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The 6" weighs 9.5kg without the PST stack and D-ERF fitted. The PST stack weighs 1100g.
So that's 10.6kg total + the D-ERF & holder. Probably another 1.5kg at a guess.
Plus 0.5 kg for the tube rings. Say ~13kg in total? Quite a hefty OTA for a 150mm/ 6" f/10.
EDIT: The complete H-alpha 6" OTA weighs almost exactly 12kg with D-ERF and its cell.
I intend to add a dew heater band and foam dewshield but these weigh very little.
The figures below will be changed by making the 6" equal to 12kg.
I still need to order some shorter, M4 stainless steel screws to replace the temporary screws holding the OTA together. Stainless steel fasteners are smarter and don't rust within a week of purchase. I see the nuts on the brand new Skywatcher tube rings are already rusting! They haven't even been used yet! This is unforgivable for a commercial product expected to be exposed to the weather, thermal cycling and dew. Penny pinching gone raving mad!
Meanwhile, the
7" main tube + focuser weigh 10.65kg.The tube rings are 2kg + 1kg for the 2" solar prism.
So that's 14kg + 5kg for the 180mm objective = say ~20kg total!
Difference = 20:13. So the balance of the two OTAs [placed side by side] on crossbars, mounted on the saddle, needs some reworking since my last post on the subject.
20kg x 4" offset = 80 kg/inches moment. [4" = 100mm]
20kg x 3.5" offset = 70kg/inches moment. [3.5" =89mm]
20kg x 3" offset = 60kg/inches moment. [3" = 75mm]
80/13 = 6.1 inches offset [6" OTA]
70/13 = 5.4 inches offset [6" OTA]
60/13 = 4.6 inches offset [6" OTA]
The C of Ms of the two OTAs can be offset from the saddle center line/declination shaft by these ratios. Depending how far apart the OTAs need to be to avoid obstructing the hinged tube rings as they are opened and closed. Placing the thumbscrews between the OTAs solves the ring/tube collision problem. At the cost of being more difficult to reach.
See images. Offsets not to scale but merely for illustration.
Counterbalancing: Both OTAs together weigh 33kg. The offsets from the PA relative to the center of mass of the counterweights is roughly 40 : 55. [1:1.375] So the CWts have the leverage advantage thanks to greater moment. 33/1.375 = 24.
Five x 5kg counterweights should balance both OTAs with enough spare to add sliding [tube balancing] weights on the OTA side. The 5kg weights are 1" thick so need only 5" of Declination shaft free. The counterweights can be adjusted along the shaft for final balance using spacers. Provided the mounting can manage 25 + 33kg = 58kg. I have had three telescopes at a time so have already proven the load capacity. Four weights could be moved to the far end of the Dec shaft if so desired.
Saturday 15th: Another storm is due to hit us tomorrow [Sunday.] I shan't bother to fit the telescopes until afterwards. Meanwhile I can be checking the exact balance points of the telescopes to save fiddling later. It is often a real struggle pushing a heavy refractor up through the rings to find the exact balance point. Particularly when you can't reach the upper rings by several feet. Climbing a stepladder with over 7' and 40lbs of telescope under one arm is an extreme sport IMO. A bit like Highland Games, caber tossing, but practiced indoors!
I have "storm-proofed" the dome with four ratchet straps from the zenith board down to the pier. All the electronics have gone into hiding and the mounting covered in a tarpaulin. The shutters are facing SSW.
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