Re: ATM self contained vibration damper....

["benoit schillings" <benoit_schillings@hotmail.com>]

I will try the oil & particule idea... simple enough.

Just to make things clear, the wind doesn't MOVE the scope...
I can keep an RMS guiding of around 2 arc/sec with a wind of
20 mph ! I'm trying to remove the last 2 arc/sec of high speed
vibration which is induced by the wind.

For the comments that I am trying to build a lightweight scope
and adding weight to make it stable, my whole (portable) scope
is already around 350 pounds for a 12 inch... imaging under windy
conditions at arc/sec resolution level is a really tricky sport

-- benoit


>From: "Dwight K. Elvey" <dwightk.elvey@amd.com>
>Reply-To: "Dwight K. Elvey" <dwightk.elvey@amd.com>
>To: atm@shore.net
>Subject: Re: ATM self contained vibration damper....
>Date: Tue, 27 Aug 2002 17:05:08 -0700 (PDT)
>
>
>Hi
>  Part of the problem is that he is looking for something
>to remove vibration from the wind. There is no dampening that
>will do this. If you clamped it to a cement wall, it would
>work but dampening does not stop outside forces from
>moving the telescope. You can either make the telescope
>real heavy ( the cement wall trick ) or block the wind.
>  Don't confuse dampening with clamping. These are two different
>problems. I'd still be curious if someone that was energetic
>would try out my bottles of oil and BB idea. One could put
>some BB's in a bottle and put enough oil to almost cover the
>BB's. The idea is that the sloshing of the oil between the BB's
>would generate some dampening. These could be placed at the
>extreme ends of a telescope ( the top ring on a Dobson ).
>  One could experiment with the location and size. If weight
>was a problem, one could try using small plastic beads from
>a hobby shop.
>  Just don't expect this to stop the wind from pushing the
>telescope around.
>Dwight
>
>
> >From: "Jim Miller" <jim@jtmiller.com>
> >
> >
> >i'm somewhat familiar with mass dampers from some work with gyroscopes.
>mass
> >dampers basically use a mass which is unlikely to move with the input
> >provided coupled to the object of interest. for a scope this would need 
>to
> >be large and coupled in two axes presumably to the eyepiece end for
> >structural reasons.
> >
> >how about digging a hole? (only slightly facetiously...)
> >
> >jtm
> >
> >----- Original Message -----
> >From: "benoit schillings" <benoit_schillings@hotmail.com>
> >To: <jim@jtmiller.com>; <atm@shore.net>
> >Sent: Tuesday, August 27, 2002 1:22 PM
> >Subject: Re: ATM self contained vibration damper....
> >
> >
> >yes, I'm well familiar with wind screens ! The thing is that
> >in order to really efficiently block the wind for a scope
> >like mine, the wind screen has to be really big and difficult
> >to setup... obvious limits there.
> >
> >Now on the issue that the vibration damper needs to be coupled
> >with something else not moving, tuned massed dampers can certainly
> >damp vibrations without that constrains for a "narrow" band of
> >frequency... the key is to know if one can make a broader band
> >damper (particule dampers ?)
> >
> >-- benoit
> >
> >
> >>From: "Jim Miller" <jim@jtmiller.com>
> >>Reply-To: "Jim Miller" <jim@jtmiller.com>
> >>To: "benoit schillings" <benoit_schillings@hotmail.com>,<atm@shore.net>
> >>Subject: Re: ATM self contained vibration damper....
> >>Date: Tue, 27 Aug 2002 13:04:10 -0700
> >>
> >>vibration dampers operate by using motion to create heat (usually). this
> >>means the moving part has to move and be coupled in a lossy fashion to
> >>something not moving in the same direction.
> >>
> >>is there no way to put the scope in the lee of some object which can
> >>deflect
> >>the wind? if you are doing ccd rather than visual work can you lower the
> >>tripod to the lowest possible height and then erect a screen upwind?
> >>
> >>jtm
> >>
> >>----- Original Message -----
> >>From: "benoit schillings" <benoit_schillings@hotmail.com>
> >>To: <atm@shore.net>
> >>Sent: Tuesday, August 27, 2002 12:07 PM
> >>Subject: ATM self contained vibration damper....
> >>
> >>
> >>
> >>One the major limitation I find when doing ccd imaging is that
> >>in most cases, when imaging from the top of a mountain good seeing
> >>is generally corelated with medium strength wind which of course
> >>has a tendency (even with my semi-heavy scope) to counter the advantage
> >>of good seeing.
> >>I use my AO-7, but in many cases, the dominant vibration of the
> >>instrument will be around 5 to 10 Hz which is hopeless to correct
> >>with a tip-tilt mirror unless I was able to correct at 100 Hz or
> >>so, something which is not common by virtue of lacks of bright guide
> >>stars.
> >>
> >>I started thinking a while back at some lower tech way to dissipate
> >>this high frequency vibration from my scope by using a long shock
> >>absorber attached to the top end of the scope and connecting to the
> >>ground somewhere around the scope, but decided that this was way too
> >>much pain to be practical, it would also likely have a prefered
> >>direction for the vibration reduction, something which is not always
> >>doable of sufficient.
> >>
> >>I remember seing in an old s&t of the idea of having a chain attached
> >>from the top of the scope and hanging into a bucked of oil... other
> >>that the fact that this is yet again a difficult setup, this would
> >>not work well if the scope is pointed toward the zenith... so I am
> >>now wondering if one could build a self enclosed system which would
> >>act in the same way but could just be attached to the top of the
>instrument
> >>and dissipate some of that vibration energy.
> >>
> >>some of the q&d ideas I was thinking about was a cylinder partly filled
> >>with oil, or maybe filled with two liquids which would not mixed...
> >>another idea would be to have a mass held by 4 springs that would
> >>be semi-tuned to the natural vibration of the scope, but I'm finding
> >>myself out of my depth & area when it comes to what would and what
> >>wouldn't work.
> >>
> >>Does anybody on the list has some idea of the subject, or better
> >>experimented in that field ? It seems to me that the same problem
> >>must exist for large dobs, and finding an easy way to kill a good
> >>deal of these vibrations would allow us all to build lightweight scopes
> >>which would be more resilient to wind & other vibration sources.
> >>
> >>
> >>-- Benoit
> >>
> >>
> >>
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