Introduction: Double and Unbalanced Electronic Pendulum

This is a project that uses an electronic magnetic pendulum drive similiar to instructables: https://www.instructables.com/id/The-Magbot-pendulum/
although the circuit I actually use is found here:  http://www.trainelectronics.com/Pendulum/article.htm   

I orginally built this pendulum circuit to work on a Foucault Pendulum which I have partially working but decided to use the pendulum drive to make this video of a double and an unbalanced pendulum.
The unbalanced pendulum is kind of interesting; there is only a certain amount of weight you can add to the top of the pendulum before it becomes disfunctional. Also you find that the heavier the little pendulum at the top, the less efficient the pendulum at the bottom. By adding a smaller pendulum to the top of the main pendulum you find the swing of the main pendulum getting reduced a bit. Not sure what is going on there.

Please watch the video to see how it works.


I haven't found any research so far that deals with double pendulums built the way this particular one has been built. I think this pendulum would be a great science fair project as it is somewhat unique. Also there seems to be no studies on this particular unbalanced pendulum as well.

I keep this pendulum in my living room and sometimes let it run for days as the batteries last forever and the pendulum makes a pleasant sound. It is also relaxing to just sit and watch it work.

Step 1: The Electronic Drive

The electronic drive is build according to this website:
Pendulum Animation http://http://www.trainelectronics.com/Pendulum/article.htm

It is a very simple circuit of only a few parts that can be gotten at a Radio Shack. I actually found some of the parts in my electronic junk box. The black box is an on/off push switch. The other components are two transistors, two resistors, a diode and an LED that ights up when the magnet is turned on. I used an IN4007 diode but I think any one will do. I built this circuit first on a breadboard and got it working before I soldered it up.
When I first plugged it all together it didn't work because my voltage was too high. Use 3 volts to 4.5 but no higher or lower.
One leadout goes to the batteries as shown, the other goes to the coil.

Step 2: The Coil

The coil is also built according to the specifications of the website shown in the previous step.
I made my coil form out of two pieces of acrylic ruler. Then drilled holes through them to fit a 3 inch by approximately 1/4 inch piece of fiberglass fishing pole. Then glued the pieces together. Then I drilled a small hole near the center of the bottom acrylic ruler piece to make an exit point for the wire lead. Then wound about 50 meters of 20 gauge magnetic wire until I had a coil about 1.25 inches across. Use any small gauge wire as it is the number of turns and how much wire you can get onto the form that matters.

You can also buy a coil but I suspect they are not nearly as strong as the one you can make yourself. 
This coil is very powerful - I have used it to build a pendulum that used a 2.5 pound weight and it motivated a 4 foot swing.

Note at the bottom of my acrylic ruler pendulum is a steel corner bracket to which two strong round magnets are attached.

Step 3: The Pendulum

The pendulum is simply an acrylic ruler with a hole drilled about a third of the way down from the top to serve as the pivot. Mount the magnets at the bottom.
I used a bicycle spoke as the axle for the pivot and used some washers and nuts to hold the pendulum near the middle of the axle and held in place by electrical tape.


Step 4: The Pendulum Mount

I mounted two acrylic rulers on a small wooden box. I used a bicycle spoke as the axle between the two rulers.
In the lid of the box I drilled a hold and set the coil into that hole.

The pendulum is started by pressing the on button and giving the pendulum a  little kid. 

I keep this pendulum in my living room and sometimes let it run for days as the batteries last forever and the pendulum makes a pleasant sound. It is also relaxing to just sit and watch it work.

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Bio: I am an American teaching English at Shangluo University, Shaanxi. I like making machines that do interesting but fairly useless things - I call them Quixotic ... More »
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