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Topic: pendulum on a string (Read 946 times) previous topic - next topic

treebykooba

Hello,

I am interested in making a 6oz pendulum swing seamlessly (i.e - no jerky motion) from a string using a motor about 12ft above...so it looks like the pendulum is in perpetual motion. I was thinking of using a DC motor with perhaps some reed switches to change the polarity of the motor with relays and an arduino to control some delays. I do not know any physics and thinking about it more and more, this seems to be a difficult task. Is this possible to do with an arduino? Is it possible at all? I couldn't find much online of anyone doing much with a pendulum from a string and a microcontroller.

Any advice as to where to go with this would be much appreciated!

kf2qd

Sounds like you are trying to make a Foccault Pendulum. Nice one in the Smithsonian. Demonstrated the rotation of the Earth. I believe that one has a switch and a magnetic coil that attracts a ring up near the pivot point.

Not much for an Arduino to do - the Pendulum will have a very predictable period and that will never change.

Yankee

One way to do this would be to use an electromagnet below the pendulum bob which could provide an impulse when triggered by a hall sensor at the appropriate time in the pendulum's cycle. This would, of course, require a magnet to be embedded in the bob.
I know I've seen this arrangement somewhere on the web to power a clock pendulum so you might try googling it.

Grumpy_Mike

Quote
I was thinking of using a DC motor

No that will not work, the speed of a pendulum is constantly changing and you do not have that degree of speed control with a DC motor. It might be possible to do it with a stepping motor or servo, but the impulse method described above is perhaps the best unless the period of the pendulum has to be  different from it's natural frequency.

treebykooba

thanks so much for your help. I'm having a real hard time finding a suitable stepper motor for this....i got one from sparkFun awhile ago that has practically no torque. it's a bipolar and i'm using the easyDriver with it.

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