large scale Baird/Nipkow Televisor project "Big Paul"

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Re: large scale Baird/Nipkow Televisor project "Big Paul"

Postby Panrock » Tue Mar 14, 2017 2:08 am

Hi Gebhard,

As you probably know, the Baird company set up a mechanical 240-line flying spot camera at Alexandra Palace at the very start of the BBC Television Service. This used a 4-spiral 60-line disc rotating at 6000 rpm in a vacuum chamber, with a rotating shutter to select each spiral, one at a time.

Windfall Films Ltd originally wanted to reproduce this for a programme to mark the 80th Anniversary of British television. I supplied a Feasibility Report (attached here). They soon gave up, and made a 60-line rig instead!

It will be very hard to do this effectively with just one Nipkow spiral. But then, if you use more spirals with a shutter, the rim speed on this large disc goes up stll further! As others have said, the problem is going to be the tiny size of the holes required. To which I would add also: the precision needed in the positioning of the holes. If they are not spot on, the picture quality will be inferior to a lower line count.

If you can visit us at the Convention on April 8th, you will see demonstrations of 96-lines and 120-lines using various techniques. Even this is 'pushing it'... :shock:

Steve O
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Re: large scale Baird/Nipkow Televisor project "Big Paul"

Postby Steve_McVoy » Tue Mar 14, 2017 11:27 pm

Here is a 300 line disk made in 1936:

http://www.earlytelevision.org/w6xao.html

(scroll down some to find it)
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Re: large scale Baird/Nipkow Televisor project "Big Paul"

Postby gary » Wed Mar 15, 2017 2:52 pm

gebseng wrote:
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.


Hi Gary,

Thanks for your post!

I already tried your great Nipkow Disc DXF Generator about a week ago, but stumbled over the 128 lines limit. Now I tried it again, and I see that you changed that, thank you so much! I was already thinking about contacting you about that, but was afraid it would be too much of a hassle.

I have some questions regarding your software:
- DXFNipkow.exe generates a .DXF file. I tried to import it to Autodesk Fusion 360, where I successfully imported other .DXF files before. However, with the NipkowDXF.dxf, I got an error message and could not open it. Do you have any idea what the problem could be? (I am not an engineer and don't have easy access to other CAD software)
- I assume, when choosing "Metric" as Drawing Unit, that means millimetres?
- What are the differences between "Create Disk", "Create Hub" and "Create Encoder"?

Again, thank you so much, this is really useful for me.

best,

geb


Hi geb, sorry for the delayed response, that was a tricky thing to track down, apparently autodesk products no longer accept a colour value of zero as valid.
Ok, easily fixed, I simply give all layers the colour 7 (black).

Yes, metric means millimetres (engineering standard) - however they really are just "units" when exported to another application.

"Create Disk" creates the DXF for the disk
"Create Hub" creates the DXF for a hub to attach the disk to a motor
and "Create Encoder" is intended to one day create an encoder template that is usually glued to the disk for sync pulse generation. (This is work in progress).

Printing from DXFNipkow is also "work in progress".

(Just as background, this software was originally only intended to generate the necessary files for me to create my disks on my home made CNC machine, but I am trying to make it more general purpose over time).
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Re: large scale Baird/Nipkow Televisor project "Big Paul"

Postby gebseng » Thu Mar 16, 2017 7:19 am

Panrock wrote:Hi Gebhard,

As you probably know, the Baird company set up a mechanical 240-line flying spot camera at Alexandra Palace at the very start of the BBC Television Service. This used a 4-spiral 60-line disc rotating at 6000 rpm in a vacuum chamber, with a rotating shutter to select each spiral, one at a time.

Windfall Films Ltd originally wanted to reproduce this for a programme to mark the 80th Anniversary of British television. I supplied a Feasibility Report (attached here). They soon gave up, and made a 60-line rig instead!

It will be very hard to do this effectively with just one Nipkow spiral. But then, if you use more spirals with a shutter, the rim speed on this large disc goes up stll further! As others have said, the problem is going to be the tiny size of the holes required. To which I would add also: the precision needed in the positioning of the holes. If they are not spot on, the picture quality will be inferior to a lower line count.

If you can visit us at the Convention on April 8th, you will see demonstrations of 96-lines and 120-lines using various techniques. Even this is 'pushing it'... :shock:

Steve O


Thanks Steve, this information is really helpful! I am confident that I can achieve the necessary precision with a CNC cutter and a 6mm Aluminum disk (with conical holes). But sticking with 120 lines seems like a good idea. About the convention: I just looked up flights, they seems to be pretty expensive, probably because of easter, but it would be a great experience to come to the convention.

best,

Gebhard
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Re: large scale Baird/Nipkow Televisor project "Big Paul"

Postby gebseng » Thu Mar 16, 2017 9:08 am

Steve_McVoy wrote:Here is a 300 line disk made in 1936:

http://www.earlytelevision.org/w6xao.html

(scroll down some to find it)


Thanks Steve, very interesting!
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Re: large scale Baird/Nipkow Televisor project "Big Paul"

Postby gebseng » Thu Mar 16, 2017 9:11 am

gary wrote:[
Hi geb, sorry for the delayed response, that was a tricky thing to track down, apparently autodesk products no longer accept a colour value of zero as valid.
Ok, easily fixed, I simply give all layers the colour 7 (black).

Yes, metric means millimetres (engineering standard) - however they really are just "units" when exported to another application.

