PSN-L Email List Message
Subject: Re: idea for an axis
From: "Geoff" gmvoeth@...........
Date: Fri, 9 Nov 2007 05:07:40 -0700
DID you clean the ink off the tip
before doing this ?
----- Original Message -----
From:
To:
Sent: Thursday, November 08, 2007 2:54 PM
Subject: Re: idea for an axis
> 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
> or less.
>
> 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.
> Ted
>
>
>
>
> ----- Original Message -----
> From: "Randall Peters"
> To:
> 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
>> 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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