The solar analemma is the shape described by the sun when photographed over the course of a year at the exact same time of day and same location.* Because the Earth's axis is tilted and its orbit is elliptical rather than circular, it generates an asymmetrical figure of eight. And a beautiful one! So I decided to make an LED chandelier with 365 LEDs, which mimicked the solar analemma and therefore acted as both a stylistic astronomical calendar and a source of illumination for our dining room. I decided to stretch the analemma in such a way that it could be cut out of a 4' × 8' piece of plywood and the LEDs could be placed accurately. This last requirement was really important to me... and made the project vastly more challenging, because every. single. last. LED. needed to be uniquely located and was uniquely spaced.
* this is a famously hard photographic challenge - the first example was recorded by Dennis di Cicco in 1978-9. Check out some of the others. My favorite has to be Tunc Tezel's "Tutulemma": an analemma photograph that includes a total solar eclipse!
Step 1: Design
Earth's orbit took care of all the pesky details of creating the beautiful shape, and Larry McNish of the Calgary Centre of the Royal Astronomical Society of Canada did all the hard work of creating the spreadsheet that computes the layout. I used his spreadsheet to calculate the solar analemma for the exact latitude and longitude of my house for the calendar year 2016, did some manipulation to convert it into the right aspect ratio to fit it comfortably on to a 4' × 8' sheet of plywood, and imported it into Fusion360 using Add-Ins > Scripts > ImportSplineCSV. That created all the points I needed. I created offset lines 50 mm out from this line on both sides, and extruded the resulting shape 18 mm (I planned to cut it out of 3/4" plywood). I then bored 364 holes (yes, 364; two of the holes at the "X" of the figure 8 almost overlapped, so I averaged their position and just made one hole there) 8 mm in diameter all the way through the material. Another 364 holes 14 mm in diameter were bored in the same position but only 15 mm deep.
Step 2: Toolpathing
I used Julie Kumar's tutorial on how to toolpath for the Shopbot using Fusion360, and wrote the appropriate files (many thanks to Julie and Mei for help with this step). Toolpathing is interesting but I feel like we're still at a pretty primitive point - it's very far from plug'n'play and CNC-ing anything takes a lot of setup. Having said that: I'm a complete newcomer to these tools and the fact that I can do it at all probably speaks to how far we've come! The Shopbot at Pier 9 had some issues with spindle speed when I was using it (it was stuck on 12,000 rpm) so all operations were performed with end mills rather than with drill bits.
The first light painting above was taken by Steve Mann, as part of his Phenomenological Augmented Reality PHOTOolpath series. Thanks Steve! The lights are tracing out the contouring toolpath used to define the overall shape of the piece. The second was taken by Reid Godshaw of Harmonic Light, who happened to be visiting the same day, much to my good fortune. Thanks Reid!
Step 3: Cut It Out
The shape was machined out of 3/4" plywood using a 1/4" waste sheet of plywood underneath to minimize breakout. It was all fascinating to watch; as someone used to cutting straight lines by hand (or machine), to watch a robot flawlessly cut curves, drill holes and make tabs was pretty hypnotic. The time lapse video below shows a small portion of the overall process.
The shape was freed from the sheet using a sharp chisel, and the tabs cleaned up using a router with an edge-trimming bit. I made the rounded corners at the "X" of the analemma sharp using a chisel.
Step 4: Edge Banding and Finishing
To cover the exposed plywood edge, hide the electronics, and to add some stiffness to the fixture, I glued on some 2" wide maple veneer edge banding on all vertical surfaces. It comes preglued and can be ironed on. I made sure to overhang it slightly so it could be trimmed flush with an edge-trimming router bit.
The resulting piece is fragile (like most chandeliers!), because of the large overhang of the edge-banding. I hot-glued lots of right-angled triangular blocks around the outside that I cut out on the laser cutter, to help reinforce it and to eliminate any waviness.
I sanded and finished it with four coats of polyurethane, sanding lightly between each coat.
Step 5: Add LEDs
You will need 364 LEDs, arranged on a string rather than a strip. I bought 8 of these ones (note: these keep going unavailable on Amazon, so try searching for rgb addressable led string if the previous link doesn't work. And/or let me know in the comments!). The spacing varies all the way around - no two LEDs are exactly the same distance apart - and the LEDs fit nicely EXCEPT where the density peaks in the tight radius of the smaller loop. You will have to take some cutters and trim the rubber material on the outside of the LEDs to make them fit. I found it easier in most cases to remove all of the casing - the harder inner core is only a little wider than the LED itself.
Initially, I used a sander to reduce the size of the LED casing, but then discovered it could be just cut and peeled off. D'oh!
Step 6: Power and Hang
Each LED is 0.3 W so 0.3 × 364 = 109.2 W total. About the same as a bright incandescent bulb, but the added efficiency of LEDs mean that it is a lot brighter in total. The bulbs draw about 50 mA with RGB all at max brightness, so that is 0.05 × 364 = 18 A (!!). So I bought a 5 V, 20 A power supply to make sure I had plenty of juice. Connecting them all up is simple: chain them together through the provided connectors, and plug into the power supply as shown. The power supply also needs a grounded cord.
I distributed the power to all of the strings separately. The same data line connected them all, of course. I just threaded the extra +5 V and GND lines through the loops, and connected them all together at the starting point. I used a thicker gauge wire to join these to the power supply.
I screwed some 1/4"-20 threaded inserts into the plywood and added eye bolts at 6 spots around the periphery and attached to them a harness made of heavy-duty steel wire. The fitting was then strung up into the ceiling of the Pier 9 woodshop and powered on. Like most chandeliers, it is fragile, so the moving and hanging was done with great caution (thanks Josh, Trent, Jeff, Mei and Scott!).
Step 7: Effects
The LEDs deserve a cool light-up sequence, and I wanted it to look like the sun is rising. So the day you're on lights up (i.e. the analemma is also a kind of stylized calendar) and the rest of the analemma then lights up like a sunrise. Switching it off reverses this process. Michael Weller (pictured above, coding right under the analemma set up in the Pier 9 woodshop, the night before the show opened) wrote these scripts, and it was amazing to see him convert my vague ideas into spectacular reality. I'm immensely grateful for his skills. Dennis Hore was also a fantastic source of ideas.
While the analemma will end up in my dining room, it is also the biggest of the pieces I made for the final showcase event of my four-month residency at Autodesk's Pier 9 workshop. As such, I wanted people to be able to interact with it in a fun way. So I made a big green button for them to push, that allowed visitors to cycle between different illumination sequences (many thanks to Scott Kildall for help with the hardware and sequencing software).
The sequence was:
1. static display of astronomical data: solstices in blue, equinoxes in green, first day of every month in red, current day in white, rest of the year in dim yellow.
2. sunrise: current day lights up white, rest of analemma illuminates from black to dim purple to red to orange to yellow to yellow-white.
3. sunset: reverse of sunrise.
4. PARTY! A crazy demo reel.
5. All LEDs off.
I made the enclosure from laser cut 1/4" black acrylic, and designed it using the super-useful Makercase website. Everything about it is deliberately oversized - check out that MASSIVE GREEN button! All it needed to hold was the Arduino Uno and a small circuit to detect switch presses. I didn't glue the lid so everything would be easy to access. The button was double-sided taped to the table saw in a prominent position for foot traffic.