New Drum monitor build

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Postby gary » Tue Mar 27, 2012 9:25 pm

BTW that "sine wave" issue (i.e disk or drum wobble) is probably one of the most common problems with "kitchen table" mechanics. It is one area where the use of a lathe is well suited, but it can also be remedied by the use of "off the shelf" hubs etc. Any conical (or self centering) solution is ideal - I think Dr Zarkov's idea of using R/C hubs may fall in to that category.
Perfecting an NBTV system is like trying to slam a revolving door...
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Postby DrZarkov » Wed Mar 28, 2012 7:56 pm

With my current project, the mechanical oscilloscope, I'm using an old harddisc. The bearing of the disk is of course very precise, it is easy to connect mirrors, drums or disc on the big, flat surface. The original motor of the disc is of course too weak to spin the whatever is glued on the disc, but as it is a synchronuos motor, it gives electric pulses with every turn. This is a good replacement for an opto-fork. (Which I don't use currently, but would be perfect for NBTV-purposes.) For spinning the disc I use a motor from a cassette-recorder, as usual, connected via a belt between the two original discs of the HD-drive. I will show the device in Loughborough in 2 1/2 weeks.
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Postby Harry Dalek » Wed Mar 28, 2012 9:07 pm

gary wrote:BTW that "sine wave" issue (i.e disk or drum wobble) is probably one of the most common problems with "kitchen table" mechanics. It is one area where the use of a lathe is well suited, but it can also be remedied by the use of "off the shelf" hubs etc. Any conical (or self centering) solution is ideal - I think Dr Zarkov's idea of using R/C hubs may fall in to that category.


Hi Gary sorry for the delay i was hoping to do the test last night but had to do family stuff ..
\
Along with a problem today i could only show you a quick 32 line test card test so far ,as you see the signwave is pretty big i was worried about a sight one on the last drum but this one is large.

I have a bit of work to fix this problem perhaps the motor on the arm is not a good idea i notice it does vibrate at speed perhaps this is causing it .

I have the Incentive to keep going seeing it can do 48 line as well...which i will show soon as can .


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The clown from the BBC testcard
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BBC Clown
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The cat test card
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Last edited by Harry Dalek on Thu Mar 29, 2012 12:18 am, edited 2 times in total.
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Postby gary » Wed Mar 28, 2012 9:12 pm

Yep, that is quite some wave (wobble) you have there - good photos though! I wish I could do as well.
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Postby Harry Dalek » Thu Mar 29, 2012 12:28 am

gary wrote:Yep, that is quite some wave (wobble) you have there - good photos though! I wish I could do as well.


Hi Gary i fixed it a little by readjusting trying to recenter the large drum better so thats helped .

I stuck a few more pic's in the above post ...

There is still a bit of vibration which is a pain at 48 lines it causes my stepper motor to clog so i have to reset all the time ,i still have to stop some vibration from the motor then i can take some pic's/i have been also testing on a kids table which shakes that doesn't help !

I haven't tried if it could do 60 lines theres still a bit more on the motor speed nice to see how close i am ,last monitor i was just below 48 ....

Oh the cameras a canon ixus 220hs only a small one but pretty good all round camera and video recording ...i found it works better with room light than trying to take the photos in the dark ...as you see they are better in the top photos than the bottom ...still harder taking video well .
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Postby Harry Dalek » Thu Mar 29, 2012 1:13 pm

Played around with higher speeds i still have that vibration problem which doesn't give great results but its better now at 48 its not to bad for the stepper motor clogging .

So these pictures are at 48 lines of again the BBC test card clown with out that little girl ! Oh and i don't think the smile is that real its my wave in the horizontal line !

The last picture of the cat test card is the monitor at top speed again not great picture my first ever at 60 line speed see if i can do better pictures next time.

So must be a nice rpm the drums rotating at .

I think i can see the problem causing it now the large drums base looks like its a bit to flexible once the speed to the drum increases it starts to oscillate..
perhaps i might be able to hot glue a dvd or 2 to it might stop it mmm. :?:
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Not a great picture so far but running the monitor top speed got a lock at 60 lines
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This is another go at 60 lines bit better
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puppet48line-48000-NBTVA48-p-II.wav
Heres the clown puppet i was trying to display ...i can see mines is reversed trying to display it
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puppet32line-48000-NBTVA-p-II.wav
heres a 32 line version of the puppet
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Postby holtzman » Fri Mar 30, 2012 10:08 am

Congrats Harry!
I am passing through a hectic period of my life sorry for delay... The wavy pattern you are getting seems to be usual for drum monitor, remember I got it too. It may be caused by several reasons.

First, the drum may be not centered on the shaft.
Second, it may wobble - if mounted not perpendicular to the shaft.
Third, the drum's cylinder surface may be deformed. This was my problem. My drum is very thin and soft, so it got deformed by centrifugal forces, I had to add small weights to balance it.

But my gut tells me your drum just is not centered, try to re-adjust it.
Best luck :)
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Postby Harry Dalek » Fri Mar 30, 2012 3:02 pm

holtzman wrote:Congrats Harry!
I am passing through a hectic period of my life sorry for delay... The wavy pattern you are getting seems to be usual for drum monitor, remember I got it too. It may be caused by several reasons.

