Moderators: Dave Moll, Andrew Davie, Steve Anderson
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
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'...
Steve O
Steve_McVoy wrote:Here is a 300 line disk made in 1936:
http://www.earlytelevision.org/w6xao.html
(scroll down some to find it)
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).
Users browsing this forum: No registered users and 67 guests