Advice on building an observatory

gregbradley · #1 29-01-2010, 03:41 PM

I plan to start construction on a new observatory soon.

I was wondering what to consider with it. The observatory I built at my dark site is simply an 8 inch 5mm thick walled steel tube bedded in concrete after I dug an 800mm hole.

Then I put pavers around the pier and made a pine frame and colorbond
cladded room. The roof is flat and rolls off on 2x 100mm zincalume steel channels with a frame to support it.

I was wondering if I should do a concrete slab with the pier section separated with an expansion joint and make the centre section that will be holding the pier about 1 cubic metre of concrete for strength.

If you used a concrete slab would that create thermal issues as the slab cools off after dark? And if so is it better then to use pavers?

Greg.

bert (Brett) · #2 29-01-2010, 04:08 PM

Hi Greg,

Its the depth of the pier in the ground that matters more than its mass. I used a steel reinforced concrete footing around 400mm diameter and 1200 deep for my observatory. Its rock solid and the mount is mounted 1800mm above ground level. Some people just put a cubic meter in a shallow pier and it can work, but its far more cost effective with the deep pier and more stable.

The slab is not likely to cause thermals, and pavers have the similar thermal mass. Slabs make things a lot neater inside as well. I built an observatory for a friend on this forum and has two piers mounted, he only isolated the pier that is doing the long focal length (3m), and not the wide field setup (500mm). I dont believe he is having vibration issues with the unisolated pier. He used expansion joint foam to isolate the pier from the main slab.

Brett

Paul Haese · #3 29-01-2010, 04:59 PM

Sorry Brett, mass is more important. My pier is 1200 with 13mm walls and the pier support contains 2 tons of concrete and steel. Hit that with your hand and it a) does not move and b) it hurts.

Mass is the way to go Greg.

bert (Brett) · #4 29-01-2010, 05:13 PM

Paul, sure mass helps. If you used 40 tonnes of concrete you would have ended up with a stabler pier. Design is the key, not brute mass.

Some interesting reading on pier design. http://www.cloudynights.com/item.php?item_id=1275

Brett

Doomsayer · #5 30-01-2010, 10:21 AM

Hi Greg
Not sure if you've seen this one:
http://obs.nineplanets.org/obs/obslist.html
A large and diverse range of observatories listed there. Some links may be a bit old and broken now.

If you want to get fancy, I have found that rendered polystyrene panels(exintex - R2.0) work well in the exposed walls. The panels are easy to work with. I know that many people will say to use metal sheet cladding on the walls relatively uninsulated so that you get quick cool down in the evening, but it can get very hot in there during the day if the walls are exposed to the sun and radiant heat. With the polystyrene and a white metal roof my observatory stays much cooler than the outside on hot days. I have a solar panel driving a 150mm 12V extractor fan in the side of the roof, which helps with heat or humidity build up inside.

I currently have a revised roll off roof installed/built by Bert (replacing the old 2 part roof) which has colourbond cladding, steel frame, bubble wrap insulation under the cladding and the solar fan plus a small whirlygig. The previous (split) roof I built was cumbersome, but had even more insulation in it - again counter to what some people will tell you to do. It had air flow ventilation (20mm gaps at the roof joins) and a solar fan. This setup was able to mantain an even 22-24 degrees on a hot 38-40 degree day. However, as you would realise the 'esky' approach of having no air flow ventilation is not advisable.

As far as dream observatories go, I really like the Russell Croman observatory megaconcrete pier, raised platform and clamshell on top - this seems to be a successful design, seen in many other high end robotic setups.
http://www.rc-astro.com/equipment/observatory/index.htm

guy

gregbradley · #6 30-01-2010, 10:56 AM

That's a couple of great links there. Thanks.
That is a serious disadvantage of colorbond cladded observtories they
can be really hot inside in summer. Given you keep your expensive gear all set up then that is really important to provide a cooler environment.

Greg.

Quote:

Originally Posted by Doomsayer

Hi Greg
Not sure if you've seen this one:
http://obs.nineplanets.org/obs/obslist.html
A large and diverse range of observatories listed there. Some links may be a bit old and broken now.

If you want to get fancy, I have found that rendered polystyrene panels(exintex - R2.0) work well in the exposed walls. The panels are easy to work with. I know that many people will say to use metal sheet cladding on the walls relatively uninsulated so that you get quick cool down in the evening, but it can get very hot in there during the day if the walls are exposed to the sun and radiant heat. With the polystyrene and a white metal roof my observatory stays much cooler than the outside on hot days. I have a solar panel driving a 150mm 12V extractor fan in the side of the roof, which helps with heat or humidity build up inside.

