PSN-L Email List Message

Subject: Re: idea for an axis
From: "Geoff" gmvoeth@...........
Date: Fri, 9 Nov 2007 05:15:10 -0700

You Will see things like 1mm medium
pens and 0.8mm fine I think that may be
the diameter of the ball ??

Why Dont People try using these things in a vacuum ?

With only Magnetic Damping ??

Put the damper above the sensor so the sensor
can get full advantage of the velocity.

How in the world can you use such a thing vertically ?

----- Original Message ----- 
From: "meredith lamb" 
Sent: Thursday, November 08, 2007 9:37 PM
Subject: Re: idea for an axis

> Dr. Peters and all,
> Am only adding some further development thoughts here.  Some ball point pens
> could likely be emptied of their contents; a replacement ball bearing could
> be
> glued in place, and the empty plastic could contain, say; whatever lead shot
> the
> axis ball bearing pivot could handle weight wise.  Of course, one could
> possibly
> retain the original ball bearing perhaps by cutting off the ink well tube
> and glueing.
> Of course the plastic is both the "boom" and the "mass" weight holder in
> one.
> One could "entertain" dual pens also for the vertical sensing approach with
> a
> suitable spring....the dual ball bearing pivot/axis points should make it
> quite stable.
> I suppose its also possible to electrically isolate the contact points of
> the
> axis points, and run wires to a bulb somewhere at the base of one of the
> pens;
> for light sensing variation output.  Of course there is other ways of suing
> light
> sensing without using a bulb in one of the pens.
> Anyway....have tried only one working ball point here.  Its a big size,
> "Gelwriter Rx", I
> got from a Costco store.  It has a screw on head.  Even the pocket clip can
> be easily pulled out of the assembly.  The only magnetic item therein was
> the
> spring.  The clip and the ID ring seem to be stainless.  The hand diameter
> size is noteably larger than the average ball point pens on the U.S. market.
> Some of the plastic is colored to look like metal.
> I tried another ball point....but, its ball bearing didn't appear to be even
> magnetic.
> Quite some time back, Chris Chapman checked out a variety of ball point
> pens, and found the ball bearing diameters can vary.
> Meredith Lamb
> On Nov 8, 2007 9:57 AM, Randall Peters  wrote:
>> Since the VolksMeter uses tungsten carbide to establish the axis
>> (extracted from
>> ball-point pens), I should have thought of the following a long time ago.
>>   A key to reducing rolling friction is to work with hard surfaces.
>>  Another key
>> to reducing friction in general (if possible) is to reduce the normal
>> force.  Both
>> are achievable by hanging a pendulum from a rare earth magnet, using the
>> ferrous
>> property of the tungsten carbide.
>>    In a brief experiment this morning I stuck a 1/2 in cylindrical rare
>> earth
>> magnet to the top of a steel door frame and then hung a ball point pen
>> from the
>> magnet.  Discovered that the tungsten carbide tip of the pen could support
>> about
>> 100 grams of weight.  Of course this arrangement is unsatisfactory for a
>> seismometer because the physical pendulum that results (swinging pen)
>> moves as a
>> spherical pendulum.
>>    To get the required planar motion I took the refills of two pens and
>> glued
>> them together.  The pair of pen points can support about 200 grams of an
>> inertial
>> mass while constrained to motion in a plane.
>>    The quality factor of this oscillator proved to be really high, with
>> the unit
>> swinging in observable free decay for many hundreds of cycles.  It is
>> clear then,
>> that the friction is very small indeed, by (i) taking advantage of the
>> hardness of
>> both the magnet and the small tungsten carbide balls; and (ii) because the
>> field
>> gradient of the magnet provides support for much of the mass of the
>> pendulum, so
>> that the normal force is reduced as compared to most other configurations.
>>     For you folks who have played with various axis types, what do you
>> think
>> about this?
>> Randall

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