Hi,  i am enjoying the input. here! Thanks to everyone. geofffrey<><
  ----- Original Message -----=20
  From: meredith lamb=20
  To: psn-l@.................
  Sent: Sunday, October 23, 2005 4:53 PM
  Subject: Crossed rod hinge/suspensions v/s ball bearings =
hinge/suspensions


  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!

  Too visualize a crossed rod hinge:  Imagine two spaced rods running up =
and down this
  page.  Now; you introduce a horizontal rod centered across the other =
two rods, and this
  is the inge suspension rod that you hook up your boom/wire too.  The =
crossed rod hinge
  suspension looks like the capitalized letter "H".  You can visually =
rotate the assembly
  to make the hinge center rod workable for your desired horizontal or =
vertical instrument.
  Of course, for the hanging pendulum (S-G), the rod assembly is simply =
placed flat atop
  a mast, and the center rod oscillates/rotates atop the two outer rods. =
 For most horizontal
  or vertical seismometers use, the assemblys two rods are placed =
against the mast, (you
  might need acouple here) and the center rod presses against these two =
rods via a boom.
  Its possible to use the same hinge for angled horizontal or vertical =
top of the mast pivots
  also.  There is NO gouged or filed slot/s in any rods to hold the =
position of the crossed
  rod; as that would ruin its lesser friction hinge or suspension =
purpose.

  In my new view...I'd even go so far as to say; ball bearings =
hinges/suspensions are
  less ideal for most seismometers as they do have a noted problem with =
higher friction
  for very small rotational displacements, whereas, crossed rod =
hinges/suspensions have
  less friction in this critical displacement area.  Other hinge designs =
like razors, points,
  cardans (typical S-G hinge), shims etc., are so bad for contact =
friction, torque/material
  self dampening, that I'll not even consider or recommend their use =
again.

  I've ran many hanging pendulum (S-G like), table top/edge tests with a =
variety of ball
  bearings on various contact surfaces in the last few weeks.  The =
purpose of the tests
  was to estimate the friction of the various test models; via =
offsetting the pendulum a
  set distance, and simply timing how long the pendulum will continue =
oscillating till it
  visually quits moving.  Ball bearings were visually observed to be =
rather consistently
  prone to stop in a shorter time where the displacement of the mass got =
down to ~1//16"
  deflection (from zero) oscillations...and usually stopped in a hour or =
two. The
  oscillations times with ball bearings ranged from 5 to 6 hours.

  In the last few days, I tried acouple different rod materials in a =
crossed rod hinge
  with the same general table top/edge test platform.  The first model, =
used 3 rods of what
  I believe is grade 304 stainless steel 1/4" diameter rods.  That =
oscillations test ran on
  for ~8 hours.  The second model used two drill rod shanks (clean round =
end), with the
  same stainless steel rod hinge across them, and that ran for ~7.5 =
hours.  Small mass
  displacements decay oscillations on the descending order of 1/16", can =
go on for
  several hours thereafter till the mass stops.  While there is alot of =
different material
  that could be tested; I think its very obvious from just these 2 =
tests, this this specific
  type hinge is very much the better choice.

  There is another hinge suspension, that has yielded longer =
oscillations decay times
  that I've worked with, and that is the Zero Torque Suspension.  Those =
models on the
  same table top/edge tests, gave a range of 10-11 hours.  However, I =
think amateurs
  will find that crossed rod hinge/suspensions will be easier to work =
with, and its more
  adoptable for all hinge situations like on a typical horizontal or =
vertical seismometer,
  whereas a zero torque suspension might reasonably only be good for a =
hanging
  pendulum (S-G).

  Credit is given to Chris Chapman for suggesting trials of these =
various suspensions
  and guidance!

  Take care, Meredith Lamb







Hi,  i am enjoying the =
input. here!=20
Thanks to everyone. geofffrey<><

  
----- Original Message ----- 
  From:=20
  meredith lamb 
  
To: psn-l@.............. 
  
Sent: Sunday, October 23, 2005 =
4:53=20
  PM
  
Subject: Crossed rod =
hinge/suspensions=20
  v/s ball bearings hinge/suspensions
  


  
Hi all,
  
 
  
Chris Chapman recently stated in a private email that he thought =
a=20
  crossed rod hinge
  
suspension would have less friction/dampening than a ball bearing =

  hinge...and he is
  
so very right!
  
