The holtzman CDM

Forum for discussion of narrow-bandwidth mechanical television

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Postby Harry Dalek » Sun Oct 23, 2011 6:08 pm

holtzman wrote:Congratulations for your working gear! I must say this is something I could not build right now as I do not have experience with ICs and flip-flops. And i still do not understand completely its working principle.
If i got it right, the drum makes 1 pulse each turn, and electronics provides other 3 in sequence? If so, you may have some problems on start because the frequency is different. And you have to adjust very fine your circuit in order to get continuous pulse sequence at the right speed of 12.5 fps.
I am going to a short vacation tomorrow so won't be here for a while sorry...


Hi Holtzman : )

What you did making a mechanical flip flop to drive that H bridge Mosfet transistor circuit was Fantastic shear genius!
The main reason i am not copying it at the start is for me thats pretty hard ! and being lazy the electronics is easier for me .
i just want to try pulse or pulses in syncing the big drum to the small ,i will use a light switch ldr as you so i want to cheat here and make the circuit do the work ....but just trying one ldr because the electonics should be doing the work of you mechanical switches.
So the big drum will be triggering a monostable and i might have another after to adjust the pulse width ,i know the light monostable works i just have to copy that again on this board ...
Its 4 pulses and i can play around with the timing...stepping .
One thing i wasn't sure about was if your motor was geared or direct drive
?
I am going to work on getting the light modulation levels best i can .

Off topic if any one knows ? if you could get a stepper to drive at NBTV speeds via direct or gearing would you need syncing once you adjusted it to the correct speed ? i mean would the motor drift or would it be locked if the timer your using doesn't drift of frequency .
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Postby gary » Sun Oct 23, 2011 6:19 pm

harry dalek wrote:
holtzman wrote:Off topic if any one knows ? if you could get a stepper to drive at NBTV speeds via direct or gearing would you need syncing once you adjusted it to the correct speed ? i mean would the motor drift or would it be locked if the timer your using doesn't drift of frequency .


Harry, when used like this a stepper motor is a synchronous motor and will be as good as your clocking circuit (and the clocking circuit of the source as well of course). Using the same clock as the source (i.e. in my case a sound card) will give perfect results. Of course you will still need to provide "framing" either mechanically, electronically, or, as I do, via software.
Perfecting an NBTV system is like trying to slam a revolving door...
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Postby Harry Dalek » Sun Oct 23, 2011 11:42 pm

gary wrote:Harry, when used like this a stepper motor is a synchronous motor and will be as good as your clocking circuit (and the clocking circuit of the source as well of course). Using the same clock as the source (i.e. in my case a sound card) will give perfect results. Of course you will still need to provide "framing" either mechanically, electronically, or, as I do, via software.


Hi Gary
thanks i was wondering any one had experimented with steppers for nbtv ,i wanted to look into this more as i have only played around with them of late.
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Postby Harry Dalek » Sun Oct 23, 2011 11:56 pm

I have been working out a Diffuser for the Luxeons ,works out 2 layers of clouldy plastic milk bottle cut to strips covering the inside holes of my small drum ...to be neat ...seems to work very well..

a little step forward :wink:
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Postby gary » Mon Oct 24, 2011 9:46 am

harry dalek wrote:Hi Gary
thanks i was wondering any one had experimented with steppers for nbtv ,i wanted to look into this more as i have only played around with them of late.


Somewhere on this forum I have described my experiments with a stepper motor - it's a little different to your requirements however as I was using it as the main drive to a disk - i.e. 750 RPM - there are some issues with getting a stepper motor to turn that fast associated with the inductance of the coils, but there are methods to get around them.

This article on using a stepper for a turntable shows the basic concept, but as it runs much slower than for our requirements there is some additional work required.

http://www.altmann.haan.de/turntable/

Note: that I used sine waves to turn the stepper as doing it the traditional way, i.e. square pulses, will exhibit some cogging - that may or may not be an issue for your application.
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Postby Steve Anderson » Mon Oct 24, 2011 2:05 pm

A year or two back I spent quite a bit of time searching on the 'net for steppers that were specified to run at 750 RPM or greater. There were very few. But in the last 10 minutes I found this site where virtually all will run at the required speed.

http://www.premotec.com/synchronous.htm

They appear to be of high quality (good) but I suspect not cheap (not so good). I couldn't find any pricing on the site which tends to reinforce that view.

