My observatory build was meant to start in the spring of 2014 however a few unexpected events delayed the start and I found myself starting the project in October instead. Clearly autumn isn't the best time of year to start so there's going to some busy weekends trying to kept ahead of the weather and dwindling light.
I'm lucky in many ways with my garden I can see Polaris and I have a 270 degree southerly view, light pollution isn't too bad for an urban location so I'm very grateful. The big challenge with my garden is the depth the picture below shows the challenge and you soon start to understand my wife's hesitance for an observatory so close to the house.
(http://www.jovets.co.uk/sites/default/files/field/image/West-view-of-back-garden.jpg)
The view of garden above is due west and as I've mentioned I can see Polaris but it's only just over the ridge tiles of the house.
(http://www.jovets.co.uk/sites/default/files/field/image/Polaris.jpg)
A roll off roof solution was quickly ruled out due to space and there is only one spot in the garden where I can locate the Observatory and see Polaris so many of my decisions have been made for me. I have a space of 3m2 to work with and to add to my challenge the garden is sloped towards the house. I also want the design to be portable, there is small chance I will be able to buy some extra land behind the house in a couple of years and I'd want to relocate away from the house if the opportunity arose.
I've looked at various designs and ideas people have created and decided to make an octagonal cylinder with a rotating top section. l considered building a dome but I now feel it adds an extra complexity which is going to exceed my DIY skills and time available. I also set myself the goal of designing a solution which could be built using standard power tools (Jigsaw, Circular saw & Drill), with no angle more complicated than 45 degrees.
Rather than build a large concrete base I chose to build footings for the posts this way it reduced the amount of concrete and also made it easier managing the levels. Using 3mm plywood I built 4 frames for the footing to support the uprights in pairs.
(http://www.jovets.co.uk/sites/default/files/field/image/Footing-cases.jpg)
For those who have tried to dig a little deeper than the initial top soil will understand it is quite amazing what you discover the further you go down. I live in a former farm site on top of a hill among the Victorian milk bottles, metal pipes, 20cm metal disc, a few dog bones I also have a wall buried about a foot below the surface.
(http://www.jovets.co.uk/sites/default/files/field/image/buried-pipes.jpg)
(http://www.jovets.co.uk/sites/default/files/field/image/pier-pit-with-brick-wall.jpg)
With all the obstacles and the fact I've started the build whilst training for a marathon progress has been slower than planned. Last weekend I managed to rope in some help and concreted the footings which was where I realised I'd made a few oversights. The first was 3mm plywood wasn't sufficiently rigid enough to contain the concrete so a couple of the footings bow at the top, this was contained using luggage straps which passed the building inspectors checks.
(http://www.jovets.co.uk/sites/default/files/field/image/Buildings-inspector-reviewing-footings.jpg)
I'd originally planned to just have the supporting posts resting on the footings figuring that the frame and roof combined should be heavy enough to prevent any movement. Whilst in the timber merchant I saw some metal fence posts brackets designed for being put on top of a flat surface and decided it wouldn't any harm to add them. My footings are oversized 10cm long and 15cm depth which wasn't enough extra space to cater for the brackets as well so the brackets overhang the footing. In addition I'd made the foundations on 1 to 7 cement to ballast mix which would have been fine for taking the weight but it couldn't cope with holes being drilled close to the edge of the footing and they were breaking in up. After much cursing a cunning plan was derived, I drilled a hole under where the post would go and countersunk the bolt top into the bottom of the post which appears to be sufficiently solid to hold. This took up most of Sunday so I only managed to get four post and cross beams in before the end of the day. This is where I am as of the 19th October.
(http://www.jovets.co.uk/sites/default/files/field/image/build-progress-20141019.jpg)
Nice report! I've only one question: "building inspector"?
Mark
The dog! Clearly I need to rewrite it, my humour bone needed more coffee when I wrote that.
I got it Ivor, excellent man a fellow jack Russel fan. Lean mix in concrete is always a mistake.. if you want to borrow a chop saw with graduated mitres I have one that you are more than welcome to borrow.
Why is the pier leaning over like that?
The conduit is merely in the pier hole, I've not cut it to size yet as I've waiting to get hold of Graham from AstroTec to get a cost for the pier top. Unfortunately he appears to be on holiday so I'm thinking about approaching it differently now.