"Create Disk" creates the DXF for the disk
"Create Hub" creates the DXF for a hub to attach the disk to a motor
and "Create Encoder" is intended to one day create an encoder template that is usually glued to the disk for sync pulse generation. (This is work in progress).

Printing from DXFNipkow is also "work in progress".

(Just as background, this software was originally only intended to generate the necessary files for me to create my disks on my home made CNC machine, but I am trying to make it more general purpose over time).


Hi Gary, thank you so much for this update, it is really helpful! Thanks also for the explanations,

best,

Gebhard
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Re: large scale Baird/Nipkow Televisor project "Big Paul"

Postby gebseng » Wed Mar 22, 2017 10:25 pm

Dear forum members,

Another question: I "downscaled" the project and will do a 1490 mm (diameter) disk with 120 apertures, 0.5 mm diameter.
Since I will have to use stronger material to make the disk stable, I will try 6 mm aluminum.
I thought of using a double conical design for the apertures, like this:



does that make any sense?

thanks for your comments,

Gebhard
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Re: large scale Baird/Nipkow Televisor project "Big Paul"

Postby gary » Thu Mar 23, 2017 8:45 am

In principle it makes sense, although I don't see the the need for two opposing cones, having just one that extends from the back to just in front of the disk (thereby producing the aperture) would be sufficient I would think.

In practice I have grave doubts about the availability of the precision needed to end up with an aperture of the correct size in the end.

The basic principle is not unknown in NBTVA circles, although the usual procedure is to counter bore (rather than counter sink) such that the surrounding area of the aperture is cleared of material, from the rear face to a depth resulting in the normal thickness of a Nipkow disk (< 1mm) at the face of the disk. This requires less precision and is relatively easy to set up machinery wise.

There is one other issue to perhaps consider, your method works only for circular apertures, these are sub-optimal, and Baird's (and others) generally used square or rectangular shapes. There are also other shapes that attempt to reduce the line visibility that mars low definition television so much.

The advantage of counter boring is that it works for all aperture shapes, however, non-circular apertures may be too advanced for your project (it is for mine ;-)).
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Re: large scale Baird/Nipkow Televisor project "Big Paul"

Postby Harry Dalek » Thu Mar 23, 2017 8:10 pm

Thinking back to Alberts tiny Nipkow he made hes tiny disk via photographic means .... I wonder if the easiest way these days is to print one out on plastic sheet and place it on acrylic sheet i suppose problems of light proofing how well the ink does this ? may be a laser printer is the way to go ..wonder if you can print layers ?
Can the best printers print this well for 120 line size holes ...
Cutting the hole in metal must be harder to do than printing ..
A bead disk as Gary suggested would be easier cutting a tiny hole .
Any case interesting i hope you will show us on the forum what you come up with :idea:
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Re: large scale Baird/Nipkow Televisor project "Big Paul"

Postby gebseng » Sat Oct 28, 2017 10:21 pm

Hello again,

After some months of preparation, pieces are starting to fall together, at least on the mechanical side. Here is a 3d rendering of the apparatus: http://a360.co/2yS4gek


I also picked up the 1.5 mtr nipkow disk last week:
Nyit1qafRxy86JI5VSxEWA.jpg




As you can see, I went for 5mm holes in the disk, which will be plugged with little 3d printed plastic inserts with 0.5mm sqare(ish) holes:
inlet test 3dee.at square 0,5mm f8.jpg


I am still waiting for the driven shaft, and the steel framework is also in the making. I'll update you once we can make the first rotation tests.

best,

Gebhard
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Re: large scale Baird/Nipkow Televisor project "Big Paul"

Postby gebseng » Mon Nov 27, 2017 9:26 pm

While finishing the mechanical side, I also started working on the electronics and have a discussion thread over at allaboutcircuits.com. Please feel free to chip in if you're interested :lol:

https://forum.allaboutcircuits.com/thre ... st-1204781

best,

geb
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Re: large scale Baird/Nipkow Televisor project "Big Paul"

Postby gebseng » Sat Dec 16, 2017 8:52 am

First test with up to 136rpm. The goal is 900rpm. Looking good so far, but further tests will need a cage around the spinning disk: https://vimeo.com/247510486
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Re: large scale Baird/Nipkow Televisor project "Big Paul"

Postby gebseng » Sun Dec 17, 2017 12:25 am

Big Paul update: another test with up to 200rpm (at which point the power supply maxed out). This time, I put a surveillance camera next to the machine and watched from the next room for safety. https://vimeo.com/247608361
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Re: large scale Baird/Nipkow Televisor project "Big Paul"

Postby gebseng » Wed Mar 07, 2018 12:20 am

A quick update: to test brightness levels, I built a small lightbox with a 5W LED inside. Since the saftey cover is still being built, I'm limited to remote operation from the adjacent room. So, I set up a camera in front of the spinning disk (with 120 0.5mm square-ish holes) and set the speed to 600rpm. The brightness levels are still quite good, what do you think?

https://vimeo.com/258751070

IMG_4176.jpeg


rNUI46roS+qFlUoB%DES8A.jpg


BvpcNmiRR6GeKePPqNtLmw.jpg


ir8qUAF4SlGkdtfbjmG6Ig.jpg


best,

Gebhard
Last edited by gebseng on Wed Mar 07, 2018 12:38 am, edited 1 time in total.
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Re: large scale Baird/Nipkow Televisor project "Big Paul"

Postby Andrew Davie » Wed Mar 07, 2018 12:29 am

I think it's mesmerising, awesome and incredibly dangerous in equal measures.
Brightness looks good!
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