# Controlling a tiny pendulum with opposing electromagnetic fields

#### jpeterman

Joined Feb 7, 2023
7
I am trying to control the movement of a pendulum by alternating current through opposing electromagnets. I have an idea how this would work but no experience in this particular area so hoping someone can provide a little guidance as to how I might accomplish this. The goal is to control the movement of a small object mounted at the other end of the pendulum in a smooth and alternating way as if it was blowing in the wind. The dimensions need to be small...about an inch wide and several inches tall. I am thinking that if this will work, the current through the electromagnets can be controlled with an ardino or some other small programmable electronic controller...maybe one controller controlling several of these movers. I am hoping to find the windings as inexpensive off the shelf type things as I need to make a dozen or so of these if I can make it work.

The attached drawing is just a basic concept and not at all to scale. the are opposite the pendulum will be longer...probably like a spring steel wire to create a more natural sway at the end. The pendulum might be as simple as a steel washer. The motion can be on a flat plane or any variation. Imagine trying to make a sea oat look as though it was blowing in a gentle wind.

Any thoughts, ideas or direction would be greatly appreciated. I have a vision of how this would work but don't really know where to start as far as actually building it and/or making it work.

Thanks!

#### BobTPH

Joined Jun 5, 2013
9,296
The fields are going in the wrong direction in your drawing. The ends of the coils need to be toward the (inverted) pendulum, i.e. rotate them 90°.

#### shortbus

Joined Sep 30, 2009
10,049
Does it need to be done with two electromagnets? One solenoid on the end that you want the electromagnets on could do it. A plunger on the end of the arm going into the solenoid, activate the solenoid and the arm goes one way, turn off the solenoid and it goes back to the staring point. Many years ago they made advertising signs that swung a part of the sign by doing that.

#### LowQCab

Joined Nov 6, 2012
4,311
This is more of a problem in Mechanical-Design,
the Electronic part needs to be tailored to the mechanical-design that is finally used.

When using an actual "Pendulum" the movement will be simply swinging
unless You use sophisticated controls to control the Electro-Magnet,
and in that case, it doesn't need to have any resemblance to an actual "Pendulum",
it can be just a thin, springy piece of Steel-Wire, like a Guitar-String.

If the Steel-Wire is used,
the Electromagnets can be mounted at a ~90-degree angle to each other,
to create motion in any direction,
or even round & round in a circle,
or just random-motions.

The Weight of the object, regardless of whether using a Pendulum, or Springy-Wire,
is going to affect the speed of motion,
and create repeating oscillations in a particular "Frequency-Range".
This may need to be experimented with to achieve a more "realistic" looking motion.

The controls may be Analog, or may use a Micro-Controller, ( if You know how to write Code ).
Either type of control can work equally well and provide a variety of effects.
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#### Ya’akov

Joined Jan 27, 2019
9,267
Welcome to AAC.

To give you a useful answer it would be very helpful to know why you are trying to do this. That is, what problem are you trying to create a solution to? So many questions we don’t know to ask would be answered with that information.

It seems what you are trying to do is possible. But as is often the case, telling you how to do what you ask is no guarantee that it will solve the problem that is prompting your question.

#### jpeterman

Joined Feb 7, 2023
7
Does it need to be done with two electromagnets? One solenoid on the end that you want the electromagnets on could do it. A plunger on the end of the arm going into the solenoid, activate the solenoid and the arm goes one way, turn off the solenoid and it goes back to the staring point. Many years ago they made advertising signs that swung a part of the sign by doing that.
It needs to be smaller than a I think I could make with a solenoid. My thought is by charging both coils to keep the pendulum in suspension. Then by altering the current very slightly, I could pull the pendulum one way or the other. Then by writing a little code using a random number generator, I could make it swing back and forth in a natural random way.

#### jpeterman

Joined Feb 7, 2023
7
Welcome to AAC.

To give you a useful answer it would be very helpful to know why you are trying to do this. That is, what problem are you trying to create a solution to? So many questions we don’t know to ask would be answered with that information.

