Electromagnetic Pendulum

by Stephen Hobley on May 25, 2010

First experiments with an electromagnetic pendulum.

The pickup coil (a steel bolt with about 100 turns of enameled wire) picks up the passing of the magnetic pendulum. This is then fed into a microprocessor that energizes the coil just long enough to give the pendulum a push.

This is the basis for the next clock I build on the new CNC.

(The Arduino is included purely for blog cred…)

Now I just need to design a suitable escapement…

UPDATE : It’s only taken me a year, but I’m slowly updating the design to function as a clock.


{ 14 comments… read them below or add one }

clicclic May 26, 2010 at 8:52 am

Why are the coolest inventions always the unnecessary ones?

Give me a lever long enough and a fulcrum on which to place it, and I shall move the world.

eric_the_orange June 1, 2010 at 11:13 pm

I’d love to see this applied to a Foucault pendulum … swinging and precessing forever.

shobley June 1, 2010 at 11:32 pm

That’s a neat idea.

Although I suspect that if I try to drive a Foucault pendulum from below it would interfere with the Earth rotation effect.

It’s worth trying though…

Neil June 2, 2010 at 12:17 am

Regarding the escapement: physical contact will alter the swing-rate of the pendulum. You might consider photo-optic detectors with a small flag on the pendulum–or even detecting the pendulum itself.


Neil June 2, 2010 at 12:25 am

Re: driving the Foucault pendulum–you probably want a ball for the bob so that air resistance is the same for all directions of swing. A magnet vertically imbedded in the bob and a vertical cylindrical coil pointed up might be a good choice for driving–just after the bob clears the coil, a pulse of current (giving a field polarity the same as the magnet’s pole pointing down) will give the bob a push.

I wonder: the bob probably should be non-magnetic (ie: brass or lead).


Les June 2, 2010 at 12:46 am

I recall seeing plans for a rather small — perhaps 4-foot-high — Foucault pendulum in an issue of Sky & Telescope from the early 1980s. It used a steel ball and steel wire on a swivel mount. A thick, washer-like contact with a small hole, centered toward the top, would complete a circuit with the wire at the top of the swing, then a simple delay would kick on a coil, centered under the base, during the downswing. When aligned and isolated, it apparently performed quite well.

Jim June 2, 2010 at 7:02 am

If you want to see this applied to a Foucalt pendulum, please see any one of perhaps dozens installed in physics departments, science buildings, and museums around the world. I have seen one at Fort Hays State University in Kansas, for example, in their science building.

Tim June 2, 2010 at 7:37 am

There is a very large electromagnet boosted Foucault pendulum at COSI in Columbus, Ohio. It works very nicely. I believe the boost is near the top of the cable though.

shobley June 2, 2010 at 12:39 pm

Thanks for all the comments.

Stay tuned – I have some mods in the pipeline
to make it waaaay more interesting than just a pendulum

Rob Cruickshank June 2, 2010 at 2:46 pm

Nice! Do you know about the Shortt Clock?

shobley June 2, 2010 at 2:54 pm

Yes I did some reading up on that. The idea for the EM pendulum came from my work building the Bedini impulse motor.

(Although after I came up with the idea it took about 3 nanoseconds to realize that this was sooo obvious it must have already been done.)

I like the Shortt clock idea, but I really want to mechanically couple the pendulum to the drive.

Tom Wheless June 6, 2010 at 10:06 pm

Hi Stephen,
I call your attention to an column that used to be published in Scientific American magazine called “The Amateur Scientist”. The one applicable to you was in the Sept, 1974 issue (might be available in your local library) and was called “Pendulum-type Clock Equipped with Quartz-Crystal Oscillator”. The author used an old pendulum clock, glued a magnet to the pendulum, and used a coil of wire driven by an electronic circuit (made of vacuum tubes, IIRC) to pulse the coil. You may find his techniques applicable to what you’re trying to do.
Best regards,

shobley June 6, 2010 at 10:18 pm

Thanks Tom, I shall certainly try to locate that…

Krutika August 6, 2011 at 2:25 pm

I m in search of a project and found this to be the best one.. can you please mail me the timer circuit of the pendulum, and connection Procedure with the pendulum.
It will help me a lot..


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