PHD2 and SB MyT mount/T-Point ProTrack

[Clayton Yendrey]

I had my First Light with my Paramount MyT mount/TSX/T-Point last night.  It took a while to work through everything the first time, but I was deliberately taking my time to make sure I made as few mistakes as possible.

I have a question concerning PHD2 and the T-Point model; more specifically does PHD2 'play well' with the ProTrack corrections or should they be disabled if guiding?

ProTrack is a special function limited to TSX/Paramount mounts where T-Point utilizes the pointing model to implement tracking corrections in real time.  I suspect that PHD2 and PT might interfere with each other but don't know if this is the case or not.  ???

FYI, my PE was very good before recording/applying a PEC.  My PE before the PEC was 2.8as pp.  After applying the PEC, my corrected PE was 1.9as pp.

Calibration and Guide Assistant run went very well - never had a mount before where the guide start never seemed to move during the GA unguided run...  ;-)  GA reported a PA error of .8'.  No discernable DEC backlash measured.

Ran a long tracking run on as star a DEC 3.5 just past the meridian for around an hour.  Guiding was excellent with a .55as ttl RMS error.  

I did try to enable ProTrack about half way through the guide run, but it seemed to destabilize the RA, so turned it back off.

Thanks in advance!!!

[Clayton Yendrey]

I forgot to mention absolutely no issues in getting PHD2 to work with SkyX.

[Brian Valente]

Hi Clayton

seeing your guidelogs would help clarify what you're talking about

In general a pointing/tracking model should not impact guiding. 

I use APCC/APPM with my AP mount which is AP's version of protrack and it works fine with guiding. It's kind of like a mount-based error correction.

It's hard to know what happened with you without seeing the details. Did you use PPEC algorithm? that could possibly impact things if you started/stopped tracking

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Brian Valente

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[Clayton Yendrey]

No, didn't use PPEC, jus the standard Hysteris algorithm on the RA, LoPass2 on DEC (no backlash compensation).

I didn't let it run but a few minutes with the ProTrack enabled - it was very late (approaching 4am) and I wasn't wanting to get into any complications at that point, just get a good baseline guiding run.

Here is the link to last nights logs: https://openphdguiding.org/logs/dl/PHD2_logs_EadW.zip

[Clayton Yendrey]

I just looked at the logs in the log viewer.  In the longer guide session, I see one fairly steep spike at 66.8sec that stands out from everything else in the frequency analysis.  Do you think if I setup PPEC with this peak/time that it would 'focus' on that area?  I don't see much else that rises high enough to be concerned about and even that peak is only around .35/.38as.

[Clayton Yendrey]

Brisn,

After thinking sbout this, I suspect a new profile is needed for the mount when using Protack, vs when not using it.  My reasoning is that the Protrack corrections will make the mount look different to the PHD2 AIs  than it does when running without Protrack.  What do you think?

[Clayton Yendrey]

Brian???

[Clayton Yendrey]

Posted logs a few days ago,  No response since those were uploaded as requested.  ???

[Brian Valente]

Hi CLayton

sorry things have been really busy but i'll look at your logs

regarding protrack, you can of course experiment or do whatever you want re: profiles, but it should not make any difference regarding guiding. the level of tracking correction is probably on the order of a handful of arcseconds per hour, so it's not going to impact guiding

at least that is my experience

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[Brian Valente]

Clayton in your log there's a 6 minute session (mostly unguided) and a 46 minute session

is there a portion here that is with protrack enabled?

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[cyen...@gmail.com]

Yes, in the 46 minute guide session.  The 6 minute is the GA run.  In the 46 minute guided run you can see when I thought about ProTrack and turned it on - just before 3:27 tic mark – the big RA and DEC spike (up and down for the RA, Down and up for the DEC).  Looking at the graph, the periodic RA spikes go away while ProTrack is running and come back in (approx. around the 03:34:30 point) when I turn it off. 