It seems what you are trying to do is possible. But as is often the case, telling you how to do what you ask is no guarantee that it will solve the problem that is prompting your question.
Fair enough. What I am trying to move will be a specialized LED bulb. The bulb is used to create water effects and has a controller with it. By grouping three of the bulbs, I can create a static projection that looks like the reflection of a pool. The only problem is that it is static. I found that by moving the bulbs slightly, the patterns interact and look much more realistic. So the problem is to make a mount for these bulbs that will cause them to move slightly back and forth in a random way. My thinking is if I have two opposing electromagnets I can sort of suspend the pendulum end in a magnetic field. I was hoping by adjusting the current (visualizing a sine wave), it would cause the pendulum end to move back and forth. a little motion on that end would create much more motion on the bulb end. I only need about an inch of travel on the bulb end but because I need three of these things to fit into a single fixture about the size of a wall sconce, they need to be really simple. The controller could be mounted separately. I need to make four fixtures (for each corner) with three units in each.
The units also have to be able to handle humidity and salt air. What I am ultimately trying to do is project a lighting effect onto the ceiling of an outdoor patio to look like it is over a pool. I was initially going to try to do it with addressable RGB strips around the perimeter but I found these bulb that do a much better job...if I could just get them to move a little.

#### jpeterman

Joined Feb 7, 2023
7
This is more of a problem in Mechanical-Design,
the Electronic part needs to be tailored to the mechanical-design that is finally used.

When using an actual "Pendulum" the movement will be simply swinging
unless You use sophisticated controls to control the Electro-Magnet,
and in that case, it doesn't need to have any resemblance to an actual "Pendulum",
it can be just a thin, springy piece of Steel-Wire, like a Guitar-String.

If the Steel-Wire is used,
the Electromagnets can be mounted at a ~90-degree angle to each other,
to create motion in any direction,
or even round & round in a circle,
or just random-motions.

The Weight of the object, regardless of whether using a Pendulum, or Springy-Wire,
is going to affect the speed of motion,
and create repeating oscillations in a particular "Frequency-Range".
This may need to be experimented with to achieve a more "realistic" looking motion.

The controls may be Analog, or may use a Micro-Controller, ( if You know how to write Code ).
Either type of control can work equally well and provide a variety of effects.
.
.
.
My plan was to use something along the lines of heavy single strand steel leader (like you use for deep sea fishing). The fulcrum would be close to the pendulum end so a little motion on the pendulum end would create much more motion on the other end. That said, I only need a little travel...about an inch or so.
So if I am understanding, are you suggesting putting the electromagnets at 90 degrees to each other but on a flat plane under the pendulum end? I was thinking two on either side in sort of a tug of war against each other...whichever side had more current would pull the pendulum toward it...by sending current to one then the other, it would pull it back and forth.

Again, the drawing does not reflect the actual circuit design...it was just something I threw together to illustrate what I envisioned it to look like. The electromagnets would actually not be wired together but would be isolated from each other and I would use an ardino to rasberry pi to trigger relays to turn each one on and off in a random pattern.

My understanding of electromagnets is very basic. I could see where if you could alter the magnetic field down the length of a single magnet, and positioned it under, you could do it with a single one. But given the space limitations, two mounted vertically and maybe hot glued to the inside of a piece of 1 1/4 pvc. The arm could be a piece of steel leader bent around a nail to create the fulcrum and then looped around a steel washer that would act as target for the magnetic field. Again, the movement doesn't need to be precise. I think I am starting to see a prototype develop here. My question for you guys is what sort of current would I need to pass through the coil to create the magnetic field? Would 12v dc work or would it need to be ac and how would that circuit work? I am guessing I would have to have a resistor or something to keep the wire from burning up.
Is there something I could buy off the shelf that I could just apply a current to that is already wrapped with whatever components would be needed and about the size (diameter) of a pencil? or maybe smaller...