I'm curious, since I built my own here in Canada about 10 years ago, but how far down did the footings go, and how deep is your pier?
Here, we have to put everything more than three feet deep (and preferably four). This is so the bottom is deep enough that the ground isn't frozen solid in the winter. Otherwise, it'll shift when the ground thaws in April.
Quote from: Canadian Roger on Oct 22, 2014, 19:40:53Otherwise, it'll shift when the ground thaws in April.
Not a problem we have here, but ground drying out and shifting is, particularly with the clay-rich soils we tend to get round here. ;)
I have mix of soil types about 15cm of top soil, 10cm of gravel/ debris (I assume comes with the former site's use), 10-20cm clay and then sandstone or sand. For the footing I went about 40cm deep and for the pier I've created a 3D trapezium shape 120cm sizes at the bottom and 100cm at the top.
I'm a more concerned about subsidence rather than frost but I'm not sure what else I can do.
I'd guess the clay would probably contribute most to subsidence. When they underpinned my house they dug right through the clay to put the concrete onto the sand below it...
27th October - update
I'm sure I wasn't the most severely hit by Hurricane Gonzalo however the gusts in Kent were sufficient to knock over the start of my frame pulling the fixings out of the footings leaving my hard work flat on the ground.
(http://www.jovets.co.uk/sites/default/files/field/image/post-Gonzalo.jpg)
With the whole frame up it will be self supporting but post Gonzalo I want to fix the frame down so I've decided to cement a lintel on top of the footings and fix the posts to that. I didn't have time to buy the lintels on Saturday as I ran Beachy Head marathon so I focused on the roof design and the top of the pier on Sunday. I've not got much to show as progress as I was strangely a little tired and these two tasks require a lot of accuracy and planning.
The roof will rotate on ball castors sunk into the wall tops, to prevent the castors creating grooves in the bottom of the roof frame I had a metal disk made by a local Engineering company, this will be screwed into plywood and form the base of the roof.
(http://www.jovets.co.uk/sites/default/files/field/image/roof-metal-ring.jpg)
As the building is made of wood with time the structure will change and warp so I'm still undecided on how rigid to make the base of the roof a little bit of flexure could allow the weight of the metal to bow down and stay connected to the casters. Equally too thin and when the roof is lifted onto the roof it will bend or break; more thought is required. In photo below shows the ring suspended with a 11mm plywood top, I'm thinking 18mm will be required.
(http://www.jovets.co.uk/sites/default/files/field/image/suspended-roof-base.jpg)
I've been re-thinking the top of the pier, my original plan was to use two metal plates supported by 4 M12 bolts however having read various articles and spoken to a number of people I'm concerned this design is flawed as it means any vibrations will occur between the plates while the concrete pier remains rigid. I've no idea of the magnitude of the problem but I can't see any real negatives from taking a different approach. My approach will be to have one plate on top of the pier and create a cavity in the top of the pier to be allow fixing the EQ6Pro to the plate. The prototype looks like this.
(http://www.jovets.co.uk/sites/default/files/field/image/pier-top.jpg)
Quoteany vibrations will occur between the plates while the concrete pier remains rigid
That means that it is the mount that will be creating the vibrations, which means you will be stuffed no matter what modification you make.
Just wondering why you think there will be vibrations Ivor. If your pier is isolated there won't be vibrations from you walking in the obsy. I have a pier with 2 plates and no vibrations there.
Old photo but same pier:
(http://www.caroleastronomy.webspace.virginmedia.com/_wp_generated/wpf7d7c484_0f.jpg)
Looking good.
That's an interesting owls' nest idea for the pier top.
Quote from: mickw
Quoteany vibrations will occur between the plates while the concrete pier remains rigid
That means that it is the mount that will be creating the vibrations, which means you will be stuffed no matter what modification you make.
Not necessarily the mount but external factors (such as wind) might set up oscillations.
My approach was still to have a plate but virtually no distance between the plate and the pier top.
(http://www.markshelley.co.uk/webdisk/observatory25.jpg)
Mark
Quote from: Carole
Just wondering why you think there will be vibrations Ivor.
It's explained in this video.
http://www.youtube.com/watch?v=AOeLnecOMeg
To be honest though, it probably only becomes a problem for high magnification planetary imaging.