The company is based in Euroland so one hopes they don't sub-contract the actual manufacturing to some shonky Chinese mob.

The turntable item is interesting, if only these guys knew what the signal went through before it even got near the Vinyl.

Steve A.
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Postby gary » Mon Oct 24, 2011 2:54 pm

It's a pity that they don't have a 22.5 degrees version so you could get 750 RPM directly off the mains (I mean frequency wise not voltage wise of course).

I note also that they won't start at their maximum speed (which is normal for a stepper) and so some mechanism for ramping up to the desired speed would be necessary.

It's interesting that the the only thing that appears to make the "synchronous" motors "synchronous" rather than "bipolar steppers" is the maximum voltage rating - i.e. capable of direct connection to the mains.
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Postby Harry Dalek » Mon Oct 24, 2011 9:18 pm

Hi viewers just some pictures and video of the drum with diffuser ,the 6 luxeons are running on 5v in these so have a bit more light power when i run them harder.

Yes Gary i find the Steppers pretty interesting i never knew of the different types till i looked into it .....i have seen some pretty high speed steppers on you tube and the smoother stepping of half and micro stepping which looks closer working to a normal DC motor...i have bit of a lucky dip coming with 10 stepper motors so i will be looking more into stepping motors for sure with these .
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Postby Steve Anderson » Tue Oct 25, 2011 12:42 am

gary wrote:...also that they won't start at their maximum speed (which is normal for a stepper) and so some mechanism for ramping up to the desired speed would be necessary..


I've always assumed that the rate of acceleration would be dependent on applied waveforms, i.e. shoving full-speed frequency into a stepper from start-up would probably result in it shuddering in a stationary position.

But once the logic is sorted out for the windings the use of the VCO section of our good old friend the 4046 :D (sarcasm) would provide an easy slow-start solution by a simple RC network on the control volts input...the output of which drives the stepper logic.

Now, once under control a stepper needs no feedback as per the usual Club arrangement, it's truly faithful, witness your printer output...gone is the variables of the loop filter, inertia and so forth....and as such, gone is the PLL. Nirvana perhaps?

I might add that I use PLL's a lot, but not with huge mechanical variations likely to be encountered here, they are as reliable as any flip-flop or gate once properly designed. The radio in your car uses one without a doubt, actually two if it's stereo...how often do they fail? Your CD/DVD player uses several...

Steve A.

I know, someone is gonna say they use a TRF AM radio in their car using those space-charge tubes that ran off 12V...
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Postby gary » Tue Oct 25, 2011 10:18 am

Steve Anderson wrote:I've always assumed that the rate of acceleration would be dependent on applied waveforms, i.e. shoving full-speed frequency into a stepper from start-up would probably result in it shuddering in a stationary position.


Indeed that is so, however these steppers indicate a pull-in rate (the maximum steps per second that a motor can be started or stopped and remain in synchronism with the waveform) of a surprisingly high speed (for a given torque) - however, I am am just noting that speed is still below that which would normally be required (750 RPM).

Steve Anderson wrote:But once the logic is sorted out for the windings the use of the VCO section of our good old friend the 4046 :D (sarcasm) would provide an easy slow-start solution by a simple RC network on the control volts input...the output of which drives the stepper logic.


Yes that is one way. In my case I prefer to use a sound card or a microcontroller, especially as it is then easier to generate sine waves.

Steve Anderson wrote:Now, once under control a stepper needs no feedback as per the usual Club arrangement, it's truly faithful, witness your printer output...gone is the variables of the loop filter, inertia and so forth....and as such, gone is the PLL. Nirvana perhaps?


Well you still have the problem of discrepancies between the stepper driver clock and the video source clock - even a small amount can result in an annoying rolling of the picture - as people who have been experimenting with NBTV over shortwave find (see my YouTube channel for an example). But this method is at least as good as using "real" synchronous motors or bicycle dynamos (in my experience better).

If you can lock the two sources somehow (I do it by using the same soundcard but some will see that as "cheating") then the speed (line lock) is perfect and only the framing needs to be adjusted. This can be done by controlling the wave form phase, and should even be possible to do automatically although I haven't tried that yet (I used all my "good" steppers on my CNC machine).

