A Pendulum should really work

[Low-Q]

First of all, a pendulum are slow, and the frequency are totally depending on its length and gravity. So, I agree that an unbalanced wheel are the correct approach, because its frequency (or rpm) are not depending on diameter and gravity. It can be made much smaller, with much higher efficiency.

Using piezo electric power source might be useful. However, the output are, as far as I know, depending on the frequency as well as the pressure. A good thing about piezo electric devices is (as probably already mentioned) the requirement of pressure difference rather than mechanical movement to provide energy.
Because an unbalanced wheel have to stay perfectly still during the run in order to not loose energy by its possible viberations. Viberations will slow down / break a spinning unbalanced wheel grately. So therefor, implementing a piezo electric device would probably be the best way because of the minimum viberations, and maximum pressure.

It might therfor be possible to feed back the energy from the piezo electric device into a high efficient motor which powers the unbalanced wheel. Even use the pulses from the piezo to feed directly into an electromagnet which in turn propells a rotating magnet.

The weight which provide the unbalanced wheel must be applied before the magnet approach the electromagnet in order to determine the direction of rotation, and rotation itself.

The magnet can be this weight, and if the coil are not placed at the bottom, but a few degrees later, the coil will be fed with energy in advace of the magnet, so it can pull the magnet towards it and force rotation.

Attached there is a drawing of a simple brushless motor which is powered by pressure on a piezo electric device.

When the magnet is on the bottom, the pressuere on the piezo are greatest. When the magnet is on the top, there is a "negative" pressure so the upper right coil have swapped polarity in order to attract the magnet. Also there should be coils which is repelling the magnet also.

On the other hand, the electricity are probably generated during the pressure difference from no pressure to max pressure, and the electricity reverse from max pressure to negative pressure. So there might be another placement of the coils, but I think you got the idea.

EDIT: The generation will occour when the magnet/weight are between top and bottom. This means that the wheel as drawn will rotate counter clockwise if the piezo are placed either at the bottom, the top, or both top and bottom.

Vidar

[conradelektro]

I did some tests with a piezo element (for a buzzer, sits on a metal plate):

See the attached drawing, photo an scope shots.

The piezo element needs "hits", pressure alone did not do the trick. So, if one builds an imbalanced wheel, the setup must produce "hits", like with a little hammer.

The stroke of the "hit" does not have to be very high, but the "hammer" must hit the element, leave and hit again, leave and hit again, ...

I could charge up a 100µF electrolytic capacitor (replacing the LED) within seconds to 3 Volt (about 5 hits per second), done by hand with a wooden stick (like rapidly making dots with a pencil).

The piezo element was sandwiched by two acrylic disks to protect it. With or without acrylic disks, the performance was about the same.

The low power red LED only gives fairly dim light pulses. I plan to use up to twenty such elements (all in parallel, each one having four diodes, feeding into an electrolytic cap) in "bouncer" with an imbalanced wheel.

Greetings, Conrad

[Low-Q]

I did some tests with a piezo element (for a buzzer, sits on a metal plate):

See the attached drawing, photo an scope shots.

The piezo element needs "hits", pressure alone did not do the trick. So, if one builds an imbalanced wheel, the setup must produce "hits", like with a little hammer.

The stroke of the "hit" does not have to be very high, but the "hammer" must hit the element, leave and hit again, leave and hit again, ...

I could charge up a 100µF electrolytic capacitor (replacing the LED) within seconds to 3 Volt (about 5 hits per second), done by hand with a wooden stick (like rapidly making dots with a pencil).

The piezo element was sandwiched by two acrylic disks to protect it. With or without acrylic disks, the performance was about the same.

The low power red LED only gives fairly dim light pulses. I plan to use up to twenty such elements (all in parallel, each one having four diodes, feeding into an electrolytic cap) in "bouncer" with an imbalanced wheel.

Greetings, Conrad

Could you load the piezo with a 10 - 20 ohm resistor, and measure the output voltage over the resistor?

[DreamThinkBuild]

Hi Conrad,

I've attached pager motors to piezo's they generate about 119khz sine wave around ~3-5volts ac out not a lot of current(uamps) from my current piezo speakers. The pager motors use very little power 1.5v+@30ma+(lowest).

http://www.goldmine-elec-products.com/prodinfo.asp?number=G17959
http://www.solarbotics.com/products/vpm2/

[Low-Q]

Does anyone here know if  there is a direct relationship between the force and deformation (Force times distance) and the energy output of a piezo?

I have imagined a pendulum with a narrow magnet on it. The magnet pass by another stator magnet which is fixed to a piezo device. Each time the magnet pass by, there will be generated a mechanical pulse into the piezo device (Therfor a narrow (and maybe long magnet). The electric current should then power a small electromagnet which pulls the pendulum in correct phase to sustain the pendulum.

Vidar