Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Vibration

DIY Observatory
  • Please log in to reply
16 replies to this topic

#1 Astognosis

Astognosis

    Lift Off

  • -----
  • topic starter
  • Posts: 16
  • Joined: 07 Nov 2019

Posted 09 May 2021 - 11:38 AM

Hi

 

having recently finished the construction of a 4.2m x 3.6 m roll off roof observatory I am testing out a 16" Newtonian mounted on an SB Paramount ME gem.  I have a 1m deep, 1.5 tonne concrete base upon which is mounted a 1m tall steel, vibration finned pier.  However,  I get traffic vibration from a nearby road which ruins my  images. 

 

Usually I separate the concrete from the ground with 50 - 70mm of polystyrene sheets which on my other telescopes in the vicinity  appears to have worked as I have no problem.  I think I forgot to include this precaution this time.  I am thinking of using   Sorbothane as a vibration dampening material placed between the concrete and the base of the pier  and/or between the top of the pier and the base oft he mount.

 

Has any body tried this solution and how have they got on?  -ve replies accepted, but not enjoyed. frown.gif

 

Regards,

 

Eric



#2 Cpk133

Cpk133

    Surveyor 1

  • -----
  • Posts: 1,801
  • Joined: 14 Mar 2015
  • Loc: SE Michigan

Posted 09 May 2021 - 12:16 PM

Hi

 

having recently finished the construction of a 4.2m x 3.6 m roll off roof observatory I am testing out a 16" Newtonian mounted on an SB Paramount ME gem.  I have a 1m deep, 1.5 tonne concrete base upon which is mounted a 1m tall steel, vibration finned pier.  However,  I get traffic vibration from a nearby road which ruins my  images. 

 

Usually I separate the concrete from the ground with 50 - 70mm of polystyrene sheets which on my other telescopes in the vicinity  appears to have worked as I have no problem.  I think I forgot to include this precaution this time.  I am thinking of using   Sorbothane as a vibration dampening material placed between the concrete and the base of the pier  and/or between the top of the pier and the base oft he mount.

 

Has any body tried this solution and how have they got on?  -ve replies accepted, but not enjoyed. frown.gif

 

Regards,

 

Eric

Should probably post this in the observatory forum.  I feel your pain.  I live on clay and I'm shocked at the way images vibrate in the eyepiece from cars driving down my subdivision.  Things start vibrating when cars are 50 meters away, if it's a truck, even further.  Worse in winter when the ground is frozen solid.  Good luck isolating your pier. 



#3 barbarosa

barbarosa

    Gemini

  • *****
  • Posts: 3,179
  • Joined: 11 Apr 2010
  • Loc: 139 miles W of the Awahnee Hotel

Posted 09 May 2021 - 12:48 PM

My understanding is that it is much more complex and difficult  than simply putting a pad underneath the pier. If that wasn't true I would expect to have seen many threads, blogs and brags at astronomy sites.

 

I do remember reading that one commercial pier maker suggested that some problems could be ameliorated by placing plywood between the concrete and the pier base.

 

There is a lot of literature on the issue of traffic induced vibration, most of it not very useful at first glance to pier builders. However one paper modeled traffic vibrations concluded that the peak energy from cars, trucks and buses was in the range of 8 to 15 Hz. That might be useful to you.

 

Sorbothane says that "Generally, an appropriate isolator will create a system natural frequency at least one-third lower than the excitation frequency." If I have this right you would need an isolator designed for ~2 to 5 Hz.

 

That might not be possible with Sorbothane. But who knows what you might learn if you call or email them for advice.


  • Alvin435 likes this

#4 spereira

spereira

    Fly Me to the Moon

  • *****
  • Moderators
  • Posts: 6,557
  • Joined: 21 Apr 2017
  • Loc: Bedford, NH

Posted 09 May 2021 - 04:16 PM

Moving to Observatories.