In the spirit of true pedantism I should point out that some printers (and a LOT of CNC machines) use servos rather than steppers because with those you actually "know" where the position is, as opposed to steppers where if you get a "slip" due to resonance or over torque, the position is lost forever (or at least until you reset the start position). ;-)

PS: talking about framing by changing phase, if you are using an "intelligent" source of video, such as a PC or microcontroller, it is generally easier to change the phase of the video source than the phase of the motor. I do this when experimenting to avoid having to build these pesky controller circuits all the time. If not using a synchronous motor (such as a stepper) then a simple bistable based circuit (a discrete version is published in the NBTV newsletter and works well) is all that is required.

BTW: How are you going with the floods Steve?
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Postby Steve Anderson » Wed Oct 26, 2011 5:37 pm

gary wrote:....talking about framing by changing phase, if you are using an "intelligent" source of video, such as a PC or microcontroller,

BTW: How are you going with the floods Steve?


Certainly something akin to the missing-sync extractor i did a while back (Vol. 35 No. 4 p4, "Eureka! I've found it!") could generate a locked waveform. It would need to be a slightly larger micro to provide the additional output(s) required, but a 14-pin device would be sufficient. A PIC16F684 for example. Altering the phase would be quite a simple software exercise.

The good old bicycle dynamo would certainly be one contender here and I happen to have a bicycle (mine) and an adult tricycle here (managements), both fitted with dynamos which are not used...another item added to the 'to-do' list...

Steve A.

P.S. Floods have yet to affect us, but the next few days are going to be the crunch-time....it's at this point I wish I still lived in a 6th floor apartment...
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Postby gary » Wed Oct 26, 2011 6:37 pm

Steve Anderson wrote:The good old bicycle dynamo would certainly be one contender here and I happen to have a bicycle (mine) and an adult tricycle here (managements), both fitted with dynamos which are not used...another item added to the 'to-do' list...


In fact, then, you have no excuse at all as it is the simplest of all arrangements - simply hook them up to a 6v transformer (e.g. bell transformer) and off they go (with a twist of the wrist at least).

Finding a way of connecting a hub to them has always been the big irritation for me.
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Postby Steve Anderson » Thu Oct 27, 2011 11:37 am

gary wrote:Finding a way of connecting a hub to them has always been the big irritation for me.


It's always been the mechanical aspects of this that has inhibited me in getting a functional mechanical display from working. I will admit that although conceptually simple it's been the practical matter of getting things made with sufficient precision that has put me off.

Of course there are many examples of kitchen-table engineering, on this very forum no less, which achieve remarkable degrees of success. I just don't have the confidence in my own abilities to pull it off.

One of the many disciplines instilled in an electronics engineer is to design-out any and all moving parts. Switches, pots...anything with moving parts must go. Of course that's impossible. As I sit here typing this, the very mechanical hard drive below my fingertips (a laptop) is whirring away like crazy. And it has done so for the past several years without ever faltering.

As Albert quite rightly pointed out, I simply have to have a go at this and learn from the mistakes, errors and failures I may encounter.

Steve A.
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Postby Harry Dalek » Thu Oct 27, 2011 2:15 pm

Hi since theres a bit of chat about Stepper motors here some time back i came across a you tube video on the Sanyo STK672-080 stepper motor chip.

I was impressed and ordered a few got my first one yesterday and the first circuit is just about finished and may replace the circuit i have been using .

http://www.youtube.com/watch?v=m8afXPslVTU

Link to he's web site and circuit for this chip is on the you tube site .

What i really like about it is and apart from just a few parts for the chip all you need is the clock and a unipolar stepper motor every thing else is built in .

Yes Steve you need to give it a go ! i think a stepper motor and you would go good together for a project you'd make that motor rotate correctly ! Hint a hot glue gun connects the unconnectable.
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Postby Viewmaster » Thu Oct 27, 2011 6:35 pm

On utube is a stepper motor running at 9375 RPM !!

http://www.youtube.com/watch?v=8cxl3B99 ... re=related

Steve (panrock) if you are reading this how about this one heavy duty but running at 1500 RPM for your heavy mirror screw...

http://www.youtube.com/watch?v=x8M_Tpqt ... re=related

But the price is over $1500 :-(
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