Compact Drum Monitor

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Re: Slit Drum

Postby gary » Tue Feb 01, 2011 10:56 pm

holtzman wrote:And the slits can be easily formed by black adhesive tape on clear PVC drum.


Hmmm your constructional skills must be far superior to mine - we are still talking about a sub-millimetre slit width for anything less than a 19" (490mm) diameter drum.

Also a clear PVC cylinder of such dimensions would cost a bomb here - if it was available at all...
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slit drum

Postby holtzman » Thu Feb 03, 2011 6:34 pm

Gary, my construction skills are good but not as much as you think :wink:
I was still talking about double speed, compact drum with just 16 slits. Its size should be around 9" which allows MILLIMETER slits. They could be made by bare hand with some caution...
The drum is just 1/2 the diameter of the disc I have already turned at 1500 rpm, so if it was disc, it was WAY easier to rotate it. What happens with drum - let's see...
By "clear PVC" drum I meant a strip of thin transparency, kind of that used for overhead projector, wrapped around foamed PVC disc. This is very cheap and easy to construct.
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Postby gary » Thu Feb 03, 2011 7:15 pm

Yes of course, but then the same thing applies to apertures, I was really only comparing slits versus apertures, I can't see how it is easier to create slits rather than apertures of the same width (whatever it is), however I will follow your implementation (if you get the time) with great interest.
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Progress in work

Postby holtzman » Fri Mar 18, 2011 11:26 pm

Here is some progress in my drum project. Thanks to Harry Dalek for inspiration, his cat food monitor made me thinking about 2 drum system

First, the clear pvc slit drum is ready and rotates. It was not so hard to build and I feel it's pretty accurate. I used isolation tape with a bit of soapy water. The water allowed some delay in adhesion, you can still move for some time a piece of tape after putting it roughly in place. This makes perfect slits in a short time. But until there is another drum synchronized with it, it's impossible to say how good shall it work...

So I built and tested stepper motor driver with opto-forks reading the main drum position. The results are promising. There is no small drum yet, but I got steady self-starting rotation of its base. The small drum gear was particulary challenging, I use so called H-bridge circuit. My driver consists of 2 such bridges, controlled by LDRs. The steps are very small, and I hope that some weight added to the drum (blue plastiline ring) will eliminate any cogging.

I can't wait to test the whole system but have not much free time to play with the stuff.
Attachments
IMG_0176.jpg
IMG_0176.jpg (70.74 KiB) Viewed 7724 times
IMG_0178.jpg
IMG_0178.jpg (75.65 KiB) Viewed 7724 times
IMG_0179.jpg
IMG_0179.jpg (64.88 KiB) Viewed 7724 times
IMG_0180.jpg
IMG_0180.jpg (59.79 KiB) Viewed 7724 times
IMG_0181.jpg
IMG_0181.jpg (69.56 KiB) Viewed 7724 times
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Re: Progress in work

Postby Harry Dalek » Sat Mar 19, 2011 6:08 pm

holtzman wrote:Here is some progress in my drum project. Thanks to Harry Dalek for inspiration, his cat food monitor made me thinking about 2 drum system

First, the clear pvc slit drum is ready and rotates. It was not so hard to build and I feel it's pretty accurate. I used isolation tape with a bit of soapy water. The water allowed some delay in adhesion, you can still move for some time a piece of tape after putting it roughly in place. This makes perfect slits in a short time. But until there is another drum synchronized with it, it's impossible to say how good shall it work...

So I built and tested stepper motor driver with opto-forks reading the main drum position. The results are promising. There is no small drum yet, but I got steady self-starting rotation of its base. The small drum gear was particulary challenging, I use so called H-bridge circuit. My driver consists of 2 such bridges, controlled by LDRs. The steps are very small, and I hope that some weight added to the drum (blue plastiline ring) will eliminate any cogging.

I can't wait to test the whole system but have not much free time to play with the stuff.


Hi Holtzman

Very happy to see what you have done on the project !
Its going to be an interesting build ,do post any working circuit schematics i for one am interested to see how to do it right ! :wink:
i'd say good luck but i don't think you need it :D
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First results

Postby holtzman » Mon Mar 28, 2011 9:03 am

Well, I am both disappointed and happy with some first images produced by my drum-stepper combination. It works with 32 line NBTVA signal.
Sorry there is no sync yet, even any speed regulator, so it's impossible to take pictures. I'll try to describe the advantage of the slit drum method.

The lines spacing looks very accurate. There are no black or white stripes between some lines which are visible in my disc monitor. This is because there are no drilled apertures with existing spacing between lines which may be a bit different. Instead, each new line is spaced from the previous automatically, the spacing depends on the small drum speed. Once the speed is deadly locked to the main drum by means of stepper/optoforks driving unit, the lines are spaced precisely from each other. And this deadly lock seems to work in my monitor!

Now what doesn't work. The wobble does exist and it ruins the image vertically. Horizontal lines in the image appear in sine-wave shape. I planned that using slits in the main drum instead of holes will solve the wobble problem. But there still is some kind of irregularity causing wavy horisontal lines.
Stepper motor cogging is not the reason: I tried to rotate manually and thr wavy lines were still wavy. BTW, the stepper runs smooth and does its job well.
Attachments
h_bridge.jpg
one half of the stepper motor driver
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Re: First results

Postby Harry Dalek » Mon Mar 28, 2011 11:40 pm

holtzman wrote:Well, I am both disappointed and happy with some first images produced by my drum-stepper combination. It works with 32 line NBTVA signal.
Sorry there is no sync yet, even any speed regulator, so it's impossible to take pictures. I'll try to describe the advantage of the slit drum method.