 
  
Too visualize a crossed rod hinge:  Imagine two spaced rods =
running=20
  up and down this
  
page.  Now; you introduce a horizontal rod centered =
across the=20
  other two rods, and this
  
is the inge suspension rod that you hook up your boom/wire =
too.  The=20
  crossed rod hinge
  
suspension looks like the capitalized letter "H".  You can =
visually=20
  rotate the assembly
  
to make the hinge center rod workable for your desired horizontal =
or=20
  vertical instrument.
  
Of course, for the hanging pendulum (S-G), the rod assembly is =
simply=20
  placed flat atop
  
a mast, and the center rod oscillates/rotates atop the two =
outer=20
  rods.  For most horizontal
  
or vertical seismometers use, the assemblys two rods are placed =
against=20
  the mast, (you
  
might need acouple here) and the center rod presses against these =
two=20
  rods via a boom.
  
Its possible to use the same hinge for angled horizontal or =
vertical top=20
  of the mast pivots
  
also.  There is NO gouged or filed slot/s in any rods to =
hold the=20
  position of the crossed
  
rod; as that would ruin its lesser friction hinge or =
suspension=20
  purpose.
  
 
  
In my new view...I'd even go so far as to say; ball bearings=20
  hinges/suspensions are
  
less ideal for most seismometers as they do have a noted =
problem=20
  with higher friction
  
for very small rotational displacements, whereas, crossed rod=20
  hinges/suspensions have
  
less friction in this critical displacement area.  =
Other hinge=20
  designs like razors, points,
  
cardans (typical S-G hinge), shims etc., are so bad for contact =
friction,=20
  torque/material
  
self dampening, that I'll not even consider or recommend their =
use=20
  again.
  
 
  
I've ran many hanging pendulum (S-G like), table top/edge tests =
with a=20
  variety of ball
  
bearings on various contact surfaces in the last few =
weeks. =20
  The purpose of the tests
  
was to estimate the friction of the various test models; via =
offsetting=20
  the pendulum a
  
set distance, and simply timing how long the pendulum will =
continue=20
  oscillating till it
  
visually quits moving.  Ball bearings were visually observed =
to be=20
  rather consistently
  
prone to stop in a shorter time where the displacement of the =
mass got=20
  down to ~1//16"
  
deflection (from zero) oscillations...and usually stopped in a =
hour or=20
  two. The
  
oscillations times with ball bearings ranged from 5 to 6 =
hours.
  
 
  
In the last few days, I tried acouple different rod materials in =
a=20
  crossed rod hinge
  
with the same general table top/edge test platform.  The =
first=20
  model, used 3 rods of what
  
I believe is grade 304 stainless steel 1/4" diameter rods.  =
That=20
  oscillations test ran on
  
for ~8 hours.  The second model used two drill rod shanks =
(clean=20
  round end), with the
  
same stainless steel rod hinge across them, and that ran for ~7.5 =

  hours.  Small mass
  
displacements decay oscillations on the descending order of =
1/16", can go=20
  on for
  
several hours thereafter till the mass stops.  While there =
is alot=20
  of different material
  
that could be tested; I think its very obvious from just these 2 =
tests,=20
  this this specific
  
type hinge is very much the better choice.
  
 
  
There is another hinge suspension, that has yielded longer =
oscillations=20
  decay times
  
that I've worked with, and that is the Zero Torque =
Suspension. =20
  Those models on the
  
same table top/edge tests, gave a range of 10-11 hours.  =
However, I=20
  think amateurs
  
will find that crossed rod hinge/suspensions will be easier to =
work with,=20
  and its more
  
adoptable for all hinge situations like on a =
typical=20
  horizontal or vertical seismometer,
  
whereas a zero torque suspension might reasonably only be good =
for a=20
  hanging
  
pendulum (S-G).
  
 
  
Credit is given to Chris Chapman for suggesting trials of these =
various=20
  suspensions
  
and guidance!
  
 
  
Take care, Meredith Lamb