A Pendulum should really work

[elgersmad]

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]

@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]

...
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]

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]

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.