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Old 02-08-2020, 10:50 PM
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5ash
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SW flex tube GOTO question

Hi , is balance important in these GOTO dobs ? I set my optical tube up with a pivot at the side bearing points and find the scope top heavy without an eyepiece. It takes more than 0.6kg to balance? Seems odd , Iím inclined to believe I should balance the scope When fully setup?
Grateful for any help , regards philip
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Old Yesterday, 12:51 AM
raymo
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Mounts that are gear driven, as opposed to ones that are belt or directly
driven, should not be well balanced when fully set up. All gear drives have some backlash in the system, and if the system is accurately balanced the
scope can flop backwards and forwards a little, and even a little movement of your target can be irritating. With equatorial mounts you have the added nuisance of tracking being affected when imaging. Your azimuth axis
wouldn't flop enough to matter, but the altitude axis needs to be balanced a bit nose heavy so that the motor which is raising the scope remains fully engaged all the time. 600g + possibly a heavy eyepiece seems a bit on the heavy side. I would velcro a 500gr weight onto the rear of the scope. You can
buy or make a bar with a sliding weight for Dobs.
raymo
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Old Yesterday, 07:31 AM
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The_bluester (Paul)
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You mean one like this? https://www.bintel.com.au/product/sk...v=322b26af01d5

I have a 10" one at home and it behaves well with everything from a little 10mm Plossl to my 30mm Nagler "Hand grenade" clone Explore Scientific EP so unless it is a really long way out I would not be too concerned. As Raymo said, in these it also helps keep the geartrain in tension.
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Old Yesterday, 08:39 AM
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5ash
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Thanks Raymo and Paul for the feedback , yes itís a 10Ē SW GOTO Paul. So should I put a weight on the mirror end as Raymo suggests , Iíve a magnetic weight of that size I can use.
Regards philip
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Old Yesterday, 12:07 PM
raymo
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Your magnetic weight would be ideal, remembering that on the rear of the scope it will be much nearer to the pivot point of the OTA, so will have much
less effect than an eyepiece or camera put into the focuser. Its good to limit the nose heaviness so as to put less strain on the motor.
raymo
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Old Yesterday, 12:10 PM
gaseous (Patrick)
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Either a magnetic weight or a small gym weight as suggested. I've put a long strip of velcro down the length of my 8" dob tube, with a small gym weight also with a velcro strip wrapped around it so it can be moved up or down depending on requirements. A decent 2" eyepiece will normally make the setup a little light at the mirror end in my experience.
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Old Yesterday, 03:07 PM
Startrek (Martin)
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I have a Skywatcher 12Ē Goto dob and have had no issues with centering accuracy once aligned slewing around the night sky from object to object with my Televue Coma corrector and 21mm Ethos hanging out from the focuser. Thatís a fair amount of torque/ weight to say the least
My base and scope are always precisely levelled
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  #8  
Old Yesterday, 06:12 PM
gaseous (Patrick)
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There must be a certain scope aperture at which the weight of the primary balances out most decent eyepiece weights- sounds like 12" might be the sweet spot.
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