PSN-L Email List Message
Subject: Re: material choices and/or configuration changes
From: Charles Patton charles.r.patton@........
Date: Tue, 16 Aug 2011 11:01:50 -0700
Pete,
I was confused, too, and would like to understand the spring being
described.
Charles R. Patton
On 8/16/2011 10:12 AM, Pete Rowe wrote:
> Hi Randall
> In your discussion of the cosine shaped strips, my mental picture got
> really fuzzy at the end. If I have 4 strips and I weld pairs together
> I now have 2 units. I have trouble visualizing the 2 units arranged
> so they have 4 fold symmetry. I missed something..
> Pete
>
> ------------------------------------------------------------------------
> *From:* Randall Peters
> *To:* "'psnlist@..............."
> *Sent:* Tuesday, August 16, 2011 8:35 AM
> *Subject:* material choices and/or configuration changes
>
> I read with much interest several of your recent comments concerning
> materials other than the conventional (standard alloy) metal for use
> in the spring of a vertical. The comment about nano tubes caused me
> to think about how I will never forget the lecture given at TTU years
> ago by the discoverer of the ‘bucky ball’ (Richard Smalley, Rice
> University Chemist). Several of us made bets on how long it would
> take for him to receive the Nobel Prize for this work. He
> ‘punctuated’ the serendipitous nature of his discovery by mentioning
> “how he expected there would have been a ‘telephone ringing from
> heaven’ had he not finally realized what ‘lay before him in plain sight’.
> How I wish that I had some samples on hand to do experiments with
> various exotic materials involving nanotubes, since my guess is that
> they just “might be the ticket’ to solving a lot of our problems. In
> the meantime, I would like to propose that somebody take the lead to
> look at possible (significantly different) other ways to maybe improve
> what we’ve presently got to live with. Would it be smart, for
> example, to try and use torsional restoration as opposed to the
> conventional coiled spring. Yes, Lucien LacCoste changed the history
> of seismology (as a tennis player, while solving a problem given to
> him by his physics professor Romberg, while at UT Austin). He ‘pulled
> a coil inside out’ to generate a zero-length configuration that is
> much less susceptible to creep than previous springs. I have often
> wondered if any of the gravimeters he built may have also used fuzed
> silica (quartz), since it is a much more stable material than most
> other types (unfortunately brittle and nonconductive).
> Then Erhard came along and invented (patented) the astatic spring to
> give similar performance. So there may be several ways to ‘skin a
> meso-anelastic cat’.
> One of my ideas that was shown as a prototype at the broadband
> conference I would like for some of you to think about. You can find
> a picture of my “compound vertical seismometer†on the IRIS link by
> simply typing the keywords into Google. And if you want to better
> understand the physics of how it works (benefit of period lengthening
> being possible by using the ‘beauty’ of the eccentric in latest
> generation bows), you might want to read the other paper that follows,
> titled “Archer’s compound bow, smart use of nonlinearityâ€.
> When I showed this prototype to some of those in attendance at
> the broadband conference—several of them were positively impressed.
> They seemed to think of it more as a toy, however, than being
> practical; but I believe Erhard was in earnest when he mentioned that
> I should try to get the amateur seismology community interested in
> doing some experiments with it.
> Be apprised that it is susceptible to creep, as shown in my
> paper, titled “creep enhanced sensitivity of seismometersâ€, online at
> http://arxiv.org/abs/physics/0508105
> The approach using torsional restoration could be closer , in
> fact, to that of operating with a coil than you might think. Few
> people in my experience realize that the spring constant of a coil
> depends on the shear modulus. In other words, it is the twisting of
> the wire of the coil that is key One of the truly impressive physics
> demonstrations, that shows that the coil actually wants (unless
> constrained otherwise) to wind and unwind under load change—is the
> Wilberforce pendulum which exhibits mesmerizing mode coupling behavior.
> And for those of you who want to retain the remarkable properties
> of force balance, there is no reason why you can’t use it with this
> compound vertical instrument.
> Also, mention was made of the possible use of single crystal silicon.
> I have used reject (previous generation 3-in) wafers to great
> advantage in some of my experimental efforts. It is very easy to
> diamond scribe and cleave them into rectangular shapes. They are more
> elastic than one might tend to believe, and it may be possible to make
> some useful springs out of them. They should be much better than any
> metals that I know about, because a given atom is far more prone to
> stay where it is supposed to.
> Finally, I would like to mention some work, involving springs,
> by the gentleman who changed the world of earth field measurements.
> Jim E. Faller pioneered the free-fall method of measuring g, by
> counting fringes as a cube-corner reflector falls in a vacuum (within
> a vacuum) to eliminate air drag. Using a laser interferometric setup
> to generate the fringes, he improved the accuracy of the g-measurement
> by several orders of magnitude.
> When Jim gave a seminar years ago at TTU, he also mentioned to me
> some ideas about springs that he had. Don’t know whether he ever
> refined and published his thoughts along the following lines.
> Take four strips of elastic rectangular pieces, several times
> longer than wide. Form a single-cycle cosine wave permanent
> (unstrained) shape in each of the strips. Take two of the thus formed
> strips and ‘weld’ their ends together to form a shape similar to the
> leaf spring of an old truck. Do the same with the other pair, and
> then assemble the four into a single structure having 4-fold
> rotational symmetry. Thus it has a stand-alone (stable arrangement)
> capability to support a load that would be placed on its top. Has
> anybody tried something like this? It should be possible to gang
> several of them together to increase the operational length and
> decrease the net spring constant (like springs in series).
> Randall
>
>
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