I went to the theater and watched the 50th anniversary Dr. Who episode with three good friends and a hoard of other Whovians. I saw my favorite Doctor (Tom Baker) on the big screen and was having a good time when I saw this shot —– what’s that in the background?
That looks like something you would see in the TARDIS, round things! But the Doctor never read the manual on using the TARDIS; he never knew what the round things did. After a careful bit of research I’ve discovered that they are environmental sensors. No Timelord could be expected to stick his head out of the TARDIS and see if the air is safe to breathe!
So begins the new project Hexadome Atmospheric Cabochon Detector or HACD. First a quick mock up with some acrylic hexagons and a small 2 inch ball that had it’s left half removed.
Size and proportions are about what I’m looking for. But I don’t have enough of those half spheres to make the entire project. No worries, I’ll learn how to vacuform plastic and make my own. That sounded a lot easier than it ended up being.
So I built a box, grabbed a shop vac, and tossed some plastic in a non-food oven and BAM! made a lot of mistakes. While I have read up on the process there were a lot of nuances to the process, and I made many mistakes. The original ball got destroyed along the way (left on top of the oven) so I purchased a 2 inch acrylic half ball, or a cabochon.
I consulted with two friends at Familab and received much advice on how to pull this off with good results.
This looked good, the dome was difficult to cut out, but a small light test and …wow. The dome glowed. That was powered by a single neopixel.
Now I only had to make 38 more cabohons and I was done, but I only had two pieces of styrene left. So when I can’t be productive I experiment and wow… I was not expecting these results
This changed everything, before this was going to be a bunch of cabochans on multiple layers of acrylic, with no standoffs. But this experiment had a better look and feel than the original. This changed everything. I went back and looked at the picture from the show. If I could do this with standoffs, I could also have some backlighting. A quick design and a bit of time on a laser cutter.
With the standoff I also created a ring, this piece had two functions. First, it would keep the light from bleeding through the entire face. It would now shine only inside the dome. The ring also supports the sytrene in between the dome and the raised hexagon pattern.
A rubber band and some tape and it’s assembled.
Added a single neopixel under the dome and 2 underneath the backing plate. I like this look: foreground and background colors.
Back to the lab, and pump out 42 of the hexadomes? Hexacabohons? Then to lasercut the backplate, ring, and standoff (this cut took 1.5 hours). After a quick gluing session, I hauled them all outside to paint.
The standoffs were painted with the same flat white that I plan to paint the backgroup, this is to diffuse the light in the backgroup. The bottom of the backplate is painted with white gloss paint to reflect ambient light back to the backgroup, to make it brighter.
Now time to get busy and assemble them all. The top of the backplate is not painted for two reasons, it’s not see and doesn’t need it… and I was running out of paint.
Ok, next question will the background light actually light up as expected and shine between all the hexadomes? Rather than cut out the entire board, I’ll make a small prototype and re-use the assembled pieces.
…but I ran out of neopixels so I’ll save that for the next blog.