MyT RA spikes???
Clayton Yendrey
I've been tweaking the DEC plunger tension and have seen some improvement but not elimination of the RA spikes. Another MyT owner suggested a slight adjustment to reduce the tension of the RA axis plungers as well since he had seen some stiction (but no stalling) in his mount that was improved (he also later cleaned and lubricated the worm gears. He didn't mention his mount's age.
The DEC/RA crosstalk is an issue that seem's exclusive to Paramounts, particularly the MyT. I have my suspects in the design as to why this is so, but not germane here.
The first two session in the log (Log #3 and Log #4) are the results after some pretty dramatic (to me) reduction in plunger tension beyond the initial recommendations by Software Bisque.
In Log #6 at approx 00:36:19, I make a slight reduction in the RA plunger tension (seen in the DEC spike). It looks to me there was a slight improvement in Total RMS vs the other two, but I can't really say the spikes are completely gone, but they do appear significantly moderated.
I think I see a 'regular' RA correction that is associated with PE. I'm thinking the plunger tension adjustments have impacted the worm gear 'following' (less stiction??) and that I need to run another PEC generation process.
I did find over the course of a previous session (log not included) that performance improved noticeably when I shortened the exposure frequency to 2 sec and tightned the min/mov to .16 (RA) and .18 (DEC) from the more permissive settings that GA had recommended. I made no config/setting adjustments other than reducing the guide camera gain slightly to keep the guide stars that PHD2 was selecting from saturating. Multi-star guide is used throughout.
Thanks in advance
I'd like your analysis to see what you think.
FYI, I have not dismounted the mount/OTA from the pier since April; that is the date of the last PA and PHD2 Calibration/GA run.
Brian Valente
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Clayton Yendrey
Brian,
Thanks for the quick response!!!
I will run a calibration tonight (looks like the last night available for observing for at least a week. I’ll also and see if I have enough ‘gap’ from the moon to get a PEC run in SkyX or if I need to wait for a darker night.
The PHD2 calibration will be the first since I started making plunger tension adjustments, so that is likely to be as much responsible for a change in mount behavior vs the previous calibration as anything else I can think of.
The new PEC tool in SkyX is completely automated now, with the exception that now it requires that the SkyX autoguide calibration for the OTA/Camera has to be completed, and still has to be done as close as possible to DEC 0 (just like PHD2).
I’ll submit updated guide logs once I complete the pHD2 calibration and the PEC update.
The last calibration was in April. I’ve attached that log file, but given the work I’ve been doing to tweak the plunger tensions I doubt it reflects the current state of the mount (based on your comments).
Sent from Mail for Windows
From: Brian Valente
Sent: Tuesday, August 24, 2021 11:09 AM
To: Open PHD Guiding
Subject: Re: [open-phd-guiding] MyT RA spikes???
Hi Clayton
a couple observations:
you should definitely recalibrate PHD - anytime i see "crosstalk" between the two axis, it usually means your calibration is invalid and should be redone. Your guidelogs did not include a calibration run so no way to really know here for sure, but you can see it plainly here:
Second, the primary RA constraint is a 269/270 second periodic error that isn't being well corrected. You might consider PEC in the mount, or you can use PPEC algorithm for RA and set the period to a fixed value of 269.3 sec as shown above
Brian
On Tue, Aug 24, 2021 at 7:06 AM Clayton Yendrey <cyen...@gmail.com> wrote:
https://openphdguiding.org/logs/dl/PHD2_logs_zshi.zip
I've been tweaking the DEC plunger tension and have seen some improvement but not elimination of the RA spikes. Another MyT owner suggested a slight adjustment to reduce the tension of the RA axis plungers as well since he had seen some stiction (but no stalling) in his mount that was improved (he also later cleaned and lubricated the worm gears. He didn't mention his mount's age.
The DEC/RA crosstalk is an issue that seem's exclusive to Paramounts, particularly the MyT. I have my suspects in the design as to why this is so, but not germane here.
The first two session in the log (Log #3 and Log #4) are the results after some pretty dramatic (to me) reduction in plunger tension beyond the initial recommendations by Software Bisque.
In Log #6 at approx 00:36:19, I make a slight reduction in the RA plunger tension (seen in the DEC spike). It looks to me there was a slight improvement in Total RMS vs the other two, but I can't really say the spikes are completely gone, but they do appear significantly moderated.
I think I see a 'regular' RA correction that is associated with PE. I'm thinking the plunger tension adjustments have impacted the worm gear 'following' (less stiction??) and that I need to run another PEC generation process.
I did find over the course of a previous session (log not included) that performance improved noticeably when I shortened the exposure frequency to 2 sec and tightned the min/mov to .16 (RA) and .18 (DEC) from the more permissive settings that GA had recommended. I made no config/setting adjustments other than reducing the guide camera gain slightly to keep the guide stars that PHD2 was selecting from saturating. Multi-star guide is used throughout.
Thanks in advance
I'd like your analysis to see what you think.
FYI, I have not dismounted the mount/OTA from the pier since April; that is the date of the last PA and PHD2 Calibration/GA run.--
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Brian Valente
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Clayton Yendrey
Brian,
I’m afraid I lied to you. I’m not going to be out tonight for a follow. Spent the afternoon in 100dgr heat pressure washing; I’m toast and not really done yet but the heat is just a killer.
Forecast shows a possibility now on Th or Fri; if not looks like it will be after the first week of August. But you never know until the day gets here (or rather night).
Sent from Mail for Windows
From: Brian Valente
Sent: Tuesday, August 24, 2021 2:10 PM
To: Open PHD Guiding
Subject: Re: [open-phd-guiding] MyT RA spikes???
Sounds good Clayton
Your original calibration looked fine, and you seem to know your way around.
