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Old 14th Sep 2020, 9:42 pm   #1
KesterLester
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Default Pulsynetic master clock: question about gravity arm roller.

I have recently acquired a pulsynetic master clock. I have not had one before. I am in the process of checking over the mechanism before firing it up for the first time. In this regard I am probably being over cautious as I am confident it was well looked after by the previous owner.

The only immediate question-mark I have after inspecting it concerns the roller on the gravity arm.

It looks to me like the roller brushes against the upper apex of the pusher ramp on each swing. It's not a strong contact, but there is a little play in the roller's mount, and the contact is enough to lift the roller slightly and reliably rotate it a little left or right, etc. Because of the slight play in the roller mount this just looks "wrong" to me. It "feels" to me like it should be 'just' clear of the apex at all times and only come into contact with the pendulum pusher when released.

Is that indeed the case?

And is it normal to have a small amount of play (wobble) in the bearing of the roller?

I could supply photos of relevant parts tomorrow if needed.

[P.S. It looks like the metal part that holds the gravity arm up (until the moment of release) has two screws at its upper end that are possibly designed to allow it's vertical position to be varied slightly. If that is so (I've not yet got a clear view of these screws, so perhaps it is not) then perhaps the intended adjustment is to raise this latch slightly, so that the gravity arm is held a tiny bit higher, so that the roller will not brush against it? ]

Last edited by KesterLester; 14th Sep 2020 at 9:49 pm.
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Old 15th Sep 2020, 8:09 am   #2
Mike Phelan
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Default Re: Pulsynetic master clock: question about gravity arm roller.

Hi,

Mine's in the garage so I'll hve a look for you later today.
I'm fairly sure that the roller should be completely clear until the moment of release.
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Old 15th Sep 2020, 8:10 am   #3
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Default Re: Pulsynetic master clock: question about gravity arm roller.

One handy hint, these clocks like to be secured to a stiff wall, standing on the floor they don't run very well if at all.
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Old 15th Sep 2020, 9:03 am   #4
KesterLester
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Default Re: Pulsynetic master clock: question about gravity arm roller.

It is not yet attached to a stiff masonry wall, but it soon will be. [PS - I whereas yesterday I was assuming that the gravity arm was perhaps resting slightly too high (causing the brushing against the roller) this morning it has occurred to me that perhaps the gravity arm is resting in the right place, but that some damage in the bearing of the roller is causing the roller to hang a little lower than it ought to. I will aim to send a picture of the roller today so that it can be checked whether it looks normal.]
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Old 15th Sep 2020, 10:40 am   #5
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Default Re: Pulsynetic master clock: question about gravity arm roller.

A picture would be great. This is something I've never been involved with and I'm trying to guess what gravity arms do and why they should want a roller. To the uninitiated, the complete shift in jargon has hints of the turbo-encabulator! I don't get this much foxed very often.

https://www.youtube.com/watch?v=Ac7G7xOG2Ag

David
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Old 15th Sep 2020, 11:31 am   #6
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Default Re: Pulsynetic master clock: question about gravity arm roller.

Until I get into my office and can take a picture of the actual mechanism, I attach here a diagram taken from the web which names the relevant parts to help with the discussion. Also there is a video of someone else's pulsynetic mechansim working here: https://www.youtube.com/watch?v=OhAOsCUvkfo though in not enough detail to give me a good answer to my question.
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Old 15th Sep 2020, 12:09 pm   #7
Lucien Nunes
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Default Re: Pulsynetic master clock: question about gravity arm roller.

Quote:
I'm trying to guess what gravity arms do and why they should want a roller
In brief, the idea is to impart the sustaining impulse to the pendulum at the centre of its swing when its impact on the period is least. Constancy of mechanical impulse is achieved by using the weight of the gravity arm to dispense a fixed measure of gravitational potential energy every half minute.

At each fifteenth swing of the two-second pendulum, the pawl of the gun lever drops into the deep notch on the scape wheel, causing it to trip the stirrup catch off the gravity lever at the next swing. The roller runs down the impulse pallet on the pendulum crutch to provide the sustaining impulse, then once its travel is complete it closes the contact, energising the slave circuit to the clocks and also the master electromagnet, which restores the gravity lever to its position on the stirrup catch and breaks the circuit. Kerchunk.

On my clock, the roller is definitely clear of the pallet until released. Any additional mechanical interference with the pendulum is to be avoided so I don't think this is normal, and may well relate to the roller bearing being out of whack.
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Old 15th Sep 2020, 1:32 pm   #8
M0FYA Andy
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Default Re: Pulsynetic master clock: question about gravity arm roller.

This diagram might help. It looks like dimension 'X' isn't correctly set?

Andy
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Old 15th Sep 2020, 1:48 pm   #9
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Default Re: Pulsynetic master clock: question about gravity arm roller.

Thanks, everyone. It's not something you could assemble in your mind from the words alone.

It's elegant how the weight of the roller is used to impart a soft force, without trying to force a position.

I think I may have used something a bit more electromagnetic, seeing as there are once per 30 second pulses on the go, but maybe that force would not be quite so stable as the weight of the roller?

The stirrup and the deepened notch on the escapement are just plain clever.

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Old 15th Sep 2020, 1:49 pm   #10
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Default Re: Pulsynetic master clock: question about gravity arm roller.

