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  #1  
Old 16-11-2016, 11:24 AM
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codemonkey (Lee)
Lee "Wormsy" Borsboom

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Difficulty rotating Sirius dome - tips appreciated

I've had my second-hand Sirius dome mostly assembled for a few days now, but I'm struggling to get it to rotate. It'll move freely for a bit, then the wheels will press into the lip on the wall and movement will become difficult. Obviously there's some eccentricity there, but how to solve? I've spent hours tapping walls in and out, loosening and tightening the walls and the dome bolts and have largely gotten nowhere, so I'm wondering if anyone out there has any tips.
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Old 16-11-2016, 12:21 PM
JA
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Quote:
Originally Posted by codemonkey View Post
I've had my second-hand Sirius dome mostly assembled for a few days now, but I'm struggling to get it to rotate. It'll move freely for a bit, then the wheels will press into the lip on the wall and movement will become difficult. Obviously there's some eccentricity there, but how to solve? I've spent hours tapping walls in and out, loosening and tightening the walls and the dome bolts and have largely gotten nowhere, so I'm wondering if anyone out there has any tips.
I'm not sure of which dome you have, however; I would start with making measurements of the diameter incrementally around the circle of the base on the running track to see where the issue is. Preferably just of the track without the dome in place and loading it. If not OK then adjust the diameter/tweak with ratchet tie downs, brute force, pipe clamps, hydraulic or screw jack or whatever and add stiffening &/or more fasteners at the joints or to the ground to help hold circularity.

Then try to do the same for the dome measurements. Then couple the 2 and fine tune further. Perhaps some images would help the thinking, particularly of the sliding track area.

Also don't forget to look at gummed up /corroded sliding or rolling surfaces.

Best
JA
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  #3  
Old 16-11-2016, 01:25 PM
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theodog (Jeff)
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Quote:
Originally Posted by codemonkey View Post
I've had my second-hand Sirius dome mostly assembled for a few days now, but I'm struggling to get it to rotate. It'll move freely for a bit, then the wheels will press into the lip on the wall and movement will become difficult. Obviously there's some eccentricity there, but how to solve? I've spent hours tapping walls in and out, loosening and tightening the walls and the dome bolts and have largely gotten nowhere, so I'm wondering if anyone out there has any tips.
Had the same worry, loosen-tighten, tighten-loosen, then it would rotate and jam to a stop. I had thoroughly cleaned the wheels and track.
I used dish detergent first as a lub, I could remove it with water if it went wrong, loosened and rotated. It rotated easily, so I washed it out and replaced with silicon lub as per something I read somewhere (actually tightened the top row of bolts while a mate rotated the dome). Still going strong but starting to need a respray.

I'm not sure if this is the correct procedure but it worked for me.
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Last edited by theodog; 16-11-2016 at 01:40 PM. Reason: extra
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  #4  
Old 17-11-2016, 08:42 AM
w0mbat (Ian)
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Do you have the Sirius installation manual? This would help a lot.
Two points I can think of:-
1. The flatness of the slab you are bolting the observatory to is very important. If not very flat you will need to pack underneath the wall segments until the top track is flat and level. If you think about it, bolting the segments down to a non-flat surface will inevitably lead to distortion of the track ring.
2. The Sirius instructions state the whole track and retaining ring must be smeared with grease.
Ian
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Old 19-11-2016, 10:06 AM
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Lee "Wormsy" Borsboom

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Thanks everyone for your advice!

I had another crack at fixing up the walls yesterday. I adjusted it incrementally until the base of the running track are no more than 3mm out, measured from the gap in between the seams; that's about as close as I can get it, and it took a while.

The running track I had already sprayed with silicone spray as per instructions. I'm not sure how much value it's adding to be honest.

The dome is still jamming hard against the internal side of the running track. Looks like (a) the dome is elliptical and not circular and (b) the rollers on which the dome turn are not all equally spaced from the wall, some are a few mm further out than others. Said rollers have fixtures that are rusted onto the dome, since Sirius don't seem to use stainless steel, so will be very difficult to adjust.

Only thing I can think of at the moment is to try and jam something inside the dome to push it out in places and thus "square it up" a bit more.

This wouldn't be a problem if I was planning on using it manually, because I can shift the dome as needed to make it move around, but I want to automate this; not sure I'm going to be able to do it at this point.
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Old 19-11-2016, 10:31 PM
w0mbat (Ian)
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Originally Posted by codemonkey View Post
Thanks everyone for your advice!