Thanks for the installation images it had crossed my mind I'd only seen both your set-ups in the dark, they're really helpful and the youtube link is excellent very enlightening. I'm really not convinced about creating a large nest of any sort and having watched the clip it confirms it. Mark in your solution did you cut a bolt to size, place the plate on the mount and then fasten it to your pier?
On reflection I think my solution isn't hugely better than bolt option and the hole could be a lot smaller all I need to be able to do is get a ratchet spanner underneath unless I take Mark's approach (if I've guessed correctly).
One does start to wonder whilst working it out at what point is it too anal?
Off topic: I've been wondering for a while is it a 40+ ( I include myself in this group) thing to call them videos? I just asked my 14 yr old daughter and she wasn't much help.
I haven't really got room for a spanner in the gap underneath because the bolts holding the blue adaptor plate to the big disk protrude underneath. So I centrally bolt the EQ6 mount onto the blue adapter plate and big disk while it's off the pier then lift the whole assembly onto the pier in one go and tighten it down. I don't overtighten the central bolt because it needs to be possible to perform the Dec adjustment.
You'll also notice the EQ6 is not mounted centrally on the pier - I'm pleased with that decision because it gives the scope far more clearance and extra imaging time beyond the meridian.
Mark
I had noticed in particular it is offset to the north, did you find polar alignment a challenge?
The normal in a circular observatory is to offset the pier south, so to do what you've done I'd have offset the pier even further south to keep the mount position slightly south of the centre of the observatory (I hope that makes sense) I'm not sure that is viable for me with the way the floating floor is supported.
I need to get the plate made, was yours made with mild steel and how thick was it?
It was mild steel 13mm thick. I sent the company this jpeg created from a Word document:
http://www.markshelley.co.uk/webdisk/pierhead3.jpg
They quoted me for the work and charged me £25 + £10 delivery for each one.
These were the guys: www.rsjsteelbeams.co.uk
Mark
Have you made any recent progress Ivor?
Yes, I'm writing it up, should post something today. The thing that pays for it all is getting in the way at the moment.
4th November
Last weekend I didn't manage to progress very far, I mortared the lintels onto the footings and filled the pier pit to 500mm below ground level. To work out where to place the posts on the lintels I drew template around metal ring.
(http://www.jovets.co.uk/sites/default/files/field/image/finding-where-to-put-the-posts.jpg)
10th November
After weeks of preparation and fine tuning this weekend was the big push, everything was pre-cut and prepared so it was a test to see if my calculations were all correct. On reflection I've made a few wrong choices on the sheet material, I originally planned to use 6.5 and 11mm thickness throughout however during the build it become apparent that this wasn't rigid enough for the larger sections so I've been forced join a number of sheets together. The ring for top of the walls was made of three sheets two 6.5 and one 11mm, which I fasten together with screws and wood glue. I staggered the joints of each circle but still keeping them within 700mm of each other so the three joints were braced between two posts and to prevent them from getting in the way of the castor placement.
(http://www.jovets.co.uk/sites/default/files/field/image/TOP-ring-joined.jpg)
To build up the frame I first made up the four sections for the footings and then attached the cross beams joining them together, with a hammer bash here and there the frame came together and I was pleased to see that all outer dimensions are within 10mm of their target. In addition the tops of the posts are level and I won't need to add any shimmies to bring the height up. Achieving this with DIY grade tools has proven painstaking, having a cutting depth of only 100mm on the mitre saw plus trying to keep the wood flat and at right angle to the blade is challenging. I'm pleased care and attention has paid off so far.
(http://www.jovets.co.uk/sites/default/files/field/image/observatory-build-141109.jpg)
If the observatory doesn't work out, you could put a liner inside and have a nice deep splash pool for the Summer!
That's an idea maybe I could make some further adaptations and a create a thunderbirds telescope coming out of the pool.
Made some good progress there Ivor.
Just wondering how you are going to fix the floor as the cross beams are at different levels presumably because the brackets were in the way.
Carole
I'm really enjoying this thread, and not just because another amateur is realizing the dream of a home observatory (although that's part of it). I like seeing the design considerations that are made due to location and weather, and how people solve these issues.
