Dave,

Just for laughs, here's the other end of the specturm in regards to mass.

They use an effective mass of 19 grams, and don't do badly at 
all.  Design by the 'other' Dave Nelson.

http://bnordgren.org/seismo/gif_images2.htm

Brett


At 07:39 PM 7/30/2011, Dave Nelson wrote:
>hi Chris
>        Am really at the end of the rope here ... just total 
> frustration...  spent all day
>yesterday improving the period got down to 11 sec. set up a magnetic 
>dampening system
>  with a strip of aluminium  1.5cm wide going in between the 2 magnets.
>   The only thing that seems to achieve is dropping my period from 
> 11 sec down to
>~ 7 sec.  It doesnt appear to do any actual dampening  as the unit 
>will just go on oscillating for ages and just slowly dying down on 
>its own  see...
>http://www.sydneystormcity.com/screen%20dump.bmp
>
>for the first 3/4 of the screen you can see it oscillating all nite 
>long.   This morning I
>gave it a nudge and as you can see the pendulum just slowly 
>decreased in amplitude
>on its own.
>
>I was so looking forward to making this work, and at the moment 
>almost ready to throw
>it all out !!
>
>BTW  I did take your bottom pivot advice.   I have a flat steel 
>plate on the end of the
>boom against the ball in the vertical
>
>maybe you can help further ?   :)
>
>cheers
>Dave


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