Said rollers have fixtures that are rusted onto the dome, since Sirius don't seem to use stainless steel, so will be very difficult to adjust.
That is strange. Every screw in my Sirius is stainless steel.
I would be very surprised if the dome was out of round. Should be easy enough to check by measuring.
Ian
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  #7  
Old 20-11-2016, 07:27 AM
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alan meehan (Alan)
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Lee houghy had the same problem ,check his post on the doghouse thread page 10 on how he fixed it
AL
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Old 20-11-2016, 08:37 AM
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Lee "Wormsy" Borsboom

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Originally Posted by w0mbat View Post
That is strange. Every screw in my Sirius is stainless steel.
I would be very surprised if the dome was out of round. Should be easy enough to check by measuring.
Ian
Oh really? Maybe they changed it in newer ones. I know of another person with one whose fixtures weren't stainless either.

The dome doesn't appear to be round, but it has some flex, so if the slab isn't perfectly level, maybe it's warping it?

Quote:
Originally Posted by alan meehan View Post
Lee houghy had the same problem ,check his post on the doghouse thread page 10 on how he fixed it
AL
ha! That's exactly what I've been thinking about doing. The problem is that while he has that nice fixed bit of metal for his wheels to push off, mine has nothing but fibreglass, since I don't have the rotation kit. I'm tossing up a few ideas at the moment, but good to know the basic idea does work.
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Old 20-11-2016, 01:21 PM
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codemonkey (Lee)
Lee "Wormsy" Borsboom

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Originally Posted by alan meehan View Post
Lee houghy had the same problem ,check his post on the doghouse thread page 10 on how he fixed it
AL
After further thought/research I'm going to follow that approach. I've got a tool on order which will simplify the bending of flat bar steel into a "perfect" circle, which I can fix to the dome. This will also help with my next efforts to motorise it. Thanks!
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Old 05-06-2023, 08:52 PM
toppy (Pete)
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Sirius dome requires much effort to rotate

Hi Lee,

It is an old thread, however just wondering whether you solved the issue. My Sirius 3.5m dome requires a fair effort to move the dome manually in either direction. By a fair effort I mean putting both hands and shoulder into moving it. Research reveals that a one-handed effort should be enough to rotate the dome. The intention is to operate the observatory remotely; however, I have low confidence that the motor will cope with the load. There appears to be little information that I can find on the probable cause and solution in my internet searches.

I did note that one wheel had come away from the dome and was sitting loose on the track. This was reseated early in the hunt for the cause of the rotation issue(s). The wheels on which the dome sit, now spin relatively freely. The track and wheels have been degreased and packed with fresh grease. After the dome was lowered onto the track little improvement was noted. In addition, the walls were freed from the concrete base and packers placed under the walls to ensure the fibreglass track on which the dome rotates is level, and the radii checked and trued in relation to the central pier. The concrete base is sound and fairly flat. It required 1 - 3mm max. packers in some spots. The dome was rotated 12 times in each direction whilst the walls were unbolted from the concrete base as set down in the manual.

I am running out of ideas. The observatory is in fairly good condition without cracks or warping. It is a 3hr round trip from home, so hoping you had success with the same problem.

If others they have seen or experienced, and ideally witnessed a successful resolution it would be very appreciated if you could share.

Thanks Pete

Last edited by toppy; 05-06-2023 at 09:13 PM.
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  #11  
Old 15-11-2023, 11:16 AM
AstroApprentice (Jason)
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Sirius dome wall repairs

Hi Pete,
I purchased a very old, neglected Sirius dome 5 years ago. Perhaps because the dome had been left for years without being rotated, the top of each wall section had sagged in the middle up to 10 mm! This made it very difficult to rotate the dome. I had spent ages making sure the dome and walls were close to perfectly concentric and rusted wheel bolts replaced etc before I noticed the sagging. It might be worth measuring your wall sections to see if this has happened to yours. If so, then the following may be of use.
I contacted Owen at Sirius and he helpfully suggested I add triangle blocks of wood under the inside wall tops and fibreglass them in. So I raised the middle of each wall section with two 1200 mm reversible quick-grip bar clamps (reinforced by placing the bar in a rebated piece of pine - otherwise they bent under weight), liquid nailed the timber blocks in, covered them and the top 100 mm of wall in fibreglass, removed clamps, fibreglassed where clamps had been, and then added a layer of gel coat. I had never used fibre glass before, but it was not a difficult job, albeit the finish improved by wall section 6!
End result is fantastic - I could rotate with one finger as manual suggests, so added automation and it has been running seamlessly for a few years now. The dome is remote, but I've added a pic from the dome webcam.
Hope that helps you or others with a similar issue, J.
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  #12  
Old 15-11-2023, 08:28 PM
toppy (Pete)
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Wall gussets

Hi Jason,
Thanks very much. I hadnít thought to check for sag in the walls. Will measure this first up on my next visit. Would be very happy to report back that this is the solution to the issue.

Much appreciated
🙏
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