Hi Chris and all,

On Mon, Jul 13, 2009 at 8:51 PM,  wrote:

>  In a message dated 13/07/2009, paleoartifact@......... writes:
>
> Hi All,
>
>     Both http://www.myeclectic.info/SeismoPivots/seismopivots.htm
>   and
> http://myeclectic.info/SeismoPivots/seismopivots.htm both seem to work on
> my Internet Explorer
>
> BACKGROUND PIVOT:  Chris Chapman's newer horizontal designs with his lower
> pivot being a boom end flat that is pivoting on a mast mounted ball bearing
> seems to be a very ideal, reliable and much more stable "standard pivot" for
> those of us endeavoring  to make a commonly used home brew horizontal
> seismometer.  It was studied in 2008 by him, Charles Patton and Brett
> Nordgren and briefly described by the web paper:
>
>     See Lehman photo
> http://jclahr.com/science/psn/chapman/2008%20lehman/lehman_prototype.jpg
>

*Chris, beautiful work on the seismo!   I agree it apparently has several
significant improvements over that of the SEP seismometer sold there in the
United Kingdom and elsewhere.  I wanted to try the pivot last year but
didn't get around
to a trial.  Perhaps (?), this year I might be able to do so...with a
"test setup" assembly I'am planning and constructing.

*For those readers interested in the SEP seismometer, and, if you have a
broadband connection; Youtube has a good
recent video of the "UK School Seismology: seismometer assembly" film
produced by the British Geological Survey.  Go to
Youtube and in the search box, enter in the title above.  The BGS has a
Youtube "channel" (index) with other interesting videos also.  The SEP uses
upper suspension and lower boom, crossed rods pivots.



>      This uses a 16 thou thick SS strip cut from a scalpel blade glued to
> the end of the arm, rolling on a 1/2" SS ball on the upright. This has a
> MUCH better stability than a ball rolling on a plane.
>     Also note the 30 lb 7 core V SS fishing trace suspension, which
> prevents the arm from rotating about it's long axis. I tested this
> suspension OK for stable periods of up to 60 seconds. Note also that the
> frame level screws use a wavy washer and a locknut to prevent rotation as
> the frame expands or contracts when the temperature changes. This seemed to
> improve the long term drift stability quite a bit. SS dome nuts make a very
> good rolling contact on the lower ends of levelling screws.
>     I find that 1/16" copper is preferable to Aluminum for the damping
> plate. Aluminum is slightly paramagnetic and the edges of an Al plate need
> to overlap the damping magnets at all times. If you don't do this, the arm
> will skate sideways to the stop if the edge of the Al plate comes close to
> the edges of the magnets.
>
>     A square section coil is attached to the underside of the Al mounting
> block. This photo was taken before the sensor cable was installed along the
> arm.
>
>  The question that comes up from all this is whether such a lower pivot/s
>>> could be ~ reliably used in a home brew short period vertical spring
>>> seismometer?  I note no reference to such a trial; but that doesn't exclude
>>> that someones hasn't already experimented with such?
>>> This excludes known boom mounted balls on a mast flat.  The size/weight
>>> of the seismometer mass in mind is similar to that of the AS1.
>>>
>>     This was effectively done with cylinders rolling on a plane with the
> EAI vertical seismometer, now discontinued. I still have a copy of the
> manual.
>

*It doesn't "sound" like they were too confident about that model; or, it
required perhaps too many adjustments by
the buyer.



>     You need to space the two balls fairly well apart on the upright to
> prevent them from slipping due to horizontal seismic motions. It is also
> desirable to design the arm so that there is no vertical force on the
> rolling contacts. You attach the spring just behind the centre of mass and
> the weight of the arm is balanced by the weight of the mass about this
> attachment point.
>     Alternatively, you can fit an I bar across the vertical and make a C
> fitting to go around it, attached to the end of the arm. You can then use
> two piano wires under tension from the ends of the C to the enclosed I.
>
>
>  I would also assume that it is likely necessary to have any such balls
> mounted on the side of a mechanical support/s to fix the spring opposition.
>
> It would necessitate two such pivots for maintaining vertical positional
> reliability...i.e.; the "boom" would need to be "T" shaped to constrain its
> otherwise undesirable lateral movement with only one pivot.
>
>
>      Regards,
>
>     Chris Chapman
>

Take care, Meredith Lamb
Hi Chris and all,


On Mon, Jul 13, 2009 at 8:51 PM, <ChrisAtUpw@.......> wrote:



In a message dated 13/07/2009, paleoartifact@......... writes:
=A0
Hi All,
=A0
=A0=A0=A0=A0Both http://www.myeclectic.info/SeismoPivots/seism=
opivots.htm =A0 and http://myeclectic.info/SeismoPivots/seismopivots.htm=A0both seem to work on my Internet Explorer




