4 ms·

The centering issue could be solved by putting two led boards on top, back to back.Perhaps one board could shift the leds over by half to create an interlacing

by tromp 3y ago

The centering issue could be solved by putting two led boards on top, back to back.Perhaps one board could shift the leds over by half to create an interlacing effect while doubling resolution.

swayvil 3y ago
There's gotta be some way to replace the rack-of-leds-spinner with something lighter. Mirrors? Acrylic light pipe matrix?
- lstodd 3y ago
  I wonder if it would be simpler to just spin two phone screens glued back-to-back. You get higher resolution in about the same weight. Bandwidth would be a problem though.
  - mistercow 3y ago
    The fundamental problem is refresh rate. If you have two phones that refresh at 240Hz (the fastest I know of), and you want your frame rate to be 12 Hz, you’ll still only be getting 20 refreshes per 180 degree rotation. So your angular resolution will only be 9 degrees. Assuming you use portrait mode, that will make your outermost voxels ~5 mm arcs. And even there, 12 Hz is probably pushing it in terms of flicker.
    - lstodd 3y ago
      Yeah, well, that's not going to work. Interesting problem all the same. For a 1 meter diameter and height cylinder at 60Hz voxel refresh and say 1mm resolution at the edge one would need the plane rotating at obviously 3600 rpm, and edge pixels switching at about 380KHz. Since rgb is nice to have that's 10 gigabit for a somewhat coarse display. Nothing impossible, but not a DIY territory yet. I think one'd want the LEDs either on the receding or the advancing halves of the plate, depending on which is best for the cooling -- not all on the same side or on both -- that would be just a waste. Or even just on one half of the plate, the other being just a countermass. This way cuts the bandwidth in two.
      - CrazyStat 3y ago
        > For a 1 meter diameter and height cylinder at 60Hz voxel refresh and say 1mm resolution at the edge one would need the plane rotating at obviously 3600 rpm The edge of such a display would also be moving at several hundred miles per hour, which creates it own whole set of problems.
      - dsr_ 3y ago
        Note that in your hypothetical 1m 60Hz display, the edge of the cylinder is moving at 422 miles per hour. I'm going to recommend an evacuated transparent bell jar for safety, at a minimum...
        lstodd 3y ago
        Of course it has to be evacuated and maybe filled with helium or something less viscous than air at low pressure; this has to be calculated wrt the heat rejection from the leds. Also centrifugal force shearing and tearing off components, imagine the fun. All in all, this is what makes it interesting, no? 1x1 meter holo tank, not those tiny Voxon shakers.
      - mistercow 3y ago
        I wonder if anyone has built multi-speed “layered” swept volumetric displays. For the center part, you would still just have one screen, but as you go further out, you’d have “spokes”, so that each screen only has to sweep a small angle (and roughly constant distance) during a frame, so that it rotates at lower RPM, and has to update fewer times. You would still need a bare minimum of 1-2 kHz, and a lot of screens, and balancing every layer would be super difficult, but I don’t think anything about it is fundamentally impossible with current technology.
        zrezzed 3y ago
        Not exactly sure what the details, but there high quality, commercial products that are probably doing something like this: https://voxon.co/products/ https://voxon.co/products/
  - deleted 3y ago
    [deleted]
  - swayvil 3y ago
    Doesn't it have to be transparent? Are phone screens (minus the phone etc) transparent?
- jacquesm 3y ago
  Why do you think the weight is the problem?
  - swayvil 3y ago
    Because EVIL = RPM X WEIGHT. And we can't reduce RPM. Get it light enough and you don't even have to center it that good.
    - jacquesm 3y ago
      Ah ok, I figured that by casting the whole thing in resin and adding a top bearing it would get rid of the air flow issue completely at the expense of some extra work and a bit less light output.
o11c 3y ago
Or just ... don't center, and change the math to acknowledge that the LEDs aren't centered?
- yafbum 3y ago
  There's another similar thing needing correction, which is that the LEDs near the center sweep a much smaller volume than the ones at the edge, and should be dimmed in order to yield equivalent luminance. LEDs describing tiny circles very close to the center would need to be dimmed a lot since they'd essentially be stationary. Wouldn't it be better then to sweep slightly larger circles at the middle anyways?
  - o11c 3y ago
    If we're going there, note also that all the LEDs not on the edge are blocked by other LEDs (or the board) part of the time; LEDs on the edge are visible even past 90°.

