Thread by @rpearl

okay now that it seems like it's probably going to work out, i'm gonna talk about an art piece me and a few others have been working on! The order of some of this might be off, but it captures the iterative process of stating a problem and simplifying it until it's solvable.

First, some ✨geometry✨(please forgive me, because all my graphics are just going to be CAD screenshots)

If you take any point on a torus, there are four circles that intersect at that point. There's one circle of the minor diameter (red), one around the axis of revolution (green), and two others, which are interesting

The others are called the villarceau circles. You can construct them by taking a plane which is tangent to the minor diameter circles on opposite sides of the origin.

In this plane the villarceau circles are just offset from the center by exactly the minor radius, and their diameter is exactly the major diameter

There's a few different art things that play with this effect. A common one is this neat sliceform papercraft torus, I believe originally discussed in this paper heldermann-verlag.de/jgg/jgg15/j15h…, but they're all over the internet now

We found that if you take one of the villarceau circles and rotate it about the center plane, you get this cool looking sculpture, and we want to make it real, and put addressable LED strips in the rings.

Then you can do really pretty things like this (...I think this is the first time I've shown off Chlorophyll with actually legible screenshots, which is a project @cwillcwont and I have been hacking on for a while now)

Okay cool I've done a bunch of math and suddenly a pretty thing popped out of it. So for like two months we've been trying to figure out how to make it an actual physical thing.

We spend a long while trying to figure out good ways to do all this... At first we thought we could maybe carefully hang the hoops in place, or maybe we could make clear minor diameter discs that acted as a sort of skeleton. Lots of CAD dead ends and half baked designs.

Eventually we hit upon the idea of putting a ring at the center of the piece to act as a frame, but we still couldn't quite figure out how to hold the rings at the right angle.

The other person thinking about this project came up with the idea of using cross braces that sweep behind the frame ring. So we'd get something which looks like this, as seen from the plane of the hoop.

Now we have some actually tractable problems to solve! We need to fabricate the braces to hold the hoops, we need to affix the braces to the frame, and we need to get power and data in to the LED strips.

One is pretty easy: we have a convenient tangent point between the frame and the hoop, where we can inject power and data.

For affixing the braces to the frame we have a few options that are all pretty viable. We could bolt or rivet it on, clamp it on, or maybe weld it.

We decided it'd be nice to not have any extra parts to lose, so we're going to weld it. Hopefully on Wednesday! We hired a (now retired) professional for it, so I'm confident in the quality of the joins. The tricky part will be holding the braces at the proper angle for welding.

A common theme of this project is "the tricky part is holding the workpiece at the proper angle". So let's talk about fabricating the braces! That just happened this past weekend.

The ideal end of the brace looks something like this: a round hole cut into the brace, but in our case since it's holding on to a hoop, the path of the cut would not be a straight line, and if we picked a straight line cut there'd be gaps.

There's some decent ways to hold a tube at an angle to cut a straight path. The tools that do this sort of thing are called tube notchers, and they vary greatly in price (and mechanism of action). Most don't go to the angle we need.

Well, if you just carefully cut two straight lines into the end of the brace, from the point where the center of the brace meets the cross-section of the hoop, you get something which is really close to right. This is a much more solvable problem with the tools we had

So the problem's been reduced to "how do we accurately cut two holes at really silly angles in a repeatable way". We already needed to drill holes in the braces, so we used those as references on fixtures plates that @tiesandbees machined to good precision.

So far, it's worked out! Next up we're going to go weld everything!

Hopefully I'll update this thread with pretty pictures once we have a sculpture and not just some silly looking pieces of metal but I hope it's been interesting so far :P

I'm gonna end with a video of the Chlorophyll model for now

Today, we bent square tube into a ring--well, two halves; they'll be welded--to use as the frame (we'll be sanding it a bit finer and eventually media blasting it)

welding time ⚡

preparing the fixtures for welding the braces. the standoffs will be welded to the table so that we can be sure everything is at the same angle

hooray

it'll never cease to be weird seeing a CAD model made real through a lot of human effort. Like... geometry made physical? wtf

a timelapse of the welding

today, testing things

yesterday we started the final build. we had a few difficult wiring things to deal with so it took much longer than expected to build the hoops (about 30min each; we were expecting 10-15)

we got 10 of 12 hoops wired, and 6 attached to the frame. we still need to build the data and power wire harness, attach the rest of the hoops, and replace the hoop suspension lines with measured fishing line

all the hoops are in place; first light soon

whee