Storing Cookies (See : http://ec.europa.eu/ipg/basics/legal/cookies/index_en.htm ) help us to bring you our services at overunity.com . If you use this website and our services you declare yourself okay with using cookies .More Infos here:
https://overunity.com/5553/privacy-policy/
If you do not agree with storing cookies, please LEAVE this website now. From the 25th of May 2018, every existing user has to accept the GDPR agreement at first login. If a user is unwilling to accept the GDPR, he should email us and request to erase his account. Many thanks for your understanding

User Menu

Custom Search

Author Topic: A Pendulum should really work  (Read 54390 times)

elgersmad

  • Jr. Member
  • **
  • Posts: 72
A Pendulum should really work
« on: March 29, 2011, 12:16:54 AM »
I know how effective a pendulum can be by itself.  Add too much to that or take too much away, and it won't work so well.  The key point is really the fulcrum of the movement.  If you support it the right way with piezoelectric disks, it should work wonderfully.

First you take a stack of piezoelectric rings, and make all of your electrical connections.  Then you send rod through it that has a universal joint just below the stack of piezoelectric ceramic rings.  They don't really move much a few millionths of an inch to generate electricity.  So, as the pendulum reaches the bottom of it's swing, all of the downward energy is then sent through the stack of piezoelectric rings.  A flat washer holds the top end of the rod in place over the stack, and the universal joint hangs out below the stack.  The more massive the weight, once it's swinging won't loose much energy due to the compression of the piezoelectric disks.  If the height of the swing is nearly 90 degrees from vertical, and nearly horizontal for the length of the swing arm, almost all of the weight will have been taken off of the piezoelectric ceramic.  That produces the pumping action to generate electricity.  When you stack disks, the square area all experiences the same amount of force no matter how high you stack the piezoelectric disks until their own weight doesn't allow for decompression.  So, you could stack nearly 20 or 30 of these disks on top of each other.  I think a bowling ball or several hundred pounds of weight would work and a solenoid to keep the swing height to peak would use the least amount of energy, if and only if the solenoid's plunger is almost all the way in and it's a pull type solenoid.  Just to add enough force to make sure that the swing height is always exact.

conradelektro

  • Hero Member
  • *****
  • Posts: 1842
Re: A Pendulum should really work
« Reply #1 on: March 29, 2011, 07:15:21 PM »
@elgersmad:

I like the idea. Could work with various pendulum arrangements, as long as pressure is put on many piezoelectric elements.

Also pressure along the swing plane could be harvested, as in the attached drawing.

Just by chance, do you know a good source for piezoelectric elements. One would need a lot of them (like 20 or 30, as you say)?

Greetings, Conrad

gyulasun

  • Hero Member
  • *****
  • Posts: 4117
Re: A Pendulum should really work
« Reply #2 on: March 30, 2011, 12:02:56 AM »
...
Just by chance, do you know a good source for piezoelectric elements. One would need a lot of them (like 20 or 30, as you say)?
...

Hi Conrad,

I do not know if this is a good price or not, a first search at RS brought this:
http://uk.rs-online.com/web/search/searchBrowseAction.html?method=retrieveTfg&binCount=1&Nty=1&Ntx=mode%2bmatchallpartial&Ntk=I18NAll&Ne=4294957561&Nr=AND%28avl%3auk%2csearchDiscon_uk%3aN%29&N=4294953991&Ntt=piezo

it is a vibration sensor. If I find later some other sources, will post.

Possible problem can be they have very high electrical impedance and a clever way of matching is to be found to get the most out of them. MAybe resonating them with a suitable step down transformer.

Gyula

elgersmad

  • Jr. Member
  • **
  • Posts: 72
Re: A Pendulum should really work
« Reply #3 on: March 30, 2011, 07:58:17 AM »
Think simpler.  The more moving parts the more friction.  It's real basic.  When the weight is in the position I drew it in, the most weight is displaced on the ceramic disks.  When it's at 85 to 90 degrees and the weight has swung up as high as it can go, it takes the weight off of the axis.  Just like on a swing when you swing high, the chain goes slack and then you drop and jerk then continue to swing.  Too many axis will act like a chain.

When the plunger of a solenoid is almost all of the way in, it has the most pull for the least amount of power in volts and amperes of current.  So, you want the solenoid to pull as the weight is still moving toward it and add to it's velocity and keep the swing height to the desired height, where a chain on a swing would go slack and there's no stress on the piezoelectric.