by tromp 3y ago

The centering issue could be solved by putting two led boards on top, back to back.Perhaps one board could shift the leds over by half to create an interlacing effect while doubling resolution.

swayvil 3y ago

There's gotta be some way to replace the rack-of-leds-spinner with something lighter. Mirrors? Acrylic light pipe matrix?

lstodd 3y ago
I wonder if it would be simpler to just spin two phone screens glued back-to-back. You get higher resolution in about the same weight. Bandwidth would be a problem though.
- mistercow 3y ago
  The fundamental problem is refresh rate. If you have two phones that refresh at 240Hz (the fastest I know of), and you want your frame rate to be 12 Hz, you’ll still only be getting 20 refreshes per 180 degree rotation. So your angular resolution will only be 9 degrees. Assuming you use portrait mode, that will make your outermost voxels ~5 mm arcs. And even there, 12 Hz is probably pushing it in terms of flicker.
  - lstodd 3y ago
    Yeah, well, that's not going to work. Interesting problem all the same. For a 1 meter diameter and height cylinder at 60Hz voxel refresh and say 1mm resolution at the edge one would need the plane rotating at obviously 3600 rpm, and edge pixels switching at about 380KHz. Since rgb is nice to have that's 10 gigabit for a somewhat coarse display. Nothing impossible, but not a DIY territory yet. I think one'd want the LEDs either on the receding or the advancing halves of the plate, depending on which is best for the cooling -- not all on the same side or on both -- that would be just a waste. Or even just on one half of the plate, the other being just a countermass. This way cuts the bandwidth in two.
    - CrazyStat 3y ago
      > For a 1 meter diameter and height cylinder at 60Hz voxel refresh and say 1mm resolution at the edge one would need the plane rotating at obviously 3600 rpm The edge of such a display would also be moving at several hundred miles per hour, which creates it own whole set of problems.
    - dsr_ 3y ago
      Note that in your hypothetical 1m 60Hz display, the edge of the cylinder is moving at 422 miles per hour. I'm going to recommend an evacuated transparent bell jar for safety, at a minimum...
      - lstodd 3y ago
        Of course it has to be evacuated and maybe filled with helium or something less viscous than air at low pressure; this has to be calculated wrt the heat rejection from the leds. Also centrifugal force shearing and tearing off components, imagine the fun. All in all, this is what makes it interesting, no? 1x1 meter holo tank, not those tiny Voxon shakers.
    - mistercow 3y ago
      I wonder if anyone has built multi-speed “layered” swept volumetric displays. For the center part, you would still just have one screen, but as you go further out, you’d have “spokes”, so that each screen only has to sweep a small angle (and roughly constant distance) during a frame, so that it rotates at lower RPM, and has to update fewer times. You would still need a bare minimum of 1-2 kHz, and a lot of screens, and balancing every layer would be super difficult, but I don’t think anything about it is fundamentally impossible with current technology.
      - zrezzed 3y ago
        Not exactly sure what the details, but there high quality, commercial products that are probably doing something like this: https://voxon.co/products/ https://voxon.co/products/
- deleted 3y ago
  [deleted]
- swayvil 3y ago
  Doesn't it have to be transparent? Are phone screens (minus the phone etc) transparent?
jacquesm 3y ago
Why do you think the weight is the problem?
- swayvil 3y ago
  Because EVIL = RPM X WEIGHT. And we can't reduce RPM. Get it light enough and you don't even have to center it that good.
  - jacquesm 3y ago
    Ah ok, I figured that by casting the whole thing in resin and adding a top bearing it would get rid of the air flow issue completely at the expense of some extra work and a bit less light output.

o11c 3y ago

Or just ... don't center, and change the math to acknowledge that the LEDs aren't centered?

yafbum 3y ago
There's another similar thing needing correction, which is that the LEDs near the center sweep a much smaller volume than the ones at the edge, and should be dimmed in order to yield equivalent luminance. LEDs describing tiny circles very close to the center would need to be dimmed a lot since they'd essentially be stationary. Wouldn't it be better then to sweep slightly larger circles at the middle anyways?
- o11c 3y ago
  If we're going there, note also that all the LEDs not on the edge are blocked by other LEDs (or the board) part of the time; LEDs on the edge are visible even past 90°.