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MCinAZ

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About MCinAZ

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  1. At Lowell's half-meter telescope, we've got a pair of 5 m USB 3.0 extenders which just barely reach from our computer shelf to the mount. One is dedicated to the mount itself, while the other is connected to a 12-port hub up by the telescopes. This works quite well, though we've seen issues with some devices if the extender is connected to a hub closer to the computer -- daisy-chaining USB hubs is generally not a good idea, so don't do that. The reason for so many ports is that we have two telescopes on the mount with several cameras along with focusers and other instruments. Not all will ever be operated simultaneously, however, so bandwidth isn't an issue. I had no previous experience with USB extenders, but so far I haven't seen any down side to using them.
  2. A variation of this has the motor and drive pinion on a pivoting plate attached to a fixed wall, with weights and/or springs used to provide engagement force. That makes for fixed wiring but still accommodates inconsistencies in the rack. There are generally three challenges associated with these types of drives. The first is start-up torque. If the motor spins up very quickly, the system can experience very large forces as the inertia of the roof is overcome. A high gear ratio which results in slower opening speed is probably the simplest solution, though in some cases DC motors are used and ramped-up to speed. If the gear drive doesn't allow for back drive (e.g., a typical worm drive), you also have to pay a bit of heed to ramp-down at the other end of travel. With a belt or spur gear reducer, you can probably get away with setting the limit switches such that the roof coasts closed approximately where you want it. A second concern is stalling during movement. If something jams, you want to be sure that some mechanism stops the motor before anything is damaged. As Stub noted, a fuse may be sufficient protection. This is always more of a concern with unattended operation since there probably won't be anyone around to hit the stop button if things start going wrong. Finally, loss of power or a drive failure needs to be considered. The last thing you want is the roof stuck open as weather is moving in. If there's a mechanism which allows override using a separate motor such as a surplus drill, that's a good start. But again, if there's a worm drive which may jam, you should probably consider options to disengage it entirely. This usually isn't too difficult with a pivoted mount if the contingency is considered during the design phase.
  3. Those latches look a lot like what I had in mind for my last build. I never found any at the time, but a pair of 6" C-clamps did the job. Not elegantly, but effectively, anyway.
  4. I saw the thermometer in my observatory in the Sonoran Desert wrapped past its 120 F/50 C limit on more than one occasion, with no detrimental effects on the equipment within. While I carried the Dell laptop computer into the house between sessions and never stored eyepieces in the observatory, telescopes and mounts stayed in the building year round. I would be concerned at those temperatures about cemented or oil-spaced optics but I doubt things will get nearly that warm in a temperate climate so far north.
  5. I've found that completing the design to the last imaginable detail in advance, along with giving consideration to the process required to complete construction, helps immensely. Of course, the second part of that is largely experienced-based -- you don't really think too much about how you're going to swing a hammer in some confined space unless you've previously created the need to do so. Perhaps the biggest error I've made (and consistently see others making) when it comes to a building with a movable roof is failure to fully consider the logistics associated with achieving adequate weatherproofing while still allowing for movement. It's not a trivial problem, but getting to the 90% completion point during construction then trying to find a solution is asking for trouble. The second and third roll-off builds I managed were much more successful only because, unlike the first build, I used a CAD program to determine where every piece of lumber and trim would go before the first shovel full of dirt was moved. It's so much easier to move a 2x4 or add 1/2" to the width of the roof trusses on a computer screen than at a building site.
  6. You may try contacting Dave Herald to see if he can help you either obtain elements which work with your software, or perhaps better, a provide a utility so that you can download and convert them yourself. The other option is to use Hristo Pavlov's OccultWatcher program, though I don't know if XP is still supported. If all else fails, you could request predictions for your locale from the folks at IOTA.
  7. Do you see much thunderstorm activity in Somerset? If so, you may want to consider running optical fiber from the house to the observatory for your network connection. We lost a PC at Lowell a couple of years ago due to a nearby ground strike. I was told that there was literally a hole in the circuit board in the area where previously there had been a serial connector. At that particular facility, the control room is perhaps 15 m from the dome. We still have one RS-232 run between the two buildings, but both ends have to be left disconnected through our summer storm season. (One of my upcoming projects: replace that copper run.) I hadn't read the particular article that you referenced, but I'm generally aware of activities to determine sizes and profiles of outer solar system objects using lots of amateur class telescopes. Some of the folks involved in observing occultations of 2014 MU69 in preparation for the recent New Horizons flyby were amateurs, one of whom I know from my own occultation work here in Arizona. Larry Wasserman published an interesting article about this work on Lowell's site last week. https://lowell.edu/chasing-shadows-to-measure-the-size-of-ultima-thule/
  8. I'm curious to know how you attached the critter barrier to the floor joists. Are there cleats on the joists to support the plywood? This is a very good looking build. With some good weather, it looks like you should be able to finish the major work in a couple of weekends. Then it will be time to decide on an observing program which utilizes the facility sufficient to justify all the money, time and effort. After completing my last observatory, I found myself feeling a bit guilty if the roof wasn't open on clear, moonless nights. Perhaps you could take up occultation timing...