You were very close based upon my description in words.  Mentally, you just didn't draw the same picture.  Those other piezoelectric elements would stop the pendulum from swinging just because they would take stress from the axis.  It might be a good idea to use just two axis as you've shown and connect the solenoid between the two.

elgersmad

  • Jr. Member
  • **
  • Posts: 72
Re: A Pendulum should really work
« Reply #4 on: March 30, 2011, 08:01:51 AM »
And I found a good place to get Piezoelectric Ceramic Disks, Plates and Rings

I don't think it'll be too cost effective to buy more than 2.  But, they are quality components.  I don't think that they should be soldered into place.  But use a combination of washers.  Nylon as an insulator, plastic tube to keep the sides from touching the bolt.  A couple of drilled holes in single sided copper clad circuit boards to get a connection in and out of there but, no direct soldering in order to keep an even amount of pressure on the disk via the stiff wash above the nylon washer and so one.  Don't allow metal to touch the sides of the piezoelectric disks.  Don't let any metal touch the disks that are not used to collect power. 

conradelektro

  • Hero Member
  • *****
  • Posts: 1842
Re: A Pendulum should really work
« Reply #5 on: March 30, 2011, 08:45:34 AM »
@gyulasun and elgersmad:

thank you, good places to buy piezo elements.

I do not understand piezo elements well enough. May be the frequency only matters when producing sound (by applying voltage)? In case of low frequency pressure, one probably can use any version of a piezo element?

I was thinking about stacking simple and reasonably priced elements like the one I attached (Piezo Element Farnell order code 1675548). They cost 54 Cents (Euro) a piece.

The metal plate is there to make a sound (bending up or down), but would not matter when stacking these elements.

The wires are already attached which might be useful. To build a stack, one could put acrylic discs in between to spread the load and to have room for the wires; making a cut out (slit) in the acrylic disks for the wires and the place on the piezo element where the solder might pose a problem when stacking these piezo elements.

It might be difficult to attach wires to a raw piezo crystal?

May be it is better to stack many elements instead of using one bigger crystal?

We need to find a specialist for piezo elements to clarify basic issues:

- Does the metal in vibrator type pieco disks matter when applying pressure?

- Stack of many elements or one bigger crystal?

- In which way does frequency matter when applying pressure?

- How to attach wires to a crystal?

- Is it important to spread the load over the whole crystal when applying pressure?

Greetings, Conrad

elgersmad

  • Jr. Member
  • **
  • Posts: 72
Re: A Pendulum should really work
« Reply #6 on: March 30, 2011, 10:36:43 AM »
We don't need a specialist.  I can read the specs.  I ordered 10 disks that are all about 1cm in diameter.  The solder is part silver. It sticks to copper, steel, silver, gold, don't worry about solder.  You shouldn't be soldering the type I've shown you.  You might go somewhere that they gold emboss bibles to personalize them to buy some gold leaf.  That will prevent the silver coating from oxidizing.  But, literally, you just rub gold on with a tool, like a plastic toothpick.  You can almost draw it on with a pencil.

Frequency, really applies to resonance and sound power.  If you positioned the cheap ones around the bolt, and the washer was wide enough equalize the pressure on three, that might work.  Those are polymer based piezoelectric disks, if you're looking at the one in picture.  At a high frequency of compression, they would actually heat up and melt.  The pendulum won't hurt em'.  If you want something that is cheap and hard, try a ceramics class.  Ceramics have a high compression strength and can be stronger than steel.  Yea, if you drop it, it will break.  But, if it's just stress coming and going, ceramics can handle allot without special purpose ceramics.  5 bucks bought me so much clay, I still haven't used it all, and it's almost been two years.  It only cost a couple bucks to get a small item fired and then I have a part I need without paying and outrageous price.  They key is working it leather hard, once you've taken the class.  Cutting it with an exacto knife, sanding it, wetting it to add a little if you must or to fix a mistake.  If you are very very careful, you can place a piece of ceramic between two neodymium magnets of any size.  It will break if the magnets clack together.  But, if you can figure a way around that happening, then it won't break.

I wouldn't stack those piezoelectric disks were showing me.  But, I would use three.  An equilateral triangle distributes force equally on all three members.  If you used a bowling ball as a pendulum, about 15 to 30 volts max.  Mostly a current, unknown value.  And that really depends upon how equally distributed the weight is.  That's just educated guess.

Here's a simple demo:
YouTube Video

Slow works

Now, this guy has built a solenoid that could be so efficient that it would work with the whole idea.

This is a link.
Super Solenoid

Needs more grease.


conradelektro

  • Hero Member
  • *****
  • Posts: 1842
Re: A Pendulum should really work
« Reply #7 on: March 30, 2011, 11:28:46 AM »
@elgersmad: A question

Do you expect that the 10 discs with 1 cm diameter (which you ordered) give more Voltage and Amperage than the buzzer disk I talked about?

