First Attempt at an Electronic Hipp Clock

[Michael GilliganParticipant @michaelgilligan61133]

.

This is your Wake-Up Call, Howi

It’s about the energy required to impulse a Synchronome pendulum, and interesting at several levels.

.

.

Credit: Frank Hope-Jones

.

MichaelG.

[John HaineParticipant @johnhaine32865]

Alas, Fedchenko's clock that impulses one per cycle at the base of the bob, rather shows that F H-J was wide of the mark in his conclusion.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by John Haine on 01/02/2023 13:00:51:

Alas, Fedchenko's clock that impulses one per cycle at the base of the bob, rather shows that F H-J was wide of the mark in his conclusion.

.

but that doesn’t preclude it from being interesting … and specifically, it does address Howi’s earlier comment about the energy required to maintain a pendulum in its swing.

[quote] I would have thought 5v power to the coils would not be enough to move a long pendulum and weight. [/quote]

MichaelG.

Edited By Michael Gilligan on 01/02/2023 13:37:43

[duncan webster 1Participant @duncanwebster1]

Without knowing how the impulse was applied by FHJ, and what he counts as external friction, it's difficult to comment. As JH says, one of the worlds most accurate clocks applied the impulse below the bob

[Michael GilliganParticipant @michaelgilligan61133]

Posted by duncan webster on 01/02/2023 13:46:44:

Without knowing how the impulse was applied by FHJ, and what he counts as external friction, it's difficult to comment. …

.

I wasn’t actually inviting comment … Simply waking-up Howi by posting something interesting.

The book is widely available.

MichaelG.

.

I think everyone interested in this topic should at least read it,

but If you don’t want a hard copy:

https://clockdoc.org/gs/handler/getmedia.ashx?moid=57393&dt=3&g=1

Edited By Michael Gilligan on 01/02/2023 14:16:37

[Michael GilliganParticipant @michaelgilligan61133]

For clarity … the part of Fig. 82 that is most relevant here is the baseline energy requirement:

.

.

… Which is independent of the points on which John and Duncan have commented.

.

MichaelG.

[S KParticipant @sk20060]

Thanks for pointing out that book. The introductory comment about quartz clocks should be accompanied by a sober-sounding narrator intoning "little did they know …"

Unfortunately, it's written in that overly wordy and flowery fashion that was common in earlier times, which makes it a slog for modern readers.

So that figure 82. What are the points being made? Seems like:

(1) That the amount of energy needed purely for keeping the pendulum in motion is the same whether spread over 30 impulses or applied in one larger impulse? Seems logical.

(2) That more energy is wasted if 30 small impulses are applied vs. 1 larger one? Also seems logical in a mechanical system, but likely irrelevant in magnetically-impulsed systems.

(3) That more energy is wasted if the impulse is applied at the bottom vs. near the top of the pendulum? I have more trouble accepting this, but I could imagine that additional friction could be encountered at the bottom because a larger throw of the impulsing mechanism could be necessitated due to the larger amplitude near the bottom. But again, this supposed additional wasted energy is likely irrelevant in magnetically-impulsed systems.

As for the ideal position for impulsing, I'll stick with the center of percussion, which would be near the bottom in a pendulum with a heavy bob.

One other point made is that the mechanical impulse was designed to be applied with nearly zero force at its onset, growing to some maximum before release. I think this could be pertinent to magnetically applied forces as well, and I had imagined using an RC network or similar to avoid an abrupt application of force.

Edited By S K on 01/02/2023 16:05:22

[John HaineParticipant @johnhaine32865]

Posted by S K on 01/02/2023 15:59:28:

Thanks for pointing out that book. The introductory comment about quartz clocks should be accompanied by a sober-sounding narrator intoning "little did they know …"

…….

One other point made is that the mechanical impulse was designed to be applied with nearly zero force at its onset, growing to some maximum before release. I think this could be pertinent to magnetically applied forces as well, and I had imagined using an RC network or similar to avoid an abrupt application of force.

Edited By S K on 01/02/2023 16:05:22

There's a certain amount of post-hoc rationalisation here. The shape of the "impulse slope" of the Synchronome pallet is essentially a circular arc or 0.75" radius. Apparently that's what they were made with but when F H-J was presenting a paper at the IEE, William Shortt who was in the audience worked out what the shape should be to apply a "raised cosine" impulse that started gradually, built up to a maximum, and then rolled off again to zero, but that shape isn't the circular arc. With the circular arc I think the idea is that the roller drops on to the pallet just before the start of the slope but that depends on the clock being very precisely set up. There's a time-lapse video on-line (or used to be, the page seems to have been removed from Brian Mumford's site) that shows this is an idealisation. Actually, except for considerations of mechanical "ringing", the shape of the impulse is virtually irrelevant for any reasonably high-Q pendulum, all that matters is the position of its phase centre. Nasty spiky forces just amount to higher order harmonics that the pendulum filters out.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by S K on 01/02/2023 15:59:28:

[…]

So that figure 82. What are the points being made? Seems like:

(1) That the amount of energy needed purely for keeping the pendulum in motion is the same whether spread over 30 impulses or applied in one larger impulse? Seems logical.