I should have clarified i wasn't too concerned about the original calibration, more that it could have become invalid between then and now.
looking at the guiding from your original, it's clear the 200-ish second came in later, you don't see it in your original guidelogs:
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Clayton Yendrey
I went through the new automated PEC process in SkyX last night. The uncorrected PE was measured as 5.6 a-s pp. After the correction was applied, the tool reported no measurable PE. I'm not sure I really believe that, but I don't know what the tolerance is within that SkyX tool. I did note that my PA was just 'OK' during the PE - the target / reference star stayed in the bullseye reticle that I overlaid on the image, but had a very slow drift in the DEC.
I ran a new calibration in PHD2, started to run Guide Assistant and confirmed that the PA was OK, but not great so canceled the GA run. I ran the PA routine in SharpCap, minor tweaking to get it excellent, then ran Guide assistant for approx 400 secs (one worm turn - Log line #5). No DEC backlash detected, PA was great, but I don't remember the exact determination and didn't screen capture the dialog box.
Unfortunately, high clouds started to move in so I was unable to get an extended guide log. The longest was the first attempt but the meridian flip occurred after the second image, then it ran another 26 minutes before it lost the stars the first time. I was imaging NGC 7000 to put the mount in the position/DEC range where RA/DEC crosstalk tends to occur in the MyT mounts. The short periods between loss of guide star prevented an assessment of that issue, but the mount appears to tracking very well when not guiding, so between the plunger adjustments and the new PEC, I may now have a solid mount. There was only twice where an image was completed without loosing the guide star. What I did notice is that even when guiding was inoperative, the tracking was good enough that the image captured for each full 5 minute exposure showed round stars - that was even with guiding restarting multiple times during the image process. N.I.N.A. is the scope/image acquisition software in use and it does not stop imaging with loss of guide star/guiding. Nightly build 135
Total RMS error varied with seeing but tended to stay below .5 a-s ttl RMS and got down into the mid .3x a-s before the clouds became an issue. Seeing has to be considered OK to impossible after the meridian flip.
Brian Valente
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Clayton Yendrey
Yes, as I mentioned clouds began moving in shortly after completing the guide assistant run so start / stop as the star was lost. Guide Assistant recommended the LowPass2 a few months back and I’ve never changed it as it seems to have a lesser tendency to over react with the MyT than the standard Hysteresis algorithm.
The Guide Assistant was recommending a larger min/mov, but I wanted to minimize changes from the previous run to get a feel on how the mount responded to the changes.
It looks like I *might* have a window tonight and possibly tomorrow night. If it works out, I’m going to update the Tpoint model and increase it 200 stars while I’ve got a dark sky/no moon. Now that I’ve got a better feel for the new SkyX PEC tool and how to use it, I may run it again since it is fairly simple to do. Hopefully between tonight and tomorrow night, I can get a guide run of a few hours in length rather than a few minutes.
Sent from Mail for Windows
From: Brian Valente
Sent: Friday, September 3, 2021 12:37 AM
To: Open PHD Guiding
Subject: Re: [open-phd-guiding] MyT RA spikes???
Hi Clayton
you have a lot of very short guide runs in this log, is there a reason for that?
overall you are right, the guiding is quite low at around 0.43"
your main constraint continues to be that 60 second error, and the 200 sec error is back as well (looking at your one longer run of about 26m)
Also i noticed you are using lowpass2 as your dec algorithm, any specific reason for that? looking at your log it seems like dec could benefit from lower min move as well. it's kind of wandering around in there, as is your RA
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Clayton Yendrey
After sending I realized this statement was bit ambiguous: “The Guide Assistant was recommending a larger min/mov, but I wanted to minimize changes from the previous run to get a feel on how the mount responded to the changes.”
What I was trying to say was that I wanted to see how the mount responded to the previous changes (RA plunger tension adjustment, new PA, new PEC, new PHD2 Calibration), before introducing additional changes such as the PHD2 tuning settings. If the session had shown an inability to guide/significant mount excursions/instability then I would have started with the recommendations from the GA run and gone from there.
What I’m seeing so far is indicating visible improvement with each change – back in June it was impossible to guide in that DEC regions and do much better than a 1.0-.7 a-s ttl rms guide error. The primary culprit was RA excursions/spikes out to as much as 3”. That issue seems to be resolved, but I need a much longer guide session before I can say that with certainty.
Brian Valente
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Clayton Yendrey
I just decided if I'm going to make a new Tpoint model (which will provide some fine adjustment detail on the polar alignment), then I'm only a couple of key presses away from a new PEC at the end of it. Tonight looks like a wash out (again), but tomorrow is still forecast to be good - we'll see.
Clayton Yendrey
I didn't stay up for the entire session, but I saw ttl rms error down to as low as .24" but the average seemed to be somewhere around mid .40's to mid .30"s. RA and DEC seemed to swapping as the which axis had the slightly higher ttl rms error. Imaging on M31 was rock solid - all frames solid/round stars. Seeing was good at the start but declined as relative humidity/haze increased. I tried again last night (just imaging) and saw similar performance on the outset that declined slightly after a couple of hours (clouds started moving across the target area around 11:20ish, so shut it down shortly after that. So two hours pre meridian was the entire frame set (NGC 7000). I did not see anything notably different to indicate that its log file would add anything so I didn't upload it.
I still see a slight peak in the frequency analysis around the 60-70 ish time frame but maginitude relative to the previousl log (before the new PEC) is much smaller. I suppose I could try the PPEC algorithm to see what it could do. Given the current performance, I not sure how much benefit there is to be had. ???
Overall I'd have to say that the reset' of the setup from Tpoint model to PEC, and PHD2 calibration (after all the axis plunger tension adjustments) has resulted in a mount that is finally meeting my performance expectations for the price point.