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Jovets Observatory build

Started by Ivor, Oct 21, 2014, 10:34:35

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MarkS

Roger is right - use the sun if your obsy is in the sun - it's exactly how I aligned mine.  Planetarium software will tell you what time when it is due south (a few minutes before or after midday).  Remember that the mount has quite a lot of azimuth adjustment on it so you have quite a lot of leeway but try to get it within a few degrees anyway - mine is accurate to within 1 or 2 degrees but I'm a bit of a perfectionist.

If your obsy is not in the sun then construct a north/south line elsewhere in the garden and then use that as a reference for measuring another north/south line through the pier.

Mark

Ivor

I'd completely forgotten about the sun as an option until it was mention here so I did some investigation and fortunately I don't need to wait for the sun to be due south otherwise I'd waiting for months for the two to happen on a weekend. However I still need the sun.
All I need to do is mark the tip of a shadow say 15 mins apart and draw a line between the two points and this will be east to west. Next I draw a perpendicular line to this to get a north to south line.  I then draw a parallel line to this line which goes through the pier centre.
I've also found an app which will give me true north which I can use for reconciliation.  The pier plate should come on Friday but the weather isn't look great so I'll probably focus on the rest of the build. I've got some mandatory leave to take so I'm extending the weekend to try and get a lot done, this is the plan:




Task                                         Effort    Day   Start   End
Bolt down frame to footings   01:30   Fri   08:00   09:30
Measure garage dimensions   00:10   Fri   09:31   09:41
Pick up Screwfix order      00:15   Fri   09:58   10:13
Pick up wood            00:15   Fri   10:14   10:29
Adjust frame connections   00:30   Fri   10:30   11:00
Add castors to top ring           00:45   Fri   11:01   11:46
Add slot for drive wheel      00:15   Fri   11:47   12:02
Secure ring to post tops      00:15   Fri   12:03   12:18
Lunch                                   00:30   Fri   12:19   12:49
Measure pier to size           00:30   Fri   12:50   13:20
setup pier for cabling          00:30   Fri   13:21   13:51
Add hatch spacers to ring   00:30   Fri   13:52   14:22
Drill out Metal ring              01:00   Fri   14:23   15:23
Join wood ring to metal ring   00:30   Fri   15:24   15:54
Add hatch uprights to ring   00:30   Fri   15:55   16:25
Add 4 side supports for roof   01:00   Sat   08:30   09:30
Add batons to roof skeleton   00:45   Sat   09:31   10:16
Cut plywood tops for dome    01:30   Sat   10:17   11:47
Lunch                               00:30   Sat   11:48   12:18
Cover roof top with TGV      01:30   Sat   12:19   13:49
Paint roof 1st coat              01:00   Sat   13:50   14:50
Add membrane to walls           00:30   Sat   14:51   15:21
Put walls battens on 6 walls    00:30   Sat   15:22   15:52
Add TGV to a wall 1           00:30   Sun   09:01   09:31
Add TGV to a wall 2            00:30   Sun   09:32   10:02
Add TGV to a wall 3           00:30   Sun   10:03   10:33
Add TGV to a wall 4             00:30   Sun   10:34   11:04
Paint Walls 1st coat           02:00   Sun   11:05   13:05
Lunch                                   01:00   Sun   13:06   14:06
Cutout pier and add piping   01:30   Sun   14:07   15:37
Secure pier into position   01:00   Mon   08:30   09:30
Cement Pier                      02:00   Mon   09:31   11:31
Lunch                                   00:30   Mon   11:32   12:02
Paint Walls 2nd coat           02:00   Mon   12:03   14:03
Paint roof 2nd coat              01:30   Mon   14:04   15:34
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MarkS

Quote from: Ivor
All I need to do is mark the tip of a shadow say 15 mins apart and draw a line between the two points and this will be east to west. Next I draw a perpendicular line to this to get a north to south line.  I then draw a parallel line to this line which goes through the pier centre.

NO!!!  That only works on equinox dates.  The rest of the time the tip of the shadow draws out a curved line.  See this site:  http://www.mysundial.ca/tsp/declination_lines.html
In figure 1 the lower curved line (orange) is the line traced out by the shadow in mid-winter and the upper curved line (green) is mid-summer.  The purple straight line is east west and happens only at an equinox.


