Vortex Spins Two LED Panels Into a Fully Walkable Three Dimensional Volumetric Display

Maker Ancient built Vortex as a swept volumetric display that hangs a genuine three-dimensional image in midair. Two flat LED panels sit back to back inside a clear plastic globe roughly three hundred millimeters across. Both panels turn together around a vertical axis at high speed while a Raspberry Pi 4 rides along with them and updates every pixel in time with the rotation. Persistence of vision turns the moving lights into a solid looking object that stays fixed in place no matter which way you circle the globe.

Each panel measures 128 by 64 pixels and uses the HUB75 interface, which is very standard for these kind of panels. The software maintains a 3D buffer of voxels in shared memory, and a Pi driver is continually scanning the appropriate slice of that buffer and uploading it to the panels as soon as it detects that the assembly is at the correct angle, which is triggered by a photointerrupter on the spin shaft. Then, half a turn later, the signal flips and the opposite side of the volume pops in, unless the timing starts to drift, in which case everything starts to shear or walk and the whole thing crashes down, so the code and motor speed are locked in incredibly tight.

Getting the mechanical balance right took a few tries since carbon rods hold the panels to a printed core that houses the Pi and its interface board, but more crucially, it houses the alternator slip ring, which allows power and timing signals to travel through the rotating shaft. There are bearings at the top and bottom to keep everything plumb, and a fairly conventional motor drives it all with a toothed belt. They used an old lighting fixture shade and simply cut the bottom off to create the clear cover, using a rotary tool fastened to a one-off fixture to ensure the edge remained clean and circular. Once you’ve got the weight perfect, it’s just a matter of letting it settle in and become quiet and steady, at which point it simply lights up the entire space.

Data flows in through the same shared buffer, as they have a sim called virtex that allows you to test out your models and games on a regular screen before you even start building anything, and on the hardware, the same buffer drives some very simple but actually quite fun objects, such as a low poly car, a glowing koi, Slimer from Ghostbusters, and even the entire run of DOOM. The key is to strike a balance between resolution and refresh rate, as you need to paint a few thousand frames every second to keep the volume seeming continuous, and the panels must be capable of keeping up. Higher resolution panels would necessitate a far larger number of slices around the circle, pushing the rate well beyond what amateur hardware can handle.

Every item, every line of code, is on GitHub, so anyone can print the frame, get some matching panels and a slip ring, and just install the program onto a Pi 4, as everything is totally open and accessible. On top of that, Vortex is just one of several machines from the same manufacturer, each of which competes with the others in different ways, such as brightness, vertical density, and viewing angle, resulting in a compact little device that can output a real volume that you can walk around, and it’s all made from existing parts and software.
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