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Hi all This is my observatory build record I thought I'd share since there are always some things which are novel and worth repeating elsewhere. I had built a telescope OTA that turned out to be too big for my mount and dome together - i could get it on the mount but couldn't move it without snagging the dome. So I made the decision to sell the dome and make or buy a new one. I always prefer to make things but one came up on Ebay that was worth bidding for at the right price and, having fought off the competition, I made a trp down to Wiltshire to pick up a 2.7m second hand polaris glass-fibre dome. This is the existing building which has since moved to Birmingham... The replacement dome came down really easily into its component parts and into the truck. Cleaning up the parts from the silicon rubber used to seal it was another matter. I probably spent at least two afternoons using a pressure washer and eventually the falt blade from a plane as an effective means of removing the silicon. The dome then spent about two months sitting down the side alley in parts while I re-worked the plot. Being larger than the previous one in diameter, the concrete block the pier sat on had to be moved from the corner of the garden further in, to the new centre of the dome. Moreover, the dome walls of the polaris dome were half a metre shorter than the previous one. So I had to do something - either slice some height off my pier or raise the floor. Tee pier is a 12" tube of steel and I like it being tall to avoid the cricked neck syndrome. Also I didn't want to start slicing the end off or trying to cut a straight section out of the middle and re-welding. Quotes from companies were coming in at silly prices. So I raised the floor. After careful measurement and calculation, with some modelling of telescope size and dome clearances thrown in, I reckoned I needed to raise the floor by about 80 cm in the worst part of a slightly sloping garden. This was to be achieved by sinking 4 4x4" uprights in a square and laying decking on it. First I had to clear the existing concrete to allow a new pier block to be poured. out with the SDS drill and chisels and an hour later, with the use of a post hole digger, I have a 3' deep hle, 12" round with a 8" deep by 30" square flat slab excavated. The flat slab sides are framed with wood to hold the concrete when opoured and some rebar suk in the middle to reinforce the long stem. This is a smaller concrete pour than the last one. One big one had been enough to show me that its not really necessary to go massive as long as you go deep and stable. I recall 9 bags of ballast and 2 of cement and some postcrete I had lying around went into the hole, along with some brick ends etc to make up the space. The cenrew was marked by a bolt in the cement which was removed later. This bolt set into a hole in the base of the pier to allow easy marking of the base holes for drilling. The holes were drilled 25mm diameter by 8" deep for 20mm studding on a 18" square pattern. The alignment of the square around the centre mark was determined by sitting the pier level on the central stud and using a piece of studding bolted into the centre of the top of the pier, the length of the stud was adjusted by moving the bolts until Polaris just crested the top of the stud when viewed from the south reference mark on the top plate. Now I had the alignment, the pier was then placed on top with the studs bolted tight in it at full length while the mortar around the studs in their drilled holes set. The pier was essentially used both to locate the holes and to ensure that the bolts were all parallel as they set. Finally the pier was set to working height and accurately levelled. The four uprights were concreted in place on a square with 3m sides. Four 8" by 2" joists were bolted to these uprights using 9" bolts and fixing spikes, 2 bolts to each end, one joist to a side. Between these joists were fixed more joists using joist hangers on a 18" center spacing, except to allow enough space for the foot of the pier to be lifted through the floor, so there was a 20" spacing there between joist sides. I had been recommended to use joist ties rather than noggins. These went in really quickly and easily and stiffened the floor up significantly. The rest of the effort was just laying the 38mm redwod decking and screwing in 100s of screws. I eventually succumbed and bought myself a new drill to do the job with. The dome went on next, we had to play with the foot ring, the wall ring and the topping ring, trying to work out the relevant positions until we twigged they were all related to the door position. Once we had that, the rest just fell into place. Thousands of bolts later, the component parts of the dome were all in place ready for sealing. The foot ring screwed to the deck, the bolts all tightened using the drill to torque and sealing mastic used to close