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Thread: Rough guiding on RA axis CGX-L

  1. #1
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    Default Rough guiding on RA axis CGX-L



    I have my PA down pretty good have a look at this calibration graph.

    Calibration 1 by Tom Whit, on Flickr

    But the guiding on RA is really ragged. I thought the guiding pulses were too high but when I make them lower it hangs out even further!

    Here is an example.

    Guiding 1 by Tom Whit, on Flickr

    It was balanced east heavy and nose heavy. I have tried neutral balance too with similar results. Is there some way to change the guiding rate? I know the nexstar has a guide rate setting but I think that is only for ST4 input.

    Oh I am using pulse guiding which goes through the handset.
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    Default Re: Rough guiding on RA axis CGX-L

    You can change the guiding rate in the HC... I'm almost certain of it. Where the backlash adjustment is, I believe...
    Yeah, that's excessive.
    your scatter graph seems to be bobbing up and down, (if yours is like mine and 90° out). If not, it's bobbing side to side...
    as well as hanging off to one side of the bullseye...


    Are you using resist switch or Hysteresis?
    without seeing the full screen for PHD, it's tough...
    I'd like to know the guiding exposure... 1-1.5 sec might be OK if seeing permits...
    the Osc. index number would be handy as well...
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    Jim
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    Default Re: Rough guiding on RA axis CGX-L

    Yes I know the guide rate can be changed but I 'thought' it was only for guiding through the ST4 port.

    But I will give it a try cant hurt.

    The 'bobbing' is side to side reflecting the scatter on the RA axis.

    Not sure why dec was 'hanging' below the centerline.
    Last edited by UlteriorModem; 08-21-2017 at 03:27 PM.
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    Default Re: Rough guiding on RA axis CGX-L

    I am not sure how the calibration graph tells you anything about polar alignment. The fact that Dec is hanging below the graph tells you that PA is off slightly. That is not necesarily a bad thing if the discrepancy is small, because it makes for unidirectional guiding inputs in Dec and therefore avoids backlash. Some people do this on purpose.

    You don't want to reduce the size of the RA guiding pulses. They need to be a bit more aggressive, since it takes a lot of them to make the mount respond. I see evidence of periodic error: the long rise and fall of the average RA position over the graph. So some PEC will help.

    Of more concern is the shorter-term oscillation, with about a 20-second period. The fact that it is so regular suggests it is a short-term periodic error from a defective gear in the drive train. PEC might be able to train it out; it is worth a try.
    Last edited by KathyNS; 08-21-2017 at 04:25 PM.
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    Default Re: Rough guiding on RA axis CGX-L

    I'm wondering if you still have some stickage in the gear meshing...
    I haven't had a chance to work on mine as we've had some actual SKY to work with...
    I will be trying that CN procedure though... Maybe you should take another look at it.
    Is this just since you made the last adjustments? Did you go a bit too far?

    Just kinda tossing suggestions out there... As I said, I have a little stickiness in RA as well, but not that much.
    I'm also carrying a 102mm f/6 scope and associated gear, so pretty evenly matched.

    Good Luck!
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    Default Re: Rough guiding on RA axis CGX-L

    Of more concern is the shorter-term oscillation, with about a 20-second period
    Thanks for the input all. I noticed that as well Kathy not sure where it is coming from but I will have to look into it. I was fairly sure I had the gear mesh in good shape but now not so much.

    I will try to get a look at it soon weather permitting
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    Default Re: Rough guiding on RA axis CGX-L

    Any update on this issue?

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    Default Re: Rough guiding on RA axis CGX-L

    I deal with this all the time with my CGEM-DX. I've all but given up on AP at the full FL (even at 0.7x). Been doing just Hyperstar or mounting my GT102 on the CGEM at 562mm. Saving up my pennies for a CEM120.

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    Default Re: Rough guiding on RA axis CGX-L

    I would open up the gear box and eyeball how long it takes for the worm to make one revolution. That 20 second periodic is caused by one of the fastest rotating components. Maybe the worm is bent because you leave it out all the time with weight and all, that may take its toll.

    PS I think you are right that the hand controller's rate works only for ST-4 not ASCOM.
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