View Full Version here: : New observatory advice
14-02-2011, 11:57 PM
I'm planning on building an observatory/shed in a dark sky location. Apologies if some of my questions sound a bit dumbass but I'm new at this and am hoping a few people with a bit of experience can help.
Shed will be built on a concrete slab (100mm reinforced). 4m wide x 5m long. The length will be aligned north/ south, with the roll on/roll off roof rolling off west (to protect from prevailing west/sw/nw winds). Shed wall height will be 2.4m high and shed will have a gable roof. Shed construction will be steel uprights (150mm x 50mm x 2mm box), walls lo clad 0.47mm and roof corrigated 0.47mm. Slab will sit on a topsoil/clay base.
The local shed guys have taken up the challenge and reckon they can put this shed kit together rated to category 2 (41 m/s) for around $7-8k (probably way more expensive than a do it yourself kit but I've had some other sheds from them and they seem to do a good job, plus I'm a bit of a novice with building my own buildings).
I'm getting a C11 on a cgem (when funds allow would like to get an AP1200 or PME mount) and want enough room for a reasonably sized refractor later on. Plan to do visual now and AP later.
I'd like to get a concrete pier put in to mount the CGEM C11 on it. I plan on staying at this location for a long time.
Hopefully someone can help.
1) Should I have the concrete pier poured with a rubber/flex join around the base to separate it from the rest of the slab to reduce vibration when walking on the slab and allow for expansion or is vibration on a 100m slab minimal (so I just get a solid footing poured under the base of the pier but its still all 'joined' with the rest of the slab).
2) Any suggestions as to the height of the concrete pier (am thinking around 1m)?
3) To allow for future mounts etc, what is the most flexible bolt configuration to have sticking from the top of the pier or should I just put in a top plate that would then bolt onto a secondary plate. The secondary plate would have all the necessary holes to bolt on a variety of mounts/ be interchangeable (not sure how the AP or OME mounts base plate compare to the CGEM).
4) Not sure what diameter pier would work (am thinking maybe 30cm?).
5) or is it simpler to just bolt down a steel pier once I have my slab poured with a section allowed for the footing (say 600mm deep and wide).
6) Any other helpful comments about my plan for the shed/pier (I've seen people suggest some pipe through the pier to allow cabling etc to be hidden).
Appreciate your help.
15-02-2011, 09:37 PM
You have raised some good questions - some of which I had to address when I built my obs. I did a lot of research on the internet - particularly of construction articles - to see what worked and what didn't for others.
Do you think that 41 m/s is high enough for your location? I designed for 160+ kph here, where gusts are the killer.
To address some of your Qs:
1. It's most important, especially when you start imaging, to have the pier mechanically isolated from the building/slab. You won't want movement due to foot traffic or wind gusts on the building transferred to your scope. So you need to design a physical gap between the two. I poured a reinforced block in the ground first, then poured a slab over it but not touching it. The concrete pier was poured soon after, and is connected to the block. There are some pics of it here in this thread http://www.iceinspace.com.au/forum/showthread.php?t=36222&page=3 (http://www.iceinspace.com.au/forum/showthread.php?t=36222&page=3)
2. To figure out your pier height you need to work backwards from your final set-up, so that you're sitting at a comfortable height when observing. I have not had experience with a GEM, but no doubt you will need to cater for variable observing heights (adjustable stools are great for this). If your walls are 2.4 m high, I would suggest that you might need a taller pier - it's occasionally good to be able to view the horizon. I have catered for future upgrades by installing a solid concrete pier to a certain height, and then bolting a steel pier on top, so in the future I can replace the steel pier with a different length if necessary.
3. You can get drawings of some mounts' bolting arrangements from the net. (Eg. the AP 1200) Since I made a sizeable pier, I spaced eight 1/2 inch studs around top of the pier so that the steel pier's bottom plate would be securely connected.
4. Since you're planning to install some solid gear on top of the pier, you need to design it so that the pier won't be a weak point. That is, you want it to be very stiff. There have been a few threads on IIS discussing the merits of concrete vs. steel, and it seems to be almost a personal preference ultimately. I have used both - as I mentioned above - and my pier is quite tall as the scope is on the second story of the obs. So I used a 457 mm dia former to pour the pier. For a GEM though, you might need to be careful that an excessively large pier did not foul the couterweights!
