John,

That looks like an interesting design that has failed in the execution. 
You should really try it again, but next time try using the extruded 
aluminum shapes that you can buy at any of the Home Depot type stores. 
They are relatively inexpensive and you can build quite rigid structures 
using square tubes and such. To make good flexure hinges use stainless 
steel shim stock, which comes in 1/2" wide strips in thicknesses from 
..001"  on up. A quick calculation will show that a 1/2 inch wide piece 
of .001 shim will support a sizeable load in tension. At least 10 pounds 
per flexure, and probably 20 pounds, if you can clamp it well enough.

Rigidity is very important for a structure such as you and Brady have 
devised, so don't skimp on materials.

Keep up the good work.
Dave...


John or Jan Lahr wrote:

> I've built a prototype horizontal-pendulum seismic sensor using a 
> design that
> Brady Romberg, a School of Mines student, came up with.  This still needs
> a lot of work, but I thought the mechanical design was quite interesting.
>
> I've posted a seismogram and some photos here:
> http://jclahr.com/science/psn/romberg/
>
> The weakness in this design is the vertical rod and it's attachment to 
> the
> horizontal plate.  I think flexure in the rod and/or attachment is 
> what limits
> the period to about 2 seconds.  Perhaps the mass needs to hang from a V-
> shaped support rather than a single rod.
>
> Cheers,
> John
>
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