James Brown
Scouring Aliexpress for LED panels for the new display, and it seems the higher resolution ones tend to be flexible. I spent a while investigating developable surfaces* to see how I could take advantage of this, but couldn't come up with a layout that offers any advantages over a flat square centred on the axis. Seems disappointingly pedestrian.
(*Twisting a sheet of paper in my hands)
I'm arranging it as two rectangular panels arranged with their bottom edges touching on the axis, which lets me update columns at the same radius simultaneously. The outer columns need to be updated more frequently than the inner columns, and one of the nice things about these LED panels is that you choose your own update strategy - you're not stuck with scanning a whole frame each time.
If the lines were completely independent, you could evenly scan a sector with half the number of line updates compared to updating the whole frame. As it is, each line has to be updated in parallel with one that's half a panel further down, so it ends up taking 3/4 of the line updates instead (because some updates have to update the outer line while scanning out black to the inner line).
The thing about voxels is that even when they’re not working, they look cool.
New display, new panels. I'm driving these ones using DPI on a Raspberry Pi, which is a handy way of wiggling 24 GPIO lines with precise timing and no CPU involvement.
The results I was getting with the new display were so much better than the original that I went back for another pass at it. Turns out there were a couple of stupid bugs limiting the refresh rate. The colour depth is now vastly improved.
This is still using software bit banging. I'm going to switch it to using DPI, but the current interface board wasn't designed with that in mind, and the GPIO mapping doesn't put all 3 displays on valid DPI pins.
If you squizz your eyes at this, you can see the 3D.
If you have difficulty converging it, it helps to make the image really small and gradually enlarge it once your eyes have locked on.
I had the opportunity to give some live demos of this thing recently. It went over well, but the noise was a real killer.
I've reworked it to use a belt drive instead of the horrible 3D printed gear - before, it screamed; now it whirrs.
I've reworked it to use a belt drive instead of the horrible 3D printed gear - before, it screamed; now it whirrs.
I massively overestimated how much lead would be needed to counterbalance the small amount of slightly off-axis electronics.
It would be convenient to address the voxel data as a stack of horizontal slices, because that's how it's exported from lots of existing tools. I have to rotate it 90 degrees though, because scanning out is faster if each column's data can be addressed as consecutive bytes.
It's a small change, but there's a 6.5x difference in speed between the two orientations, which directly translates into voxel density in the final output.
It's a small change, but there's a 6.5x difference in speed between the two orientations, which directly translates into voxel density in the final output.
Trademark flickery mess
I really need to get a hobby where missing my framerate target doesn't make me physically nauseous.
Help me Obi-Wan Clownobi
I've implemented parts of a content pipeline for rendering a scene on the PC and streaming it to this display, but writing video streaming code is so much less fun than playing with voxels that it may take a while to finish.
Here, I've stored the animation uncompressed on the display itself, and am updating it as fast as the Pi's SD card can handle. (Not very fast.)
Here, I've stored the animation uncompressed on the display itself, and am updating it as fast as the Pi's SD card can handle. (Not very fast.)
My target for this display is 600 rpm - lower than that and it's too flickery; higher than that and I can't refresh fast enough to get 400 voxels around the circumference without dropping to 1 bpc. I'm nudging 400 rpm here, and it's still pretty unfilmable and absolutely terrifying to be close to. I have to decide whether the overall approach is worthwhile enough to start spending money on aluminium and polycarbonate.
Slightly higher rpm, slightly longer shutter.
The other problem I have is that to sell the 3D effect I need to move the camera around a lot, so I'm going to have to put some effort into building a studio backdrop.
Incidentally, those models are from Cheello's voxel Doom: https://www.moddb.com/mods/doom-voxel-project/addons/voxel-doom - It's a lovely mod, and makes Doom feel more like my memories of playing it than the real thing does.
Latest flickery mess
I had a panel left over, and I thought I should have another stab at an oscillating display. I wanted to give it an undulating motion and came up with what seemed like a nice linkage, but the end result looks like it was designed by Trevithick.
