PSN-L Email List Message

Subject: Re: Video of a experimental pivot
From: "Geoffrey" gmvoeth@...........
Date: Fri, 24 Jul 2009 16:11:57 -0700

Hello Meredith lamb,

There is one other question I may ask ;

Have you ever tried a torsion spring
with this design ?

I have tried using an aluminum alloy
antenna element that is a tube split down
the middle with a slot its full length.
It seems to act as a spring quite well
but not sure if its actually suitable for the job.
It would totally eliminate the bulky extension spring.

If you wish to derive the spring constant
you can hang a water bottle with a measured
amount of water to get enough weight to
extend the spring maybe 10 inches then use
a bit of math. You may control the overall temp
of a working device ( I think two devices are necessary
to be proper ) by placing gallon jugs of salt
water brine surrounding the devices to make a thermal
inertia to average out temp changes or so
I believe.

I think any linear constant extension spring made out of
steel can do the right job if you can get at least
11 or more inches of extension.

You must allow for any pretensioning because
that will have an effect on its overall extension.
The pretensioning will work out to some added
extension amount to the measured results.
Sort of a second degree correction factor
to think about. That is how much water weight before
spring shows first signs of extension.

No reason you can not easily work out the spring constant
for amateur needs.

I like your Georgia Design But would absolutely need two
such sensors for a complete whole.

Please use eye protection, I blinded
myself in one eye accidentally
with a wild spring once, thank
goodness it lasted only a few seconds
before returning to normal.
Springs can be dangerous to anyone's
quality of life. No one is mistake free.

Also Century Spring Company, they will build custom
springs but charge a terrible initial setup fee of a
few hundred dollars I think. You want to have
maybe a hundred springs made all at once.


----- Original Message ----- 
From: "meredith lamb" 
Sent: Friday, July 24, 2009 11:23 AM
Subject: Re: Video of a experimental pivot

On Thu, Jul 23, 2009 at 11:09 PM, Geoffrey  wrote:

> Howdy Meredith lamb,
> Neato, Would it be possible to change the ratio
> of the pivot point to 18 to 25 centimeters on the weight side
> and one centimeter on the spring side and greatly reducing
> the mass to get a longer period ?
> I guess you need to reduce the mass by the
> mechanical advantage of the ratio.

***Geoffrey; a lot of the "trials" of this design literally depends on the
specific spring itself and its placement both
on the end of the boom and where it is connected....which "could be" both
behind the pivot point or in
front of the pivot near the mass.  I first tried a Servalite # 59 (which has
seen a few other mentions on PSN);
but that didn't seem to work very well, on this setup....regardless of

> What kind of washers are those so shiny
> you can see the JVC camera in it ??
> Filing cabinets in the reflection.

***Those are the two pivots, that the rolling rod rests on the inside hole
edge.  I think they are actually computer
hard drive disks coated in nickel chrome...but which were rejected for some
reason.  I did make the mistake
of assuming that people already know what they are.  Yes; they do look like

> Range limits are necessary so the device can be
> carried/moved.
> Where would the damper go ?

***Normally the dampening usually goes near the mass as with most
seismometers.    Their is no dampening
or sensor pickup on the video for the pivot (and quite literally the spring
also) test.  I am definitely not technically
oriented to be up front.  Perhaps the best summation of the test is that
pivot "could" work, and that perhaps also
that the Servalite spring #200 could be of much more major amateur interest
and use in such.

***A note on the spring.  While Ace hardware is where I got the spring from;
Truevalue hardware or other
hardware stores "may" have such.  One would literally have to call their
hardware stores and ask if they have
a Servalite spring assortment.....and....if they have that specific spring.
I think it cost ~ about 3 dollars.  Most
hardware stores are small and they don't have such.  However; they may be
able to special order such, likely
at a higher cost.

It would be nice to have two such devices
in opposite directions to cancel out tilt
in a diff amp.
Two such matched devices are necessary
for proper operation.

Where would a magnetic damper go ?


***The steel test base I used would normally be "condemned" for the
temperature expansion & contraction...but
it was just a readily made test platform.

Take care, Meredith Lamb



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