PSN-L Email List Message
Subject: Re: Anniversary clock spring
From: John Lahr johnjan@........
Date: Sat, 15 Dec 2007 21:36:50 -0800
The sensor that you've designed will be sensitive to rotations of the
ground with a vertical axis. The problem is that such rotations are
very small and thus difficult to detect. This is a budding field of
seismology. See, for example: http://pubs.usgs.gov/of/2007/1144/
Of course the inverted T will also swing like a normal pendulum with
period determined by the overall length of the blade, unless it's
constrained to remain vertical.
At 10:40 AM 12/15/2007, you wrote:
>Hi Folks, This is an observation and a question. I have an
>Anniversary clock, perhaps also called a 500 day clock, as you only
>need to wind it once a year, or so. I know very little about
>clocks, but have worked on a few clock movements and
>escapements. I have some old clocks which are 8 day movements. I
>wondered why the big difference in power consumptions, and spring
>properties between the two types.
>The 8 day movements use a short pendulum which is maybe 1/2 second
>natural period. The anniversary clock has a short spring, instead
>of a pendulum, which is like a flat thread. This spring is fixed
>at the top and has four masses, brass balls on the free end. One
>period of this spring is about 8 seconds. The mass in motion,
>twist the thread like spring, until the power of the spring stops
>the mass, and swings it in the opposite direction. A different
>coiled mainspring then add a kick to the mass and the cycle repeats.
>Always looking for different ways to obtain a 20 second period, I
>took a band saw blade, cut it and suspended it from my shop
>ceiling. It now hangs similar to the thread like movement spring of
>the anniversary clock. At the bottom of the 72" band saw blade, I
>attached a 36" yardstick. This now looks like an inverted "T". I
>added a mass to both ends of the yardstick. I twisted the spring
>and released it. I found it rotated back and forth and it period
>was about 8 seconds. I keep adding equal mass to both end of the
>yardstick, and the period was 24 seconds.
> The yardstick seems to always come to rest at the same point, as
> the spring wants to untwist.
>My question: Has anyone tried this approach? If so, could anyone
>direct me to more information about it on the internet?
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