# how to reduce speed/ amplitude of electronic pendulum??

Discussion in 'Electronic Repair' started by Bill Walston, Oct 11, 2012.

1. ### Bill WalstonGuest

I recently purchased an electronic pendulum to be used in a clock I
recently digitized:

http://www.klockit.com/products/dept-356__sku-20071.html

The pendulum take a single AA battery. I used a lithium battery which
didn't last very long. I have several goals I want to try and implement:

a) I would like the battery to last much longer. What's the best way
to make this happen? I was thinking that resistance inserted between
the battery and circuit might do the trick, but unsure.

b) The pendulum runs too fast and has too much amplitude, with the
latter so much so that it keeps hitting the insides of the clock. It's
not a loud sound, but far from your typical "tick-tock" which is
desired. I'm thinking an added resistance might reduce both battery
drain as above and reduce the pendulum amplitude, but what about
frequency?

Thanks in advance for any help.

Bill

2. ### mikeGuest

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

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.

3. ### Guest

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

4. ### William SommerwerckGuest

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

5. ### Bill WalstonGuest

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.

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

6. ### BeeJGuest

I recently purchased an electronic pendulum to be used in a clock I recently
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.

7. ### Franc ZabkarGuest

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

8. ### William SommerwerckGuest

Excuse my ignorance, but how does your circuit
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.

9. ### Guest

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

10. ### hr(bob) Guest

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

11. ### N_CookGuest

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

12. ### Guest

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

13. ### Franc ZabkarGuest

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

14. ### William SommerwerckGuest

Assume the pendulum is supposed to have a period of one second.
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.

15. ### William SommerwerckGuest

I've only seen one electronic pendulum. it used a sensing coil
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.

16. ### N_CookGuest

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

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.

17. ### William SommerwerckGuest

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

18. ### Franc ZabkarGuest

Perhaps there are two different design philosophies.

In one case the pendulum is tuned to a frequency of 1Hz and the
electronic circuit functions to compensate for losses due to friction
and drag.

In the second case the electronic circuit provides an accurate crystal
controlled time base and it keeps the pendulum synced to this time
base.

In other words, perhaps in the first instance the pendulum is driving
the clock movement, while in the second case the clock movement is
driving the pendulum.

- Franc Zabkar

19. ### William SommerwerckGuest

What you say makes sense -- but the drive circuit will always compensate for
losses, regardless of design philosophy.

Therefore, it makes sense to have the pendulum swing a tiny bit slow, and
have the drive circuit force it to the correct frequency. This would also
make trimming the frequency a simple matter.

20. ### Guest

To me the way that makes the most sense is to completely uncouple the
two functions. The accuracy of the cheapest quartz movement is far
better than you can get with the most precise pendulum. The most
efficient pendulum is one that oscillates at it's native frequency.
Googeling electronic pendulum drive circuit yields a great deal of
information, including some designs that simply provide a boost to a
pendulum at it's native frequency. Most of the designs did nothing to
optimize drive current.

PlainBill