First, the drum may be not centered on the shaft.
Second, it may wobble - if mounted not perpendicular to the shaft.
Third, the drum's cylinder surface may be deformed. This was my problem. My drum is very thin and soft, so it got deformed by centrifugal forces, I had to add small weights to balance it.

But my gut tells me your drum just is not centered, try to re-adjust it.
Best luck :)



Hi my friend yes your idea version 2 here ..... :wink:

Yes you are right i recall you talking about this problem on your build and took that in today ...last night trying 60 lines its very easy to see the problem as the back of the dvd holder case moves inwards vibrating a near on a CM the plastics not strong enough it does move with the centrifugal force as your thinking ,so today i have been working onit and very near to fixing it ...if i had any thing stronger like steel plate that would stop it ...yes centering thats other problem your right there for sure hard to get it right .

Heres todays work and thanks always for the great monitor idea ! your scanning idea is much better than what some of the past inventors did on this type of idea .

Here the felix cat test card backward on my monitor with the improvements .

This is at 32 line ..my camera just needed recharging when i was trying the higher speed 48 line ,i post more tests as i do them.

just adding a 48line test this night this avi is it running at that speed...
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monitor doing 48line speed
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clown at 48 line
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The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Postby Harry Dalek » Sat Mar 31, 2012 9:29 pm

Today i worked out why my stepper motor was clogging with monitor vibration at top speed ended up just being a bad solder point on ground on my stepper motor circuit board .

The monitor doesn't work to bad now at normal 32 line see video ,i have noticed as speed increases to 48 and 60 line ...60 line more so the stepper really should increase faster than what my motor is doing at the moment as the picture becomes small and you need the increase speed to spread the lines out ,thinking about it 12 frames at 32 lines the stepper would have to do this twice as fast at 60 line don't you think ?

I could increase the number of slots on the small drum that might help and get the stepper in range without trying to increase stepper speed .

The horizontal line still sways but its not to bad .

So far switching back to Holtzmans cdm i have with this build i have learned you can do a multisystem mechanical monitor thats a good thing even though this still works best at old 32 line speed ,I suppose i should try and tackle Sync yakes :roll:
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Nice video of the test cards right way around
sorry about my kids noise forgot about them !
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Postby Harry Dalek » Sun Apr 01, 2012 8:21 pm

Ok today working on the Hall effect sensor which i have worked on before but never really finished the idea for the to fork replacement but i will do my best this time .

See photos of the magnets where the holes would be for the opto fork gives a pretty good signal as you see for the circuits pulse monitor led and bistable switch Led .

So over the next few days i will see if i can get this bugger to work i don't feel i will ever be a true NBTVer if i fail on syncing a mechanical monitor .

I find this part a bit tedious but i will try my circuit and show any results.
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A hand test of the Hall effect fork
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The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Postby Metallica Man X » Wed Apr 04, 2012 6:31 pm

Looks good! Can't wait to see it in action.

How did you measure out the distance for the magnets to keep it balanced?
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Postby Harry Dalek » Wed Apr 04, 2012 9:16 pm

Metallica Man X wrote:Looks good! Can't wait to see it in action.

How did you measure out the distance for the magnets to keep it balanced?


Hi been run of my feet last few days so but off work now so i will get back to it ...

The little magnets didn't cause me any problems at speed last time as theres one per line slit so they are balanced that way the measuring was done on the line slits so not much to think about where to place them....i think it would of been better to put them on the base of the drum but i will see how this gos...so they may end up there if there are problems at speed .
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Postby Klaas Robers » Wed Apr 11, 2012 3:53 am

Harry,

about the wobbly sync-line:

1. your DVD-drum should run smoothly, without radial movements. If you touch the drum gently with your finger while it is running, you should hardly feel it bumping against your finger. So no wobbling of the drum is allowed. Wobbling will introduce wobbly horizontal lines.

2. The distance of the slits on the drum should have equal distances. That is difficult as they should carefully allign a certain number of slits around the drum. Also unequal slit distances around the drum will introduce wobbly horizontal lines as well.
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Postby Harry Dalek » Wed Apr 11, 2012 2:42 pm

Klaas Robers wrote:Harry,

about the wobbly sync-line:

1. your DVD-drum should run smoothly, without radial movements. If you touch the drum gently with your finger while it is running, you should hardly feel it bumping against your finger. So no wobbling of the drum is allowed. Wobbling will introduce wobbly horizontal lines.

2. The distance of the slits on the drum should have equal distances. That is difficult as they should carefully allign a certain number of slits around the drum. Also unequal slit distances around the drum will introduce wobbly horizontal lines as well.


Hi Klaas

Yes lining up the drum 100% in Balance is a problem i suppose is harder than trying on disc ,as well its only held on one side which doesn't help on a plastic or any sort of drum but do the best you can with what you have got ..and live and learn ! I have learned that the base of the drum needs to be pretty strong to stop wobble .

I have not tackled the small drum yet as theres a slight wobble there since it was home made which might be causing wobble to as well.

So i have a few more things i want to try like that and controlling the small drum from the large .

I think i did better on the wobble problem on the last drum direct drive ,but the pulley system did let me show i could run the drum to view 48 and 60 line ....the last poorly but got there .

The advice is noted Klaas if i do a 3rd drum monitor i will be trying with my poor construction skills do better i will get it right in time ... as always you would always do if different if you did it again :roll:
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