A pier question!

[carastro]

Yup, I know what works for me and what doesn't, I'll just take every-ones word for it as it's not something I need to have to worry about.

Carole 

[ollypenrice]

GoTo works perfectly if the mount isn't level. Witness Takahashi mounts which cannot be levelled. My Tak Go To is first class.

You can have a Tak mount polar aligned before a regular mount user has got the tripod level. That is literally true.

My point wasn't about the speed of levelling, though, and Steve's right that it is better to level a mobile (non Tak) mount because of the interaction between azimuth and altitude drift iterations. My intention was to comment on a fixed observatory pier, the OP's topic, in which many designs compromise rigidity in order to offer levelling which is simply not needed. In a pier you want rigity.

The real pests are the manufacturers who design mounts to be secured onto tripods or piers from below. For piers this pointlessly introduces the need for some form of access, so we get into ratboxes and owls nests and all sorts of silliness. Nowadays most manufacturers have woken up to this. Avalon, Mesu, iOptron, 10 Micron and many others now have systems which require no central access from below. Hooray!!

Olly

 

[Andrew INT]

Thanks oncr again folks for your invaluable knowledge sharing; its always a learning curve!

My Skyshed pier is purhaps not the best design, but hhopefully it is sufficiently robust for the job. Time shall tell...

[pyrasanth]

On ‎29‎/‎01‎/‎2016 at 17:19, Andrew INT said:

After dithering about for ten years, I have finally decided to start building my own observatory. The first step was to order a telescope pier (and twenty bags of ready mix cement)

Have put in a reasonable amount of research, I purchased an altair skyshed pier which is yet to be set in cement until the weather warms up a little more.

My question is this: do any owners have vibration issues with this pier? The reason I ask is that I came across this link today which has made me re think things a little more: https://youtu.be/AOeLnecOMeg The guy is talking about the "rat cage" part of the pier head. Is this REALLY an issue, or just (mainly) a sales pitch angle.

Hopefully someone will help put my mind at rest that my new purchase is actually ok!

 

(Edited for typos)

I use a similar type of pier, albeit a different model http://www.altairastro.com/altair-skyshed-8-observatory-pier.html, & it happily supports my Paramount MX+ & a fully loaded Celestron C11 Edge. My T-point model gives me a SKY RMS & PSD of under 12 & if there was anything wrong with the pier I would know about it. My pier sits on a modest 30" of embedded concrete & I filled the hollow tube with bags of sand for extra dampening.

The design makes polar alignment a breeze. I made a graduated degree scale & added that to the pier so its easy now to fine tune alignment although I've not done this for a year which proves its a solid mount. If I had any doubts I would have got rid of the pier very quickly so all is good.

I quite like the rats cage type configuration as it is fairly straight forward to level the top & I've not had any perceived problem with vibration or movement. This also makes a useful space to put power supplies & other small items under the mount. I have a four port cigar type lighter adapter & various power supplies under the mount.

All in all a worthy additional to your observing happiness.

Edited March 7, 2016 by pyrasanth

[Andrew INT]

Thanks Pyrasanth; that's good to know! I think it looks like our two piers are the same. I'm pleased that it certainly feels pretty solid. I haven't filled mine with sand bags simply because I had originally intended to run all my cables through the centre. However, the pre-drilled holes are pretty small ( a USB lead wouldn't pass through). I think I would also be a bit nervous about having electrical power leads out of sight on the inside of a metal tube!

Did adding the sand make a noticeable difference to the dampening? I've only really just started work on my observatory (  http://andrewrichens.wix.com/astro-nerd#!observatory/c5dt ) but now the pier is in place I can at least start doing a little bit of observing and imaging...provided this rain stops...and the clouds go....and the council sorts out a street light....and I don't run out of money...

[Peje]

On 06/03/2016 at 12:29, pyrasanth said:

I use a similar type of pier, albeit a different model http://www.altairastro.com/altair-skyshed-8-observatory-pier.html, & it happily supports my Paramount MX+ & a fully loaded Celestron C11 Edge. My T-point model gives me a SKY RMS & PSD of under 12 & if there was anything wrong with the pier I would know about it. My pier sits on a modest 30" of embedded concrete & I filled the hollow tube with bags of sand for extra dampening.

The design makes polar alignment a breeze. I made a graduated degree scale & added that to the pier so its easy now to fine tune alignment although I've not done this for a year which proves its a solid mount. If I had any doubts I would have got rid of the pier very quickly so all is good.