the gaps for waterproofing. Finally the foot ring was sealed on the outside using window frame low modulus rubber. It flowed easily into the decking ruts and gaps and seems to have taken well. Sealing out the dew that rolls off the roof. Issues to face have been: The original concrete was set in the ground where a compost heap had been. It had all dried out and contracted 8 inches. Hence the ground level was 8" lower than expected once uncovered. So I had to lower the entire decking by 8" or the height of a joist, or build up the concrete 8" higher than expected. I chose to lower the joists since at that point I hadn't put anything more than the 4 side joists in. For power I put in a small frame to mount an external waterproof socket pair at the end of 50m or armoured cable from the house. This has an eight- way individually switched distribution board plugged in to power the computer, screen and ethernet-over-power adapter. I also cut a new hole in the pier at the top - so there is now a pair of 4" holes, front and back and a new one at the decking height. This all helps with cable management inside the pier. The internal lighting of the dome I copied from elsewhere - a 8m strip of red leds was fitted around the dome under the top ring, controlled using one of those Ebay PWM controllers. At the minimum setting it is still a touch bright so needs a limiting resistor in series. I also built a curved desk which hangs off the top ring bolts and carries a monitor stand pillar. This shelf supports another longer shelf below, where the keyboard, mouse and light controller sit. it all works rather well actually. If anything it needs to be bigger, with holes for eyepieces in and enough space for a log book. The final twiddles include: Remote desktop screen at the telescope pier, its a usb touchscreen to present CDC maps. Add electric lock/unlock to the dome shutter. Continuing work going forward: Motorise the dome for rotation. I am removing two side centering wheels and attaching them to motors to drive on the inner overhanging dome lip and writing a dome driver in c# under ASCOM. Motorise the roof shutter. Its an up-and-over two-part shutter which slides on teflon sliders but is quite heavy. I have an idea to use 1mm wire rope to pull it up to the slot top on a winch and pull it back using the same size wire running in bike wire sheath along the slot to the bottom where it pulls the shutter down when the winch is reversed. Illuminate the steps. Its dark there - I have bought a PIR sensor to detect people approaching and will use this to turn on leds under the steps for footing . Since the wife also painted the door (see down) I thought I would also add a sound player with tardis noise playing when triggered. Add an external scope mount on top of one of the uprights. So I can do visual while photographing in the dome. Last but not east - the wife redid the door with some custom paintwork... And the dome interior with the telescope that caused all the grief in the first place - the 12" f/10 Cassegrain.
Hi, I need to lift off the dome of my 2.2 metre Pulsar observatory so I can smooth out the joints between the 4 sections. They are causing problems when the dome is rotated. When I bought the dome it was installed by Pulsar so I have no experience of lifting the dome on or off the walls. My plan is to use 4 Acrow props to do the lifting so I can do it as a one man operation. I assume that it is best to place the props outside the dome and lift using the edge of the dome. Can I ask anyone with experience of these Pulsar domes if this is the right way and are there any snags? Thanks, Hugh
Like many of us, I was a little bit peeved at the time it takes to move about 50-100Kg of kit, set it up, make all the electrical connections, polar align, calibrate the GOTO system and fix anything that has gone wrong (it always does) prior to starting out a session - and that's if it's still clear. And then there's the packing it away again at the end of the night. It was such a chore that unless the forecast was clear all night long I tended not to bother. To make my hobby enjoyable again, I needed an observatory. There are a number of options: 1) Roll-off roof 2) Roll-off shed 3) Clamshell 4) Dome These all have their pros and cons. 1 & 2 are cheap, but need additional garden space to roll them off. The way my garden was set up, and the location I wanted the observatory, meant that I discounted them. The only clamshell easily available in the UK is the SkyPod, and whilst I considered it for some time, I finally got put off by the trouble imaging straight up and the reports of leaks. So that left a dome. The problem with a dome is that they are expensive - and for imaging they need automating (even more expensive). Still, that seemed like the best solution for me. In The UK, the dome that is most easily available is the one from Pulsar observatories. It is available in 2.2 and 2.7m sizes and can be made in