It's a nice fluid motion on the panel, but overall it doesn't bring me joy.
There must be at least 6D here.
I rewired the back of the panel to tidy up all the loose flappy cables. It now manages 600 rpm, which is not too flickery.
In the continuing quest for higher rpm, I've moved the controller down below the screen and across the axis of rotation. It's a lot harder to get at if I need to rewire anything, but it does improve the balance.
It feels as though I'm endlessly rebuilding it, for diminishing improvements. But in the most recent rebuild I finally solved a mystery that has been bugging me. When the display had been running for a while, it would quite abruptly lose balance and start vibrating. After the last occurrence, it was never quite the same. On stripping it down I found this.
That's the mount for the slip ring. A cylinder carrying a couple of copper bands fits over the pillar, and an M4 bolt goes own the middle to hold it all together. It has very clearly become bent, and without any signs of cracking. Presumably, as it spins, it heats up enough to soften the PLA, and the spring loaded brushes push it out of alignment.
I've reprinted it in ABS; going to see how well that lasts.
I continue to fail to shoot footage of it that does it justice.
This feels like a good match of style and content.
I’m now suspicious of all the PLA parts. The little pit with the Pi in it is getting very warm.
kind of feels like it needs monsters?
I do like an ample window and natural light, but it makes it hard to see the leds. Hence this pirate astronaut.
Doom running at a larger scale. Easier to make out what's going on, harder to see what's shooting at you.
https://youtu.be/bRe1OSkeiQg
https://youtu.be/bRe1OSkeiQg
Voxel Doom
This display works by spinning a matrix display rapidly about a vertical axis, lighting up each LED as it passes through part of a 3D image. The way you update the displays has a big impact on the quality of the image.
In this gif, each dot represents a column of LEDs - we're looking at the device from above. Here the panel is treated like a 2D display which just happens to be moving. Each scan line is repeatedly visited in turn, sweeping out a set of slices where the image can be displayed.
In this gif, each dot represents a column of LEDs - we're looking at the device from above. Here the panel is treated like a 2D display which just happens to be moving. Each scan line is repeatedly visited in turn, sweeping out a set of slices where the image can be displayed.
If you turn the panels 90 degrees so their scan lines are now columns, you can do a bit better. The update doesn't have to be sequential - instead of stepping one column at a time, you can skip a few each time. As long as you pick a number which is coprime with the number of columns, and you wrap around once you go past the last one, you'll still visit each of them but spread out more evenly throughout the volume.
The real improvement comes when you adjust the update rate for each column to match the length of the track they have to sweep out. Instead of wrapping around when you reach the last column, you wrap around when your counter reaches the square of the number of columns, and you update the column corresponding to the integer square root of the counter. This gets rid of the bright dense region in the middle, and adds more updates out at the edges making them less sparse.
In practice it's complicated by the fact that these panels update two lines at once. Every time you update a column in the outer half, you're also updating one in the inner half. I couldn't find a simple procedural update strategy to spread these evenly, so I ended up generating a lookup table for it using simulated annealing.
First test of the new design, and already I’m happy. Quiet, high refresh rate, and doesn’t feel like it’s seconds away from embedding itself in my face.
Dynamic balancing using a tray of marbles and iPhone slowmo.
In motion https://youtu.be/na7pvihXhYs
So many complaints about the framerate on that last video, so I decided to upload one with a shorter exposure and more flicker. But I still ended up keeping it below 30 fps, so I suspect the complaints will be about both framerate and flicker. Just have to hope the algorithm doesn’t go so large on this one. https://youtu.be/gBfclb9hXCI
New dome!
There are many advantages to moving to smaller panels in the new design (momentum etc), but the price drop going to a 300mm dome from 400mm would be justification enough.
There are many advantages to moving to smaller panels in the new design (momentum etc), but the price drop going to a 300mm dome from 400mm would be justification enough.