Quote:
Originally Posted by M0FYA Andy View Post
This diagram might help. It looks like dimension 'X' isn't correctly set?

Andy
Ah - thank you. That's a handy diagram to have. Good to see both (a) where and why the adjustments are mandated, and (b) the recommended overlaps and clearances. I will adjust X.

Looking at that diagram, I suspect that my `Y' setting may have too much overlap too .....
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Old 15th Sep 2020, 2:28 pm   #11
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Default Re: Pulsynetic master clock: question about gravity arm roller.

At last I have been able to make a small video showing the play in the roller and the way it contacts the pallet.

I couldn't figure out how to upload it here so I placed it at the following address:

https://www.hep.phy.cam.ac.uk/~lester/pulsynetic_01.mov

If I make the 'X' adjustment mentioned by M0FYA Andy I will certainly be able to get the roller to clear the pallet. However after doing that there remains the question of whether the amount of "play" observed in the roller is normal or not.

How does the roller play on mine (seen in the video above) compare to others out there?

[ P.S. I also attached an image here which shows the current Y clearance. Because the stirrup design is slightly different from the one in M0FYA Andy's diagram, it's not clear whether the ideally Y-clearance is measured in my clock as the distance from the top of the gravity arm to the nearest face of the stirrup, or if instead Y represents the distance which the stirrup should have to move to cause disengagement. I suspect its the latter as the smallest amount of movement the best. At present the point of the stirrup in contact with the gravity arm has really a long way to go (with my clock as currently set up) -- more than 1.5x the thickness of the metal of the stirrup. It `feels' to me like less than half that is needed. ]
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Old 15th Sep 2020, 2:30 pm   #12
Mike Phelan
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Default Re: Pulsynetic master clock: question about gravity arm roller.

Hi there again,

I've just had a close look at mine now - answers / comments below:

Quote:
Originally Posted by KesterLester View Post
The only immediate question-mark I have after inspecting it concerns the roller on the gravity arm.

It looks to me like the roller brushes against the upper apex of the pusher ramp on each swing. It's not a strong contact, but there is a little play in the roller's mount, and the contact is enough to lift the roller slightly and reliably rotate it a little left or right, etc. Because of the slight play in the roller mount this just looks "wrong" to me. It "feels" to me like it should be 'just' clear of the apex at all times and only come into contact with the pendulum pusher when released.

Is that indeed the case?
Until the release, the roller should be about 2 mm away from the ramp on the pendulum (X).
This setting is adjusted with the two screws on the vertical bar.
Quote:
About 2 mm.
And is it normal to have a small amount of play (wobble) in the bearing of the roller?
Quote:
It doesn't matter too much unless really excessive.
The roller moves about 1 mm front to back on mine.
Others have filled in some of the relevant details, but I'll leave the post on.
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Last edited by Mike Phelan; 15th Sep 2020 at 2:38 pm.
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Old 15th Sep 2020, 2:32 pm   #13
KesterLester
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Default Re: Pulsynetic master clock: question about gravity arm roller.

Thank you Mike. That's helpful!
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Old 15th Sep 2020, 2:40 pm   #14
Mike Phelan
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Default Re: Pulsynetic master clock: question about gravity arm roller.

Not to be kept in the bedroom!
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Old 15th Sep 2020, 3:52 pm   #15
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Default Re: Pulsynetic master clock: question about gravity arm roller.

I had one of these 10 years ago and can't remember answers to your question, but I would say if you mean to mount it indoors for domestic use, it's very noisy as regarding the clunk that's made when the solenoid resets the arm (pardon me if this is gibberish but the details have faded from the memory!) Bottom line was in my case that although it seems ok in the day, at night the regular clunks make sleep impossible and I had to sell it. Shame as it was a lovely thing!
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Old 15th Sep 2020, 4:03 pm   #16
KesterLester
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Default Re: Pulsynetic master clock: question about gravity arm roller.

It will be mounted indoors, but in the hallway of the office where I work. This is two miles from where I live and sleep, so I hope I won't find it too noisy. Cross fingers.
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Old 15th Sep 2020, 5:57 pm   #17
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Default Re: Pulsynetic master clock: question about gravity arm roller.

Quote:
Originally Posted by KesterLester View Post
This is two miles from where I live and sleep, so I hope I won't find it too noisy.
I used to work in acoustics, and sometimes dealt with outdoor sound propagation and environmental noise nuisance. I think in this case you'll be OK
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Old 15th Sep 2020, 8:18 pm   #18
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Default Re: Pulsynetic master clock: question about gravity arm roller.

...but you'll dream it.
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Old 16th Sep 2020, 2:15 am   #19
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Default Re: Pulsynetic master clock: question about gravity arm roller.

With my working 1930s clock there is very little play in the roller bearing.
I do have a 1960s clock in my to do pile and there is so much play itís almost falling off. But it was still working when taken out of service.
I have my clock in the utility ,not ideal and the constant change of temperatures does muck up the accuracy.it was put they because of the noise.
We have got used to the light clunk of all the slave clocks round the house and donít mind them at all Andy
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Old 16th Sep 2020, 12:19 pm   #20
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Default Re: Pulsynetic master clock: question about gravity arm roller.

...So...it's not got a tick-silent knob like my marble Metamec...
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