the printed circuit board). Because the channel is exactly the size of the PCB, the PCB stays in its channel with just friction.
By the way, to print a part with exact sizing like that, you should totally use a digital caliper. They're so cheap... I use this one [Amazon] that's available for less than $20.
The arc reactor has some decoration on the front, so I made that too.
Here's what one of the little wiring brackets looks like. (I printed ten of these.)
Finally, to hold everything together I made a little contraption to go on back. There are three clips to hold the center cylinder, five clips to hold the ring, and five "pads" that rest on the back of the ring. The pads give it an admittedly funky shape, I'll explain why later.
I printed the pieces that hold the LEDs (the ring and the cylinder) using clear PLA, so the light will shine through. The other assorted bracket pieces are all in black PLA. I snap the LED ring in the channel on the back of the ring, snap the ten wiring brackets to the front of the ring, and then wrap some 24-gauge red copper wire [Amazon] around the brackets. I didn't even solder them, I just bent the ends underneath.
Here's the center cylinder (upside down) with its 7-LED jewel and black grille, pictured along with the 5-pointed back frame.
The cylinder and grille, viewed from the front. The grille's little arms are exactly the size of cylinder, making a friction fit. But to make sure it doesn't fall apart, I put a drop of acrylic adhesive [Amazon] on each arm to make sure.
It looks like Tony's arc reactor is underneath his t-shirt, but I was too proud of my work to hide it like that, so instead I decided to wear it on top of a t-shirt. To hold it on, I epoxied snaps onto the reactor and sewed the matching snap-backs onto the fabric. That's why the pads on the back bracket are circular — to give me something to glue the 10mm snaps onto. The snaps serve a double function of conducting the power and signal from a Flora controller, so I soldered wires on to them before gluing them on.
Using alligator clips to connect the snaps with the Flora (and its battery and control switch), I can test that everything's working so far. The data signal is daisy-chained from the central NeoPixel jewel to the outer NeoPixel ring, effectively making a chain of 31 LEDs (7 in the center, 24 on the outside).
On the t-shirt, I couldn't just solder wires on to the snap-backs, because they're on the front of the t-shirt and the Flora had to go on the back. So instead, after sewing the snap-backs on using regular thread and two of the four holes, I soldered each of the wires from the Flora back onto itself to make a tiny loop. Then I used some conductive thread to sew through one of the remaining snap-back holes, through the t-shirt, through the wire-loop, and back through the t-shirt. I went around like that about five times before tying it off with a square knot, and then securing the square knot with a drop of clear nail polish (because otherwise, the knot in the conductive thread would come loose). Here's what the connection on the back looks like:
On the front, notice that two of the holes have regular thread and a third has conductive thread:
Mostly Tony's arc reactor just glows a solid blue, but because I have NeoPixels and a controller I couldn't resist playing with them a bit. I made them throb and swirl a bit with some white highlights, and they have a little red warm-up animation when they're turned on or off.
Here's my OpenSCAD model arc reactor.scad and the Arduino sketch react.ino if you want to play with them yourself. This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. Happy hacking!
Questions or comments? Email me at .
2019 Oct 31