Canadian Roger

Mark...thanks for pointing out that site.  I'd often wondered about the popular notion of finding a true east-west line using the tips of a shadow, and it didn't seem to make perfect sense to me.  What it seems to me is that as long as you do it no more than a couple of hours either side of solar noon, you're going to get very close.  Certainly, you'll get close enough so that the normal range of azimuth adjustment will get you to true north.

The other point, which I thought was a good one, is that as long as you know the exact time and location, measuring the azimuth of any astronomical body will tell you where true north is by looking it up using planetarium software. 

If it's a clear night, for instance, you could note when a star winks out as it goes behind a chimney (assume the chimney is vertical) as seen from directly behind the middle of where your pier is going to go.  Looking up the azimuth of the star at that exact time will tell you the direction to that chimney, and consequently, where North is. 

I suppose if you wanted to get really accurate, you could set up a green laser pointer a good few feet away that is aimed as vertical as you can get it.  You could then check the time that Rigel, Betelgeuse and Sirius cross the beam.  You should be able to reduce your error somewhat by having three different observations.  You could do even better if you observe over several nights.

The stars will move 1 degree every four minutes (actually about 2/3rs of a second less, if memory serves), so if you know how much adjustment you have in the azimuth setup for your mount, you'll know how accurate you'll need to be.

Roger
in frozen Canada...it's -8C outside just before midnight.

Mike

Wouldn't it be easier to get your GoTo system to point to the sun and then rotate/adjust until the sun is in your fov? Then your mount is pointing north. Once set up do final tuning with the alt/az bolts.
We live in a society exquisitely dependent on science and technology, in which hardly anyone knows anything about science and technology. Carl Sagan

Ivor

OK thanks I'll avoid that mistake. The probability of me being at home around midday and there is a clear sky any time soon is unlikely so I'm back to a compass. I checked the app last night and it seems alright and this site help http://www.geomag.bgs.ac.uk/data_service/models_compass/gma_calc.html lets you calculate the magnetic variation for a specific location; for me it is 2d 34' west of grid north. This site explains the difference between the 3 norths well. http://www.ordnancesurvey.co.uk/resources/maps-and-geographic-resources/finding-north.html
The bottom of OS map for Tunbridge Wells states at the centre of the map true north is 1d 53' west of grid north so True north is 41' west of magnetic north so very close so I'm less worried it being way off when it.

I've been busy today the frame is bolted down, 6 walls are on and painted in "Sage green" and the I've cut the pier to size, what do think does this look right?



Ivor

Had a big push over the weekend, the pier is cemented in, 6 walls are on with 2 coats of paint and the base of the roof is bolted onto the metal base. Sorry no photos I forgot to take some before it got dark this afternoon but I'm pleased with my progress considering on Saturday it rained all day.

Next weekend I plan to cement in the mount plate, add the remain wall and the door. If I'm lucky my father in law will be able to spare a day so I can get the skeleton of the roof built as well.  We tried to put the slot on today however our initial building approach didn't provide enough rigidity so the approach needs to change. 

I'm really concerned about the time I have left especially for painting the walls it's already taking 12 hours for the paint to dry so I have to get the final wall up this weekend before it gets cold.

During the week I've been working on an ASCOM dome driver I now have CduC sending commands to an Arduino and displaying them on an LCD, I'm now playing with a stepper motor, bluetooth connectors and a digital compass to track the dome position. I do get funny looks on the my commute with the arduino and breadboard on my lap and the PC on the table :)

Carole

Sounds like some good progress Ivor. 

Carole

Canadian Roger

Quote from: Ivor on Nov 24, 2014, 22:09:47
Had a big push over the weekend, the pier is cemented in, 6 walls are on with 2 coats of paint and the base of the roof is bolted onto the metal base. Sorry no photos I forgot to take some before it got dark this afternoon but I'm pleased with my progress considering on Saturday it rained all day.

Next weekend I plan to cement in the mount plate, add the remain wall and the door. If I'm lucky my father in law will be able to spare a day so I can get the skeleton of the roof built as well.  We tried to put the slot on today however our initial building approach didn't provide enough rigidity so the approach needs to change. 

I'm really concerned about the time I have left especially for painting the walls it's already taking 12 hours for the paint to dry so I have to get the final wall up this weekend before it gets cold.

