[time-nuts] A different timenuts interest

[jimlux]

Morris Odell wrote:
> 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.
>

Google should be your friend.  This is a pretty standard thing, and I 
recall seeing drawings of optical schemes with phototubes to detect when 
the wire passes through vertical (and triggering the pulse through the 
electromagnet below the bob).