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 ----- 
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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