BACKGROUND PIVOT:=A0 Chris Chapman's newer horizontal designs with=
 his lower pivot being a boom end flat that is=A0pivoting on a mast mounted=
 ball bearing seems to be a very ideal, reliable and much more stable "=
;standard pivot" for those of us endeavoring=A0=A0to make a commonly u=
sed=A0home brew horizontal seismometer.=A0 It was studied in 2008 by him, C=
harles Patton and Brett Nordgren and=A0briefly described by the web paper:=
=A0

=A0=A0=A0=A0See Lehman photo=A0http://jcla=
hr.com/science/psn/chapman/2008%20lehman/lehman_prototype.jpg=A0
<=
/blockquote>

=A0
*Chris, beautiful work on the seismo!=A0 =A0I=A0agree it apparently ha=
s several significant improvements over that of the SEP seismometer sold th=
ere in=A0the United Kingdom and elsewhere.=A0 I wanted to try the pivot las=
t year but didn't get around

to a trial.=A0 Perhaps (?), this year I might be able to do so...with =
a "test=A0setup" assembly I'am planning and constructing. 
=A0
*For those readers interested in the SEP seismometer, and, if you have=
 a broadband connection; Youtube has a good
recent video of the "UK School Seismology: seismometer assembly&q=
uot;=A0film produced by the British Geological Survey.=A0 Go to
Youtube and in the search box, enter in the title above.=A0 The BGS ha=
s a Youtube "channel" (index) with other interesting videos also.=
=A0=A0The SEP uses upper suspension and lower boom, crossed rods pivots.

=A0
=A0


=A0=A0=A0=A0This uses a 16 thou thick SS strip cut from a scalpel blad=
e glued to the end of the arm, rolling on=A0a 1/2" SS ball on the upri=
ght.=A0This has a MUCH better stability than a ball rolling on a plane.
=A0=A0=A0=A0Also note the 30 lb 7 core V SS fishing trace suspension, =
which prevents the arm from rotating about it's long axis. I tested thi=
s suspension OK for stable periods of up to 60 seconds. Note also that the =
frame level screws use a wavy washer and=A0a locknut to prevent rotation as=
 the frame expands or contracts when the temperature changes. This seemed t=
o improve the long term drift stability quite a bit. SS dome nuts make a ve=
ry good rolling contact on the lower ends of levelling screws.

=A0=A0=A0=A0I find that 1/16" copper is preferable to Aluminum fo=
r the damping plate. Aluminum is slightly paramagnetic and the edges of an =
Al plate need to overlap the damping magnets at all times. If you don't=
 do this, the arm will skate sideways to the stop if the edge of the Al pla=
te comes close to the edges of the magnets. 

=A0
=A0=A0=A0=A0A square section coil is attached to the underside of the =
Al mounting block. This photo was taken before the sensor cable was install=
ed along the arm.




The question that comes up from all this is whether such a lower pivot=
/s could be=A0~ reliably used=A0in a home brew short period vertical spring=
 seismometer?=A0 I note no reference to such a trial; but that doesn't =
exclude that someones hasn't already experimented=A0with=A0such?

This excludes known boom mounted balls on a mast flat.=A0 The size/wei=
ght of the seismometer mass in mind is similar to that of the AS1.
=A0=A0=A0=A0This was effectively done with cylinders rolling on a plan=
e with the EAI vertical seismometer, now discontinued. I still have a copy =
of the manual.
=A0
*It doesn't "sound" like they were too=A0confident about=
 that model; or, it required perhaps too many adjustments by
the buyer.
=A0
=A0

=A0=A0=A0=A0You need to space the two balls fairly well apart on the u=
pright=A0to prevent them from slipping due to horizontal seismic motions. I=
t is also desirable to design the arm so that there is no vertical force on=
 the=A0 rolling contacts. You attach the spring just behind the centre of m=
ass and the weight of the arm is balanced by the weight of the mass about t=
his attachment point. 

=A0=A0=A0=A0Alternatively, you can fit an I bar across the vertical an=
d make a C fitting to go around it, attached to the end of the arm. You can=
 then use two piano wires under tension from the ends of the C to the enclo=
sed I.


=A0



I would also=A0assume that it=A0is likely=A0necessary to have any such=
 balls mounted on the side of a mechanical support/s to=A0fix the spring op=
position.
=A0
It would necessitate two such pivots for=A0maintaining vertical positi=
onal reliability...i.e.; the "boom"=A0would need to be "T&qu=
ot; shaped to constrain its otherwise undesirable lateral movement with onl=
y one pivot.=A0

=A0

=A0=A0=A0=A0Regards,
=A0
=A0=A0=A0=A0Chris Chapman
=A0
Take care, Meredith Lamb