white or green (possibly other colours too, white and green are the only ones I have seen). I had seen a dome at a fellow astronomers house - and he had successfully motorized it which meant that I could follow his plans. I'm, OK at tinkering with things, and can actually even be good at it, but for expediencies sake I'd rather get something off the shelf and I'd be rather upset if I found that I couldn't motorize it as I wouldn't be able to image which is my only interest in the hobby. So when Pulsar adjusted their design (see later) and made a fully motorised observatory "off the shelf" an option I decided to go for it. I bought a dome, dome controller, shutter controller and a Shelyak Dome Tracker. Pulsar 2.2m Dome Oberservatory Shelyak Dome Tracker I took a while building the base in my garden - there's a separate thread for that. It needs at least a 2.4m circular or square concrete slab. I went the circular route as it's much harder to build. They suggest a 1m square base for the pier, but I decided 75cm would be more than enough. I made a £500 deposit by credit card (for the protection it offers) and then the rest was paid by bank transfer 3 months later when the dome was ready to deliver. Unfortunately they are built in Norwich and I live in Somerset, so there was a hefty delivery charge. They also offer to assemble everything for a small fee and given that I was into this for quite a sum already, I thought I may as well ensure it got set up properly. I bought an Astro Engineering pier from them too. On the appointed day the guys from Pulsar arrived and set about work, fortunately in good weather. They were finished by mid-afternoon and showed me how the observatory worked - as well as installing up the basic Shelyak Dome Tracker software on my PC. Unfortunately we hit a bit of a snag here, as it wouldn't work! I got a second laptop out, and fortunately it did work on that - but when I checked it again a few hours later after they had gone, it didn't work anymore. Time to pull my hair out! To cut a long story short, I had email communication with the guys from Shelyak and Pulsar over the next 24 hours - they identified a problem with a component not working properly at low temperatures (a December install) and they sent me a new unit. They also wrote a new driver, which meant that the faulty component wouldn't cause trouble anymore anyway. Good service. When I finally got permanent electricity installed to my observatory, I set up my kit properly. The dome moves by two motorised wheels (blue) pressing on the side of the dome. These are powered by a 12v 10a transformer. There is another wheel (the grey one) which is attached to a rotary encoder so the dome knows how far it has travelled. The "home" position is set by a metallic sensor - mine is at 290 degrees. You can see it in between the IR sensors below - it's just a bit of tin foil. When the dome is told to home itself, it rotates until it finds the home sensor and then sets its internal position to 290. From there on, it counts clockwise and anticlockwise motion via the rotary encoder. In addition to the computer control, the dome can be set to track at sidereal rate (or various fractions/multiples thereof - remember, the dome isn't equatorially mounted) if you didn't want to use a computer. The Shelyak unit is nicely hidden away behind the dome controller metalwork too. It connects to the computer via RS232, but they throw in a USB-RS232 cable in case you need one. The shutter mechanism is attached to the dome part which makes getting power to it more difficult. The solution that Pulsar have come up with is a 12V battery and a solar panel. To send signals from the Shelyak Dome Tracker, they have utilised an IR connection. The open/close shutter will thus only work when the dome is at the home position, as this is when the IR sensors are aligned. It closes the shutter by means of a chain and sprocket. There is a manual open/close button in addition to the computer control. To get the dome automated you need to enter a few details, such as the size of the observatory, the number of steps for a full revolution, the position of the pier how high the centre of the scope is above the rotation axis of the mount. After that, it's plain sailing - rather than use the normal ASCOM driver for the mount, you use the ASCOM Dome Control driver instead (comes with ASCOM) - which itself connects to the dome and to the mount. You slave the dome to the mount and then when you issue slew commands, it moves both the dome and the mount to the right position and keeps them there throughout the night. And this is it in action:
I have a steel pier for sale. This was purchased along with a pulsar dome and believe it is an older Pulsar model. The pier sat in a yard, exposed to the elements for a few years before I purchased it so there is some surface rust and flaking paint but will clean up nicely. £250 and buyer will need to collect from Suffolk.