🚀 go-pugleaf

In article <17...@husc6.harvard.edu> kara...@husc8.harvard.edu (P.J. Karafiol) writes:
> In article <77...@tut.cis.ohio-state.edu> John R. Mudd <j...@cis.ohio-state.edu> writes:
> [Grace Hopper and rubber palm tree stuff deleted]

> And I once had a clock that would occasionally take it into its head to start
> running backward.  Had nothing to do with polarity of the plug, time of day,
> anything that we could tell.  Pretty frightening.  But it fell off a table
> one day and died.

I once fixed a clock that had a fixation for running backwards.  The thing
had a very simple synchronous AC motor that worked like this:


		Electromagnet====    H========|========H
                                     +        |        -

What this is supposed to be is an electromagnet hooked up to your fine
60 Hz line current, sitting next to a permanent magnet that is mounted
on a shaft.  When the electromagnet reverses polarity, the magnet wants
to turn 180 degrees on the shaft so that the opposite polarities line
up.  The shaft would just vibrate back and forth at 60 Hz if it wasn't
for momentum.  Momentum causes the shaft to continue turning in whateverr
direction it happenned to start turning in.  Then the shaft is turning
exactly 60 revolutions per second, and if you gear it down you've got
a clock.  In order to assure that the thing started turning in the right
direction, there was actually a mechanism in this clock that would
mechanically catch the shaft and fling it in the opposite direction if
it started turning in the wrong direction.  The mechanism would just
freewheel in the correct direction.

In the clock that I fixed the flinging mechanism was broken and I fixed
it.  I've seen clocks which have a sealed motor, but I assume that its
pretty similar inside, just more integrated.

							Joe


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Joe "Augi" Augenbraun                   ucp: {uunet|ihnp4|rutgers}!cbmvax!augi
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