Drive coil ampere turns for seconds pendulum

This topic has 7 replies, 3 voices, and was last updated 14 September 2026 at 20:33 by John Haine.

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13 September 2026 at 02:58 #864630
carlw
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@carlw
I have started a pendulum clock based upon John Wildings’ version of the ME Jubilee Clock and using my electronic Hipp drive circuit. The seconds pendulum has a 10 lb bob and I hope to be able to fit the four optos within a 2 – 3 deg swing. Bit of a space problem here that I hope to suss out.

What I need is a starting point for the drive coil. The coil core will be nylon so that I can use a NIB magnet in the end of the pendulum. Any suggestions for ampere-turns of the coil would be most welcome.

Carl W
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13 September 2026 at 08:08 #864635
John Haine
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@johnhaine32865
https://sound-au.com/clocks/free-pendulum.html

The coil design in this might be helpful.
13 September 2026 at 10:41 #864651
duncan webster 1
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@duncanwebster1
At some point you’ll have to tell us why it needs 4 optos
13 September 2026 at 18:45 #864723
carlw
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@carlw
John Haine: Thanks for the link.

Duncan: I’ll give you the real story. I built most of John Wilding’s Large Balance Wheel Clock and found it to be quite noisy. So, I designed and built an electronic Hipp drive circuit that is entirely quiet. It was published in ME magazine in issues 4694 – 4696. The circuit requires 4 opto-interrupters and there is a lot of room to accommodate them below the 5″ diameter balance wheel. A flag mounted on the balance wheel travels through the opto apertures, decides if the balance wheel requires an impulse, times the impulse, and its duration. A seconds pendulum swinging 2 -3 degrees may not have the equivalent length for the optos to perform the same functions if they are mounted linearly.

I do not know much about clocks. I had assumed that the heavy bob would need a lot more force than the balance wheel. So, I just now did the experiment that I should have done: I pushed the pendulum and then pushed the balance wheel. Not a lot of difference. Now it is apparent that the real question is: will I need a much larger drive coil for the pendulum. The circuit is not required to start the pendulum from rest, only to make up lost energy. IIRC, the balance wheel is operating on 3vDC from the 5vDC TTL power supply so I may be able to use the design that I used for the first clock. There are more ampere turns available by increasing the voltage.

Anyway, Duncan, thanks for the ping and getting me to thinking better.

Carl
13 September 2026 at 21:46 #864738
John Haine
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@johnhaine32865
The impulse only has to provide enough energy to overcome the energy lost since the last one. This does not depend on the bob mass but more on its aerodynamic drag. Without knowing the configuration of your drive coil and magnet it’s very difficult to comment on the AT needed, but probably much less than you might think.

You should be able to use only 2 optos, one at bottom dead centre (BDC) for the impulse, the other at the nominal turnaround point (TAP) to govern amplitude and tell the control which side the pendulum is. I have a clock which uses only 1 opto but has an Arduino and uses a gravity escapement.
13 September 2026 at 23:41 #864756
duncan webster 1
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@duncanwebster1
Using a magnet on the end of the pendulum implies something like a fedchenko drive, so you only need one opto or hall effect to detect end of travel. I’m away from home at present, will dig out the relevant ME when I get home if I still have them.
14 September 2026 at 03:24 #864760
carlw
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@carlw
Righto! I began my electric clock experiments with both single and dual coil Fedchenko drives using single and dual transistor switches. I mined the Internet for circuits. Not knowing much about clocks, I started out doing things wrong with a light-weight bob on a seconds pendulum with flexible mounting. The vibration was intense. Some thought suggested that the problem was that the sudden turn-on of the impulse occurred while the pendulum magnet and the drive coil were at or near their point of maximum engagement. It was effectively a hammer blow. I accidentally discovered a serious problem with this type of drive. A single opto at “bottom dead center” will have the same problem.

I designed a different drive circuit in which the drive coil is energized when the coil and pendulum magnet are some distance apart, and their interaction is significantly less abrupt because the force increases gradually. The drive impulse is turned off when the lead edge of the magnet is at the center of the coil to eliminate any drag if the center of attraction goes past ‘bottom dead center.’ The electronic Hipp drive also will impulse only when the pendulum swing has decreased a pre-determined amount. Measuring the swing and independently timing the initiation and duration of the drive impulse requires 4 optos, four set-reset flip-flops and a transistor power switch.

May I suggest that you visit your favorite artificial intelligence to inquire about this known problem with Fedchenko drives.

PS: I remember reading about a sinusoidal drive impulse. Perhaps this idea could be applied to the Fedchenko drives to reduce the vibration.
Carl
14 September 2026 at 20:33 #864894
John Haine
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@johnhaine32865
I’m not quite sure what you mean by a Fedchenko drive exactly. If his drive suffered from vibration it certainly didn’t stop it being the most precise pendulum clock made in series production, being clearly able to detect tidal g variations. Fedchenko’s magnet and coil arrangement is tricky to make but gave a very clean unidirectional impulse in the direction of pendulum motion.

There’s a class of clocks that have an axially mounted magnet on the end of the rod swinging over a coil, which might be what you are referring to, in the fashion described in the link I gave. I’ve made a couple of these, vibration wasn’t a significant problem with either. Perhaps because only a very small impulse is needed. Generally they apply the impulse by repulsion just after BDC and usually use the voltage pulse induced in the coil to sense position, as did Fedchenko’s mk2 clock.

Synchronome clocks have a very hammer-like impulse and lots of resulting rod vibration but nevertheless can be very accurate.

In my limited experience of AI it usually gives uninformed and misconceived anwers to horological questions.

I know of 3 people who have made successful sinusoidal drive clocks. I don’t see how this could be applied to a Fedchenko drive, please explain.
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