I currently have a revised roll off roof installed/built by Bert (replacing the old 2 part roof) which has colourbond cladding, steel frame, bubble wrap insulation under the cladding and the solar fan plus a small whirlygig. The previous (split) roof I built was cumbersome, but had even more insulation in it - again counter to what some people will tell you to do. It had air flow ventilation (20mm gaps at the roof joins) and a solar fan. This setup was able to mantain an even 22-24 degrees on a hot 38-40 degree day. However, as you would realise the 'esky' approach of having no air flow ventilation is not advisable.

As far as dream observatories go, I really like the Russell Croman observatory megaconcrete pier, raised platform and clamshell on top - this seems to be a successful design, seen in many other high end robotic setups.
http://www.rc-astro.com/equipment/observatory/index.htm

guy

gregbradley · #7 30-01-2010, 10:57 AM

Thanks Bert.

I will keep that in mind. I will be building next to a fairly large swimming pool. I believe the builders hit rock there so perhaps I can attempt to get down to the rock.

Greg.

Quote:

Originally Posted by bert

Hi Greg,

Its the depth of the pier in the ground that matters more than its mass. I used a steel reinforced concrete footing around 400mm diameter and 1200 deep for my observatory. Its rock solid and the mount is mounted 1800mm above ground level. Some people just put a cubic meter in a shallow pier and it can work, but its far more cost effective with the deep pier and more stable.

The slab is not likely to cause thermals, and pavers have the similar thermal mass. Slabs make things a lot neater inside as well. I built an observatory for a friend on this forum and has two piers mounted, he only isolated the pier that is doing the long focal length (3m), and not the wide field setup (500mm). I dont believe he is having vibration issues with the unisolated pier. He used expansion joint foam to isolate the pier from the main slab.

Brett

gregbradley · #8 30-01-2010, 10:58 AM

Thanks Paul.

A bunch of concrete and steel isn't that expensive so shouldn't be hard to implement.

Greg.

Quote:

Originally Posted by Paul Haese

Sorry Brett, mass is more important. My pier is 1200 with 13mm walls and the pier support contains 2 tons of concrete and steel. Hit that with your hand and it a) does not move and b) it hurts.

Mass is the way to go Greg.

gregbradley · #9 30-01-2010, 11:09 AM

What I am leaning towards after reviewing some of this data is this:

1. 100mm slab isolated from the pier with an expansion joint. Makes for a clean and easy to use floor. I may put some astro turf or areas of carpet around the pier in case of anything falling. Perhaps even rubber matting.

Pier 10-12 inch steel tube 5mm wall thickness bedded into concrete plug as deep and large as practical.

2. Metal frame for strength and ease of construction and quick cooldown.

3. The exintex wall panels and render the outside to match the house which would make it insulated plus aesthetic. Walls 2.5 metres high minimum to help create wind protection.

4. A lightweight steel framed truss roof with foam cored aircell insulation under .42mm trimdek colorbond roofing. The roof will slide off sideways not lengthways. This enables more clearance for the scopes (don't want the bottom of the truss to hit a scope) also enables a smaller rolloff roof receiving frame which is usually ugly.

5. Build a wind frame for creeper plants in front of the roof receiving frame to hide the ugly frame and in the future help reduce wind.

6. Size of observatory around 6.6 x 3.6 metres and 2 piers one for long focal length and one for a 2nd scope (Planewave CDK17 on a Paramount ME and TEC180FL/AP140/TEC110FL on Tak NJP mount). Leaves a bit of room to setup computers etc.

A few more questions.

My dark site observatory is often a mess of cables, transformers. I use a little outdoor table to mount my laptop/monitor/pc. Its all a bit messy.

Any suggestions on cable control and a space for the computers, monitors?

I know Fred laid some PVC pipe under his floor and up into the pier. Not sure how cable come out through a 10-12 inch steel tube which will have some capping plate that the mount will sit on.

Is it best to use a double mounting steel plate with several adjustable bolts or are you losing a lot of that rigidity you carefully created with the high diameter pipe when you do that?

Thanks for all the valuable input.

Greg.

bert (Brett) · #10 30-01-2010, 12:44 PM

If you get down to rock drill some holes and chemset some starter bars in it to tie it in to your concrete and that pier will be going nowhere. The observatory at kandos I built is similar dimensions to the one you are proposing and we used a 100mm slab and a 100x 300 thickening beam in the slab edges and that was class 'm' moderate reactive soil there from memory. Is the area granite or reactive?