I turned it back off for two reasons

1. I didn’t like the divergence I was seeing between RA/DEC, and my total RMS error had ticked up .02”  It gradually worked back down through the remainder of the run.
2. I realized I was screwing up my baseline recording by introducing an on mount ‘correction’ in the middle of it.  So I turned it back off.
   
   

As I mentioned, I have created an alternate profile to run through setup again that will be based on ProTrack being on.  I’m trying to keep the profiles aligned with what I have done/active in TSX so there isn’t a ‘mixed’ set of mount responses being incorporated into a single profile.  I don’t know if this really makes a difference?

Excluding the short period that PT was running, there is a definite period to the RA spike that repeats through the guide session; the 2” scale makes it look rougher than it really is, at least as compared to my previous mounts that had to be shown at 4-8” to keep the trend spikes on the graph.  😉  When I put the scale back at 4” which was my typical minimum scale previously, things look fairly smooth.  That periodic spike was leading me to consider the PPEC algorithm for the RA, at least if ProTrack is not running in TSX.

Given the PEC result of the mount (1.9”pp), I would think that very little guide input is desired.  For this reason, I think the aggression settings might need to be toned down/PHD2 input as a whole ‘softened’ if that is the right term.

 

I know this is a mish/mash of several different small items, sorry about that. And Thanks again for your help in tweaking this setup!!

Clayton Yendrey

Sent from Mail for Windows 10

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[Brian Valente]

So just to clarify you enabled protrack at 3:27 and turned it off... when?

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[cyen...@gmail.com]

Approximate 03:34:30 – you can sort of see it in the RA graph – the periodic RA spikes stop just after ProTrack starts, then return just after ProTrack is turn off.

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[cyen...@gmail.com]

Brian,

As I keep looking at the guided graph, I’m noticing a fairly consistent RA/DEC counter point in movement.  This is a brand new mount, but is this what the cross talk issue for Paramounts typically looks like?  I mean the overall performance is good, but I understand this is typically a plunger adjustment on one of the axis??

 

Clayton Yendrey

Sent from Mail for Windows 10

 

[Brian Valente]

okay great thanks

It also seems visually apparent when you turned it on and off

During the period from roughly 3:27 - 3:34 your overall RMS was 0.50" with RA and DEC RMS roughly equal (in other words, really good guiding)

If i invert the selection and look at the guiding minus the duration noted above, i can see that DEC is fairly consistent but RA is noticeably higher

One other corroborating bit of data is the DEC not changing much while the RA improved, which is largely what i would expect from a tracking model in this amount of time (DEC will of course adjust, but in my experience it's less movement over a longer duration)

Given the bit of guiding data and details from you, i'd say protrack ON and your current guiding parameters result in empirically better guide results

 

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[Brian Valente]

>>>This is a brand new mount, but is this what the cross talk issue for Paramounts typically looks like?

i can't speak to Paramount products, it seems like that would be a question for Bisque?

>>> I’m noticing a fairly consistent RA/DEC counter point in movement. 

I'm not sure I see that in the graphs you sent or i'm not understanding what you mean by counter point. Can you point out where you see that?

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[Clayton Yendrey]

It seems that there is a pattern of the DEC moving opposite to the RA.  The movement scale isn’t much and I didn’t really see it until I started expanding the horizontal scale to see more detail around the RA petiodic ‘spikes’.  It seems foolish to look at these details giving how goid the mount has performed on its first outing.  I am going to run with PT on in TSX so those ‘spikes are going to be minimized anyway.

So I guess my next questions are:

1) Any reason to give PPEC a run?

2) Any reason to reduce aggression settings or other tuning adjustments?

