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StellaLyra 12" Dob - the good and the bad


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Michael, think back to when we last met at Lucksall. Do you remember how impressed you were when using Grant's 16" StellaLyra Dobsonian? 

His telescope does the same. Here is a video he just sent me.

In normal use people don't grip the top of their Dobsonian telescopes and shake them so the AZ bearings, designed for downward load, work well. 

Nothing to worry about. 

HTH, 

Steve 

 

 

 

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40 minutes ago, Mr Spock said:

@Steve I don't see what there is to be faulty. It's just pieces of particle board bolted together!

Here it is wobbling.

 

IMG_0758.MOV 75.53 MB · 25 downloads  

 

After reviewing your video, the first thing I notice is it seems to wobble on the AZ axis.  This is probably a function of the undersized bearing for it.  Ideally, the bearings should come all the way out to the edge of the AZ board.  You could substitute Teflon pads riding on textured FRP wall board or other nubbly, yet glossy, board.

Try separating the rocker box from the ground board and repeat the rocking action again with the rocker box directly on a smooth, solid surface.  This would show how much improvement is possible by redesigning the AZ bearings.

I can't really tell where the wiggliness in the ALT bearing is coming from.  It's hard to tell if it's rocker box flexure or simply the long tube amplifying small flexure at the pivot axis.  If that is the case, you'd need to increase the diameter of the side trunnions to reduce the flex coming from that connection point.

This is really an engineering problem.  Isolate the cause of the "failure" and then try to find a fix, or at the least, a workaround.

Even giant, custom Dobs exhibit a bit of wobble sometimes in some orientations and motions.  Trying to rotate around Dobson's Hole at zenith comes to mind.  This is where the Mag 1 Portaballs had it in spades over the traditional two axis Dob design.

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The design of the Stellalyra base seems to be a lacking a vertical brace on each side (compare to the Skywatcher 12" version).  I think this would help to stiffen up the entire base.  There doesn't seem to be anything to stop movement in the horizontal axis without this brace on the outside?

 

 

Edited by Davesellars
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I'll be building a new base, something more substantial. Glued and screwed so it's free of flex. I'll be getting an EQ platform soon from another member so I'll wait to see what size that is (large!) before commencing.

I'm sure full size or larger az bearings would help but I'm not sure they make them larger. I've not found any online. It may have to be Teflon pads.

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I know it probably doesn't help anyone, but I can't get the mount on my 8" to wobble at all, no matter how hard I shake it. As both I and AstroKeith have said, it may be just a problem of weight and scale - what works at one size/weight won't necessarily work at another.

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I used one of these lazy Susan bearings on the Zhummel 12” and it worked well.

https://simplybearings.co.uk/shop/Bearings-Lazy-Susans/c3_22/index.html?selection=Lazy+Susan+Turntable+Bearings

As I recall, the rocker box was solid as a rock but there was some play in the Az connection to the base. I those three Alt bearings we actually pretty good, with adjustment for balance and tension.

DAB7AD63-3CC3-410E-A274-AD36D4CA5999.png

D2C255DF-EB5B-4510-8F7E-56BC432F5E83.png

616E362A-0C9C-41CD-9ECF-43CDBAF01C58.png

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13 hours ago, Louis D said:

What is the diameter of the stock lazy Susan versus the diameter of the ground board and rocker box?

The turntable size is 630mm and the bearing 320mm. Hopelessly undersized and responsible for about 50% of the wobble.

Just ordered a 600mm bearing which cost... gulp! But as this scope is a keeper I think it's worth spending on and refining.

Next step is to construct some side pieces similar to the Skywatcher equivalent. They obviously recognise flexure as a problem.

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I think eliminating one by one all the small niggles will make this a scope for life. 

Of the larger scopes I've had over the years, a 140mm Mak with ⅛ PV optics, a 150mm Mak, a C9.25, two 10" Newts, this 12" is by far the best in terms of optical quality. I've probably, for once, just got lucky.

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Just watched the video.  I would be hard pressed to accept that much wobble in my scope base.  My 10 inch is the exact same style and I have no wobble at all. 

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4 minutes ago, Mr Spock said:

I think eliminating one by one all the small niggles will make this a scope for life. 

Of the larger scopes I've had over the years, a 140mm Mak with ⅛ PV optics, a 150mm Mak, a C9.25, two 10" Newts, this 12" is by far the best in terms of optical quality. I've probably, for once, just got lucky.