The kandos observatory we used a welded steel frame with .42 monoclad (stramit's trimdek) and used a similar product to aircell, but it had a bubblewrap, and I really have no idea which is the best to use with that or the foam aircell.

The extinex panels are polystyrene? If they are they work great, as Guy mentioned he has used polystyrene and it looks great and insulates well without having a huge thermal mass that will leak heat well into the night.

Walls 2.5 high is pretty high, unless your pier is quite high as well, Which come to think about it if you swinging a long refactor....

I have a hollow pier and I drilled holes for running cables up the pier, but I didnt use them, I read some where to carpet the pier which I did, and its way more practical than I would have imagined because a)velcro stick to it (think power supplies, usb hubs, focus contollers, dew controller etc) and being able to attach it where you want b) I ran the cable between the carpet and the pier, it looks tidy and you can run the cables wherever ie no 240 and data together. c) its easy to make changes.

Freds idea of running the pvc works great.

The adjustment of bolts at the top of the pier works well, use fine threaded bolts and a huge plate, since you are using a paramount, you can use the pier adjustment plate made by bisque and the hard work is done for you.

Brett

Doomsayer · #11 30-01-2010, 03:39 PM

Re the computer and monitor

My observatory is quite small so I decided to make a simple timber cupboard which is bolted to the wall. I think it is about 500mm deep 800mm wide and 900mm high and has a horizontal shelf spiltting it in to 2 equal halves. I have 2 rolladoors which I got from Ikea installed. The rolladoors are space efficient and keep the PC gear protected and shields stray light from the monitor to the scope. The top shelf is at eye height when sitting and has a wide screen LCD on a swing arm. The PC and keyboard sit in the shelf below - I use a compect PC to save space. My legs/chair can fit underneath.

I also run cabling up the pier and have 240v at the pier and on two walls - I used exterior grade powerpoints. Just prerun the 240v flex through conduit and get the electrician to finish it off.

As Brett suggests if you have solid rock, secure some reo into holes drillied into the fresh rock and form the concrete around these with a sticky mix - not going anywhere after that assuming the rock has good strength such as fresh Hawkesbury sandstone.

Putting a good sheet of sarking under your floor - in my case thick formply isolated from the pier - helps with further heat/pest shielding. I also lined the interior of my observatory with ply painted black - this is optional I guess.

guy

gregbradley · #12 02-02-2010, 11:06 PM

Thanks for the tips.

I hope the exintex don't trap a lot of heat. Colorbond certainly doesn't but colorbond does make for an oven.

Cheers,

Greg.

Quote:

Originally Posted by bert

If you get down to rock drill some holes and chemset some starter bars in it to tie it in to your concrete and that pier will be going nowhere. The observatory at kandos I built is similar dimensions to the one you are proposing and we used a 100mm slab and a 100x 300 thickening beam in the slab edges and that was class 'm' moderate reactive soil there from memory. Is the area granite or reactive?

The kandos observatory we used a welded steel frame with .42 monoclad (stramit's trimdek) and used a similar product to aircell, but it had a bubblewrap, and I really have no idea which is the best to use with that or the foam aircell.

The extinex panels are polystyrene? If they are they work great, as Guy mentioned he has used polystyrene and it looks great and insulates well without having a huge thermal mass that will leak heat well into the night.

Walls 2.5 high is pretty high, unless your pier is quite high as well, Which come to think about it if you swinging a long refactor....

I have a hollow pier and I drilled holes for running cables up the pier, but I didnt use them, I read some where to carpet the pier which I did, and its way more practical than I would have imagined because a)velcro stick to it (think power supplies, usb hubs, focus contollers, dew controller etc) and being able to attach it where you want b) I ran the cable between the carpet and the pier, it looks tidy and you can run the cables wherever ie no 240 and data together. c) its easy to make changes.

Freds idea of running the pvc works great.

The adjustment of bolts at the top of the pier works well, use fine threaded bolts and a huge plate, since you are using a paramount, you can use the pier adjustment plate made by bisque and the hard work is done for you.

Brett

Quote:

Originally Posted by Doomsayer

Re the computer and monitor

My observatory is quite small so I decided to make a simple timber cupboard which is bolted to the wall. I think it is about 500mm deep 800mm wide and 900mm high and has a horizontal shelf spiltting it in to 2 equal halves. I have 2 rolladoors which I got from Ikea installed. The rolladoors are space efficient and keep the PC gear protected and shields stray light from the monitor to the scope. The top shelf is at eye height when sitting and has a wide screen LCD on a swing arm. The PC and keyboard sit in the shelf below - I use a compect PC to save space. My legs/chair can fit underneath.