 

smp



#5 speedster

speedster

    Astronomy Architecture and Engineering at McCathren Architects

  • *****
  • Vendors
  • Posts: 826
  • Joined: 13 Aug 2018
  • Loc: Abilene, Texas

Posted 11 May 2021 - 01:24 AM

A pad of sorbothane (or plywood) between bolted plates is unlikely to do anything positive as the vibes are still transferred by the bolts.  Instead of a pad, look for a vibration isolation mount.  Part of it mounts to the concrete and another part of it mounts to the pier base and the pier base is not directly coupled to the concrete. 

 

https://vibrasystems...-isolators.html

http://www.serviceru...solation-mounts

 

For about 4x that price, https://www.coleparm...AyABEgLm2PD_BwE.

 

If money is not object, https://www.techmfg....tacis/stacisiii.



#6 archer1960

archer1960

    Viking 1

  • *****
  • Posts: 811
  • Joined: 26 Jul 2011
  • Loc: Southern New England

Posted 11 May 2021 - 02:48 PM

I would think that those vibration isolators would flex a LOT (omparatively) as your mount tracks and the weight shifts around. If you are trying to image, I'd think that would cause some pretty poor tracking results. After all, we're concerned with a concrete column flexing by a few arc-sec...



#7 gwd

gwd

    Mariner 2

  • -----
  • Posts: 240
  • Joined: 27 Aug 2011
  • Loc: PyeongTaek ROK

Posted 11 May 2021 - 10:45 PM

Ever since my first image stabilized binoculars I wondered why the technology isn't incorporated in telescopes.   When I observed from an apartment rooftop, the elevators and HVAC equipment bothered the view.   This thread reads like there is a market for image stabilized Astro cameras.  When I brought my Questar in for its 20 year checkup I asked them if they had considered including image stabilization.  I thought urban customers would like it.  The man who received my scope said he'd not heard of using IS for telescopes.  



#8 gregj888

gregj888

    Mercury-Atlas

  • -----
  • Posts: 2,697
  • Joined: 26 Mar 2006
  • Loc: Oregon

Posted 13 May 2021 - 01:05 AM

Astro, can I ask where you are located?

 

First, make sure everything is solid to the base.  You don't want anything picking up resonates.

 

To the same end, if the pier is  steel, fill it with play sand (beach) or pea gravel.  You want something that doesn't pack to absorb the energy (well converts it to heat I assume).

 

You might put a shallow bowl of water on the top of the base and see if you detect the vibration there (Jurassic Park Style).  If so, that's the place to start.

 

As far as complaint material, you want it between the ground and the block of cement.  F=MA, F = force through the suspension /wrap, M = supported Mass, and A describes the vibration.  This is the first order effect, it gets more complex from here.



#9 PrestonE

PrestonE

    Vanguard

  • *****
  • Posts: 2,397
  • Joined: 29 Apr 2005
  • Loc: San Miguel de Allende,Mexico

Posted 14 May 2021 - 04:38 PM

Eric,  I found some interesting mounting methods in Unusual Telescopes and currently use the

Springless Damper Oil Filled mount designed by Rafael Lopez Velez of Mexico seen on page 108...on my Roof Top Observatory atop my Concrete home in San Miguel de Allende, Mexico...with a 12 inch reflector.

 

It totally decouples the mounting from the earth and is Tunable by changing the level or viscosity of the oil...

 

I would post a print, but it violated Copyright law and rules of CN....sadly...

 

If you are interested, I could email you a drawing...

 

Best Regards,

 

Preston



#10 Raginar

Raginar

    Cosmos

  • *****
  • Posts: 9,807
  • Joined: 19 Oct 2010
  • Loc: Pensacola, FL

Posted 17 May 2021 - 07:13 PM

Hi

 

having recently finished the construction of a 4.2m x 3.6 m roll off roof observatory I am testing out a 16" Newtonian mounted on an SB Paramount ME gem.  I have a 1m deep, 1.5 tonne concrete base upon which is mounted a 1m tall steel, vibration finned pier.  However,  I get traffic vibration from a nearby road which ruins my  images. 