A fellow I knew in Arizona was mostly worried about the 35degree Fahrenheit swings between day and night. The need for ventilation was at odds with trying to keep snakes and scorpions out.
I have to be concerned about the ground freezing solid for a few months. I also have to worry about the local wildlife, but in my case it's a skunk that tried to make it's home underneath the raised wooden floor (it was not fun the night I realized where the little bugger had made it's home).
A very good friend in the Atacama desert in Chile has to worry about the dust: there's a good proportion of volcanic glass in it, and it's incredibly fine. There's a fair bit of salt in it, too...all in all, it's not very friendly to fine optics and electronics.
So, I'm looking forward to more updates, and hoping the weather doesn't stop you from working outside.
Quote from: Carole on Nov 12, 2014, 23:07:50
Just wondering how you are going to fix the floor as the cross beams are at different levels presumably because the brackets were in the way.
Carole
Good spot, you are right about the cross beams the current ones will be only used to support the structure. I am planning to add additional cross beams slightly in from the frame to support the floor.
Glad you are enjoying the thread, I have to admit I find it difficult to decide which bits to put in and which to leave out as a lot of it has been thinking up until now and attention to detail. Wildlife for me is more likely to be hedgerow creatures so I need to make sure I protect the cabling, the mice chew through just about anything.
After this weekend work will die down and I've got to take mandatory leave between now and the end of the year so hopefully I will get most of it done by the end of November. The last two really technical bits are the pier and the roof, I hope to complete them next weekend so I can put the walls up.
Quote from: Ivor on Nov 13, 2014, 06:50:17Wildlife for me is more likely to be hedgerow creatures
Main problems round here, wildlife-wise, are usually foxes (and badgers?) digging holes and chewing things, squirrels getting in under the roof, and slugs and snails getting into things (with a side order of fallen leaves, which do a great job of helping timbers rot if they get a chance). There's sometimes the slight risk of the neighbours' cats getting locked in, too...
In other words, don't bother, concrete over your entire garden, it's safer. Plus you have somewhere to rest your tripod !
In parallel to the physical build I have been writing an ASCOM dome driver using an Arduino, I now have C du C sending basic commands to the Adruino and displaying them on an LCD. I'm now trying to work out the best motor and drive wheel combination which is a little difficult as I don't know the force required to move the roof which I estimate is less than 50kg and will rotate on 6 ball castors. The top max slew rate for the EQ6Pro is 3.4 degrees/sec which equates to 71mm travel per second for the dome. Where it's not necessary to have the dome keep up with the telescope it would be nice to get close. I haven't looked yet but I'd like to at least have the dome be able to go the same speed as the ISS so I could have option to image it in the future.
I've seen a NEMA 23 used in one observatory and it appears to pack a punch for it's size but I'm not sure how to decide which specification to use for mine both from a dome and arduino view point. The majority of the Arduino stepper motor drivers go up to 2A so I've been looking at motors below that rating but I'm not sure what calculation to apply to make my choice.
I spoke to a chap at the company below and he recommend this model, but I don't understand why.
https://www.motioncontrolproducts.co.uk/products/2/6/nema-23-60mm-high-torque-stepper-motors/ (https://www.motioncontrolproducts.co.uk/products/2/6/nema-23-60mm-high-torque-stepper-motors/)
Any advise gratefully received.
Are you having a round slotted dome or a 6 faced roof which you were considering at an earlier stage?
Since you have created a circular ring for the top of the walls, I am guessing a slotted dome which would be better since you will be able to reach the Zenith.
Carole
Why would you need a stepper motor? Is the dome going to rotate with the scope? If so what method are you using to ascertain which direction the dome is pointing in?
Quote from: Carole on Nov 14, 2014, 00:31:19
Are you having a round slotted dome or a 6 faced roof which you were considering at an earlier stage?
Since you have created a circular ring for the top of the walls, I am guessing a slotted dome which would be better since you will be able to reach the Zenith.
It's going to be a mixture of both, imagine an eight sided squash bottle top with a slotted roof through the middle. Being so close to the boundary line I've got to keep the 2.5m limit and the walls needed to be high to get over the fence. It's hard to describe hopefully I'll start to building it up this coming weekend.
Quote from: Mike on Nov 14, 2014, 12:47:02
Why would you need a stepper motor? Is the dome going to rotate with the scope? If so what method are you using to ascertain which direction the dome is pointing in?
