Electrically sync a mechanical clock?

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Recently I picked up a big mantel clock for $5 at a garage sale down the street. The clock uses a hidden pendulum. Like any mechanical clock, with much fiddling it can be made to keep reasonably accurate time, but that's not good enough for my wife.

It occurred to me that some form of electromagnet pulse could be used to sync the pendulum (with magnet attached) to keep it running at the right speed. Might be a fun project. Anybody have any knowledge or experience in this area?

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Well, that is exactly how Foucault pendulums are kept going. The electro-magnet is at the bottom, so it pulls toward the center at twice the pendulum frequency (pull once every zero crossing). The magnet is turned off as the pendulum starts to swing away from dead-center. By tweaking the time when the magnet is turned on, you can vary the speed. I suspect that the pendulum is adjusted to be slightly slow and the electromagnet speeds it up, but not sure about that.

I don't think that the Foucault Pendulums have a magnet at the bottom, just a piece of soft iron.

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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Now I really like the above approach, but I also really like having options.

Option #2, in this case, is to install a small (3 x 3 x 1/2 inch) clock module that runs on a AA battery, such as is found in a numer of inexpensive wall clocks you can get at Wal-Mart, etc. Then the Pendulum is just for show.

Not too techie, but certainly fast, easy, and out-of-the-box solution, (Out-of-the-box both intellectually and parts wise!).

JC

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Another tack on Option #2 is Build a WWVB Radio Controlled Nixie Clock.
It uses a radio clock movement.

"Dare to be naïve." - Buckminster Fuller

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Na, you guys are missing the point! He doesn't want a modern clock, he wants an electronically regulated mechanical clock.

Besides desperate, not to mention futile, attempts to make a living, I've wondered about this myself.

You adjust the speed of your clock by carefully adjusting the length of the pendulum. Unfortunately, lots of things, like temperature, upsets this. So, how 'about comparing the time your mechanical clock says with the time of a hidden electronic clock, and adjust the pendulum automatically? Of course, you don't need to electronically read the hands, just count the ticks.

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It's easy to stop breaking the 10th commandment! Break the 8th instead. 

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Or..........
Get a wife that is not so picky. :?

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Adjusting the effective pendulum is pretty hard.

The center pull electromagnet requires NO change to any of the moving parts with the possible exception of adding an iron "pull-piece" at the tip of the pendulum arm if everything is non-magetic. You might want to add a photo-sensor to detect when the pendulum starts to move away from dead center, as the signal to turn the electromagnet off.

It is worth pointing out that Foucault Pendulums do not require a specific swing frequency. So, in that case, all the magnet does is add a little bit of energy on each half swing to make up for air friction losses.

In this case, it would be a sort of feedback system in which the magnet pulse width controls the acceleration or deceleration rate of the clock. The photo cell provides the frequency information which can phase compared to the AC line, and if the phase begins to lag, you turn the magnet on a little earlier to accelerate it slightly. If the phase starts to lead, then you turn the magnet on a little later.

The Foucault Pendulum uses a magnet at dead-center because pendulum can be swinging at any azimuth angle with respect to the compass rose that is normally displayed on the pendulum base. In this case,the angle remains fixed so that is not an important factor. Instead, I recommend it simply because you only need one magnet, and it can be placed so that it is less obtrusive. Further, anything opto or any other supporting parts and pieces are needed only once and can probably be hidden out of the way.

Actually as I think about this, a single photo sensor should work., You turn on the electromagnet while the pendulum is still some angle away from dead center. Do this on a feedback-controlled time basis. Then, as the pendulum approaches dead center, turn the electromagnet off. This way, there is never any hazard of having the magnet on long enough to retard the motion as the pendulum moves away from center.

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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Na, it's a wound, or maybe weight operated clock.

You just hide a threaded rod in the pendulum and use a motor to turn a nut or somesuch. Then compare the clock's time with the real time every hour or so and say, "Hmm, a little slow this hour, shorten pendulum by 1/2 turn," and so on. Each hour may be a tick or two off, but I'd bet you could keep it right on day by day.

(I'm thinking of my dad adjusting the clock by turning the knurled nut at the bottom of the rod.)

Remember all the fancy bars on a grandfather clock? They're to make it temperature stable. The bars are different metals with different C of expansion. The goal is to keep the bottom of the pendulum at the same position as the bars expand and contract at different rates.

http://en.wikipedia.org/wiki/Gri...

Hehe. Here's one that uses a vial of mercury. :D

The largest known prime number: 282589933-1

It's easy to stop breaking the 10th commandment! Break the 8th instead. 

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What you need is called a "Hipp toggle." such were used on astronomical clocks before modern oscillators were cheap. It is hard to describe this. Basically it is a little ratchet lever (toggle) that is loose on the pendulum. This drags over a notched fixed block connected to a micro switch. When the energy is depleted the trip lever will catch in the notch pushing down the fixed block making contact on the switch. The top of the block that the toggle rides over is curved in away to minimize friction.

The Foucault pendulum uses something called a "Charon ring." Usually made of nickel. An old clock magazine I have says to drill out the center of a coin to make the ring. Silver wire is wound into the support cable, when the wire no longer conducts then an impulse is made to inject energy back into the system. If only I had a room with a 32 foot roof. (Although the plans were for a half length pendulum. as I recall.)

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I remember that trick from an old amateur scientist article. Yup, all the way back in 1974.

http://jesseenterprises.net/amsci/1974/09/1974-09-body.html

Maybe some ideas can be (re) used.

-carl

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Read that with much interest. Instead of adjusting the length of the pendulum like I've always imagined, he "adjusts gravity" with a magnet.

The largest known prime number: 282589933-1

It's easy to stop breaking the 10th commandment! Break the 8th instead. 

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I guess what you are really trying to do is to "syncopate" rather than "synchronize". IIRC, this has come up before as a thread on AVRFreaks.
About 8 years ago, I built a "syncopater" for this steam powered clock, to improve it's accuracy. IIRC, it used two solenoids driven by a p-c. It was accurate to about two seconds a year, until the vandals got to it!

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Riddle me this...How did the serpent move around before the fall?