[time-nuts] A different timenuts interest

J. Forster jfor at quik.com
Wed Jul 21 20:29:06 EDT 2010


The problem is straight forward, except for sensing the position of the
pendulum so the impulse is applied at the correct phase.

There must be a bunch of published designs, but if I were to try it, I'd
use something optical or capacitive.

For optical, I'd put a annular ring of IR LED/Phototransistor assemblies
around the center, wired OR the outputs, and use the signal to trigger the
impulse. The bottom of the pendulum should be polished or mirrored.

For capacitive, I'd copy a "proximity detector" circuit and use that. One
plate would be the pendulum, the other an annular conducting ring just
below it. It might also work with two, concentric rings and an
electrically isolated pendulum.

Best,

-John

===========


> Hi all,
>
> I have been asked to help with the construction of a Foucault pendulum.
> This
> is a long pendulum which oscillates in a slow stately fashion in a fixed
> plane which appears to move as the earth rotates. In reality the
> surrounding
> environment is really moving relative to the plane of oscillation.
>
> The pendulum requires a sustaining system to compensate for the inevitable
> energy loss with each swing. The system is located in the building and
> therefore rotates relative to the pendulum. It needs to provide an impulse
> which does not affect the plane of oscillation of the pendulum. I was
> thinking of an electromagnet located below the centre of the swing which
> would be pulsed appropriately as the bob passes over it.
>
> Has anyone here had any experience with such a system of have any
> suggestions regarding the sustaining system? This is an interesting and
> challenging project.
>
> Cheers,
>
> Morris
>
>
>
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