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  1. #1

    Default Moonlite NiteCrawler Rotator PA Issue

    I've been having trouble getting the mechanical angles of my Moonlite NiteCrawler rotator/focuser to match up with the PA in ACP.

    The first thing I did was manually slew the rotator to 0 degrees. I took an image using MaxIm, analyzed it with Pinpoint and got an offset of about -4.5 degrees. Not great, but this alignment corresponded with my visual inspection.

    So this evening I tried using Scheduler to run dusk flats and the rotator was immediately told to rotate to the mechanical angle 254. Obviously nowhere near a PA=0 or PA=180. i'm not sure where that number came from. I tried using the calibrateguider and centerscope scripts to get the PA in ACP to match the 4.5 degree offset but the results were all over the board.

    I went ahead and set up a plan in Planner to take an image series. I manually rotated to mechanical=0 and then started the plan. The first thing that happened was the rotator was told to rotate to 71.2 degrees. As FocusMax went through its routine I noted that the rotated angle of the plate solve was 66.7 degrees (71.2-4.5=66.7). After FocusMax completed its focus run ACP took a pointing image and saw that there was a 71.1 degree rotator error. The rotator was told to move to 142.3 degrees. Not sure what is going on. I've attached the log of the Plan run.

    I do know the NiteCrawler is set up to move to a position in either direction using the shortest path. My limits are set at +190 and -190 in order to avoid cord wrap.

    Suggestions welcome.
    Attached Files Attached Files
    Dan Simpson
    Galisteo Observatory
    Santa Fe, NM

  2. #2
    Join Date
    Oct 2005
    Location
    Mesa, AZ
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    Hi Dan --

    ACP does not care at all what the difference between the mechanical rotator PA and the sky PA is, as long as it stays constant. One thing to check is the rotation direction. It must be counterclockwise against the sky. Let's get back to basics:

    Don't do anything manually with the rotator. Just do a straight ACP run of a couple of images unguided and without focusing (autofocus as needed before this run). No scheduler. Just a simple ACP/AcquireImages run with some different PAs. Here's one that should do it for your location at 8PM this evening:

    #interval 60
    #binning 2
    #filter Luminance
    #posang 0
    test1<tab>06:25:17<tab>-00:09:40
    #posang 90
    test2<tab>06:25:17<tab>-00:09:40
    #posang 220
    test3<tab>06:25:17<tab>-00:09:40

    Then send me the log. I need to see at least a couple of images to see what's going on with the mechanical to sky translations.
    -- Bob

  3. #3

    Default

    Hi Bob,
    Thanks for the help. I believe my problem with the difference between the mechanical rotator PA and the sky PA is it doesn't seem to stay consistent. At least that's the way I'm seeing it.

    In any case, thanks for the script. I'll see what we come up with tonight.

    I'll leave the slew constraints as is at least initially. My thought is to modify the slew constraints so that the rotator rotates in one direction only (CCW) and then run the script again. Does that make sense?

    And, just to clarify, using the FOVI I've set up in TheSkyX as a guide, if the FOVI rotates in the CCW direction on the screen that is the direction we're looking for, correct?
    Thanks,
    Dan Simpson
    Galisteo Observatory
    Santa Fe, NM

  4. #4
    Join Date
    Oct 2005
    Location
    Mesa, AZ
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    Ahhhh. if the offset doesn't stay constant, then you'll never get there from here. Something is slipping, the stepper motor is "cogging" (insufficient power supply or too stiff or overloaded). I don't know what you mean "slew constraints". From my perspective, the rotator simply must go to the commanded mechanical PA and tell me when it has gotten there. How it gets there, and whether it has to reverse or ??? to manage cord wrapping is not for me to know.
    -- Bob

  5. #5

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    Hi Bob,
    I put together a plan that included the images in your script and ran it a few minute ago. Seemed to go fine.

    I've zipped up a folder with the results but the DC3 site isn't letting me upload (It's 8473kb) I find I can't even upload one photo at a time. I did manage to upload the log file. I could email the zipped photos directly to you or set up a link to a shared folder or whatever, let me know how to proceed.

    I've checked and rechecked the rotator and cables. None of the cables are snagging or hanging up at all. I can manually slew the rotator (using the Moonlite App or TheSkyX) to all points without any problem. Manually operated, the rotator always lands right where I ask it to.

    By slew constraints I'm referring to the NightCrawler setup dialog where I can set the rotation to occur in one direction or both as well as set limits on how far each direction can rotate. Both directions is nice as it can take the short way around to a target. I have mine set to rotate up to 190 degrees in each direction. I wasn't sure if that was causing a problem with ACP but it sounds like it isn't.

    Let me know how to get you copies of the .fit files.
    Thanks,
    Attached Files Attached Files
    Dan Simpson
    Galisteo Observatory
    Santa Fe, NM

  6. #6
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    For PA of 0

    It thought it was already at 0

    03:54:41 (no rotate, already close enough to desired PA)

    03:55:20 Imager sky position angle is 185.8 deg.
    03:55:20 Rotator mech. position angle is 358.5 deg.
    03:55:21 PA error of 174.2 deg. detected. Correcting...