  9. Be careful to avoid creating a water trap if you put the EPDM on the inside of the joint. Not that I've ever done such a thing, mind you. [Not after the first build, anyway.]
  10. You may want to consider consolidating to two supplies, a larger capacity model for the drives, heaters, filter wheel and focuser, and a smaller, very clean supply for the camera. While the camera will certainly incorporate internal linear regulators for the critical rails, keeping the input voltage as stable as possible can only eliminate some potential noise sources. As for voltage levels, I would review the specifications for each piece of equipment to be sure that you're supplying a value which is within design limits. Some telescope drives which will operate at 12 V can tolerate and may perform a bit better at higher voltages, but that may not be true for other equipment in your inventory. I've found re-purposed laptop power supplies to be suitable for applications requiring stable DC voltages across a range of load conditions. Most of your equipment won't be affected by a small AC component or occasional voltage spikes superimposed on the DC level, but it isn't a bad idea to measure the AC voltage level at the load end when everything is operating. This would be most important for your camera, but if you dedicate a good quality supply to that device, you should encounter no difficulties. As discussed in James's build thread, be sure to adequately size your DC supply cables if they are of any significant length to avoid series drops.
  11. Current rating (as James is most likely aware) is a function of cable length, whereas voltage rating is determined by insulation material and thickness. Here in the US, 15 A circuits are generally wired using 14 gauge wire, while 12 gauge wire is used for 20 A circuits in residential applications. That's a relatively useful guide, but assumes wire lengths typically found in single family housing. A competent electrician will use larger wire to supply outlets at the far end of a McMansion. Cables for dew heaters, thermoelectric coolers, telescope drives and any other high current (whether continuous or surge) applications requires some forethought. It's never a bad idea to measure the voltage at the load end under operating conditions after (or even before) pulling a new cable if there's any question about series drops. As for conduits supplying the piers, my experience suggests making them plenty large and leaving a pull string in place. In the three years I had my last observatory, I changed wiring configurations at least half a dozen times as I added and replaced equipment. I supplied only low voltage to the pier, so I eventually needed separate 16 V, 12 V and 5 V runs in addition to a couple of separate USB links, Gb ethernet and one or two dedicated control/status cables. My conduit was about 60 mm ID, which was plenty for the cables themselves, but pulling the last few cables with connectors attached through the elbows was a bit of a challenge.
  12. A nice looking build. For scale, how tall is the door opening on the west wall? I can't see well enough from the pictures if you have gussets at the top of the vertical portion of the rolling roof where it meets the pitched supports. I would be a bit concerned about parallel shifting under wind or snow loads without some type of bracing in the east-west direction. Of course, this may be addressed when you close in the south gable. Is snow load a concern in Somerset? It wasn't for the three observatories I built in the Phoenix area, but certainly is in northern Arizona.
  13. That building had a small roof, so I needed only four wheels to support it. Each had its own lift mechanism. I chose that approach because the observatory was in the Sonoran Desert where we get a lot of dust storms in the summer. It all worked quite well in the end -- the lift mechanism proved to be entirely reliable and I had no worries about rain or dust intrusion regardless of weather conditions. I bought a small (15 l) compressor to operate the pneumatic cylinders. Provided that I remembered to close the valve on the tank immediately after opening or closing the week, it stored sufficient air for three to five nights of use before needed to be repressurized. I helped a friend build a similar observatory, also in the desert, but we took the more conventional approach and used fixed tracks, relatively small gaps and baffles built into the trim to minimize dust intrusion. While that building doesn't stay as clean through the summer as mine did, the owner finds the level of protection to be adequate. If I eventually build on my present property, I won't go with the lifts. There is much less airborne dust here in northern Arizona and I'm convinced that careful design and construction are sufficient. Apologies for straying from the thread topic.
  14. Though somewhat manual, I agree that turnbuckles are a good solution. I've used these on the two conventional roll-off observatories I've built. I recommend installing them at a about a 30 degree angle to horizontal. If you add stop nuts to the pair at one end of the roof, you can adjust then fix the close position, then use the other pair to pull the roof securely into place at the end of the night. Avoid light duty alumin(i)um parts you might find at a mass merchandiser. Though not on an observatory roof, a friend of mine had one of these fail when the threads pulled out of the Al block. The turnbuckle was used to set polar axis elevation on his German equatorial mount and the failure nearly resulted in his custom 0.35 m astrograph going all the way to the ground.
  15. My decidedly low-tech yet effective approach. I should note that the building incorporated pneumatic lifts so that when closed the perimeter of the roof rested on a foam seal. The C-clamps, one on each side, were only needed to keep the roof from lifting as it could not roll when lowered. We saw winds one night in excess of 110 kph and everything stayed where it belonged. It was my intention to find something similar to the latches Gina suggested but the C-clamps worked so well that I never pursued the notion. And now that the observatory has been decommissioned, I have a nice set of clamps for my workshop. If I still had a workshop. :-(
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