PSN-L Email List Message

Subject: Crossed rod hinge/suspensions
From: meredith lamb paleoartifact@.........
Date: Tue, 18 Oct 2005 20:15:22 -0600


Hi Chris, and all,
 I'd think that a crossed rod hinge might be a vast improvement for one or
more
"hinges" on about any "garden gate" horizontal, or, for a vertical
seismometers
lower hinges; or, for a "S-G" hanging pendulum. It all depends on how you
need to orientate two of the three rods for the specific seismometer being
designed for; or, to replace the existing hinges on such.
 Just to be sure we're on the same setup plain...I can visualize; say, a ro=
d
running straight horizontally (like across this page), and one can then
introduce two rods underneath the horizontal rod, on the outer extremes tha=
t
can go up and down (top to bottom of this page). The horizontal rod would
have a centered "boom" attached that leads to the mass. One would then
either have a wire (for a hanging gate horizontal), or a spring for a
vertical. On
a S-G of course, the boom/mass would just hang down. Of course, a vertical
would (likely) need two such hinges on the bottom hinge area...and it could
be possible to have the angled upper hinge of the same crossed rod design.
 Have never tried crossed rods as such, but, I'd think it might be as good
as a
ball bearing hinge design...and likely without near as much mechanical
adjustments fuss; as a ball bearing hinge can need. In many ways I think;
this crossed rod hinge is quite similar to ball bearings suspensions, as th=
e
small contact area is similar. The best forced offset of the mass for
harmonic
motions in timed trials I've seen (table top/edge test) for ball bearings o=
n
a
variety of contact surfaces (without dampening), was about 6 hours. Too me,
the longer a mass oscillates (without dampening); that means the hinge/
suspension has less friction, and thus the mass's enertia would be more
sensitive to external local earth movements.
 ....................................
 For a S-G like, hanging pendulum (horizontal sensing), I'd think you
previously
mentioned zero torque suspension (zts) would be far more sensitive or
friction
free, but it is abit harder to build. As you know...via emails and alot of
your
generous help; the current table top/edge experiments here with that trial
suspension, can freely oscillate up to 10-11 hours on average. My old S-G
with its two thin straight hanging suspension strips, would only oscillate
(without dampening), up to 35 minutes.
 Can heartily agree now, with your stressing trying new hinges, whether it
be
ball bearings, crossed rods, or the zero torque suspension, as they will al=
l
have alot less friction, as opposed to the older, pointed boom pivot
(horizontal)
razor edge boom pivot (vertical), or simply hanging strips of metal like on
a
S-G (horizontal), that create alot more friction/torque sensitivity
limitations
in the hinge/suspension contact area/medium which affects the mass enertia
response to stay in one place "in space", while the earth moves.
 Take care, Meredith
Hi Chris, and all,
 
I'd think that a crossed rod hinge might be a vast improvement for one= or more
"hinges" on about any "garden gate" horizontal, or= , for a vertical seismometers
lower hinges; or, for a "S-G" hanging pendulum.  It all= depends on how you
need to orientate two of the three rods for the specific seismometer b= eing
designed for; or, to replace the existing hinges on such.
 
Just to be sure we're on the same setup plain...I can visualize; say, = a rod
running straight horizontally (like across this page), and one can the= n
introduce two rods underneath the horizontal rod, on the outer extreme= s that
can go up and down (top to bottom of this page).  The horizontal = rod would
have a centered "boom" attached that leads to the mass. = ; One would then
either have a wire (for a hanging gate horizontal), or a spring for a = vertical.  On
a S-G of course, the boom/mass would just hang down.  Of course, = a vertical
would (likely) need two such hinges on the bottom hinge area...and it = could
be possible to have the angled upper hinge of the same crossed rod des= ign.
 
Have never tried crossed rods as such, but, I'd think it might be as g= ood as a
ball bearing hinge design...and likely without near as much mechanical=
adjustments fuss; as a ball bearing hinge can need.  In many ways= I think;
this crossed rod hinge is quite similar to ball bearings suspensions, = as the
small contact area is similar.  The best forced offset of the mas= s for harmonic
motions in timed trials I've seen (table top/edge test) for ball beari= ngs on a
variety of contact surfaces (without dampening), was about 6 hours.&nb= sp; Too me,
the longer a mass oscillates (without dampening); that means the hinge= /
suspension has less friction, and thus the mass's enertia would be mor= e
sensitive to external local earth movements.
 
.................................... 
 
For a S-G like, hanging pendulum (horizontal sensing), I'd think you p= reviously
mentioned zero torque suspension (zts) would be far more sensitive or = friction
free, but it is abit harder to build.  As you know...via emails a= nd alot of your
generous help; the current table top/edge experiments here with that t= rial
suspension, can freely oscillate up to 10-11 hours on average.  M= y old S-G
with its two thin straight hanging suspension strips, would only oscil= late
(without dampening), up to 35 minutes.
 
Can heartily agree now, with your stressing trying new hinges, whether= it be
ball bearings, crossed rods, or the zero torque suspension, as they wi= ll all
have alot less friction, as opposed to the older, pointed boom pivot (= horizontal)
razor edge boom pivot (vertical), or simply hanging strips of metal li= ke on a
S-G (horizontal), that create alot more friction/torque sensitivity li= mitations
in the hinge/suspension contact area/medium which affects the mass ene= rtia
response to stay in one place "in space", while the earth mo= ves.
 
Take care, Meredith
 
 

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