There’s now an accelerometer in the base, synced to the rotation of the screen. I’m hoping this will help me get it balanced better. I don’t entirely understand the shape it’s producing, but the line is pointing in roughly the direction I think it should be pointing.
2D video of 3D projection of 4D object.
There’s a fair bit of planning involved in finding the true centre and height of these domes. When I come to make the cut it feels like cleaving the Cullinan diamond.
With the previous dome the cut had a somewhat hand made look to it, so I printed a thin piece of trim to slip over the edge and keep it neat. It was too big for the printer so I used TPU, printing it in a spiral and flexing it back in to the right diameter. An unexpected benefit was that it was way quieter with that isolating the dome from the base.
This time the cut went better, but I’m still going to give it a gasket for that reason.
This time the cut went better, but I’m still going to give it a gasket for that reason.
25 fps. That's an actual frame rate.
John TimaeusA while ago there was a discussion on what the difference was between jitter and judder. This is peak judder. Saving it as a training point if you don't mind.
Devil Doll, Esq.23.97, tho?
Harvey Sandstrom@ancientjames Now 98% less forbidden to touch.
@cd0 don't get fingerprints on my bubble
one of a number of patricks@ancientjames this self effacing alt text is top shelf
Adam Cafolla@ancientjames
I have no idea how this works, but it's incredibly cool.
I have no idea how this works, but it's incredibly cool.
@adaliabooks it’s like those hologram fans, but instead of spinning a 1D strip of leds to make a 2D image it’s spinning a 2D screen of leds to make a 3D image.
Chris Combs (he/him)@ancientjames omg nice jig!
Isocat now → @isocat@tiggi.es@ancientjames What do these domes do?
@Isocat they go over the spinny bit of the displays upthread. Keep fingers out & air in.
Matt Gagle@ancientjames really enjoying watching this evolve!
NeatNit@mgagle @ancientjames really enjoying watching this revolve!
Erik Tjernlund@ancientjames Knight Lore!
KB Sezfantastic!!!
Rue Mohr@ancientjames Next we will start with a 5D cube....
Justin Derrick@ancientjames And I imagine that the data stream that feeds this device is a one-dimensional array of integer numbers (representing colour, which is fed to a strip of LEDs, one number per ‘pixel’).
cocolinofan
chris actual@ancientjames this is the coolest thing ive seen in a while. good work
Zack Stern@ancientjames killer app: crystal ball display
Jeroen Baert@ancientjames love everything about this project, so inspiring. You probably already have a good voxelizer, but if you need another, I wrote this: https://github.com/Forceflow/cuda_voxelizer
Tim Artz@ancientjames I can’t stop thinking about this display. Even if it’s bare bones please document this. It’s so beautiful.
Tommy Thorn@ancientjames That's spectacular. I hope to see it in person one day
tobozo@ancientjames subarashi 😻
Tom Hannen@ancientjames I love seeing the updates to this project. One day you should get hold of a 3D camera rig to film it with depth - it's so hard to imagine how it looks from these video clips & images. I hope you end up commercialising it!
Stellar 🇫🇷 (
era)@ancientjames this is so awesome!!! 
bee 
@ancientjames this is looking so cool!!!
Wintermute_BBS@ancientjames wow, this looks great!! 🤩
@ancientjames Looks amazing! Can't wait to see more!
Francis 🏴☠️ Gulotta@ancientjames looks awesome
Greg Bell
Den of Earth
@ancientjames I love how persistently you stay with the project and keep iterating. That’s how real progress is made. Are you think of selling these eventually?
@tommythorn I don't see it as a product, but it may end up as an installation.
Nathan Manceaux-Panot@ancientjames Looks incredible!
Alexander Dyas@ancientjames Just read through most of this thread, your work is great! Loving watching the evolution of it.
allie
@ancientjames could you add radar indicators to show the direction of enemies?
raspberryswirl@ancientjames dump question, but why not having a 1st person view?
@raspberryswirl that would be a good fit for the stereoscopic display, but on this one everything has to fit inside the volume and 3rd person seems natural.