During the week I've been working on an ASCOM dome driver I now have CduC sending commands to an Arduino and displaying them on an LCD, I'm now playing with a stepper motor, bluetooth connectors and a digital compass to track the dome position. I do get funny looks on the my commute with the arduino and breadboard on my lap and the PC on the table :)

That's a lovely mental image...travelling home, opening the briefcase, and everyone expects a laptop, the crossword, or some papers and out comes a circuit board, wires, motors and who knows what else?

Good luck with the weather...is it possible to paint the wood for the final wall inside?  Take out all the screws in the wall, put up a tarpaulin to keep the rain out of the observatory and carry the wall inside your garage to paint it?

Ivor

My garden already resembles parts of Calais so I don't think I can put up anymore tarps.




Painting has to be outside as I'm putting the tongue and grove straight onto the frame so all I can do is one coat per day. The weekend weather is looking promising so fingers crossed I'll be putting the roof on next week once I've roped in some mates to lift it.
 

Ivor

A mixed weekend some successes and a few complications meant some things have taken longer than expected. My pier adaptor was made by AstroTEC consisting of a top plate with three threaded rods connected to a secondary ring which will be cemented into the pier.



My first problem was trying to find true north so I could cement in the pier adaptor, I'd created a plywood template to avoid messing up the real pier plate, I drew a line through the centre point and peg and connected to the pier adaptor.




I place this inside the semi filled pier so I could align it to true north however the pier seems to create a large magnetic field, so when I placed any compass on top of the plate, north would shift around 90 degrees. Both the android app and the map compass presented the same problem, however I found having the compass about 20cm above the pier removed the issue. Fortunately I'd just bought some downpipe as the next job is replacing the guttering on garage so I cut a 30cm section off and marked the diameter on the downpipe and then aligned it to the line on the top of the wooden pier plate and placed the compass on top. Luckily this worked and I was able to mark true north on pier and filled the remainder of the pier with cement and placed the adaptor in. This should have been it but on Sunday when I tried the real plate out for size it wouldn't fit, the threaded rods have moved very slightly and it means the plate won't go on without a little help from a mallet; not a solution with a mount screwed in. Frustratingly I don't a 17mm drill bit to open up the hole so it looks like another trip to Screwfix is required.
The roof has been a challenge as well this has mainly been caused by the slope on my garden making really difficult to work out whether the roof hatch is true, adding the roof top added some rigidity however it wasn't enough to counterbalance the slope.



We added some additional support under the lower end on the slope which made the frame closer to level but it wasn't enough to make the main shutter perpendicular to the bottom ring. In the end the only way we could get the frame close was to build out the whole frame and then go around adjusting each support until they lined up with the expected sizes. This proved really challenging trying to get a tolerance of 10mm across 2540mm when the parts aren't cut perfectly by a laser cutting takes many iterations. Anyway we got there in the end (albeit outside this tolerance) and the frame looked like this.



The next few challenges are the door and its security, I want to put a door bar across the front as well a standard mortice lock, just paranoid about someone taking a crowbar to the door. I'm also trying to decide how best to arrange the floating floor, I trying to use some of the waste from cutting the large circular sections out but I also need access to do the cabling; more thinking required.

MarkH

Ivor if you still have the luxury of adjustment to the roof, the easiest way to check levels over a large distance is a clear hose filled with water and topped up to the level you are trying to check...exact to the millimeter :)

Mac

QuoteThe next few challenges are the door and its security, I want to put a door bar across the front as well a standard mortice lock, just paranoid about someone taking a crowbar to the door

I bought a cheap car alarm with remote, the car alarm has a shock sensor, which when fitted to the back of the door get set off if its knocked hard,
plus its remote controlled and as 99.9% of us have car batteries as power supplies its very easy to fit. Plus it has a flashing red led.

Similar to this.
http://www.amazon.co.uk/BestDealUK-Practical-Protection-System-Control/dp/B009URG8JG/ref=sr_1_1?s=automotive&ie=UTF8&qid=1417536159&sr=1-1&keywords=car+alarm

Mac.

Ivor

That's an idea, I wonder if I could take a feed from that and send it to arduino so I could get an sms message. I shall ponder some more.

Ivor

Planning to put a 12V supply on the pier to support the dew heaters and I was thinking of using a down lighter transformer like this http://www.screwfix.com/p/halolite-low-voltage-electronic-transformer-20-60va/48058. This would give me a maximum of 5A at 12V is there any reason why this is a bad idea?