Initially I plan to count the steps of the motor and have the Arduino keep track of position. ASCOM sends the target degree to the dome driver and once I know the maximum speed the dome can go without slippage, I should be able to keep it accurate enough. Later I will look at using a magnetometer for more accuracy.
So an octagonal cylinder with a flat top? The slit to go up one side and right across the top?
How wide will the slit be? The roof could have to move very quickly if a satellite you want to track goes through, or near, the zenith. The wider you make it, the better.
I'm intrigued by this, as my Chief Financial Office recently approved freeing up some funds for a springtime renovation. I've often wondered about modifying a cylindrical polyethylene water tank, or a calf nursery like this one:
(http://www.polydome.com/Calf_Nursery-1.jpg)
These can be had for about $300, or (where's the Pound Sterling symbol on this keyboard? Ahhh...cut and paste from somewhere else) in the region of £150.
You are close, the hatch will be in two parts with the vertical bit will hinge at the bottom and the top section will slide back. The automation of these part will be in phase 3 as it's more a nice to have and I can delegate this responsibility if I'm not at home when starting the session.
The slot will be 1m wide so plenty wide enough for any scope I'm likely to have.
I love your idea but I'd be weary of the thermal coefficient of polyethylene. I looked into using HDPE as an alternative material to wood but I was discouraged when I discovered a sheet 2.4m x 1.2m sheet would expand/contract 6mm in a temperature range of -10c to 30c which would lead to no end of leaks. I imagine it would be even worse for you.
I would not count on the steps of the motor for position at all. There are many reasons why a pulse would not cause a step or why the dome would move on it's own for other reasons. If I were you I would use some kind of encoder technology or magnets for getting precise positioning.
Will the top of the octagonal cylinder (the roof) be sloped to allow the rain to run off?
I'm now very intrigued to see this roof. My observatory is 8 foot by 6 foot, and an octagonal cylinder with a sloped end sounds like it might be something that could be retro-fitted on to my existing sctructure.
Quote from: Mike on Nov 17, 2014, 12:55:40
I would not count on the steps of the motor for position at all. There are many reasons why a pulse would not cause a step or why the dome would move on it's own for other reasons. If I were you I would use some kind of encoder technology or magnets for getting precise positioning.
OK thanks Mike, I bought a couple of bluetooth boards and a GY-273 HMC5883L magnetometer, I'll run this off a seperate Arduino.
Quote from: Canadian Roger on Nov 18, 2014, 04:17:41
Will the top of the octagonal cylinder (the roof) be sloped to allow the rain to run off?
I'm now very intrigued to see this roof. My observatory is 8 foot by 6 foot, and an octagonal cylinder with a sloped end sounds like it might be something that could be retro-fitted on to my existing sctructure.
Yes either side of the opening will be sloped, I'm keen to be careful with any angle though having seen Mark's misfortune I don't want to create a wing.
My design has been driven by the standard size of sheet plywood 2.44m X 1.22m (8ft x 4ft). In the UK you can get a larger sheet 10ft x 5ft I've used this to make the roof oversized on the ring so the roof doesn't hit the walls when it rotates.
I have a new question I can't see north as the house in the way who have other determined north for the pier plate alignment? I have a GPS compass I thought this might be the best approach rather a map compass. Also how accurate does this really need to be, if I think about my current manual approach with a tripod, surely placement of the peg needs to be somewhere between true north and magnetic north.
Ivor, when you say you can't see north, do you mean you can't see Polaris? If so how about using a ra calculator at a precise time and triangulating of of other known stars.
I can see Polaris for my imaging (see first page of the thread) but to align the pier plate prior to concreting it in I need to align it to north. See Mark's pier plate as an example.
http://forum.orpington-astronomy.org.uk/index.php?topic=9071.90 (http://forum.orpington-astronomy.org.uk/index.php?topic=9071.90)
What would you be trying to see north had the house not been there?
I could choose a reference point due north of the pier from an OS map and use that as well as a compass to reconcile any inaccuracies. In the current situation all I have is a compass, which might be enough I'm not sure how precise I have to be.
If you find no alternative I have a polar mate, which used with my tripod gives an observatory recognized standard for alignment I'm happy to help out if need be.
