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Tracking issue with ServoCat on my Obsession 15

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#1 leetje

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Posted 24 September 2020 - 09:25 AM

I have some questions about the ServoCat on my Obsession 15 classic that I hope viewers of this forum can help me with. I have had the telescope for a little over a year now and am still in the learning curve.

 

I have been looking at Mars the past few nights. Using higher magnifications with my 11mm ES EP (156x) and 6.7mm ES EP (256x), with tracking, I’m noticing some gradual downward drift of the telescope in the early evening, that is, when Mars appears above the horizon up to about 30 degrees. As the night continues and Mars rises, the drift is less and less and eventually stops or is hardly noticeable. Could this be due to improper balancing? How should I orient the weights on the mirror box? I’m still not clear how these should be positioned. I’m thinking that when the telescope is near low or near horizontal, that gravity is overtaking the ability of the altitude motor and cable to hold it in place. Could the cable be in need of replacing or should I find away to further increase the tension?

 

I never really noticed this before, as I typically do not observe planets with high power for extended periods of time. Any drift would be less noticeable at low power. I have also tried the local sync and autolock feature but still have the same problem. Not sure I’m using this correctly. I also wonder if some setting needs to be adjusted in the programming?

 

Or could it be due to choosing the wrong alignment stars?  Since I’m only looking at Mars I did this to facilitate tracking. Is there a way to start tracking without doing the alignment?

 

I have had the telescope, a little over a year now, but have not had the issue of downward drift until just recently, as I described. Otherwise everything seems to work fine. 

 

So far my main problem with Mars is poor seeing from my CT shoreline location as I have a hard time seeing any defined surface features. I am able to see the polar ice cap. I have been trying some of the Celestron filters like ND and orange #21, these help a little but so far it’s been somewhat frustrating. Even as we approach the opposition, I'm still finding Mars to be a tough target for visual astronomy. Thanks for reading!


Edited by leetje, 24 September 2020 - 09:28 AM.


#2 bunyon

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Posted 24 September 2020 - 09:41 AM

It could be all of the above. My rig is exactly the same as yours and I also notice trouble with movement in altitude sometimes, especially low. I also suspect balance, though I've not been motivated to correct it. I've also had trouble with slippage on the cables occasionally if they come loose. I had a screw chew out the wood on the alt clutch and that caused problems. (I've had my AN and SC for about ten years).

 

But the most obvious problem is what you say, slight misalignment that is causing a tracking error worse in one dimension that slowly smoothes as Mars changes course (in alt/az) across the sky. If it seems to track okay most of the time and all you're having to do is nudge the alt button occasionally, you're fine. Remember, this system is not designed to give EQ like perfect tracking. Keeping Mars in the FOV of a high power eyepiece for minutes at a time is exactly how it should work. Nail the alignment and have all mechanical parts working optimally and you can do a little better. But it's not the end of the world if not.



#3 Blueox4

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Posted 25 September 2020 - 05:11 AM

If you use Nexus DSC with SC you can Go to settings on Nexus. Go to object lock. Ensure it is checked. Then make the delay 120 seconds or so. This gives you two minutes to precisely center the object after a GoTo. Do a GoTo, center your object. Then press the left over key on Nexus and check "add syncpoint". This will then zero out your numbers, and object lock sends code to ServoCat that overrides any slight inaccuracy in ServoCat settings. Now you'll have absolutely precise tracking.

 

 

if your using SC alone Download the program for Superuser (see manual). This can be a frustrating process (at least for me), as it is an older Dos Shell like program.

The second way can be done day or night. Look in the manual under improve tracking accuracy. It is a pretty straightforward process, but it can take some time. The longer you spend tweaking, the more accurate you can get it.
When I put the gear ratios for all of my scopes into the alt/azumith settings, it is basically a tape measure measurement, and then use the formula given by ServoCat. This is precise enough to have the object in the eyepiece for us minutes to an hour (sometimes more). But ServoCat can be more precise still by following the previously stated procedures.


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#4 stubeeef

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Posted 26 September 2020 - 08:35 AM

@Blueox4 are meaning Astro lock?



#5 Blueox4

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Posted 26 September 2020 - 08:46 AM

Yes, Astrolock. This process works as I’ve used it. Have not used Superuser yet as the Nexus pointing is dead nuts after that. 


Edited by Blueox4, 26 September 2020 - 08:48 AM.


#6 Keith Rivich

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Posted 26 September 2020 - 02:50 PM

I had similar issues with my 25". I pretty much fixed it by making the sure the telescope is slightly bottom heavy with everything attached. The motor does not have to work quite as hard to raise the scope. 

 

It took a little doing to get it right for all altitudes but it wasn't bad. 


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#7 leetje

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Posted 26 September 2020 - 04:26 PM

Update: I lowered the two weights attached to the mirror box, to make it more bottom heavy, and that seems to have helped. I also checked the location time and date settings and discovered it was set for Tucson AZ and not my home in CT. I heard back from Gary Myers (the StellarCAT guy) that that planets are especially sensitive to errors in location settings (date/time/location) in the Argo Navis program.
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