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Equipment Discussions >> Mounts

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khobar95
member


Reged: 01/08/12

Loc: Arizona
SSAG & PHD odd behavior? new
      #5452943 - 10/03/12 12:31 AM

I just received my SSAG autoguider today and thought I'd try it out this evening.

Previous attempts at autoguiding used a webcam type setup with PHD and controlled my CG5GT via serial port. PHD would calibrate, lock on, and guide for a short amount of time (a few minutes), then would seem to get tired and no longer send appropriate compensation controls to the mount. Thus the star would start drifting.

That's exactly what I'm seeing using the ST4 port. I see PHD go through its cal routine, and it locks, and it guides for a little bit and then the star starts to drift.

Do I have to take out the backlash compensation? Is there anything else I need to do (other than polar align) to get this to work successfully? Thanks.


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Raginar
Postmaster
*****

Reged: 10/19/10

Loc: Rapid CIty, SD
Re: SSAG & PHD odd behavior? new [Re: khobar95]
      #5453057 - 10/03/12 04:19 AM

Take out all your backlash compensation. Just check all your configurations again. Reboot the computer (silly, I know). Finally, try downloading a new copy and reinstall. I've had it where the software goes wonky and just won't guide.

If all else fails, you can get a voltmeter and check to make sure your St-4 port is sending commands and then trace it back to the mount.

Chris


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khobar95
member


Reged: 01/08/12

Loc: Arizona
Re: SSAG & PHD odd behavior? new [Re: Raginar]
      #5453293 - 10/03/12 09:55 AM

Hi Chris and thanks.

I will do as you suggest.


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MikeCMP
super member
*****

Reged: 07/12/11

Loc: Chardon OH
Re: SSAG & PHD odd behavior? new [Re: khobar95]
      #5453850 - 10/03/12 04:51 PM

You might also increase the max guide pulse phd can send to the mount. What seems to happen to me is initially the guider needs to make huge corrections after calibrations for some reason, then settles down. I set the max to 1000ms or something like that. Once it settles, it sends very smal corrections, but if your polar alignment is significantly off you could need to send bigger corrections.

Mike


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Craig H
super member


Reged: 04/08/09

Loc: Portland, OR
Re: SSAG & PHD odd behavior? new [Re: MikeCMP]
      #5454423 - 10/04/12 12:34 AM

Are you sure the issue is with the software? If you see at the bottom of the PHD window that corrections are being sent to the mount then it's doing its job. I have/had a similar issue as you describe but in my case the issue was not SSAG/PHD but the mount. While I love the CG5 for visual, it's a bit more of a challenge to get it to track for good AP use. A couple of suggestions to get better performance that improved things for me

(1) polar alignment - I once thought I could just guide my way out of polar alignment, but the more you're off the bigger the correction signal PHD has to send and the greater the odds of a big swing in your guiding graph
(2) Try preventing PHD from switching the DEC guiding -- if it flips from north to south backlash'll kill you
(3) Make sure the max pulse guide PHD can send to the mount is enough to keep you on track, as Mike suggested above. I think I went up to 1200 ms
(4) If you haven't already, try taking your DEC axis apart, and replace the *BLEEP* sticky original grease with a good white lithium grease and maybe give the shaft a good buff with emery cloth if you feel any roughness anywhere. Instructions for this can be found on www.astronomyboy.com.

After doing the above I was getting reliable two-to-three minute subs, at 5-min subs I was about 60-70% success rate, and once in a while I could try to sneak in a few 8-min subs. Others more skilled in the art may be getting better performance :-)

Hope this helps

Craig.


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khobar95
member


Reged: 01/08/12

Loc: Arizona
Re: SSAG & PHD odd behavior? new [Re: Craig H]
      #5455123 - 10/04/12 01:40 PM

Outstanding - thanks!

It seems unlikely to be an issue with the software.

Polar alignment - I have not done a precision polar alignment using the drift method. I do a rough polar align, then a 2-star align plus a calibration star.

Prior to getting the SSAG I could take 20 second exposures without too much error. I am hoping that even with a non-precision alignment I can get 60 seconds or more.

Hmm...I have now removed backlash compensation. I'll see what happens and report back. Is the N/S DEC thing a setting?

3) I will take a look at increasing the pulse width. I suspect this will likely fix much of my issue.

4) Oh boy, tell me about it! I have cleaned all that glue out and replaced it with white lithium grease. I did run some emery cloth over some rough spots but no where near a pro job.

I'm hoping for clear skies tonight to try out the suggestions!


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Craig H
super member


Reged: 04/08/09

Loc: Portland, OR
Re: SSAG & PHD odd behavior? [Re: khobar95]
      #5455761 - 10/04/12 09:29 PM

I wasn't clear from your post if you are using the guide graph, if you're not it's the way to go as far as judging your guiding capability. It's a great tool for troubleshooting. The N/S Dec setting is an option (the 'Brain'), I think it's the top right setting (I don't have PHD on this computer so I'm going by memory) and the default setting is on Auto. Anyway, your initial goal of 60s should be achievable, especially if you've already done the dec axis 'hypertune'.

And finally, the CG5 has a polar alignment routine in the handset. After your 2-star align plus a calibration star, try the polar alignment routine -- it's pretty slick, although it puts off your pointing alignment. For this reason many people recommend doing the alignment routine a second time after the polar align. I'm usually in too much of a hurry to do that and I just use the 'precise goto' function instead -- discovering that function made my life *so* much easier.

Cheers!


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