    It now knows your camera is upside down and will make that 180-ish degree correction. It takes the image and starts a pre-rotate to 90 for your next target

    04:02:02 Start rotate to PA 90.0 deg (raw rotator angle 251.1)

    04:01:00 Imager sky position angle is 11.6 deg.
    04:01:00 Rotator mech. position angle is 172.7 deg.

    It missed by 11 degrees. I would say the rotator is slipping or cogging. This is a big error.

    Now for a 90 degree PA

    04:03:53 (no rotate, already close enough to desired PA)

    It sees that the pre-rotate went to the correct 251 ish degrees which would be right for 90 PA per the above

    04:05:10 Imager sky position angle is 293.2 deg.
    04:05:10 Rotator mech. position angle is 251.1 deg.

    Wow! The PA ended up at 293 not 90. What happened?

    04:06:13 Start rotate to PA 220.0 deg (raw rotator angle 177.9) Pre-rotate

    Still has a 40 degree difference between sky and mech, not 180.

    04:06:25 Imager sky position angle is 293.2 deg.
    04:06:25 Rotator mech. position angle is 251.1 deg.

    Same with the final image.

    And the PA 240 one

    04:09:15 Imager sky position angle is 6.4 deg.
    04:09:15 Rotator mech. position angle is 177.9 deg.

    Well this time it went to 177.9 mechanical but the sky PA is now 6 degrees?

    04:10:29 Imager sky position angle is 6.4 deg.
    04:10:29 Rotator mech. position angle is 177.9 deg.

    and again for the final image.

    Conclusion
    : This rotator is not working right. Did you check the rotation direction? Is there a reverse switch? Early Optec rotators had to be reversed to be correct for the convention of PA (COUNTER-clockwise against the sky).
    -- Bob

  7. #7

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    Hi Bob,
    Thanks for looking at the log. I thought things seemed out of wack. However, I don't believe this is a mechanical problem. Using the NiteCrawler Remote program or connecting via TheSkyX I have sent the rotator to any point I want consistently and without fail. There is no sign of cogging or slippage.

    I'm wondering if this is an ASCOM driver issue. I've attached snips of the driver properties setup dialog with my original setup and my new settings. I've taken out the bi-directional choice and checked the reverse direction box.

    After updating my setting I've connected manually and I'm again able to slew to any point except now the rotator only rotates in a positive direction. Positive in the sense that upon selecting a destination position the position numbers go up or down in sync with how the TheSkyX FOVI is rotating. If the position numbers are increasing the FOVI is rotating in the CCW direction on TheSkyX screen.

    The weather has taken a turn for the worse here so it may be a couple of days before I get a chance to rerun the script. We'll see how it goes.
    Thanks,
    Attached Images Attached Images
    Dan Simpson
    Galisteo Observatory
    Santa Fe, NM

  8. #8
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    OK I mentioned reversal as a possible issue. Hopefully this will sort it out. It's definitely not doing what it is supposed to :-)
    -- Bob

  9. #9

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    Hi Bob,
    So last night turned out basically cloud free and I was able to work the script using various settings for the rotator. I believe I've solved the problem by checking the Reverse rotation direction box and telling the rotator to rotate the full 360 degrees in only one direction.

    One thing I found was when ACP started the script it would immediately send the rotator off to an incorrect location using the previous incorrect information. This would happen even when I had manually set the camera at least close to sky PA=0.0 (using a previous manual image and a PinPoint solve). ACP would immediately tell the rotator to slew to the wrong location and just wouldn't find its way back to the correct orientation. I finally tried hitting the rotator abort button in TheSkyX before the rotator had moved more than a degree or so. At that point, when ACP figured the expected rotation was completed, it took a final plate solve, found the PA was close, made a small adjustment and started the main image. After this initial calibration got completed correctly the subsequent runs seem to be completing successfully. I'm going to try a few more with different angles to be certain but it looks very promising.

    Question: Is there a script available that would simply take an image, determine the mechanical rotator/sky PA offset, slew the rotator to sky PA=0, take another image to plate solve and confirm the offset and, finally, put the result where in the place where ACP will refer to it when starting subsequent image runs?
    Thanks,
    Dan Simpson
    Galisteo Observatory
    Santa Fe, NM

  10. #10
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    Default Moonlite NiteCrawler Rotator PA Issue

    Having analyzed your log and reported in detail, and responded to your other post about the meaning of PA and which side of the meridian the target is on, I don’t know what more to say at this point, so let’s set up a phone conversation for next week when we’re back in the office. No worries, I’m not going to give up on this.

    PS the normal logic of ACP does the rotate-measure-correct for every target, and saves the offset for the next target. No separate script needed.
    -- Bob

 

 

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