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Topic: Perpetual Wave Pendulum (Read 2411 times) previous topic - next topic


Hi guys,

I'm looking to build a wave pendulum such as this one: http://www.youtube.com/watch?v=yVkdfJ9PkRQ

I was hoping to build one with 14 balls with magnets on the bottom, and use the Arduino Mega 2560 to sense a ball coming close and then a kicker circuit like this one: http://home.earthlink.net/~lenyr/magkick.htm to impart a kick via electromagnet (I was planning on building 14 electromagnets, one to go under each ball).

Is this a project that is doomed to failure, or do you think it's feasible? It doesn't matter to me if I have to initially start the pendulum by hand, but after it begins running, I would love to be able to modify its path by adjusting the amount of kick given to individual balls.

If it were to work, other ideas down the line include incorporating motion / light sensors to trigger various patterns, or even synchronizing them with music, or simply generating new patterns randomly.

Any tips or advice you may have are greatly appreciated. I apologize if I'm a little under-informed, but I thought I'd just check first off to see if this is a pipe dream or not before delving into the nitty gritty. Thanks a lot, and if I start on this, I'll definitely keep you posted.


May 21, 2011, 06:04 pm Last Edit: May 21, 2011, 06:07 pm by thomy Reason: 1
Hi again. Sorry to bump, but I wanted to give more details of my plan to see what you thought.

Basically, I'd just need to run 14 MOSFETs using PWM to vary the strength of my electromagnets. I'd need of course a separate power supply for the electromagnets . Then, 2x14 reed switches: two for each ball so I could tell both direction of travel and speed pre/post boosting to tune the boost PWM frequencies to ensure that I got the speeds I wanted.

The magnets would not need to be large at all, as the balls I'm planning on using only weigh about 55 grams each. If it's necessary I could always add some weights to the fishing line I'm using to suspend them if it turns out to be too sensitive (or could add some weight to the inside of the balls if things are so far off due to variation in ball mass that they are untunable via PWM variation).

Does this sound feasible, or is there a big hole somewhere? I'm planning to just do this all on breadboard . . . it doesn't have to be pretty yet. Thanks again for any suggestions!


The project only makes sense to me if you have all strings the same length and want to "magically" adjust the swing frequency different for each pendulum to get something like the video shows. I do not think however you can change the frequency that much for each pendulum.

So I suggest you do a single pendulum experiment first, time the frequency (see how long 20 swings take) and then see how much you can influence it with your electromagnet. The distance ball/magnet should be only a few mm, the magnetic field strength falls off quite fast with distance (quick google; I cant remember - dipole strength by distance from pole is a ... inverse cube.)

For sensor I would suggest a reflection/proximity sensor, two if you want to know where the pendulum comes from (well, you should know in the Arduino software, it comes from each side alternativly  :D )

If you use MOSFETs make sure you (a) use a diode to absorb the turnoff/backpuls, and (b) use a "Logic level" MOSFET (fully turns on at 3 or 5V, not the usual 10V).

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