The Sun will be due south at noon, plus or minus any offset for being east or west of the meridian for your time zone (should be easy for you!). You could use the door jamb at the right time and mark where the shadows fall.
Of course, the requisite sunny day may be an issue...
I don't think the pier orientation needs to be "spot on" as you can adjust the mount head, but obviously it's best to get close.
Suggestions:
a) Can you not find a way to put a marker on something when you can see polaris at night, and use the marker during the day. Obviously if you don't get clear skies then this is not an option.
b) The plates on the top of my pier can be rotated (see the bolt underneath the top plates) and as there is a double plate with bolts in between, the level can also be adjusted. If you do a similar top plate then hopefully if you get it slightly wrong it could be adjusted afterwards. (see the photo of my mount b= post 12).
Carole
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
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
|
[/font]
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.
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.
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.
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 (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 (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?
(http://www.jovets.co.uk/sites/default/files/field/image/calculating-pier-height.jpg)
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 :)
Sounds like some good progress Ivor.
Carole
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?
My garden already resembles parts of Calais so I don't think I can put up anymore tarps.
(http://www.jovets.co.uk/sites/default/files/field/image/Covering-everything-up.jpg)
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.
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.
(http://www.jovets.co.uk/sites/default/files/field/image/pier-adaptor.jpg)
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.
(http://www.jovets.co.uk/sites/default/files/field/image/pier-plate-template.jpg)
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.
(http://www.jovets.co.uk/sites/default/files/field/image/trying-to-get-the-roof-straight.jpg)
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.
(http://www.jovets.co.uk/sites/default/files/field/image/roof-frame.jpg)
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.
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 :)
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 (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.
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.
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 (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?
The top of the roof is cover tgv and has a 2nd coat of paint, as the sides walls will be lower the base of the ring I can't put them on until the roof frame is in place on top of the walls.
(http://www.jovets.co.uk/sites/default/files/field/image/2nd-coat-of-paint-on-the-roof.jpg)
All 7 walls and the door are on and I've even managed to put the floor in all that is needed is a couple more coats of paint during the week, ready for next weekend.
(http://www.jovets.co.uk/sites/default/files/field/image/floor-is-in.jpg)
I have to admit I'm a little nervous about the roof going on next weekend, it's the most important part of the design and I've no way of being 100% certain of there not being a issue; fingers crossed.
A shot of the outside
(http://www.jovets.co.uk/sites/default/files/field/image/outside-of-the-observatory-141208.jpg)
Great progress Ivor. What a great little space underneath for wildlife to shelter, what a kind gesture. :cheesy:
How are you going to hold the roof on Ivor?
Carole
Yes it had crossed my mind some wild life might check, however our jack russell should keep any permanent residents out. To keep the roof and wall rings aligned I'll fitting 4 right angled brackets to the bottom ring facing upwards about 10mm away from the true position. If this doesn't work I'll look to put some casters on the brackets and moves it closer to the roof rim.
For protections against high winds I'll probably use the same clamps as Mark did.
Good progress Ivor. It's certainly coming together now.
What are the bathroom fittings on the pier?
The roof sections look fairly flat - what will prevent rain leaking through the tongue in groove?
Mark
Quote from: 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 (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?
Interesting idea. It's probably OK for dew heaters. I certainly wouldn't use it for sensitive electronics.
Mark
Quote from: MarkS on Dec 08, 2014, 17:13:45
Good progress Ivor. It's certainly coming together now.
What are the bathroom fittings on the pier?
The roof sections look fairly flat - what will prevent rain leaking through the tongue in groove?
Mark
The sides have a 5% slope it's not so obvious from the angle of the image. I'll also use sealant in all the gaps to reduce the chance of leaks, if there are big problems it won't be hard to remove the top in sections so I can add a water barrier as well.
The bathroom fittings are for the cabling the other end is under the floor, I'm building a wooden frame and faceplate to go over the top which will have the 240V , 12V power and USB sockets on. I couldn't use standard electrical conduit as it's too small for a USB cable to go around the bends inside the pier.
Quote from: MarkS on Dec 08, 2014, 17:20:58
Quote from: 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 (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?
Interesting idea. It's probably OK for dew heaters. I certainly wouldn't use it for sensitive electronics.
