## PSN-L Email List Message

Subject: Re: Crossed rod hinge/suspensions v/s ball bearings hinge/suspensions
From: Brett Nordgren Brett3kg@.............
Date: Tue, 25 Oct 2005 10:37:29 -0400

```Hi,

It was interesting to hear about some real-world testing of the
zero-force/zero-moment hinge design.  A few years ago I did some analysis
of its geometry aimed at seeing how well it simulated a pivot about a
single point, i.e. how well the end of a pendulum using that hinge would
track a true circle, and where was the center?  At the time I was looking
at using the design in a leaf-spring horizontal.

See: http://bnordgren.org/seismo/zerohng2.pdf

Although, when I worked on it, I knew the design had been around before, at
the time I wasn't aware of how long and how widely it had been in use.

Rather than trying to do a mathematical analysis, I used a CAD program to
draw the pendulum in various positions and tried to see how well the locus
of the pendulum endpoints would fit a circle.  For the test, I assumed
pivot rods of 1-inch diameter with a pendulum only 5-inches long, measured
from the center of the "lower" pivot rod.  Even for that extreme case the
pendulum tip tracked a circle  within  0.00025" [0.0063mm] over the range
of +/- 5 degrees of swing.

There had been some discussion about where the center of the arc would
be.  From what I could see, the effective center of the arc was very near
the crossing point of the support flexures/wires.

Regards,
Brett

At 12:21 AM 10/24/2005 +0000, you wrote:
>Meredith Lamb,
>Could you post pictures of the  rod hinge/suspensions "your setup"
>This sounds like somthing I would like to try.
>Thanks Bryan Goss
>
>
>
>From:    meredith lamb
>To:    psn-l@..............
>Subject:    Crossed rod hinge/suspensions v/s ball bearings hinge/suspensions
>Date:    Sun, 23 Oct 2005 20:54:01 +0000
>Content-Type: Multipart/alternative;
>  boundary="NextPart_Webmail_9m3u9jl4l_2531_1130113284_1"
>
>Hi all,
>
>Chris Chapman recently stated in a private email that he thought a crossed
>rod hinge
>suspension would have less friction/dampening than a ball bearing
>hinge...and he is
>so very right!
>

Take care, Meredith Lamb

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