This is the same question as: Is it better to use a bigger crystal than a thiner one?

Or: what is the special feature of the disks you ordered, that made you choose them?

Greetings, Conrad

elgersmad

  • Jr. Member
  • **
  • Posts: 72
Re: A Pendulum should really work
« Reply #8 on: March 30, 2011, 11:45:27 AM »
That's for a different project.  I was simply stating that I had bought some...  It's enough to test my idea.  But, I think it has been done before and I just can't find an article or technical paper on the subject.  I'll find out, quick enough.

conradelektro

  • Hero Member
  • *****
  • Posts: 1842
Re: A Pendulum should really work
« Reply #9 on: March 30, 2011, 07:39:18 PM »
I read a bit about piezo materials:

The output is proportional to volume, so a bigger piezo junk gives more Voltage and power. But there seems to be a limit, therefore they usually build multiple layers.

Now, how much output can be expected? Well, this is discouraging, the best achieved is in the order of a few 100µW (not even a Milli Watt) per actuation (for a very short time).

So, the usual way to handle this is to have a few million actuations per second. A pendulum therefore is not good, one should have something turning fast, beating very often against the piezo crystal.

May be one should think about a heavy unbalanced flywheel turning with 1000 revolutions per minute or more. The unbalanced flywheel should only be slightly unbalanced so that it can turn very fast. The piezo elements are somewhere near the axis of the flywheel which wants to wobble.

The problem, can one get enough electricity from the piezo elements (see drawing) to drive the flywheel? May be with a pulse motor, the flywheel having evenly spaced magnets on its circumference (or at least one magnet opposite the mass).

Greetings, Conrad






conradelektro

  • Hero Member
  • *****
  • Posts: 1842
Re: A Pendulum should really work
« Reply #10 on: March 30, 2011, 08:13:28 PM »
An other idea:

A unbalanced flywheel is fixed to a table and the table rests (swims) on twelve piezo elements harvesting the electricity from the vibrating table.

The flywheel could turn very fast and does not have to be very unbalanced to induce vibrations into the table (20 Hertz = 1200 rpm). May be there are higher frequency harmonics building up in the table if the table is 2 mm steel.

I imagine a 250 mm diameter flywheel made from 10 mm acrylic with one heavy magnet, which is for the pulse drive and is at the same time the mass for the imbalance.

Greetings, Conrad

elgersmad

  • Jr. Member
  • **
  • Posts: 72
Re: A Pendulum should really work
« Reply #11 on: March 30, 2011, 10:12:40 PM »
It'll work.  But, you'll need to bolt down your generator or it'll be walking all over the house.  How many vibrating pets do you have?  How about sticking that eccentric wheel on a plywood dog cutout?  One big angry chuaua.  The imbalanced wheel is a good idea.  If you use really good bearings and solid mounts it might even last awhile.  Given a push, wouldn't take much energy to keep going.

conradelektro

  • Hero Member
  • *****
  • Posts: 1842
Re: A Pendulum should really work
« Reply #12 on: March 30, 2011, 11:32:18 PM »
Attached a possible pulse drive circuit with piezo elements.

The reed switch is not a very good solution, but will work with very low power. For proof of principle it will suffice.

One can add more piezo elements, each one needs four diodes. Stacked piezo elements might be connected in series?

The pulse drive could also be used for a pendulum.

In general (imbalance wheel or pendulum) the power from the piezo elements should not be enough to drive any setup as a perpetuum mobile (according to accepted theory of everything).

I will go hunting for parts, just for fun, it is weird enough to be built. Should not make a racket as long as the flywheel is driven rather slowly.

May be someone has an better idea how to drive an imbalanced flywheel with piezo elements. Better circuit to harvest the energy from the piezo elements? Other drive method?

Greetings, Conrad

elgersmad

  • Jr. Member
  • **
  • Posts: 72
Re: A Pendulum should really work
« Reply #13 on: March 31, 2011, 12:36:27 PM »
I would use a higher impedance circuit.  The reed switch uses power, like anything else.  But, MOSFET OpAmp would use less power triggering Power MOSFET, MESFET, or IGBT.  Battery saver style ICs can do a better job and use less power, even when the MOSFET kicks in to dump the capacitor.  A Piezoelectric Element works as a source of AC.  When you compress electrons move in one direction, as it decompresses electrons go back to where they came from.  So, every element requires a bridge rectifier.  They have no real polarity even though they often connect red and black leads when you're generating power.  It's like a sponge filled with electrons, they leave one side of the disk and go to other when you compress it.  The electrons return to their initial starting point when the disk decompresses.