I quite like the rats cage type configuration as it is fairly straight forward to level the top & I've not had any perceived problem with vibration or movement. This also makes a useful space to put power supplies & other small items under the mount. I have a four port cigar type lighter adapter & various power supplies under the mount.

All in all a worthy additional to your observing happiness.

 

On 08/03/2016 at 13:29, Andrew INT said:

Thanks Pyrasanth; that's good to know! I think it looks like our two piers are the same. I'm pleased that it certainly feels pretty solid. I haven't filled mine with sand bags simply because I had originally intended to run all my cables through the centre. However, the pre-drilled holes are pretty small ( a USB lead wouldn't pass through). I think I would also be a bit nervous about having electrical power leads out of sight on the inside of a metal tube!

Did adding the sand make a noticeable difference to the dampening? I've only really just started work on my observatory (  http://andrewrichens.wix.com/astro-nerd#!observatory/c5dt ) but now the pier is in place I can at least start doing a little bit of observing and imaging...provided this rain stops...and the clouds go....and the council sorts out a street light....and I don't run out of money...

I'd also be interested in knowing if the sand is actually necessary, I just got the Altair 8" pier

[Peje]

On 28/01/2016 at 21:12, carastro said:

I have the Skyshed pier and have no problems with it at all using an NEQ6, I like the design, it's is easy to install.

I did have a bit of problem when I previously had a CG5 GT on the pier as being smaller I could not see through the polarscope as the top pier plate was right where my chin needed to go, but once I swapped that for an NEQ6 that problem went away.  

Works better with a piggy backed guidescope than a side by side arrangement as less risk of scopes clashing with the pier plate.  

Contrary to what has been said about not needing the pier level, I did accidentally "slightly unlevel my top plate" once when removing the mount for Astro camp (this is because the top plate needed to be removed in order to get the central rod out).  I had not realised I had done this and it took me quite a long time to fathom out why I could not get a decent polar alignment or do an alignment procedure properly.  I also could not do a polar alignment using Alignmaster until I levelled that top plate.  

I don't remove the mount any more and no further problems.

 

A quick question, did you use the standard center bolt to attach the EQ6? I'd like to not use this (given the huge length) so was wondering what length of bolt I need? I'd like to order it before I take the head off my current tripod as I am sure the second my kit is out of action we shall see an unprecedented number of clear nights and celestial marvels!!

[pyrasanth]

1 hour ago, Peje said:

 

I'd also be interested in knowing if the sand is actually necessary, I just got the Altair 8" pier

I believe the sand helps as it increases the mass of the pillar & is a great damping agent. I did not bother putting it into bags- I just filled the hollow pier! (even if it rots the metal in 20 years!)

[Peje]

For all a couple of bags of sand will cost I suppose it's worth doing. Why would it rot? surely if no water is getting in it'll stay fairly dry, due to the mass it should be fairly resistant to temperature change also..though I'm not sure how helpful this will be

[900SL]

On 01/04/2016 at 21:54, pyrasanth said:

I believe the sand helps as it increases the mass of the pillar & is a great damping agent. I did not bother putting it into bags- I just filled the hollow pier! (even if it rots the metal in 20 years!)

I found this old thread after reading the current discussion on this subject over on CN

There's a danger that Astronomy could veer into the psuedoscience babble that is Hifi speak at times (AKA parts of the aforementioned video), but hopefully astronomy is less subjective and can be 'measured'

Anyway, I decided to do a quick model of a rats cage design as follows:

16mm bolts, 150mm long, 12mm top plate, subject to an off axis load of 10kg along the bolt line (eccentric load)

The associated rotation was around 8 arc sec and the modal torsional frequency 120 Hz

My take on this is as follows:

1 A bolt cage is less stiff than a solid pier

2: The bolt cage may be subject to deflection and resonant vibration depending on bolt diameter, length, plate thickness, bolt/plate fixity and applied load

3: The assembly behaves as a 'spring' coupling, with reduced lateral and torsional stiffness

Also, as an observation, a 4 bolt cage is not the best way to level a mount anyway (you don't see 4 legged tripods for a reason)

If you use a bolt box, keep the bolts short (deflection is a function of the length cubed), use an appropriate diameter (minimum M16 or larger depending on details), similarly with the top plate, and ensure the bolt/plate connection is rigidly fixed and not floating around in tolerance holes (for improved stiffness)

A dense rubber pad sandwiched between plate and pier head may also help (similar to an isolastic bearing)

 

 

 

 

[tomato]

I have an Altair pier with the 3 bolt rat cage and 70+ kg riding on it and regularly image at 1 arcsec per pixel. If, as the man in the video says, the vibrations generated by the operating mount are always present and limit the seeing performance that can be achieved, why do I get variations in the FWHM numbers from one night to the next?

