[time-nuts] A different timenuts interest

[Hal Murray]

> ... Foucault pendulum ...

> 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. 

Several years ago, I found a web site for a commercial place that made them 
for museums.  (I forget why I was looking for that sort of stuff.)  You might 
find interesting stuff/ideas via google but I didn't find a similar site with 
a bit of searching.

----------

Here is what I would try:
    Put a magnet on the bottom of the pendulum.
    Put a coil below it.  (obviously centered)

    Use the coil as a sensor to measure the timing.
    Use the coil as a motor to pull the pendulum every N-th swing.

The question is how accurately centered do the magnet and coil have to be?  I 
don't know.  It sounds like a fun mixture of theory and engineering.

One of the variables is how far away is the pendulum when you are pulling.  
The farther away it is, the smaller angle you have from the ideal.  You can 
change that by varying the start/stop times on the pull pulse.

I'd probably put the coil on a crude X-Y table, set it up as good as I could, 
then see if it worked.  Then I would deliberately move it off a bit and see 
what happened.  Or try to servo it to the best place, probably by manual 
changes every day or week or ???

I'm assuming this is for a school or museum.  The required positional 
accuracy is actually a real science experiment.  The idea of "experiment" to 
test an idea is more important than the basic Foucault pendulum itself so you 
get two exhibits in one.

Of course, another question is how fast does it decay?  Or rather, how long 
will it run with no energy input?

This says 2 hours:
  http://www.cmnh.org/site/AtTheMuseum/OnExhibit/PermanentExhibits/Foucault.as
px
for a 270 lb bob, but I don't know how tall that is.  (But it says 6.2 
seconds, so I should be able to calculate it.)





-- 
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