PSN-L Email List Message
Subject: Re: idea for an axis
Date: Thu, 8 Nov 2007 10:12:50 -0700
Randall, I think this is brilliant, and well worth dinking with, which I
think I will do. Thanks, Ted
----- 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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