 

Usually I separate the concrete from the ground with 50 - 70mm of polystyrene sheets which on my other telescopes in the vicinity  appears to have worked as I have no problem.  I think I forgot to include this precaution this time.  I am thinking of using   Sorbothane as a vibration dampening material placed between the concrete and the base of the pier  and/or between the top of the pier and the base oft he mount.

 

Has any body tried this solution and how have they got on?  -ve replies accepted, but not enjoyed. frown.gif

 

Regards,

 

Eric

Look up helical springs.  They're designed to separate large industrial equipment from the floor.  You'd be using them in reverse essentially.  They're not terribly expensive and you'd put them between your pier and the plate for the mount.



#11 555aaa

555aaa

    Vendor (Xerxes Scientific)

  • *****
  • Vendors
  • Posts: 2,172
  • Joined: 09 Aug 2016
  • Loc: Ellensburg, WA, USA

Posted 18 May 2021 - 03:38 PM

You can use lead washers to help with higher frequency isolation. So when you bolt the mount down the clamp force is through lead which adds dampening. I personally like the wire rope isolators. I’m curious to see how well air isolation would work. I bet it would work very well provided that the total mass is large.

Edited by 555aaa, 18 May 2021 - 03:40 PM.

  • PrestonE likes this

#12 Astognosis

Astognosis

    Lift Off

  • -----
  • topic starter
  • Posts: 16
  • Joined: 07 Nov 2019

Posted 22 May 2021 - 12:36 PM

Apologies to all for not replying sooner.  Many thanks for your replies.  There is some reading and taking on board to be done.

 

I manged a few hour  test imaging a few nights ago.  I had earlier tightened up the RA and DEC balance adjustments on the  MA paramount  so that there was a little less movement - some is needed to stop jamming when the mount slews.  I had no obvious  issues with vibration.  This may have been due to a much quieter night with regard to the volume of passing traffic.  I shall have to monitor the situation on a busier night.

 

Greg, I'm from the UK, 40 miles from London so deep ground frost is not an issue.  The soil is clay and sand, in fact there is a sand quarry a couple of miles away.

 

One often reads of filling  metal piers with sand to reduce vibrations.  Has anybody actually any empirical results.  Has it been tried before and after sand is introduced to the pier. I have given up on the idea of introducing dampeners such as  Sorbothane or rubber bobbin types. 

 

The vibration frequencies of road traffic alluded to i.e. below 20Hz are of similar values I have found in my research.  20Hz is also given as the lower limits of human hearing.

 

The idea of using lead as a dampener  is interesting.  If it transpires to be a good material I could then make some lead mounting bobbins with a threaded bolt encased and  protruding to bolt the mount adapter plate to.  Off course I would have to make it so that it is not pulled out the concrete pier top.  I have collected a significant amount of lead over the years which I could use.

 

The ideal answer would be to move, but my wife doesn't want to.

 

Many thanks to all,

 

Eric



#13 speedster

speedster

    Astronomy Architecture and Engineering at McCathren Architects

  • *****
  • Vendors
  • Posts: 826
  • Joined: 13 Aug 2018
  • Loc: Abilene, Texas

Posted 22 May 2021 - 02:12 PM

There is anecdotal evidence of sand helping but I doubt you find anything empirical as, structurally, sand is a fluid so it can change the frequency but does little to change the amplitude of the deflection.  All we care about is the deflection.  It doesn't matter if the pier if vibrating at 20, 2,000, of 20,000Hz as long as the deflection is below what the camera can detect.


  • archer1960 likes this

#14 archer1960

archer1960

    Viking 1

  • *****
  • Posts: 811
  • Joined: 26 Jul 2011
  • Loc: Southern New England

Posted 22 May 2021 - 03:25 PM

There is anecdotal evidence of sand helping but I doubt you find anything empirical as, structurally, sand is a fluid so it can change the frequency but does little to change the amplitude of the deflection.  All we care about is the deflection.  It doesn't matter if the pier if vibrating at 20, 2,000, of 20,000Hz as long as the deflection is below what the camera can detect.

