Need help controlling vibrations in scope, please.

[mental4astro (Alexander)]

Hi all,

The scope I use for my lunar and planetary sketches is a 30 year old orange tube C8, and set it up in my backyard. Problem is the street in front of my place is an old concrete thing that was made to deal with military vehicles when the park across the road had WW2 barracks. So every single car that goes by induces vibrations in the fork mounted scope, and trucks and buses are even worse. And it's not like a ping on the scope that dies quickly, the vibrations are long lived as the cars roll past.

Anyone have suggestions on what I could do to help control these? Yes, the old scope is its own worst enemy, but it's what I've got.

Cheers,

Mental.

[MrB (Simon)]

Maybe a couple of these?
http://campchestnutridge.org/wp-cont...our-Orange.png

[raymo]

Wood is very good for dampening vibrations. Three pieces of soft wood [such as pine] about 100mm square by 15mm thick, topped off with standard anti vibration pads, should help significantly. Stand your tripod
on grass or soil if possible, although you will obviously have a bit more bother levelling the tripod than you would on a solid surface.
Also, hang something under the centre of the tripod that is as heavy as the tripod can happily support.
Hope this helps.
raymo

[mental4astro (Alexander)]

Originally Posted by MrB

Maybe a couple of these?
http://campchestnutridge.org/wp-cont...our-Orange.png

Not as silly as you would think! As the land all around here is sand, the constant vibrations & thunk-thunk of tyres slapping over junction lines, the telegraph poles all have a lean on them! The one in front of my place is being replaced & has a lean of some 15° towards my house! The pole that is replacing it has been in place for about 2 months & is starting to lean too!!!

Thanks for the suggestion Raymo. I set up on turf so better than concrete. Leveling is neither here nor there as I need to do it every time I set up.

[julianh72 (Julian)]

Have you tried hanging a bit of weight off the tripod spreader?

Rubber furniture leg carpet protectors are cheap as chips, and can be surprisingly effective as vibration dampers for a tripod. If they help, you can try the more sophisticated (and more expensive!) dedicated tripod vibration dampers.

[leon]

Alexander what Julian has said is quite right and it dose work, even a short chain with a small weight will do the trick.

I have not used this myself but have heard and researched and it is supposed to work well, just hang it off the end of the tube somehow

leon

[louie_the_fly (Stew)]

I've been looking into designs for vibration mountings using a liquid silicon bed. Like the consistency of a gummi bear that's been sitting in a warm place. I think this would work where you have a piece of equipment and you don't want to transfer vibrations to a base structure. I.e. skid mounted pump units that are mounted on other equipment, like oil & gas drilling platforms, ship's hulls, etc. But when it comes to a telescope you want some inherent stability in the mountings. So my design won't work. I think you want some anti vibration pads of around 25 - 30 Shore A hardness. Urethane is probably OK for what you want to do.

[tlgerdes (Trevor)]

I got some terracotta tiles about 15cm square, then glued camping foam mat to it

[OzStarGazer]

Maybe these?
http://www.ebay.com.au/itm/331106276...84.m1423.l2649
I have them on my eBay watch list, and when I added them they were the cheapest on eBay.

[GeoffW1 (Geoff)]

Very interesting

[Steffen]

Originally Posted by tlgerdes

I got some terracotta tiles about 15cm square, then glued camping foam mat to it

I've tried that, also (much stiffer) machine mounting pads – anything that feels the slightest bit squishy between the fingers is going to be too springy under tripod legs with the typical load of tripod+mount+scope. The whole thing is just going to bounce around.

Cheers
Steffen.

[graham.hobart (Graham stevens)]

I made my own - made a square mold and made a triple sandwhich of rubber car mat and silicon caulking adhesive to about 3/4 of an inch thick. Worked well under my CGEM on a bouncy wooden deck!
Graz

[mental4astro (Alexander)]

Many thanks for the suggestions. I'll start looking into some of these tonight when I pull out the C8 for a sketch. I hope the forecast cold front comes in late...

[Camelopardalis (Dunk)]

Vibration suppression pads? I use these when I'm on a hard surface, damps the vibrations from surrounding elephants quite nicely

[Wavytone]

Alex,

There are two solutions I'm aware of.

The first is vibration pads - http://www.bhphotovideo.com/bnh/cont...=REG&A=details

The second is tricky and utterly counterintuitive. Basically... a telescope and mount has a resonant fundamental frequency and harmonics. Vibrations close to this will incite oscillations at the fundamental and harmonic frequencies. To stop these there is another choice.

This involves lowering the fundamental frequency so that it is much LOWER than to the exciting frequencies in the noise (coming from vehicles via the ground).

Stiffening the mount often fails - actually makes it worse - in that the stiffer it becomes, the better it is able to track the driving frequency of the noise.

The solution is to perch the scope on a "sloppy" mount that cannot respond to high frequencies, yet is stiff enough to use. The example I am aware of is an 8" f/7 Newtonian mounted on a tall pole (10cm diameter steel pipe, 4 metres long) to get above a house and surrounding trees. The pipe was filled with a viscous oil and it had a sway damper attached near the top to the house, I don't know what this was exactly but probably similar to a shock absorber. The owner was mechanical engineer, BTW.

Steady as you could wish, and didn't respond to vehicles passing. If you pushed it, yes it would sway a bit but always came back to its original position.

For your C8, this would be like mounting it on about a 1 cm diameter pipe, 1 metre long, set in a concrete block with something to damp the motion. Yes it will move a bit if you nudge it or in a breeze, but keep your mitts off.

In vehicles there is a similar analogy - airbag suspensions, used in the Millennium and Waratah train and buses, and also used by Mercedes. These are utterly unlike conventional springs in that they have a very low fundamental frequency, far lower than can be achieved by coil springs - and results in the "magic carpet" ride these vehicles have, utterly immune to the dreadful lumps and bumps in the track below - as a Tangara passenger will feel.

[mental4astro (Alexander)]

Hi Wavy,

I am looking at vibration suppression pads.

Your post has also had me think about another solution that does not require sitting the mount on secondary blocks. How about firmly wrapping the tripod's legs in foam rubber? The example you gave of that scope sees the pier filled with oil. The oil serves to absorb a lot of the energy - I would have thought nearly all of it. I could also look at wrapping the tynes of the fork as it is these that are vibrating. The whole mount is at fault here as the wedge is transmitting the vibrations. If I can somehow alter the mount, this would change the fundamental and harmonic frequencies.

I've just been thinking about the tripod legs and the mechanism by which they extend. The tripod I use is a metal surveyor's tripod, so it does not have a central brace. But it has chains that stop the legs from over extending. Suspending some weights from these chains will change these harmonics too.

Thanks again Wavy. Your explanation has given reason to how and why many of the solutions that have been proposed here actually work, and inspired others in my mind too,

[malau (David)]

How about set the mount above the yoga mat?