Finally, there have been a number of excellent roll-off-roof observatories described on this forum for starters.
Good luck with the design!
15-02-2011, 10:53 PM
Thanks again Chris (per advice on the other thread).
Yes I think you're right, might get them to increase the strength a bit from 150km/hr to 180km-200km/hr or so just in case.
I am now leaning towards a solid steel pier bolted onto the concrete base/footings to allow for that flexibility of changing the height when I change mounts or scopes and am thinking a wooden floor will be easier to separate from the pier to reduce movement. The shed uprights can be put into concrete footings rather than a slab (saves some money as well).
Looks like a very impressive setup you have there and lets hope for some clear weather soon.
Appreciate your comments.
16-02-2011, 06:32 AM
I went with a raised wooden deck. Allows for airflow underneath, and importantly is NOT a heat sink!
so theres NO heat plumes when viewing :astron: in hot months
Also 2 mt. walls with fold downs to 1.5 mt. on N,E,W sides
North wall fold down is needed for Andromeda in Oct/Nov as she's low on the horizon 14deg :thumbsup:
with 2 mt. height walls Max horizon I can get down to is 47deg. ;)
16-02-2011, 08:09 AM
one thing to note with the clay soils - they will expand and shrink with moisture content - to help reduce this effect of continual movement of the soil please consider a packing sand buffer before you pour your peir base. to give an indication of the shrinkage. I allowed for a 100mm for my backyard setup. so far it seems to be working. also having a seprate floor is important as any movement can be picked up by the mount, no matter how carefully you shuffle
18-02-2011, 03:31 PM
Here's another idea: a telescopic pier. Check out http://www.pier-tech.com/index.html (http://www.pier-tech.com/index.html)for some ideas.
18-02-2011, 03:42 PM
Mike, when pouring the concrete for our clubroom/double obs, there is a strip of styrofoam between the clubroom floor and the obs floors.
The concrete is one long strip 14 metres long with the clubroom sitting on the centre 6m.
The 4m each out end is for the obs.
This way the obs floors, even though joined, are actually isolated by 10mm of styrofoam.
People can jump around in the clubroom, but not affect the obs at either end.
Point of the story: Yes, isolate the pier :lol:
18-02-2011, 03:53 PM
Ok thanks. I have decided to go back to a concrete slab with an isolated pier footing/pier base. the slab will hopefully ensure more stability in the walls to ensure roof runners stay true. Walls of 4 x 5m shed will be reduced to 2.1m height to allow lower angle views for the scope. Now to level the area, pour the footing, get the slab pourer and get shed erected!
Not sure about the telescopic pier. I would assume there could still be some movement in it? Will heed the advice on the packing sand buffer and styrofoam or similar isolation layer.
18-02-2011, 09:31 PM
I don't have any pics of the pier footing but I isolated my tiny slab from the footing with expansion joint foam. Although it's seen very little use as it's not finished yet, it has been used and seems to work fine.
18-02-2011, 09:48 PM
Mike, best not to use styrofoam around a pier. It will look terrible as it chips apart over time.
Better to use some sort of very soft spongey rubber strip from Clark Rubber.
We used Styrofoam coz it doesn't matter if our strip falls out or breaks apart. I won't be seen.
Yours will, and crumbling styrofoam looks ugly. :thumbsup:
18-02-2011, 09:49 PM
I have built 3 observatories now.
Wall height of 2.1 metres sounds fine. My latest is 2.3 and that works for it. My country one is 2.2 metres.
Wind protection is probably more important with a country area observatory and if you are using long focal length.
You won't be able to image at all if your gear is wind affected so you don't want the top of your OTA sticking into the windstream above the walls. You can get away with that with a refractor and a decent mount but not a mirrored compound long focal length scope.
My current observatory has 2 pads. One is a pier about 1 metre deep and 850mm square with a fair bit of steel reo in it.
It is isolated from the main floor (I used pavers on top of road base and base sand, easy to lay, no transmission of vibrations.
I have a 2nd slab for a pier mounted setup.