It may not change the amplitude, but it should dampen out the vibrations quicker than a hollow tube would.



#15 Astognosis

Astognosis

    Lift Off

  • -----
  • topic starter
  • Posts: 16
  • Joined: 07 Nov 2019

Posted 22 May 2021 - 07:03 PM

Jim,

 

Thanks for the additional information

 

Following on from the initial post I then took   a look at similar vibration idolaters to one of the links you provided ,  http://www.serviceru...solation-mounts, here in the UK  for which the vibration material was rubber with upper and lower bolts isolated.  The feed back I got from one of the UK  suppliers of similar products was not very helpful. Have you experience of such solutions being used with astronomical piers?  it may be possible to use 4 such items to connect the steel pier to the Paramount's ME adapter.  If I give up on the pier and resort to additionally casting  tapered concrete pier I could try these.  I'm given to understand that the choice of size of such dampeners are related to the load and frequencies applied.

 

What  problems are experienced by concrete piers themselves?  Pier movement in the ground may not be such a problem, seasonal weather shifts are not too extreme here.  Maybe there is an easier transmission of the  vibration energy through the concrete or restitution time from vibrations are too long?  As mentioned the existing block is 1m x 0.75m^2. If I was to cast an extension it would have the same dimensions upwards for ~ 1m, but be tapered to 14" maybe 16" square to take the ME mount's adapter plate.  Weight of the mount and telescope would be about 195 kg.

 

Viking thanks for you comments re the use of sand  in a hollow pier it complements  Jim's and explains what purpose it may serve.



#16 555aaa

555aaa

    Vendor (Xerxes Scientific)

  • *****
  • Vendors
  • Posts: 2,172
  • Joined: 09 Aug 2016
  • Loc: Ellensburg, WA, USA

Posted 22 May 2021 - 09:58 PM

You might be better off isolating the pier base from the concrete, reason being that you want a large mass that is on the floating side of the point of isolation. This to me needs an engineered solution but without measurements we are shooting in the dark. A video image at high magnification might show the direction, amplitude, and frequency of vibrations from the ground. Vibrations are also sometimes self excited from either camera fans or the drive itself. Striking the mount gently with a soft mallet can show the chief resonant modes of the system ( while videoing or via other instrumentation).
  • PrestonE likes this

#17 gregj888

gregj888

    Mercury-Atlas

  • -----
  • Posts: 2,697
  • Joined: 26 Mar 2006
  • Loc: Oregon

Posted 28 May 2021 - 09:50 PM

Eric,

 

Sorry, haven't checked in for a while either.  UK is a long way from Portland OR.  I have a vibration survey tool and would have been happy to take a reading but that's a bit far. 

 

Sand is not a fluid, nor is pea gravel in this case.  There is conservation of energy but you can change the kinetic energy into heat and sound, at least I believe that's what the sand will do inside the pier. On my old tennis racket I had a piece of silicon tubing at the base of the string, made a huge difference...  Sometimes it doesn't take much

 

Sorbathane or foam between the floor and and pier base, fine, not sure I would put it under the base.  Springs and fluid dampers can work, but should really be engineered.  Anything in this relm will have a resonance, usually at the low end (where you don't want it) where it actually amplifies the vibration trick is not to have it line up with the excitation or anything else.. 

 

Assuming you can't or don't want to hack up the 1.5 tonne chunk of concrete to suspend it from springs nor dig around it to back-fill with something complaint.  Load up one of the vibration apps on your cell phone.  Start with the base and work your way up, tapping or thumping the base, pier mount ect.  You are looking at for anything that stands out or anything that follows the traffic pattern.  

 

Sorry, wish I could help more.  It's generally easy to vibration isolate something, but it isn't easy to isolate it and maintain the ability to align it with the stars.




CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics





Also tagged with one or more of these keywords: DIY, Observatory



Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics