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Monday: I have to collect my new compact pulleys from the local parcel shop. Hopefully these will offer lower friction when lowering OTAs. Collected, but they are quite tiny so difficult to thread. Despite which they run very freely on the 5mm rope once the ropes are in place. Provided, that is, the ropes do not cross.
The answer seems to be to organize the ropes with the pulleys quite close to each other. Then, once the are separated they will have a minimum of rope crossings. I'm very tempted to buy the next larger size for more separation and greater freedom between the pulleys. These things really are almost jewel-like in appearance with their shiny stainless steel.
I
fixed a 2 meter [6'6"] long alloy pole to the OTA to check dome
clearances more easily as I slewed around. Only to discover that ideally
I need to move the mounting base a full 30cm [12"] to the south to be
dynamically symmetrical with the dome.The big GEM's natural offset pushes the center of rotation [where the lines of the axes cross in the Dec housing] well to the north. The heavy support fork leans the opposite way but the PA leans north too.
Quite how this bodily movement of the mounting will be accomplished is quite another matter. Extending the thick plywood, top plate of the pier would be dead easy. But then the lower halves of longer telescopes would hit the pier when pointing up high. Which is a complete non-starter unless more frequent meridian flips become acceptable.
I could chop off the pier at floor level and add a tubular pier top somehow. Or, even make a leaning top section if it would help. All this assumes that I can still climb the internal stepladder up through the pier. Which can't be taken for granted with most pier modifications to the present, hollow, pyramidal section. The larger square, formed by the pyramid at lower heights, could be used to offset a tubular pier extension.
A suitable counterweight at the focuser end would solve most of my mounting's spherical asymmetry. The weight would allow the straight refractor to be shoved much further up through the rings. Though that wouldn't help with the 10" f/8 Newtonian mirror waiting patiently for its latest reincarnation.
I had rather imagined a parallel layout in the same, square section, Porsa tubing as the folded refractor. Fixed side by side on the big GEM they would be absolutely massive! Over 6'6" x 2' x 1' in Olde Money. Or 2m x 60cm x 30cm in New Fangled.
Another way of reducing the northerly bias [slightly] is to move the 11" wormwheel to the bottom of the PA. This would move the axis cross about an inch and half south and lower it about 2" into the bargain. The downside is finding room for the worm and motor assembly, lower down, even if the wheel missed the mounting. Which is why I never bothered to pursue that particular layout at the time.
The worm assembly could be mounted on top of the PA housing but it would look very 'untidy.' Not to mention its vulnerability to knocks and bumps during fitting and removing OTAs.
The mounting base would have to be completely redesigned to find room underneath the 11" wheel for the motor and worm. Unfortunately I haven't found any more 20mm scrap aluminium. It is very unfortunate that I so badly misjudged true north when planting the foundations for the pyramidal pier. The mounting is badly skewed on its plywood platform. Which means chainsaw wood butchery to find room for the motor underneath.Extending the pier's top plate south, even by a couple of inches, would make much more room underneath. The image gives a rough idea of what is needed. Had the pier been rotated north the entire octagonal building would have had to follow suit. Or the entrance doors would probably have been obstructed by a pyramid leg.
Putting the motor/worm assembly on the side of the PA housing is also possible but would probably look like an extremely clumsy afterthought. I'll have to continue to mull all the possibilities. Leaving a problem to stew unsupervised often produces a much better final result.
Aha? The tines on the mounting's supporting fork could be shifted a couple of inches south. That would mean drilling and tapping new holes from underneath. It would certainly provide lots more clearance from the hefty base plate to allow the worm/motor assembly to be hung underneath.
The motor/worm support plate would be moved down too. Once inverted it would provide exactly the same drive geometry without any other change. Then the entire mounting would be moved to the edge of the pier plate. Another couple of inches gained towards the south. Probably leading to 6" overall?
That is around half the present northerly bias of the Dec/PA crossing point. Moreover, the mounting base plate would see a much more even load. At present the load is cantilevered outside its own footprint towards the north.The gain would mean I could use the straight tubed OTA without hitting the dome support ring. And/Or reduce the necessary counterweight required to balance the typically, nose heavy refractor. This would mean having to disassemble the heavy mounting components, the gains might be worth all the effort. The head conjoined, folding stepladders and chain hoist would be needed for increased safety. I'm not sure I can trust the block and tackle just dangling from the top of the dome. Even if the dome survived it could open up all of the panel joints.
It all looks so easy until I measure the height of the worm/motor assembly's overhang beyond the PA housing at 12cm. Finding room underneath the mounting plate is too problematic. The Astromount[UK] puts the motor on the side of the PA housing but I think it would make mine too vulnerable to collisions with the OTA.
Click on any image for an enlargement.
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