gary wrote:No, that was understood, this circuit is not designed to frame lock (this is still somewhat of a holy grail).
I spent an hour or so tonight experimenting and analysing the behaviour of the circuit, with various placement of the masked hole, and adjustments to the speed control. I did not play with the dampening setting -- I should probably do that next.
What I did find, much to my surprise, is that there are settings where I get line lock AND frame lock, with the one proviso. That is, occasionally when attempting to lock the circuit will go haywire and the Nipkow disk will accelerate and never come back down to speed. If I manually slow the disk and let it try again (especially if I do this when it's near frame lock) then it tends to lock line AND frame OK.
If I turn down the speed control then I tend to get the frame 'pulling' effect that I mentioned before. Basically, not a stable frame, and quite annoying. So I up the speed control until I get a stable frame -- and if I leave things, all is OK. However, when restarting the track and it attempts to lock again, then it tends to get to the "too fast, always too fast" stage. Again, I slow it down, let it lock -- and I have perfect frame AND line lock. Mind you, this only works with one particular position of the masked hole on the Nipkow disk. I can't explain why -- but in any case, it's probably because I hadn't had the exact same settings on things for other holes.
So really the problem I have now is that occasionally the 'kick' that the motor is given by the synch circuit is so great that the motor kicks past the next synch hole, and then it thinks it's too slow, goes faster, etc., etc. That's what I surmise is happening. So my guess is that my gearing ratio on the motor is too high -- there should be a smaller 'hub' on the motor, and a larger one on the Nipkow disk. The other guess I have is that the Nipkow disk is too responsive, and too easy to accelerate. Were it a more massive disk -- and I've been thinking surely one wants a massive disk in the first place because that would tend to maintain a constant speed with greater ease -- then it would also be less likely to be 'kicked' by the motor.
I think the above could explain why I was getting good frame lock with no masked hole -- the motor is kicking the disk so much that it gets kicked back into lock straight away, if that makes sense.
So the next thing I think I should try is another motor, or a smaller wheel/hub combination. I think it's very very close to working properly now -- and as I said, I'm particularly pleased with the fact that it currently frame AND line locks when it does lock at all.
I should note that during my experimentation with this I have seen all sorts of interesting behaviour -- there are definite 'modes' that the circuit/system gets into, for example rapid on/off pulsing of the motor (which is audible and partially visible, as I placed a mark on the motor's wheel) -- producing in this case an excellent lock, but very annoying sound. Also, there's a 'half frame' lock, where the picture is vertically displaced downwards, again with the noisy on/off pulsing -- one would slow the disk down and give it another chance, and it would then tend to lock OK (line only).
But as I said, now I have an almost working system. If I can solve the problem of it kicking too fast and going out of control, then what I have will be sheer perfection