Pulsar 2.2m dome DIY option

[robin-m]

As I'm away from home a lot (usually the nights that are clear) the plan is to build an observatory that I can fully remote control. As a starting point I chose the Pulsar 2.2m dome DIY option. I wanted to build the base higher than the Pulsar one but also wanted to reduce the amount of white fibreglass on show as the wife can be fairly picky about such things.

The base was laid with a 24" sqaure by 36" deep concrete block poured then insulated with polystyrene before the outer slab was laid.

As I only have limited consecutive days at home I wanted to fashion as much as I could as a kit of parts that could be assembled quickly when the weather allowed. The following is a trial fit of the doorframe in the dry fit frame to check for size and fit.

Finally the bank holiday weekend afforded some time and dry weather to begin construction and the frame went up quickly...

Once the frame was up it was skinned with 6mm exterior ply scored at the back to allow it to bend easily and the top ring which the aluminium track sits on installed

Once skinned the structure was wrapped with a breatheable waterproof membrane

The entire structure was then clad with spruce cladding and the dome placed on top.

There is still some work to do on the exterior including a step outside the doorway and flashing around the base where the frame meets the concrete but it's essentially finished. Of course fitting out the interior and motorising / setting up the remote control is going to take a lot more work. I've pretty much worked out how I'm going to handle the dome rotation / co-ordination with the scope however I'm still scratching my head over motorising the opening and closure of the aperture. If anyone has successfully implemented this I would be very grateful to hear how they did it.

Next stage is to build a steel pier that will be bolted to the concrete block, then onto motorisation / remote operation.

Robin

[robin-m]

Oooops pictures out of sequence. The one that is supposed to show just the plywood skin actually shows the outer cladding of spruce on before the dome went on top. The actual plywood skin is shown here:

[skybadger]

I want to know more about the skinning process. Are the cuts in a v , how far apart ,how deep?.

Really neat job.

Thanks. Mike

[robin-m]

Mike, fortunately I have a tablesaw without which much of the build would not have been possible (and a bandsaw for the curves) the cuts for the scoring are by lowering the blade to approx 4mm depth and running the ply though at 20 mm intervals. The kerf of the blade is 3mm. It was by far the most tedious part of the entire build with each panel taking about an hour to score.

Robin

[laser_jock99]

Looks like a neat job- be interested to know how the automation goes.

[Gina]

That's a really nice looking job

[Steve Ward]

This would save you a lot of faffing about kerfing sheets of ply ....

http://www.lathamtimber.co.uk/ProductDetail.418.html

Steve.

[r3i]

That looks very smart - nice job indeed

[Teslar]

Looking good and well worth the effort

[nytecam]

Oooops pictures out of sequence. The one that is supposed to show just the plywood skin actually shows the outer cladding of spruce on before the dome went on top. The actual plywood skin is shown here:

Looking good Robin - well done ! Just a query - will the obsy floor and walls be raised to avoid rainwater penetration from surrounding 'patio' or are you using some special edge sealant to the patio ?

[robin-m]

Nyte, all the wood was heavily teated with preservative before construction. The bottom ring was then given a good bead of silicone sealant on the bottom before being bolted to the concrete. After the waterproof membrane was wrapped around the plywood a bead of silicone was then put round the bottom embedding the membrane and sealing it to the concrete (in the picture showing the membrane you can just see a white bead at the bottom. The spruce cladding was then left deliberately short of the concrete so it didn't take up moisture. I am now going to work out some form of flashing to seal the gap. The flooring I lay inside will be waterproof.

Hopefully that should keep the water out and the frame in good condition.

