James BrownIf my calculations are correct, when this baby hits 300rpm you're going to see some serious shit.
It's already slightly terrifying.
This is the current approach for reducing the horizontal field of view of the screens - a big heavy box o' slats. I'd like to make a lenticular array, but that's a whole side quest.
The black filament is surprisingly shiny. My first attempt turned out to be a light pipe, and didn't restrict the view. In this version, the slats have a zigzag profile.
It’s very unbalanced with only one collimator attached, so I’m spinning it too slowly for persistence of vision. But I’m sort of able to convince myself I’m seeing depth. There’s a lot of mechanical stuff I need to do before I can start cranking it up.
I have a habit of building displays that are just a confusing flickery mess on video.
The slat based collimators are such a pain, I've decided to go for it and try making lenses instead. I think a 3D printed mould will be good enough - the layer height is very much smaller than the LED size, and a bit of scattering is actually desirable. I'm printing this vertically so the lens profile gets the high resolution. It's going to be precarious when it reaches the top.
I had to turn the print 90 degrees - it wiggles rapidly doing the lens profiles, and when that was on the bed slinging axis it shook the whole room. It's a lot less dramatic when it's just moving the head.
I think I can live with it. I printed it vase mode for speed, so I was expecting it to need a stiffer structure to hold it flat.
I did have another swing at it. The first one I’d hoped to slip intact around a stiffer carrier. This one I made wider, and corrugated, so it printed better.
How can I be out of silicone?
Following a series of poor decisions, I now have both a mould and a vacuum chamber coated in uncured silicone.
Well I got a lens out of it in the end. It does make it more directional, but there’s more light off axis than I need.
I went back to the slats, and finally got all the bits hooked up together.
It sort of works?
You can see what's going on a bit more clearly with a simpler shape. It looks better when you can use both eyes on it!
The depth is smeared more than I want because the collimators are too shallow (because I don't like prints that take more than 16 hours to complete). I want to make them tighter, and spin the whole thing faster to compensate.
The nice thing about these LED panels is that they're very high framerate (and cheap!). I'm updating these at 1.5 KHz - with 3 of them in a ring, that's 4.5 KHz. Just driven in software from a (somewhat dizzy) Raspberry Pi.
Just realised that I can increase the resolution by progressively offsetting each panel by 1/3 the LED pitch.
Making parts for this has been a real saga, so while I wait for a faster printer to arrive I tried removing the collimators and running it as a swept volume display. Now I’m thinking maybe that’s what I should have built in the first place.
The thing I've been trying to make creates its 3D effect by displaying a whole different view in every direction, which means it can handle occlusion and fancy lighting at the cost of vertical parallax.
To turn that setup into a swept volume (where it's lighting up the LEDs according to where they are in space - full 3D, but glowy and transparent) I keep everything but the collimators, and just render each view with the near & far clip planes set really close together.
I'll probably make two displays now - finish off the autostereoscopic one, but then rearrange the geometry so that I can sweep through more than just a thickish-walled cylinder.
A quirk of these LED matrix panels is that they simultaneously update two rows at once, separated by half the panel. So on a 64x64 panel, you update rows 0 & 32, 1 & 33, 2 & 34 etc.
However, if you want to sweep one around an axis, you ideally want to update the outer LEDs at a faster rate than the inner ones, and this layout prevents that.
However, if you want to sweep one around an axis, you ideally want to update the outer LEDs at a faster rate than the inner ones, and this layout prevents that.
I’ve mentally moved on from this design, but I went ahead and built it to the point I can call it finished.
The advantages of this approach - occlusion and view-dependent lighting - are undermined by the fact that too much of the colour depth is sacrificed to hitting the necessary framerate. The sort of simple scenes it can display could be displayed better by a swept volume.
Most of the time we don't move our heads up and down very much, so the lack of vertical parallax seemed like it wouldn't be a big limitation. But one of the situations where we do move our heads quite a lot is when presented with a neat little 3D effect sitting on a desk.
Anyway, the new display is going to be amazing.
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).
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.
Keir Rice ⬢@ancientjames That is amazing.
Sublingual Multimedia@ancientjames This is a wild machine - incredible!
@Jo It's hard to get across on video, but it's eye-popping in the flesh.
Tom Armstrong@ancientjames I’ve been watching your project in fascination for a while now, without knowing a heap about it. Thanks for your selfless exposure to masses of dangerously whirling homebrew plastic and electronics in the name of cool posts 🫡
Out of curiousity: what is the current limiting factor for the rotation speed? Concern for the strength of the panel?
@tom_armstrong The balance in general is quite poor - the design is fundamentally asymmetric, and relies on lumps of lead to keep it from shaking itself apart. I've been pretty haphazard in my approach to getting that right. It also flexes. There's one bearing under the turntable, and a bunch of off-axis weight above it. It has a tendency to lean outwards with increasing speed, which I've tried to address with a counterweight sticking out above it. It needs to be stiffer overall.
@ancientjames Oh yeah. Balance does seem like a huge challenge, lacking access to commercial-scale fabrication facilities, and/or the means to get things built to a custom spec (or so I would imagine, as a near-total electronics and hardware neophyte)
zl2tod@ancientjames
Synchronising the camera with the turntable will be a challenge. Else make the shutter open time a multiple of the rotation time.
Synchronising the camera with the turntable will be a challenge. Else make the shutter open time a multiple of the rotation time.
Filomel@ancientjames I feel like someone could make a video game like this. I love to see some serious tinkering.
Rob Sogomonian
We will watch your career with great interest
J. Peterson@ancientjames Very impressive! The soundtrack moves it right into spacepunk sci-fi territory.
Henner Zeller@ancientjames Very nice project.
I started some rotating hub75 display years back, but never finished.
Wonderful to see yours in action!
Graham Sutherland / Polynomial@ancientjames hot damn that is sharp
Paul Griffin (he/him)@ancientjames Looks amazing! This whole project has been one of my favorite things to follow here.
Any chance of a video of doom guy?
Space Hobo
Tim AidleyIt's a shame all the Star Wars holochess models appear to be untextured for 3d printing
Randy Tayler@ancientjames proof the moon landing was fake
Menno@ancientjames
That thing is dancing!
Sounds like you already have a beat. Just at a tune and you have a TikTok hit 😁
That thing is dancing!
Sounds like you already have a beat. Just at a tune and you have a TikTok hit 😁
SAMURAI_GLOBAL@ancientjames holographically creative.
Sponge Of Density🏳️🌈@ancientjames That's very cool.
Olm-e@ancientjames works with a cardboard vr viewer ;)
amd@ancientjames I love this project and all the updates
GNU/overflo
Matt Gagle@ancientjames this is incredible!
@mgagle I was this close to giving up on it.
@ancientjames yeah, I get that. Glad you didn’t.
Jonathan@ancientjames that is awesome. I want to build one.
@jonbro I've been wondering about putting the stl files somewhere - it's all very specific to the parts I happened to have (and almost none of it is how I would make a second one).
@planettimmy @jonbro Fusion 360
@ancientjames yeah - realistically I just want to read the instructions. Building one is likely too much for me.