The lines spacing looks very accurate. There are no black or white stripes between some lines which are visible in my disc monitor. This is because there are no drilled apertures with existing spacing between lines which may be a bit different. Instead, each new line is spaced from the previous automatically, the spacing depends on the small drum speed. Once the speed is deadly locked to the main drum by means of stepper/optoforks driving unit, the lines are spaced precisely from each other. And this deadly lock seems to work in my monitor!

Now what doesn't work. The wobble does exist and it ruins the image vertically. Horizontal lines in the image appear in sine-wave shape. I planned that using slits in the main drum instead of holes will solve the wobble problem. But there still is some kind of irregularity causing wavy horisontal lines.
Stepper motor cogging is not the reason: I tried to rotate manually and thr wavy lines were still wavy. BTW, the stepper runs smooth and does its job well.


Hi thanks for the update !

I am interested so you are getting pictures with out sync only on the stepper motor controling speed ?

Hows the light levels..i found it low for 2 drums and what are you useing for the lights .

Also i am not sure if you are using a slit drum for the small drum .

Thanks for the schematic stuff it that is very useful !

Can you video it running ? seeing how it works not working 100% at this stage is useful to see.
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Postby holtzman » Tue Mar 29, 2011 8:28 am

There is no sync yet between the signal and the main drum speed because there is no phonic wheel built.
I do use small slit drum for horisontal scan. It is fully synchronised with the main drum as it sits on the stepper shaft. The stepper is of bipolar type, it's driven by 2 H-bridges controlled by LDRs.
Sorry but I've already ruined the small drum so no videos at this stage :( I destroyed it while trying to figure out the reason of the sine wave distortion. I wrongly suspected the "cogging" of stepper motor was the reason of it. So I loaded extra weight on the small drum, but he sine wave was still there... I uderstood that the problem is NOT in the stepper but in the main drum, its wobble.
For the lights I use 24 leds and it seems OK.
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Postby kareno » Tue Mar 29, 2011 8:41 am

Do I understand this correctly - the smaller drum is driven by a stepper motor whose step pulses come from opto sensors on the main drum?

That's brilliant!!!!

One query: How will you get the two drums back in correct phase relationship should they become de-synched (e.g. lost pulses, power removed before main drum stop or movement of drums during transport)?

That's the only flaw I can see.
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Postby holtzman » Wed Mar 30, 2011 2:02 am

kareno wrote:How will you get the two drums back in correct phase relationship should they become de-synched


They just don't get de-synched during operation. The stepper motor rotates mainly itself, there is no much resistance in the small drum. So once the picture is "in frame", it stays there. I guess if there was a missing hole pll synchronizer, the picture would not be in frame automatically. But I am planning to use either a phonic wheel, or my "alternative synchronisation". Both already require initial manual frame adjustment.
Hope to get some more time to proceed with the small drum resurrection and solving the wobble problems
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First Videos of the Drum

Postby holtzman » Fri Apr 01, 2011 9:56 am

Surprisingly, two small plastiline pieces were enough to balance the whole thing and sine wavy pattern has gone :)
The small drum does not need any additional weight for smooth rotation. The image is good and the machine is very quiet. Viewing angle is wide because isolation tape is thin.
Of coarse, this wisper operation may be ruined by humming phonic wheel...but for today I'm satisfied.
Attachments
MVI_0071.avi
How it works
(8.43 MiB) Downloaded 681 times
MVI_0073.avi
Jean Harlow
(16.73 MiB) Downloaded 659 times
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Postby gary » Fri Apr 01, 2011 10:33 am

Great work - very impressive!
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Re: First Videos of the Drum

Postby Harry Dalek » Fri Apr 01, 2011 12:27 pm

holtzman wrote:Surprisingly, two small plastiline pieces were enough to balance the whole thing and sine wavy pattern has gone :)
The small drum does not need any additional weight for smooth rotation. The image is good and the machine is very quiet. Viewing angle is wide because isolation tape is thin.
Of coarse, this wisper operation may be ruined by humming phonic wheel...but for today I'm satisfied.


Hi Wonderful work Holtzman that didn't take too long at all and see told you you didn't need any luck ! :D

OH yes not only does it look good and better than the last one its beautiful !

Looks like a hot rod of the nbtv world !
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Postby AncientBrit » Fri Apr 01, 2011 11:14 pm

That's pretty amazing work Holtzman.

The images are good.

Well done,

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Thanks!

Postby holtzman » Sat Apr 02, 2011 7:31 am

Thanks everybody for such positive feedback! I will keep you posted as soon as there is any progress with the project.

"Hot rod of NBTV world" - I like this :wink: but it better fits to my previous 60 line tv, there is a sewing machine motor stuck into its body and the disk edges go 130 km/hour.
Here I wanted to build kind of "hybrid car" - 2 motors working in cooperation, something silent, efficient...
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