wrote:
>
> In a message dated 17/09/05, paleoartifact@......... writes:
>
> Hi Meredith,
>
> Randall's capacitative sensors don't require a particularly small spacing=
,
> but they may be able to move +/-2.5 mm. Where this type of sensor really
> wins over the standard S-G type is that there is no pneumatic air damping=
.
> He can also increase the sensitivity by adding more, but narrower, sensin=
g
> areas. He does not use any force feedback as far as I know - it can be
> noisy.
>
> However, this approach does need a very high sensitivity. He complains
> about the ocean background, but he hasn't filtered it out. He does not da=
mp
> the pendulum arguing that the frequencies in which he is interested are f=
ar
> below resonance. However, trying to sort out small slow digital signals f=
rom
> large fast noisy ones is not a method that I would choose. I prefer to
> reduce the noise coming into the ADC as far as possible.
>
> I am quite happy with ball bearings so long as they are not too small. Th=
e
> curse of fine points and actual knife edges is that the blade material is
> far too highly stressed. Adding fine wire loops is really not a problem s=
o
> long as you have the fine wire with polyurethane fusable coating. You jus=
t
> use a hot soldering iron and the coating varnish melts.
>
> I would be happier to try out two figure of 8 loops of fine wire or foil
> around two horizontal circular rods. The gives a zero torque suspension a=
nd
> a well defined rotation axis. It can also be made resistant to large quak=
es,
> with a couple of dobs of epoxy.
>
>
> Regards,
>
> Chris
Hi Chris,
Aside from Mr. Randalls commercial pursuit and opinions with a conduct=
ive ball bearing and surfaces....for just a
plain ball bearings (and non-conductive) that is resting on surfaces o=
f carbide...I would like your judgement of a
more desireable diameter size of ball bearings where they would suppor=
t, say, a range of boom/mass (heavy
weight) S-G's where they range from roughly 1 to 5 pounds?
Have to admit that your "figure of eight" lead wires suggest=
ion for a trial; kind of leaves me wondering more of how
it is totally configured; and/or arranged for hook up to a S-G; as som=
ehow I can't quite grasp that aspect?
All these past email messages on ball bearings did indeed inspire me t=
o try out a table top experiment using
such along the material lines as you have suggested over time. T=
he results I'am seeing are amazing, in as far
as the free and undampened oscillation times before it visually decays=
from a lack of visual eyeball movement
with a S-G type ball bearing setup; which essentially is a indication =
of friction or other restraints therein. My old
2 strip suspension hinge S-G had only about 35 minutes of free os=
cillation (no dampening or hookup wires);
whereas, the experimental ball bearing hinge had slightly over 4 hours=
for a same 2" mass offset for visual
oscillation decay tests. Also, as you mentioned, one can indeed&=
nbsp;eddy current dampen the mass even though
the ball bearings are on a flat smooth level carbide surface. Ve=
ry interesting successful test/s and educational
results! I've put up a temporary web page with 3 pictures and so=
me text of such for anyone interested:
Take care, Meredith Lamb
On 9/17/05, =
ChrisAtUpw@....... <ChrisAtUpw@.......> wrote:
<=
span class=3D"q">In a message dated 17/09/05,
paleoartifact@......... writes:
Hi Meredith,
Randall's cap=
acitative sensors don't require a particularly small spacing, but they may =
be able to move +/-
2.5 mm. Where this type of sensor really wins over the standard S-G type is=
that there is no pneumatic air damping. He can also increase the sensitivi=
ty by adding more, but narrower, sensing areas. He does not use any force f=
eedback as far as I know - it can be noisy.=20
However, this approach does nee=
d a very high sensitivity. He complains about the ocean background, but he =
hasn't filtered it out. He does not damp the pendulum arguing that the freq=
uencies in which he is interested are far below resonance. However, trying =
to sort out small slow digital signals from large fast noisy ones is not a =
method that I would choose. I prefer to reduce the noise coming into the AD=
C as far as possible.
I =
am quite happy with ball bearings so long as they are not too small. The cu=
rse of fine points and actual knife edges is that the blade material is far=
too highly stressed. Adding fine wire loops is really not a problem so lon=
g as you have the fine wire with polyurethane fusable coating. You just use=
a hot soldering iron and the coating varnish melts.
&=
nbsp; I would be happier to try out two figure of 8 loops =
of fine wire or foil around two horizontal circular rods. The gives a zero =
torque suspension and a well defined rotation axis. It can also be made res=
istant to large quakes, with a couple of dobs of epoxy.
&nb=
sp;Regards,
Chris