Mark
ou should plan on having a couple if you have several heaters. Get these LED lighting controls boxes (http://www.ebay.co.uk/itm/2-pcs-Lot-LED-Dimmer-module-12-24-volt-DC-8-amps-for-flex-modules-bars-/121512253173?pt=US_Wall_Fixtures&hash=item1c4ab1d6f5) off Ebay as dew heater controllers, they handle 8 amps each and are ready to mount somewhere with the down light transformers.
(http://thumbs2.ebaystatic.com/d/l225/m/mejiIr50DyHD9zNxR8aQlZw.jpg)
Ivor I have a box full of those dimmers if you want a few.
Mike
I already have a PWM for the dew heaters however I could use one on the 12V lighting as well as having a spare. I plan to come to the Christmas quiz are you going Mike? If so for the appropriate amount of silver I would happy to take a couple of your hands.
Last weekend was full of problems, the roof was put on Saturday morning and from that point onwards things general went downhill. I'd designed the the base of the roof to have a 15mm gap between the top of the walls and the bottom of the roof base, this has been proven to be too small. With the weather and having the roof resting on stilts for the last month to keep it level during the build phase the base has warped and is catching on the roof top. This problem is compounded by slight differences in the levels of the wall uprights which weren't apparent earlier; my fault again, I checked the levels of the posts across the whole width of the buildings frame where 5mm over 2.4m wouldn't show up on a level, I should have also checked against adjacent posts as well.
(http://www.jovets.co.uk/sites/default/files/field/image/roof-on-top.jpg)
I've mitigate the gap problem by adding plywood padding under the bearings and by placing clamps on the areas with the most bowing it has reduced the variance in the roof base to ensure there is a sufficient gap. To keep the roof in place when it is being rotated I'd planned to put 4 rollers on the inside like below.
I knew the initial wheels were too thin but I'd hoped to iron out the kinks with these and then buy some wider ones once I'd worked out the details. Well this have proven to be a non started there doesn't appear to be an easy way to give them sufficient rigidity to push back on the roof base.
(http://www.jovets.co.uk/sites/default/files/field/image/roof-stabilty-prototype-1.jpg)
I could give them greater rigidity by securing them to the roof base and having them hang down and push against the wall ring this causes problems later on as I want to automate the roof and as these rotate they would hit any motor I placed on the wall.
(http://www.jovets.co.uk/sites/default/files/field/image/roof-security-bracket-down.jpg)
This film shows you what the inside currently looks like
https://flic.kr/p/q9gWb3 (https://flic.kr/p/q9gWb3)
If I'm honest the roof is an eyesore it doesn't work aesthetically, it's better with the cladding on (sorry no picture I finished that at 18:00 on Sunday in the rain so had to cover it up quickly so I'll add it later) and my very patient wife who has let work on this solidly for the last 10 weekends is not impressed; at least if it worked I'd have some leverage. As I was running out of time as we headed towards Christmas I've had to rush the roof, I can't do anything major now until the new year but I'd like to get the roof rotating manually so I can at least do some imaging.
Feeling deflated and frustrated so any thoughts or ideas gratefully received.
I'm not surprised you feel deflated. I kind of know the feeling - in a week's time one year ago, my own flawed design led to the loss of the whole roof in the Christmas Eve storm. Your design is quite "adventurous" so it allows plenty of possibilities for problems. If I understand things correctly, the way I see it is as follows:
1) You have four(?) wheels attached to the shed that the roof sits on. It is crucial that these lie in a horizontal plane with solid support underneath each one so they cannot drop with the weight of the roof on them.
2) It is essential that the roof "ring" that sits on the wheels is flat, without any warping and supported with sufficient structure to prevent it bending under the weight of the roof.
e.g. maybe the ring should be solidly screwed to the underside of some kind of framework built of 3" x 2" like this:
++++++++++++++++++++++++++++++++++++++
+ + + + + +
+ + + + + + + + + +
+ + + + + + + + + +
+ + + + + + + + + +
+ + + + + + + + + +
++++++++++++++++++++++++++++++++++++++
You may need to detach the roof from the ring, add the supporting structure for the ring and then attach the roof back to the supporting structure. However, such a structure would make it feel more claustrophobic inside the observatory. But I do think the roof ring requires extra support.
Mark