Thank you guys for your time and help. I know I am probably asking terribly stupid questions. I have just never had the opportunity to make something like this before but strangely excited about it. :-D

#### jpeterman

Joined Feb 7, 2023
7
I updated the drawing to reflect 2 isolated electromagnets

#### Jerry-Hat-Trick

Joined Aug 31, 2022
591
I did something similar: The top picture shows the upper part of the pendulum with a cut nail through it, just inside the mouth of a solenoid. The suspension feather is just a small length of thin metal cut from a beer can. The second picture shows the thin "knife" at the bottom (made of the same material) which passes through an opto interrupter which can either trigger a pulse from an arduino or a 555 monostable - both work fine. The trick is to make the solenoid pulse equal or slighly less than one quarter of the natural period of the pendulum so it's only pulling when the swing is in the outward direction. If you use a dual opto interrupter you can make the arduino drive the solenoid (via a transistor) when the pendulum is moving towards the solenoid but it still works if it pulls when the pendulum pulls in both directions as the pull is very small when the pendulum is swinging to the right.

The wrench is just to stop my assembly falling over, the PP3 batteries are in lieu of a pendulum bob! This was a bit of a lash up, they are the only pictures I have.

Hope this helps.

#### Alec_t

Joined Sep 17, 2013
14,413
move slightly back and forth in a random way
A pendulum or a springy wire has a natural resonant frequency, so your magnet(s) would have to overcome that if you want true random movement.

#### MrAl

Joined Jun 17, 2014
11,733
I updated the drawing to reflect 2 isolated electromagnetsView attachment 287082

Hello,

There are a couple things you should change.

First is the orientation of the two electromagnets.
Second is the attracting piece you have labeled "steel" (although you could stick with the steel piece if you like).
The distance 'd' shown in the attachment should be as small as possible without having the piece be stuck to one of the electromagnets.

The two electromagnets should be orientated as shown in the attachment.
The attracting piece(s) should be rare earth magnets, or even just one rare earth magnet. The polarization of the magnet(s) should be as shown in the inset.
The distance 'd' should be as small as possible.
The friction of the fulcrum should be as constant as possible, probably a needle bearing.
You could also experiment with the magnets orientation, flipping one on one side for example so both N poles face outward.
You do have to experiment with the electromagnet pulse timing because the movement will have a tendency to rock back and forth with a given time period depending on various factors.

#### Attachments

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#### shortbus

Joined Sep 30, 2009
10,049
I found that by moving the bulbs slightly, the patterns interact and look much more realistic. So the problem is to make a mount for these bulbs that will cause them to move slightly back and forth in a random way.
If that's what your after, couldn't you mount your leds on a membrane, like a the material used in latex gloves, mounted on a hoop, like a embrodery hoop. The use a solenoid to randomly hit/nudge the membrane. This, membrane, would act like the surface of a pool of water with the leds projecting from that.

#### jpeterman

Joined Feb 7, 2023
7
If that's what your after, couldn't you mount your leds on a membrane, like a the material used in latex gloves, mounted on a hoop, like a embrodery hoop. The use a solenoid to randomly hit/nudge the membrane. This, membrane, would act like the surface of a pool of water with the leds projecting from that.
That's a thought...I like it!
I was thinking last night if I mounted the three wires together, I would just need one mechanism to move each group. I am liking the solenoid idea more and more provided they aren't too costly.

#### BobTPH

Joined Jun 5, 2013
9,296
The membrane idea is a good one, but I think the frequency it would vibrate at would be way too high.

#### MrSalts

Joined Apr 2, 2020
2,767
The membrane idea is a good one, but I think the frequency it would vibrate at would be way too high.
Frequency would be anywhere from a slow slosh to a ping. It really depends on how mush water is in the membrane (latex glove).

#### djsfantasi

Joined Apr 11, 2010
9,188
The membrane idea is a good one, but I think the frequency it would vibrate at would be way too high.
Instead of hitting the membrane, mount two small magnets on the perimeter of the membrane at 90° to each other. Then mount an electromagnet under each one.