Its great when that happens felt like that about my CC

Once again congrats. As you say. You got it where it counts

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I wouldn't agree with the I just got lucky on the optics.  GSO is making some pretty solid mirrors these days.  I have a friend who has a 16 inch Orion GoTo and it gives images that are on par with scopes that cost 2 or 3 times the cost.  I would be interested in see the points of contact on this base and see if something has changed in the assembly.  If I remember correctly mine was just screwed together but it had inserts driven into the particle board and pulled nice and tight.

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3 minutes ago, Mike Q said:

If I remember correctly mine was just screwed together but it had inserts driven into the particle board and pulled nice and tight.

The bolts are really tight. As I'm keeping it and therefore don't need to dismantle it in the future, I'm taking it to bits, adding glue and adding braces. It will be solid as a rock when I've done with it.

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2 hours ago, Mike Q said:

I wouldn't agree with the I just got lucky on the optics.  GSO is making some pretty solid mirrors these days.  I have a friend who has a 16 inch Orion GoTo and it gives images that are on par with scopes that cost 2 or 3 times the cost.

Teeter Telescopes offer(ed) GSO mirrors as the lowest cost mirror option for their telescopes.  They must have been pretty good to be putting them into multi-thousand dollar telescopes.  Why would you risk your custom telescope business's reputation on crappy mirrors?

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On 16/03/2022 at 10:07, Mike Q said:

I wouldn't agree with the I just got lucky on the optics.  GSO is making some pretty solid mirrors these days.  I have a friend who has a 16 inch Orion GoTo and it gives images that are on par with scopes that cost 2 or 3 times the cost.  

Ade Ashford was similarly impressed. 

“Jupiter, despite its current low altitude from the UK, revealed considerable detail when seeing conditions permitted. On 21 October 2021 at 10:50pm BST, I watched the close appulse of Jovian moons Ganymede and Callisto, while the Great Red Spot approached the planet’s central meridian.

Later that same night, the Moon was one day past full and presented a wealth of crisp, fine detail along the waning terminator. I noted a string of mountain peaks in the heart of 177-kilometre-wide crater Gauss catching the last rays of sunlight. They looked like a string of beads at the limit of the instrument’s resolution, something I had not seen in this region before during four-and-a-half decades of observing.”  

Review by Ade Ashford for BBC Sky at Night (pdf)

Steve

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Just had a few minutes getting the collimation right via a star test.

As for the mount... new bearing fitted, two side braces fitted, and, the jelly has gone. It now passes the two second tap. The occasional strong gust of wind moves it slightly, but it settles quick. A bit on money spent, but a job well done. It's not perfect, but good enough.
I got glue every where though - I'm just too clumsy these days :biggrin: Clean up and paint job tomorrow.

Next job - a counter balance to stop the finders/focuser from tipping it over when pointing high up. At the moment I've got the az tightened really tight to stop it happening.

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19 minutes ago, Mr Spock said:

Just had a few minutes getting the collimation right via a star test.

As for the mount... new bearing fitted, two side braces fitted, and, the jelly has gone. It now passes the two second tap. The occasional strong gust of wind moves it slightly, but it settles quick. A bit on money spent, but a job well done. It's not perfect, but good enough.
I got glue every where though - I'm just too clumsy these days :biggrin: Clean up and paint job tomorrow.

Next job - a counter balance to stop the finders/focuser from tipping it over when pointing high up. At the moment I've got the az tightened really tight to stop it happening.

Sounds crazy but try a large aquarium algae magnet. Both halves are padded and can be slid easily up and down the scope without scratching it.

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On 16/03/2022 at 08:43, Louis D said:

Teeter Telescopes offer(ed) GSO mirrors as the lowest cost mirror option for their telescopes.  They must have been pretty good to be putting them into multi-thousand dollar telescopes.  Why would you risk your custom telescope business's reputation on crappy mirrors?

I ran my Skyline next to a Teeter last year, there is no doubt that the it outperformed me, everything was brighter....but it had a 6 or 10 inch bigger mirror.  So it was really a apples and oranges comparison.

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First coat of paint on. It looks a bit grubby at the moment as it's not finished. I don't suppose it matters, only being out at night and all 😜

You can see how large the bearing is. The bracing works well too.

278480677_DSC_0230_DxO1200.jpg.69ce5158cc95b090c02ff47e8c9dd9d3.jpg

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