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Thread: Flexure/stiction - or something else

  1. #11
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    Default Re: Flexure/stiction - or something else



    Quote Originally Posted by UlteriorModem View Post
    Your dither is off the charts crazy high! Also did not see any real 'cool down' from it either.

    it might just be it is struggeling to recover from the dithers.

    Oh yea the first calibration was not great.
    The cooldown is set to 10 seconds. That is set in BYEOS, don't know if that would show in the PHD log. I can certainly increase it. I have no idea how to tell how well the calibration went just yet, but I'll figure it out.

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  2. #12
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    Default Re: Flexure/stiction - or something else

    You may have some thin cloud cover up there and losing the star.
    My eyes
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  4. #13
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    Default Re: Flexure/stiction - or something else

    Quote Originally Posted by Sundedo View Post
    This is what I use to read my logs

    PHD2 Log Viewer - PHD2 Guiding
    Don - what a great tool - Thanks! I now see what Tom meant by bad calibration, they were a bit off-axis. I never did any drift alignment that night, as I had trouble getting everything going and was running later than I wanted to be.

    Quote Originally Posted by Leveye View Post
    You may have some thin cloud cover up there and losing the star.
    There were some high thin clouds passing through that night, not much wind, if any at all.


    Bob
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    Default Re: Flexure/stiction - or something else

    Try running some subs without dither just to rule it out. Like I said its kind of aggressive.
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  7. #15
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    Default Re: Flexure/stiction - or something else

    Quote Originally Posted by UlteriorModem View Post
    Try running some subs without dither just to rule it out. Like I said its kind of aggressive.
    I am unwilling to give up the benefits of dithering, but I will bump up the cooldown time from 10 to 30 seconds and see if that reduces the occurrences, or the length of the trails. Thinking about the pattern I am seeing, it makes sense it is something either at the beginning or end of the exposure, a bright star point with a dim trail. Either the guiding is off at the beginning of the sub and the trail is created while reaching the final position, or it is happening at the end of the sub, with the guiding going off just before the shutter closes. Given those possibilities, the trail at the beginning of the sub makes more sense. There is nothing happening at the end of the sub to create motion, but you are right, dithering runs before the shutter reopens for the next sub.

    Thanks to all for the fresh eyes, the tools, the suggestions, and your willingness to help. I think Tom may be on to something here and will test it out if I can get a clear night for imaging soon.

    Bob
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    Default Re: Flexure/stiction - or something else

    It would be consistent with flipping over in DEC due to an imbalance form a nearly-balanced situation. Maybe a bit of counterbalance in DEC would fix it.
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  10. #17
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    Default Re: Flexure/stiction - or something else

    Quote Originally Posted by CamelHat View Post
    It would be consistent with flipping over in DEC due to an imbalance form a nearly-balanced situation. Maybe a bit of counterbalance in DEC would fix it.
    Thanks for the heads-up on that. I admit to concentrating on making sure I am East-heavy for RA. I believe the DEC preference is to be slightly mirror-end heavy on a Newt. Is that correct?

    Bob
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    Default Re: Flexure/stiction - or something else

    Other way round the 'objective' end heavy or in a newts case the 'front' of the scope so that the motors are 'lifting' the load instead of lowering it.

    Still did not address if you can reduce the amount of movement for a dither.
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    Default Re: Flexure/stiction - or something else

    Quote Originally Posted by UlteriorModem View Post
    Other way round the 'objective' end heavy or in a newts case the 'front' of the scope so that the motors are 'lifting' the load instead of lowering it.

    Still did not address if you can reduce the amount of movement for a dither.
    I'm not sure the concept of "lifting the load" makes much sense to me on the DEC axis. The scope could be moving in either direction in DEC, assuming the polar alignment is good. Ideally it wouldn't move at all in DEC. It is a bit different than East heavy for RA. In that case it is easy to see how being east-heavy keeps the RA gear engaged.

    About the dither, I really don't want to reduce the amount or the randomness, so I propose making the cooldown period longer. It is currently 10 seconds, and I will raise that to 30. In actual use the sequence using BYEOS is 1) the sub exposure ends, 2) the mount is dithered, 3) the cooldown period begins, and 4) after the cooldown period the next sub starts. In other words, the dithering doesn't take up part of the cooldown period, they are two separate actions. After I looked at the graph (thanks for the pointer to the tool, Don) I can see wide swings in Dec that roughly (but not exactly, and not one for one) match up with the exposure end and dither times for the first half of the shooting run. By swings I am talking 30 arcsec at a time, and always in the same direction. It takes a few guiding pulses to get the plot back to the line, then things level out until the next spike occurs. Interestingly in the last 30 minutes of the run, this behavior doesn't appear at all.

    It is just weird! What else can I say. I am now wondering if there is some sort of DEC backlash in play. Too many variables!

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    Default Re: Flexure/stiction - or something else

    Quote Originally Posted by bobharmony View Post
    No coiled cables, the one that runs from the starshoot autoguider camera to the mount autoguide port is flat. I have setup for ASCOM control in the past (mostly to upgrade the hand controller firmware, and I am thinking of going that route for autoguiding as well, which will reduce the number of cables coming off the OTA by one - and eliminate the flat cable entirely. Thanks for the suggestion.

    Bob
    You don't have a coiled cord from the R.A. axis to the Dec.? I do and I have to make sure it's set on the R.A. housing properly or it drags like crazy...
    Jim
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