The first pier has a Sirius Optics pier which is really solid and really well built. It is about 1.2 metres high and 6mm wall steel with reinforcing and a mounting plate on top with stainless steel rod and nuts to adjust and level the top plate. It was drilled for a Paramount ME.
I drilled anchor bolts into the pier and fixed it with about 6 or 8 large anchor bolts. No flex and solid for a Planewave CDK17 which weighs about 60kg with camera etc.
I suggest also using Aircell Insulbreak insulation which is put on under the roof and the walls. Even during recent 40 degree C days inside the observatory was never super hot and certainly no hotter than outside. It seemed a tad cooler.
I haven't taped the insulation sheet together which would make it even more effective although it is overlapped quite heavily. This will protect your gear from the extremes of heat in summer and also reduce heat plumes coming off the slab at night. Perhaps pavers cool off faster in that regard as they have smaller mass.
I also made a little side room with a bench for the computers etc. I have a heater and a fan for my comfort and it probably does not affect the scope.
Most imaging is the east to the west through the zenith and some to the south. Very little is in the north (Pleiades, Dumbbell and thats about it). The rest are too low to image properly. So consider your line of sight to these areas.
My pier ended up being a tad higher than I expected with the Paramount and the Planewave CDK17. In hindsight I would have made it a tad lower.
My country dark site observatory often gets strong winds so not sure what your site is like but country areas seem to get more winds than city areas so keep that well in mind when designing it. Don't make the walls too low.
Drainage. Make sure the resulting slab/floor is about 75mm or more higher than the outside ground. My country one isn't particularly and the edges get wet when it rains heavily. Dig a trench around the outside of the observatory and fill it with crushed rock for drainage. Make sure the
floor is considerably higher.
Insect control. I would recommend vermin guard to the floor of the slab and silicone the ends of the cladding sheets to it to discourage insects making nests. My country property observatory is a haven for spiders. Last year it was heaps of redbacks. This year it was heaps of mouse spiders. Big fat ones. If you live there I suppose you can spray regularly.
A roll off roof implies an air gap at the top so there is some access for insects to get in but a lot like to go on ground.
18-02-2011, 10:23 PM
The only advice I can offer in concurrence with much of the other already given is for the mounting method onto the pier.
I dug a hole almost 1 metre square, and a metre deep. I placed quite a bit of steel within that hole, but welded it together. As the pier started (approx 30cm in diameter formed with surplus slow-combustion heater flue), I brought 4 star pickets up through the middle, evenly spaced and welded to the metalwork in the base. About 30cm below my intended pier height, I welded a length of 3/4" threaded rod on top of each of the star pickets. These extend approx75 cm past the top of the concrete I poured in the pier.
The large cubic base and pier were pretty much poured as one exercise.
The floor for the observatory (approx 100mm thick)was laid over the cubic base and separated from all by the expansion joint rubber stuff readily available from Bunnings inter al.
At the top of the pier, I have a steel plate with holes drilled to fit over the threaded rod(s). I levelled this plate with a sandwich of nuts above and below the plate at four points. The Mount (Tak EM200 in my case id fitted to that top steel plate.
If I need to change mounts, I can replace my existing steel plate with another fitted with an appropriate base for the new mount (maybe Paramount... dreaming).
My Obs is in suburbia, but I have no noticable vibration coming through from nearby road or foot traffic.
I also agree with a separate control-room area from the pier room.
I have a roll-off roof. My roof rolls back over the control room saving the real estate required.
18-02-2011, 10:31 PM
You might get some ideas here as well.
sheds were Titan garden sheds @ 2 meter wall height.
23-06-2011, 09:14 PM
Finally some progress being made on the 4 x 5m roll off roof shed. I cheated a bit and used professional contractors, which is probably just as well as the temp has been <5C during construction. Hope to have to have it finished in the next few weeks. The door has yet to be cut in if you're wondering.
24-06-2011, 11:13 AM
Two Piers !! Nice !!
24-06-2011, 07:53 PM
Thanks Brent. Yes one pier eventually for astrophotography or visitors and the other for visual. When its all done it would be great to see the stars. Haven't seen them for a while with our great 'la nina' cloud event.:(
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