how to reduce speed/ amplitude of electronic pendulum??

First thing to do is state the problem. "very long" "much longer" We talking minutes? years?

Can't tell from the link. You make a pendulum slower by making it longer. But google would have told you that in the first hit. You make it more efficient by reducing drag. You probably don't want to use a vacuum enclosure, but you might be able to reduce bearing friction. Then you "kick" it in resonance to reduce the battery drain. The link doesn't say how the "kicker" works. You reduce the energy "kick" to the point that the energy in balances the pendulum losses at the amplitude you want. Resistor might help the amplitude, but may not help the battery drain. Unless the "kicker" is designed for it, the amplitude will change with the battery age.

Frequency is dependent on the length of the pendulum and the strength of the gravitational field. To slow the pendulum down either increase the length of the pendulum or reduce the strength of the gravitational field. Either use a D cell or an external power supply to increase the battey life.

PlainBill

Point... As this pendulum is designed for a clock (I assume), wouldn't it have a specified period appropriate for a clock?

Well, the former lithium 1.5V battery powered it for maybe 4-5 months. I'd like to stretch this out to a year at least.

Can't tell from the link.

The circuit is a 2 transistor design with resistors, capacitors and of course the coil. I didn't try to map it out, but it looks similar to the 2 transistor pendulum circuits on the web.

I know we can change the frequency by increasing pendulum length, but there's no room in the enclosure. Why wouldn't a simple capacitor change in the circuit accomplish the same goal? Isn't the coil just part of a resonant LC circuit?

Bill

No. The resonance is mechanical, the coil just applies a little energy to overcome friction and keep it moving. All changing the circuit's frequency will do is waste the battery's life as heat.

No, the RC or LC timer in the circuit does not set the pendulum swing rate. it really can't, the pendulum is WAY too massive for a tiny, battery-powered circuit. So, first, you need to fix the pendulum.

Second, you need to reduce the kick the circuit applies to the pendulum each swing. That might be done by adding turns to the coil that provides the kick. Or, the RC timer is leaving the coil current on too long, so reducing the cap value might reduce the energy imparted, as well as preserve battery life.

Jon

Cut out the sides of the clock to allow it full swing. If this is a pendulum designed to tick at the correct rate then you have to modify the cabinet structure to accomodate it not the other way around. So when you cut out the sides of the clock cabinet you will have a more unique conversation piece. Put up a photo after you get it working.

On Thu, 11 Oct 2012 13:22:02 -0400, Bill Walston put finger to keyboard and composed:

Would there be any way to utilise a solar panel and a NiCad or NiMH battery, or maybe a super capacitor? For example, you could cannibalise a cheap solar garden light.

Excuse my ignorance, but how does your circuit know when to apply a kick? If the kick were to come when the pendulum is on the rise, then that would work against it. Therefore the circuit would need to know when the pendulum has begun its descent and apply the kick at that time.

Furthermore, if the pendulum's amplitude is growing too large, then the circuit would need to refrain from kicking it until the amplitude subsides, if only to conserve the battery.

Therefore ISTM that the circuit must be sensing the pendulum's position, in which case you would need to adjust the sensor in order to set your desired amplitude. Or am I way off?

- Franc Zabkar

It doesn't.

Assume the pendulum is supposed to have a period of one second. You design it to be a little bit longer, then make the driver circuit operate at exactly one second. The pendulum will eventually sync with the driver.

Remember when TVs had hold controls? The principle is the same. The most-stable operation is obtained when the oscillator runs a tiny bit slower than it should, with the sync signals "kicking" it at the right frequency.

The specific product he identifies is designed as an add-on for a quartz movement and comes with a pendulum with an adjustable length arm. I'm unsure of the correlation between pendulum length and amplitude of the swing, but I would expect a shorter pendulum to swing through a wider angle.

PlainBill

If I remember correctly, a larger weight on the pendulum will also slow it down.

slower

Human clocks are the same. Put a human in a cave, out of touch with the outside world, and his natural day-length reverts to about 24.5 to 25 hour days, requires the sun etc to sync him to 24 hour days

You don't. The effective length of the pendulum (distance between the pivot and the center of the mass) and the gravitational force are the only things that affect the speed. Remember the experiment Galileo did a few years before he turned his eye to the heavens.

PlainBill

On Fri, 12 Oct 2012 14:02:31 -0700, "William Sommerwerck" put finger to keyboard and composed:

Thanks. I'm still trying to understand how it syncs, though.

I'm trying to envision an equilibrium where the kick comes at a regular point in the swing. Does the pendulum sync so that it gets a kick at the beginning of the downswing, or does it come at the end of the upswing, or can it come at any point in the arc?

- Franc Zabkar

I've only seen one electronic pendulum. it used a sensing coil to detect the approach of the pendulum, and fired a pulse to add to the stored energy.

There is no "intelligence" to the synchronization process. Because the pendulum swings at a different frequency with respect to the drive circuit, it has a continually varying phase relationship with it. So, at some point the kick will occur when the pendulum is near the energized drive electromagnet. The cycle starts at this point.

On the next swing, the pendulum will be slightly "late". But if it's "close enough" to the energized electromagnet, it will receive another kick. And so on, and so on...

I assume at the end of the upswing.

I'm not sure that would work correctly. You want the drive coil to fire at a fixed frequency. Otherwise, the pendulum would be synched at its lower native frequency.

If I remember correctly, a larger weight on the pendulum will also slow it down.

from

Q. Why do the people who regulate "Big Ben's clock use adding or subtracting old pennies to the weight on the bottom?

- John Gifford, London

A. Yes the period of pendulum is governed by its length and is independent of the mass at the end. But if you add an old penny to the bob of the pendulum of Big Ben, then you slightly alter its length; in fact you make it a bit shorter, because the centre of mass of the bob is slightly raised. Similarly if you take pennies off, you will in effect slightly lengthen the pendulum. This seems an odd way to do it, but it is obviously very convenient, and simpler than winding the bob up and down by a minute amount.

Nope. The period depends on the length of the pendulum and the acceleration of gravity.

Physics courses often include units analysis. * Such an analysis shows -- without even performing an experiment -- that length and the strength of the gravitational field are the factors that matter.

• That probably isn't the right term, but I can't think of what it is.