Steve, good spot on the flexible ply. I wish I'd seen that before I spent so many hours re-inventing the wheel

Robin

[nytecam]

Nyte, all the wood was heavily teated with preservative before construction. The bottom ring was then given a good bead of silicone sealant on the bottom before being bolted to the concrete. After the waterproof membrane was wrapped around the plywood a bead of silicone was then put round the bottom embedding the membrane and sealing it to the concrete (in the picture showing the membrane you can just see a white bead at the bottom. The spruce cladding was then left deliberately short of the concrete so it didn't take up moisture. I am now going to work out some form of flashing to seal the gap. The flooring I lay inside will be waterproof. Hopefully that should keep the water out and the frame in good condition. Robin

Thanks Robin - it's good you've thought about abutments and sealants etc [so few DIYers do ]and hopefully the modern sealants are better than in my day

[ronaldo999]

Did you put anything between the timbers on the floor and the concrete????

[Teslar]

Any wood that comes into contact with the ground should be pressure treated/tantalised, just giving it a few coats of preservative will not protect it properly IMHO

[Gina]

You need damp proof course (plastic or rubber membrane) between concrete and timber.

[Tinker1947]

Very nice job, is there a reason for not using Marine Ply as its very bendy and has built in damp proofing so when its gets damp it doesn't expand like normal ply, and would have saved a shed load of cuts....

[robin-m]

Ronaldo - No, other than a liberal coating of silicone sealant there is no barrier between the concrete and the base of the frame. With hindsight that was probably a mistake, especially as I have a large roll of the stick on flashing tape that would have easily done the job lying around in the garage. However I don't believe that the moisture penetrating through the concrete will seriously degrade the structure within it's lifespan.

Tinker - No reason at all other than availability. My local B&Q had large quantities of 8*4 6mm exterior ply.

Like all of these things you make it up as you go along, my reason for initially posting was to invite such questions so that any mistakes that I have made are taken on board by those who are contemplating the same thing. However I am confident that as I have built it, it will last a good few years and that's good enough for me at the moment.

[Tinker1947]

Well wants built it built, its a good job and other's can learn by any errors in this build, so just enjoy it now.

[ronaldo999]

My thoughts were to lay a damp course on the concrete base where the timber comes in contact, too late now though unless you can jack up the whole thing. Tanalised timber is treated but the lifespan will be severly reduced by being in contact with the concrete. The wood will draw any moisture up through the concrete. Sorry to put a downer on it. I am sure you will get many years out of it but the damp course would have given you more.

[robin-m]

Ronaldo, you haven't put a downer on it. I'm going to unbolt the frame then raise the whole structure by a few inches and slide in some dpc. It shouldn't be too difficult and the structure is strong enough to take it. Right now though I'm concentrating on the pier. Last week a length of 140mm mild steel tube and some steel sheet was delivered. My welding skills are pretty poor but should be good enough to fabricate what I need. I'll update the thread when I have some finished bits..

Robin

[robin-m]

The pier has now been welded together and sprayed. My welding won't win any prizes for neatness but the joints are solid which is the main thing

The adaptor for the mount was machined out of a billet of aluminium. I still have to drill and tap a hole for the locating pin but I'm almost there.

Next, automating the dome rotation. I also think I've worked out a mechanism to open and lose the dome as well but that's a way off yet...

[fwm891]

All looking very nice indeed

[robin-m]

It's been a while since I updated this.. The dome has been operational for a while with power and a built in computer however time constraints have prevented me from getting the automation side sorted which has been annoying. Having to go outside every 20 mins or so to jog the dome around has been a real pain so I've finally knuckled down to getting at least the slaving to the scope sorted. To that end a carrier for a 3.1 nm stepper has been built, the stepper driver is controlled by an arduino which also connects to a magnetometer for azimuth readings. I've written an ASCOM driver for the thing and everything tests okay. All I need now is to bolt it into the dome and wait for clear skies... (if they ever come back again!)

[Gina]

Looks good

[pmlogg]

I'll be really interested to read/see more about the slaving system, how it will be bolted to the dome to deliver drive to it.

So far I've only seen details of one DIY system for Pulsar Domes - by GeoC (DIY -Dome Automation), put onto a 2.7m version. I don't think is yet directly slaved to the telescope. It like Pulsar's own system uses a battery mounted in the dome.