Then by varying the polarity and current or voltage (the latter is easier with PWM), you can control the movement of an LED mounted on the membrane (or on a stalk of flexible material).

Developing the mechanism might take some experimenting. But I think it would work. I developed the idea after initially thinking of a gimbal controlled by servos or steppers or even this magnetic idea. ThenI realized the membrane could replace a complicated gimbal assembly.

Just an idea.

#### shortbus

Joined Sep 30, 2009
10,049
The membrane idea is a good one, but I think the frequency it would vibrate at would be way too high.
That would have to do with how tightly it's stretched. the tighter the higher the frequency. Think of how a guitar string vibrates. Maybe it would need some experiments with latex glove, trash bag material or?

#### LowQCab

Joined Nov 6, 2012
4,311
You stated something about some very vague space-limitations ...........
Wall-Sconce ???, there are a million Wall-Sconce designs,
are You referring to a Wall-Mounted-Electrical-Junction-Box ???
What is 1-1/4" PVC-Pipe all about ???
Where will these LED Actuators be mounted exactly ???,
in the Floor ?, on a piece of Furniture ?, in a decorative Planter ?, on a Wall angled vertically ?,
do You intend to create Custom-Wall-Sconces that contain the LED-Actuators ?,
or maybe use existing Wall-Sconces ?,
All this needs to be outlined precisely.

You stated that You had found an LED that would suit your purposes ...........
"" What I am trying to move will be a specialized LED bulb. ""
Manufacturer ???, Part-Number ???, Spec-Sheet ???,

A picture is worth a thousand words.

Here is a suggested Solenoid .........
These Solenoids can be configured into a group of 3-Solenoids, placed side-by-side, in a "circle",
which each will then "push" a 1.5" diameter Steel-Washer with
the LED Mounted in the center of the Washer.
This will allow the LED to be aimed in any direction,
( within a limited number of degrees of course ).

The Controller ..........
3- Op-Amp "Relaxation-Oscillators" will provide either Square-Waves, or Triangle-Waves,
each at an "Odd-Preset-Frequency",
which can control any number of LED Actuators via 3- N-Channel-FETs for each Solenoid-Coil.
The maximum-Current to all LED-Actuators will be regulated via the
Voltage adjustment of the main Power-Supply for all Actuators.
This will provide additional fine-tuning adjustment to the Random-Motion effect of the Actuators.

If this seems like a project that You are comfortable in taking on,
I'll make further efforts in creating Drawings and Schematics for the Electronics.
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#### MrAl

Joined Jun 17, 2014
11,733
Hello again,

I just re-read some of this thread and it seems that the only goal is to move some LEDs around to create some special effects.

Well if that is the case, this can be done in a purely electrical way with no moving parts.
The idea is that if you move a single LED around it creates a sense of movement, of course, but you can also do that using two or more LEDs.
If you mount a second LED next to the first LED and turn them on at different times (including both partly on at the same time) you can create the illusion of physical movement. That's because the two LEDs will shine out at slightly different angles and that makes it look like something is moving when the light intensity is varied for the two LEDs. This is also a way to simulate a camp fire or a candle.

The best way to do this is to PWM each LED with some random pulse widths and timing. You can get some pretty nice effects.
If you want to get even more realistic effects, use three LEDs mounted in a close nit "Y" pattern. That will give a 3d movement effect.
If you like a little color in there you can also use different color LEDs.
You can also try using the three color LEDs alone, because the dies inside the LED package are mounted in different physical locations so when you turn each one on it also creates the illusion of movement.

You can also place some frosted plastic around the LEDs to diffuse the light a little and that is nice for simulating a camp fire. A small piece for a candle flame.
They also make LEDs that blink randomly that you can use to simulate a fire burning, and no electronics needed other than a battery and resistor. Using two or more together creates some interesting effects.

It's interesting and a little fun to experiment with this. The advantage is of course that nothing has to move so long life, high reliability.

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