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''gebseng wrote:I want to share my research efforts so far, it would be great to get comments from you all!
gebseng wrote:Since I did not find a software that allowed me to design a Nipkow disk with the parameters I need, I started doing my own calculations, which you can find here:
Andrew Davie wrote:
There are standards (32 lines springs to mind) which would make your life easier. More particularly, there's software that converts from video format into those standards. I'm not sure 240 lines is a standard, but in any case the software I'm referencing is "Video2NBTV" by Gary. It would make your life easier to consider these pre-existing formats. You also have chosen a completely different aspect ratio to the standards I know. So again - why be different?
I was looking at the size of your disc (!) and thinking "gosh, that's going to be dangerous!" - you haven't mentioned a frame rate. Although you've massively increased the scanlines over a "standard" NBTVA format (which is 32 lines), you're actually displaying a tiny image. 32 scanlines gives suprisingly good pictures, done right. Anyway, frame rate will determine how fast the disc has to spin (currently 12.5Hz = 750rpm). I've done lots of playing by using an audio editor to "speed up" some of the videos I play, and to some degree they look "better" because they're (slightly) less flickery, but ultimately you're affected by the amount of light that gets through any hole.
If you're increasing the scanlines then you're decreasing the hole diameter (for a given disc size) so that's a consideration - are your holes big enough to allow sufficient light through. You may have to consider an incredibly bright lights source. Let's assume you are going with the 12Hz frame rate, then you have your outer edge travelling 4,680.973 mm (circumerence) * 12.5 (frame rate) mm/s = I make that 58 m/s. I don't do 3-digit precision so to the meter is close enough . That's hefty, and probably dangerous. I am unsure if you will have issues, but I expect a huge motor will be required!
I would assume if the motor isn't noisy, the spinning disk probably will be!
I suggest you slightly enlarge your holes (just a fraction) to give a bit of overlap between them - and consider the shape. Round holes, diamond holes, square holes - they all have characteristics which affect the picture.
Now a general comment - I understand you're exploring technology and alternate ways of showing images, particularly related to TV. One alternate that I haven't seen anywhere is to place the holes on a very long looped belt and pull that through in front of the light source at high speed. You could get a much bigger picture, but with a really weird mechanism. The picture would be totally rectangular rather than arced. The technological challenge is pulling a long (very) belt efficiently and somehow managing it once it's passed the viewing area. If the image was (say) 10cm high, and we had 32 scanlines, then the belt would be 320cm long. That seems manageable and already you have an image that's way bigger than any Nipkow disk. You'd have to pull it through at 10*32*12.5 cm/s which is 40m/s and although do-able, quite the technical challenge I think. Anyway, just throwing that one out there.
Back to your concept - in summary
* wow, that's a big disk
* holes may be too small at 240 line resolution to actually see an image?
* format you choose is non-standard, requiring lots more work to create content
* picture is tiny!
* frame rate is undefined, but affects heavily the practicality of using that big disk.
Klaas Robers wrote:When you go to higher line counts, the untransparency of the disc grows quadratic. For just 32 lines the disc is for 99.9% black, you get only 0.1% of the light. For 240 lines this is quadratic worse. Look:
Assume a square image, 240 x 240 pixels = 58 000 pixels. One is transparent. That is 1.7 10^-5. You will end up with a very, very dim picture, even with many ultra bright LEDs behind the disc.
It is a good plan to do things that others didn't bring to a good end, may be you are brighter. But the normal Nipkow disc looks to be unable to solve this problem.
I would advise you to start with a 32 line disc. Make it 1.5 meter large and see what you can.
Then switch to 60 or 64 lines, and solve the problems you encounter.
When you have a working system, make live again 4 times more difficult: 120 lines.
Following that road gives you experience with the growing problems and how you can solve them.
And then Vic Brown has invented solutions to make larger pictures by multi spirals on the disc. But that invests in greater disc speeds and with a disc of 1.5 meter, you will find the speed of sound your limiting factor.
gebseng wrote:For fun, I tried to calculate Nipkow disk diameters and rim speeds for contemporary video resolutions:
PAL (768 vertical lines, 25 fr/sec, 14” screen (4:3) = 285 x 213 mm):
1.500 rpm
768 scan holes
hole diameter 0.37 mm
disk circumference 164 meters
disk diameter 52 meters
rim speed 8,900 km/h
Full HD (1920 vertical lines, 60 fr/sec, 40” screen (16:9) = 886 x 498 mm):
3,600 rpm
1,920 scan holes
hole diameter 0,5 mm
disk circumference 956 meters
disk diameter 304 meters
rim speed 206.531 km/h (0,02% speed of light, mach 169?)
can the more mathematically inclined among us corroborate these numbers?
best,
geb
gary wrote:NipkowDXF has an inbuilt calculator that you can use to verify your calcs:
http://users.tpg.com.au/users/gmillard/ ... Nipkow.zip
Just go to "disk/Create Disk" enter your required parameters and press calc next to "aperture step".
"aperture step" is, of course, the optimum width of the aperture, it is quite common to increase this size to provide some overlap to reduce line structure, hence it is referred to as "aperture step" rather than "aperture size".
In addition, by convention, we assume the aspect ratio to be at the mid point of the aperture area so there may be a slight variation to your own calculation depending on where you have taken that value to be.
Andrew Davie wrote:I haven't checked all of your figures, but just wanted to talk about your use of comma separators and/or dot separators and/or no separator.
It's a bit confusing! You use "1.500" and "8,900" and "206.531"; it's pretty important to be consistent because the first I believe you are saying "1500", the second "8900" and the third "206531". Just thought I'd note that.
mach number = 57300/340
= 168.5 CONFIRMED
Looks good to me
Gan't wait for Geb's Relativistic Effect Televisor
Klaas Robers wrote:Any way consider to run the disc in a vacuum chamber (a 1.6 meter sphere, with a small flat area where the viewing window is. That will limit the needed power very much, and the noise the disc will be making with these speeds. Have you already made a estimation of the amount of sound? When you need a 1.5 kW motor, I assume almost all that power is going to be sound?
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