[Brian Valente]

Clayton i'd say for now just start guiding and see how it goes

Of course you'll want to do a good calibration (celestial equator/meridian, etc.) and run the guiding assistant for recommendations, but you're guiding already seems really solid, so without more data or specific problems i'd say you are good to go 

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[Clayton Yendrey]

Just to post the latest.  It is definitely the dreaded Paramount DEC/RA crosstalk issue.  Unfortunately, observing nights over the last 60 days have been hard to come by, so work to resolve is progressing intermittently, if at all.  The typical signature of this issues is little no problems in/around targets at Dec 0dg, with the problem becoming more apparent/larger at higher declinations.  The problem is getting worse as I use the mount (now at 42 hrs of run time since first light in Feb) with spike of 8 a-s on M51 at the end of April.  I made a small preliminary adjustment of the Dec plungers on the recommendation of  SB Support.  It did reduce the magnitude of the spike when I was able to observe again; down to 4 a-s but did not eliminate the problem.

So I went to a complete reset of the plungers per the SB plunger adjustment procedure.  I am, at this time, waiting on an observable night to test the result (Astropheric says another 10 days at best).

SB Support has been responsive, to the extent that they know this occurs.  They have a strong resistance to accepting this is not an acceptable design 'feature'.  There is a hint that some key folks at SB are not particular fans of guiding even within TSX, so aren't terribly concerned about a 'feature' that discourages guiding.  From my searching on this issue, it seems to affect the MyT more than the other mounts in the SB line, but none are immune to it.

Is there a way to use PHD2 in Guide assistant to measure this in daylight (without stars)?  The problem can be seen / monitored during adjustment by using direct commands to DEC in rapid series with reversals while running Guide Assistant.  I've read that the PHD2 star cross test can also reveal this problem.  Suggestions/recommendations?

[Brian Valente]

>>> Is there a way to use PHD2 in Guide assistant to measure this in daylight (without stars)?  The problem can be seen / monitored during adjustment by using direct commands to DEC in rapid series with reversals while running Guide Assistant.  I've read that the PHD2 star cross test can also reveal this problem.  Suggestions/recommendations?

you can't evaluate mount performance without actual stars. 

I have heard rumors that you could try using a very limiting filter such as an HA filter to try for star acquisition during the day.

However I tried this and could not get it to work properly (3nm HA). 

Biran

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[bw_msgboard]

Hi Clayton.  Unfortunately, there isn’t going to be any way for PHD2 to measure this stuff without real stars.  The mount can definitely be “exercised” with whatever pattern of guide commands you want, but there wouldn’t be any way for PHD2 to measure what happens.  If SB wanted to apply direct hardware instrumentation to measure what both axes are doing, then an exerciser tool like this might be useful.  But I’d think they already have those capabilities in their factory.

 

Good luck,

Bruce

 

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1.      I didn’t like the divergence I was seeing between RA/DEC, and my total RMS error had ticked up .02”  It gradually worked back down through the remainder of the run.

2.      I realized I was screwing up my baseline recording by introducing an on mount ‘correction’ in the middle of it.  So I turned it back off.

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[Clayton Yendrey]

Brian,
I apologize but I think we need to get the discussion regarding PHD2 back here rather than in the AP-GTO group forum.

To repeat my reply to your question posted in that group:   I do understand that, but although I leave the mount on the pier in the backyard, I do not leave the OTA there.  For safe carrying, I have a D plate handle assembly; to use it I remove the guide camera/scope from the top D plate and install the handle to carry the OTA safely/securely.  Since I am 'disturbing' the guide scope assembly each time I mount/dismount the OTA, I perform a calibration.  On the few times I've actually had back to back viewing nights, I have left the OTA on the mount and have not recalibrated.
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I have another question in regards to the DEC settings in PHD2.  After making the first DEC plunger adjustment, I ran a new calibration to see what, if any, impact it had on the guide calibration.  The DEC backlash had shown up for the first time a couple of session ago, and I noticed in the session before the plunger adjustment, GA measured DEC backlash at around 480ms.  After the plunger adjustment, the DEC backlash was back to undetectable, as it had been when I first started using this mount.  

What I forgot to do is to turn DEC backlash compensation off after no backlash was detected.  I do had the LowPass2 algorithm applied as that was recommended by GA when backlash began appearing.

My question is:  What is the affect of having DEC backlash compensation enabled when there is no measurable backlash?  Could/would this contribute to the DEC/RA crosstalk problem?