[…]

.

I dug it out mainly because I remembered that FH-J had quantified the energy required to keep a Synchronome pendulum swinging … and such information is relatively scarce.

Given Howi’s remark about Voltage, I thought it worth posting here.

We all know [or can easily find] the design details for a Synchronome pendulum, so it seems like a convenient benchmark for anyone wishing to start designing a clock.

MichaelG.

[Tony JeffreeParticipant @tonyjeffree56510]

Posted by John Purdy on 31/01/2023 22:23:50:

Dave

About your comment about the "twang" I think you are correct in saying the the impulse is more powerful than needed. I am going to try and put some resistance in series with the coils and see how far I can lower the voltage and still get sufficient impulse to keep the pendulum going. Or I could also just lower the coils to increase the distance from the coils to the armature on the pendulum rod to decrease the magnetic flux.

I don't think there is a problem with the timing as the coils are de-energized just as the leading edge of the armature reaches the centre line of the coils.

John

Edited By John Purdy on 31/01/2023 22:39:23

I've just been experimenting with my clock and it is very easy to induce the dreaded "twang" by varying the timing of the impulse and the position of the coil. If you are getting a "twang" then essentially some of the impulse energy is being dissipated in unwanted vibration (and corresponding disturbance of the pendulum motion), so it is well worth figuring out why this is happening – I suspect it will actually prove to be a timing issue in your case. If the timing is wrong, then the magnet will initially accellerate the pendulum, but if you don't switch it off soon enough (i.e., before the swing reaches the point of max attraction) it then acts as a brake for the last part of the "impulse" and causes the pendulum to twang.

My impulse coil activates with the pendulum near enough at BDC, but I have offset the electromagnet sufficiently to the right of BDC so that the impulse is guaranteed to have finished before the armature attached to the pendulum reaches/passes it.

I can induce the "twang" very easily by shifting the coils left too far and/or by making the pulse length too long. With my current setup the pendulum swings for about a minute between impulses and the impulses are completely silent.

[Tony JeffreeParticipant @tonyjeffree56510]

The two sensors that determine the pulse length are set approx 13mm apart and the coils are offset approx 35mm from BDC.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by John Haine on 01/02/2023 16:35:13:

.

There's a certain amount of post-hoc rationalisation here. The shape of the "impulse slope" of the Synchronome pallet is essentially a circular arc or 0.75" radius. Apparently that's what they were made with but when F H-J was presenting a paper at the IEE, William Shortt who was in the audience worked out what the shape should be […]

.

Not sure if this will be of any interest, but it’s a plot that I did for someone back in 2018, so I might as well chuck it in the pot here:

.

.

.

.

MichaelG.

[John PurdyParticipant @johnpurdy78347]

I've just moved the coils down so the gap between the armature on the end of the pendulum rod and the coils is 3/8" instead of the 1/16" previously but kept the same lateral distance from BDC as before. The impulses are now at 32 second intervals vice the 3 1/2 minutes previously and the "twang" is gone. Which seems to indicate that the magnetic flux was much stronger than necessary at the closer distance.

John

[Roger JelbertParticipant @rogerjelbert74854]

It's great to see that enginners are still experimenting with the idea of making a "free pendulum" clock using modern electronics. My two clocks are still going well after about 6 years and I find the best way to live with them is to ignore the day to day variations in seconds. I decided that unless perfect correction for temp, pressure, humidity and even perhaps gravity (tides !) is incorporated once a well built clock is regulated as best as is possible it will average out to be a good timekeeper. A friend who has kept records of the going of a Synchronome clock by computer comparison with NTC reckons he can see the changes through the seasons of the year. It seems to me pressure variations are the greatest issue.
On the question of Post Office clocks, although the exchanges are (were?) powered by 50v batteries only the contact making circuits were connected directly from that voltage (50v relays and series loop clock circuits). The circuit for driving the Hipp controlled drive magnet were electrically separate in the clocks and were fed from 50v via a high value resistance. The drive EMs of a PO clock are about 9ohms and will work happily from 4.5 volts.

[Author]

Posts