[StevieDvd]

A lot of the discussions on this have veered off on the side of an over engineered design/cost for what can be a simple tripod substitute. Of course if you are building an observatory, that's going to shelter a massive mount and scope payload, and you are working/walking about in, then design for that. But using the same argument for the more modest setups just seems to suggest that certain piers, retail or diy, are not up to the purpose.

I think the cheap tripods provided in a mount package are more of an issue for most.

 

 

[900SL]

4 hours ago, tomato said:

I have an Altair pier with the 3 bolt rat cage and 70+ kg riding on it and regularly image at 1 arcsec per pixel. If, as the man in the video says, the vibrations generated by the operating mount are always present and limit the seeing performance that can be achieved, why do I get variations in the FWHM numbers from one night to the next?

I suspect the video is alarmist, and geared towards selling a product. The stuff about welds is utter nonsense. If you don't have significant vibration from motors at resonant frequencies, significant lateral load or out of balance loads, I think in the majority of cases you will  be fine. But avoid long small diameter bolts

[Tomatobro]

your pier will be fine so don't worry. Stuff gets repeated so often it takes on the status of fact.

[fifeskies]

I have the Altair pier with 4 bolt rat cage set at about 100mm spacing between plates.

Guiding my EQ6-R with around 15kg on it , I get guiding of around 0.4 to 0.6 arcsecond accuracy most nights with a balanced payload.

This is already better than seeing in UK skies so the rat cage is not causing degraded performance as far as I can see.

I also have a pulsar pier with no rat cage in my ROR, guess what , I don't see any better guiding with my AZEQ6 , tho I usually only have my smaller rig (8kg) on that pier.

So in my experience, for my location and rigs, there is no difference in performance to having a rat cage top to the pier or having no rat cage.

 

 

for reference my pier has 4 x 16mm diameter threaded rods between the plates.

(if you were to have thin long rods , say 300mm long 8mm rods , then you will probably encounter significant vibration)

Edited May 17, 2023 by fifeskies

[tomato]

On 07/03/2016 at 12:29, pyrasanth said:

I use a similar type of pier, albeit a different model http://www.altairastro.com/altair-skyshed-8-observatory-pier.html, & it happily supports my Paramount MX+ & a fully loaded Celestron C11 Edge. My T-point model gives me a SKY RMS & PSD of under 12 & if there was anything wrong with the pier I would know about it. My pier sits on a modest 30" of embedded concrete & I filled the hollow tube with bags of sand for extra dampening.

The design makes polar alignment a breeze. I made a graduated degree scale & added that to the pier so its easy now to fine tune alignment although I've not done this for a year which proves its a solid mount. If I had any doubts I would have got rid of the pier very quickly so all is good.

I quite like the rats cage type configuration as it is fairly straight forward to level the top & I've not had any perceived problem with vibration or movement. This also makes a useful space to put power supplies & other small items under the mount. I have a four port cigar type lighter adapter & various power supplies under the mount.

All in all a worthy additional to your observing happiness.

The rat cage is useful place for the mount’s power supply, handset etc, and a mug of tea.😉 This doubles as a vibration indicator until it is drunk.

[SamAndrew]

With a switch to an unbalanced harmonic drive mount, I'm now experiencing issues with pier flexure when switching sides of the meridian, one side of the pier / bolts are under compression, the other under tension, which then reverses. It just wasn't something I considered at the time which now requires me to address the issue by beefing the pier and bolts up.

[bwj]

You might want to take a look at this topic over on Cloudy Nights. Pretty in depth discussion on piers, including rat cage setups. The OP includes tables showing deflection and how to figure it. The thread is 23 pages long, with several contributors. 

https://www.cloudynights.com/topic/652025-pier-engineering/?fromsearch=1

To be honest, the OP did end up putting out an e-book on pier design and has started a business selling piers. However, he is quick to encourage DIY and provide helpful advice, unlike the guy in the video in the first post here.

 

Clear Skies!

Edited May 18, 2023 by bwj