I also run cabling up the pier and have 240v at the pier and on two walls - I used exterior grade powerpoints. Just prerun the 240v flex through conduit and get the electrician to finish it off.

As Brett suggests if you have solid rock, secure some reo into holes drillied into the fresh rock and form the concrete around these with a sticky mix - not going anywhere after that assuming the rock has good strength such as fresh Hawkesbury sandstone.

Putting a good sheet of sarking under your floor - in my case thick formply isolated from the pier - helps with further heat/pest shielding. I also lined the interior of my observatory with ply painted black - this is optional I guess.

guy

Doomsayer · #13 03-02-2010, 01:31 PM

The exintex would trap heat I'd expect if you have a relative air seal in your observatory (humidity would also be a problem in that case). However, if you have some passive and active air flow vents this is not a problem. The exintex has a bonded webbing on the outside for strength and good adhesion to rendering. The polystyrene has some sort of rock dust mixed in with it and so has a good fire/pest rating and excellent thermal properties. I have also recently used it again in a small 1800x800x800 enclosure for an EM200 mount near the pool. This also has 2 vents and a solar powered fan. It keeps the mount much cooler than the outside and so far shows no sign of heat build up issues.

I'll be using the same panels for the next level of the house when we get around to it.

guy

rogerg (Roger) · #14 03-02-2010, 04:05 PM

Quote:

Originally Posted by gregbradley

If you used a concrete slab would that create thermal issues as the slab cools off after dark? And if so is it better then to use pavers?

My obs has 1 cubic metre of concrete for the pier which is isolated from the surrounding concrete floor (single slab, 100-120mm thick) by an expansion gap with filler. Colourbond shed on top.

The concrete stays cool all year around, I don't have a problem with it heating up at all. The colourbond comes down to cover most of the outside edge of the cocnrete and the rest is covered by surrounding dirt. The inside has carpet squares on it. Whenever I've removed the carpet and touched the concrete it's been cool.

The colourbond shed doesn't get more than 4 degrees warmer than outdoor ambient temperature since I painted the roof white. It was a wheat colour, and that cooked, the walls are still wheat, but the white roof was enough to significantly alter the internal heat, taking it down to ambient except for the few mid afternoon hours where it creeps up to a few degress above ambient.

Once the sun leaves the shed (fairly early for me, about 4pm this time of year) it cools extremely quickly to ambient and below ambient by sunset.

In winter dew can be an issue on the inside of the roof. Apparently painting the inside is enough to solve that, I haven't yet.

I insulated half my obs and it's good for my comfort but a nightmare to cool off after a hot day, unlike the open half with the telescope.

Highly recommend this type of setup, has worked quite well for me.

Roger.

gregbradley · #15 04-02-2010, 03:05 PM

Thanks again for the tips. Most helpful.

Greg.

Moon (James) · #16 17-02-2010, 03:20 PM

Sorry I'm a bit late here...

Quote:

4. A lightweight steel framed truss roof with foam cored aircell insulation under .42mm trimdek colorbond roofing. The roof will slide off sideways not lengthways. This enables more clearance for the scopes (don't want the bottom of the truss to hit a scope) also enables a smaller rolloff roof receiving frame which is usually ugly.

Greg,
The other option to consider is a roll-over roof design. You don't have the 'ugly' frame taking up space in the garden and no trusses to hit the scope. Only negative is the small triangle that remains on the opposite wall, but I guess you could put hinges on it.
If you do it in steel, should be easy. Can be done in wood too.
James

gregbradley · #17 17-02-2010, 04:02 PM

Quote:

Originally Posted by Moon

Sorry I'm a bit late here...

Greg,
The other option to consider is a roll-over roof design. You don't have the 'ugly' frame taking up space in the garden and no trusses to hit the scope. Only negative is the small triangle that remains on the opposite wall, but I guess you could put hinges on it.
If you do it in steel, should be easy. Can be done in wood too.
James

Hi James,

What do you mean by rollover roof?

Cheers,

Greg

Moon (James) · #18 17-02-2010, 04:07 PM

Where the observatory roof rolls over the top of the warm room. There are some pics here.
It's easier to do than you might think.

James

gregbradley · #19 18-02-2010, 02:48 AM

Thanks James. Nice looking observatory.

Is the building plastic wrap for dust protection only or does it have some insulating properties as well?

Greg.

Moon (James) · #20 18-02-2010, 07:39 AM

The wrap is to stop condensation from the roof dropping down onto the gear.
But it also ensures there are no gaps where dust and critters can get in under the eves or in the corners etc.
I have avoided any form of insulation to ensure fast cool down.
I think the best way to keep the temp down during the day is simple ventilation.
James