You have a bridge rectifier and connect the cheap piezoelectric disk too it.  Then you'll get a pulse of light from a single LED when you press on it, and again when you let go.  Just a simple bridge rectifier experiment will reveal that.  Just press and keep the pressure on it, then suddenly let go.

Good start though.

The importance of polarity really applies to producing sound and which direction it can move first.  Most piezoelectric materials must be compressed first.  So, which direction the electrons move is important when you are driving it to produce sound.
This MOSFET

This OpAmp

Then use 2 Zener Diodes in series to control power on after the bridge rectifier.  Then it goes even farther to detect the right voltage based upon a threshold knob.  Open Loop Gain.  When it's on, it's on.  The output of the opamp directly drives the MOSFET's gate.  The capacitor should be a large value and feed a capacitor that holds the ideal charge for a transformer/converter.  So, if we want 10 volts out of the transformer, if we want 30, we can change the turn ratio and have 30.  So, first it fills a fat capacitor to keep the spikes away from our circuit.  Then it fills a small one that will produce the pulse width we want.  Capacitor in parallel, resistor in series with the load, pulse capacitor, zener diode pair in series and parallel with the load.  Then off of the low zener diode the opamp is biased and above the high is the full voltage we want for the MOSFET about 30 volts.  You don't want to dump anything off but if it's just pendulum that should work.

You'd need a higher voltage MOSFET for the eccentric wheel and motor.  That would do allot more faster and may require some effort in splitting up the outputs of the piezoelectric disks to produce a split supply and operate a Bridge H MOSFET Circuit.  FM style relatively high frequency.  On that one, I would really need to sit down with a meter, measure the voltage and current to think about which style of power up I'd want to use.  Basically, when there's not enough, the zener voltage divider prevents anything from getting power or starting up.  The opamp doesn't take enough to hurt that.


If you wind up hearing the circuit, each pulse should the same width when the circuit fires a pulse for the transformer.  The resistor between the large capacitor and the small one is chosen to produce a square wave with a 50% duty cycle maximum.  Each on pulse is always the same width.  The off pulses vary in time with the amount of power produced by the piezoelectric disks.  As the pendulum starts from it's highest point and falls to it's lowest, the frequency of pulses will rise, then when it starts riding back up, it will drop in frequency to almost clicking.
« Last Edit: March 31, 2011, 01:48:37 PM by elgersmad »

conradelektro

  • Hero Member
  • *****
  • Posts: 1842
Re: A Pendulum should really work
« Reply #14 on: March 31, 2011, 03:19:42 PM »
@elgersmad: sorry, I have difficulties imagining a circuit from words. May be you could draw your circuit and post it.

I am afraid, the piezo elements are not able to power an OpAmp. The one you mentioned has a
Quiescent Current per Amplifier of 25µA at 6 Volt resulting in 150 µW.


150 µW is a top performing multilayer special production piezo element for "energy harvesting". What we will see from inexpensive run of the mill piezo elements is less (hopefully 10 µW).

This is the reason why I came up with the reed switch. The energy for actuating the reed switch comes from the permanent magnet of the pulse drive and does therefore not have to be provided by the piezo elements. All energy (besides the loss in the capacitor) goes into the coil of the pulse drive when the reed switch closes (when the magnet has a certain position near the coil).

I would switch the pulse drive in a "push away" set up: when the magnet is exactly at the mid point (when its natural attraction to the core of the coil is a maximum), the reed switch should feed the electricity to the coil in order to push the magnet away (in the direction of rotation). The reed should stay ON till the magnet is well away from the coil. In case of little power fed to the coil, this means, the magnet is less attracted to the core of the coil than before and can therefore leave the sticky point with a little net gain. The capacitor will be exhausted completely. There will be no electricity left for any active component.

Keep in mind, piezo elements show a "static electricity phenomena" which means rather high voltage (up to 50 Volt), but very very very low amperage.

The US-army wanted to produce shoes which generate electricity when walking by help of piezo elements. Well, they gave up. One had to walk for hours to produce very few Milli-Ampere-Hours.

Attached see a photo of one of my pulse motor experiments. I used toroids instead of coils. The magnet is attracted to the ferrite material of the toroids, but when current is driven through the windings on the toroids, the magnet "does not feel" the ferrite material any more and can leave the sticky point. I like to call that "attract the magnet and then hide at the sticky point". This allows to drive such a pulse motor with very little power (but it will have very little torque). I achieved 800 rpm with 0.16 Watt (no load, just free run). But with the piezo elements it should work with 0.000016 Watt (16 µW), which is to be doubted.

Greetings, Conrad