PSN-L Email List Message
Subject: Re: idea for an axis
Date: Thu, 8 Nov 2007 14:54:20 -0700
Randall, I did this also, and got similar results. With no special effort
I just hung a ball point pen, from a nice rare earth magnet, added enough
mass to NOT FALL, and pushed the pendulum about 20 degrees. It rocked or
circled for 30 mins, and my estimated count of cycles was 2500. I had done
other crude pendulums timing, testing hinges and got about 400 cycles, more
I have a room full of different sensors, but now I would like to try this
concept on a mini-sensor. Someday.....
Thanks for the idea.
----- Original Message -----
From: "Randall Peters"
Sent: Thursday, November 08, 2007 9:57 AM
Subject: idea for an axis
> 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
> property of the tungsten carbide.
> In a brief experiment this morning I stuck a 1/2 in cylindrical rare
> 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
> 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
> them together. The pair of pen points can support about 200 grams of an
> 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
> 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
> about this?
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