Meredith,

The 2 instruments are two copies of almost exactly the same design.  There 
are a few minor evolutionary changes, but the only significant difference 
is in the design of the pressure containers surrounding them.  It is much 
fun (for me anyway) to watch them draw out virtually identical traces of 
the microseisms, right along with the Guralp.

One thing we have learned in working on this design is that the pivot 
flexures have almost no effect.  All my earlier efforts at making 
zero-moment designs just aren't necessary.  Any slight restoring moment 
that the flexures create is completely cancelled when the period is 
adjusted as Dave described, by tweaking the spring length.  And the angle 
that they flex through during normal operation is essentially zero because 
of the feedback.

For Kay:

I just checked on the Garden Shed/Vault that I believe Dave had used:

Rubbermaid RHP3673  Approximately a 6' x 6' base.

In looking for the model number I ran across this somewhat amusing clip of 
a couple assembling a similar shed.
http://blog.rubbermaid.com/home/2008/06/heres-how-to-bu.html

Regards,
Brett

At 11:51 AM 8/14/2009 -0600, you wrote:
>Hi Brett and Dave,
>
>I'am "assuming" the "2" instruments is really the one ~ same ~ vertical 
>(?), with either mechanical changes and/or
>feedback changes?
>
>As usual (for me), the main spring (phosphor bronze) and the two pivot 
>flexure assemblys (with presumably 6 total pieces) are of quite some 
>curiosity.  Of what material, size/s, thickness are you guys using?  Some 
>of the flexures shown almost look
>like cut thin flat spring steel from the photo.
>
>Take care, Meredith


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