Old Mount New G2 Controller unable to get out of the gate

[Dawn, Paul, and Elizabeth Romero]

Hi all,

Thank you to the developers for your Astro Imaging Channel controbutions....they have led me to this forum.

Here is a link to my log file: https://openphdguiding.org/logs/dl/PHD2_logs_GvXv.zip

I am unsure about what I am seeing in the Guiding Assistant and the Calibration Review screens, and I hope you can help me understand. I have an OAG on a 2032mm focal length scope, and I am able to get a calibration successfully. However, the question is whether my mount is capable of providing the tracking necessary to get a good astrophoto. In the past, I have been getting repeated warnings about orthogonality on my calibrations, and they refer to the RA axis often.

Here are snippets of the above mentioned screens:

I am ready to tear the mount open, and I have some guides as how to refurbish it. Thank you for your tips and advice!

Paul

[wave...@talktalk.net]

Hello Paul,
As a recent starter with an old Schmidt Cassegrain (FL >2000 mm) and high Dec backlash, I know what a steep cliff you're trying to climb. However, there's a couple of things I'd suggest you do before dismantling the mount in the hope of a fix. Firstly, I'd look carefully at what the Calibration results recommend. Guiding at a scale of 0.39"/px is a big challenge. I guess you're using an OAG, so binning the guide camera at 2x2 will double the image scale and reduce the problem somewhat. The calibration wizard also suggests that, but it will still be difficult. Your calibration was not the best and might be improved. Remember to run the calibration at the optimal area of the sky immediately after removing the Dec backlash using the handset. See the Best Pactices guide for more on this. Always follow PHD2's recommendations following a calibration.
I'd also try to get a better picture of the mount's basic, unguided performance by running a Guiding Assistant session for several worm cycles, which appears to be around 4 minutes per cycle. Let the GA run for 15-20 minutes and upload the logs for the experts to check over and advise. Similarly, run another session following the help document on How to Create a Baseline for Guiding from which the experts will give you a lot more advice than I can.
Hope this helps a bit.
- Jack

[Dawn, Paul, and Elizabeth Romero]

Hi Jack and Bruce,

I have done my best to tune my mount by replacing some couplers, cleaning and regreasing, and basically learning what makes it "purr like a kitten". In addition, I've adjusted the polar alignment.

Here is the link to my log file (should contain both GA and guided segments): https://openphdguiding.org/logs/dl/PHD2_logs_2oPb.zip

For reference, here are some screen shots of before and after adjustments:

BEFORE:

CALIBRATION AFTER:

GA BEFORE:

GA AFTER ADJUSTMENTS:

Im hoping to come to some conclusions with advice from the experts:

1)How is my mount's performance? i.e. what is the peak to peak in RA and DEC? Is this in the approximate range of some of the newer, midrange mounts such as the EQ7 ir 8?

2) Which Axis nees more work? I can replace the gearbox in the RA with a longer shaft new one, and that might get the oldham coupler tigher.

3) Thank you for your time in responding!

Clear Skies,

Paul

[wave...@talktalk.net]

Hello again Paul
Good progress with the calibration step and the PA. An orthogonality error around 4 degrees is pretty good so I'd stick with that without further adjustmnt.  As to the mount's performance, I believe you'll get better data by running a Baseline Guiding session, preferably for half an hour or so. From that, the experts will be able to advise you on the mount's performance and capabilities. There's a link to running this on the main PHD2 website. I'm only familiar with my old Meade fork mount, which like me, is rather old and crochety, so after uploading the Baseline log, I'm sure Bruce et al. will tell you what you need to know.
Cheers,
Jack

[Dawn, Paul, and Elizabeth Romero]

Hi Jack and Bruce et al,,

I was able to get an approximately 45 minute Baseline Guiding Session for you to evaluate! I raced the dawn before work to get it, so I do not have a nonguided baseline at this time. The thing that got me flustered was the guiding performance from what I thought was an extremely good calibration and subsequent GA session and adjustments about two weeks ago. The guide corrections were way too high this time! So, I established a new calibration and then did the adjustments the GA advised. This time the guide corrections kept the star in place for 45 minutes! I hope to get an unguided baseline soon.

Could you advise as to my mounts capabilities? I have a scope that is F8 and FL of 2032 that I'd like to use for astrophotography. I'm looking at an f4 fast newtonian on the market, also, and I hope to get some direction as to which way to go based on the guided session.

Here is the link to the log: https://openphdguiding.org/logs/dl/PHD2_logs_fkan.zip

Clear Skies,

Paul

[wave...@talktalk.net]

Hya Paul,
Your log suggests to me that you're making good progress, especially at 0.75"/px image scale. The traces are also providing a bit better data on the state of the mount and your basic control under PHD2.
I hope the experts will check through how I see it and g you an authoritative view.
Using the tools available in the Guidelog Viewer, you can zoom in and examine sections of the RA and the Dec traces and get some clues on how to proceed.
The associated guide to Log Analysis is also indispensible for starters like us and from that, I think there's one or two things to look at. Here's a section from the 39 minute baseline session, RA is in blue and  Dec is in red,

I think the sky conditions may not have been perfect and assuming you're in the UK, the seeing will probably be poor to mediocre and two pointers to this are in the traces. The RA looks inherentlly pretty good, but with too low a Minimum Move setting for RA control. Your low guide speed setting of 0.5x siderealmaybe  causinthe saw tooth effect in the trace. I think I'd set the guide speed to 0.8x or 1x sidereal and see if it improves things.
The exposure setting of 1000ms is may also be too low to compensate for the seeing. I think the help guide would suggest 2000-3000ms to reduce the effects from chasing the seeing. Another thought I had was to ensure any mount controlled Dec backlash is off. The PHD2 Dec pulses seem to be a bit odd and needs an expert's eye on it.


The 8 minute GA run also notes this and suggests an increase for RA MinMove.
Though the worm period appears to be around 240s I'd personally run this for 2-4 cycles to get a good idea of the mount's periodic error. from the limited data in the GA log, there's around 8" Peak to Peak. A three or four cycle GA run would define this better.

I'm sure there's more to glean from your logfile but that's my half-educated take, so hope it helps.

Cheers
- Jack

[Dawn, Paul, and Elizabeth Romero]

Hi Jack et al,

I went ahead and did a 16 minute GA session, but when I tried to guide aftewards, I ran into alot of trouble. I finally had to recalibrate PHD2 and start over. However, I did get a log. I hope you can look at it, especially the 16 minute GA session you suggested I get for a better look at my mount. Speaking of my mount, I am wondering as I have for a very long time why there are funny quirks about it that I do not understand. Like, why do I need to recalibrate my PHD2 every night? Like, why does my mount report to PHD2 that it is far from the celestial equator when less than an hour before I plate solved it, never moved the mount manually and am certainly still near the equator? A new platesolve corrects this. These two items are big hurdles for me, especially as I would like to get some sleep for my job and family.

Thanks in advance for your advice and interpretation!

Paul

Log for tonight: https://openphdguiding.org/logs/dl/PHD2_logs_uHfj.zip

[Brian Valente]

HI Paul

How old is this mount?

>>> I am wondering as I have for a very long time why there are funny quirks about it that I do not understand. Like, why do I need to recalibrate my PHD2 every night? 

If your equipment doesn't change, particularly the guidescope, you don't need to calibrate it every night. Not sure where you got that notion?

 

>>>why does my mount report to PHD2 that it is far from the celestial equator when less than an hour before I plate solved it, never moved the mount manually and am certainly still near the equator? A new platesolve corrects this. 

I'm not sure what you mean here. How are you determining the mount is reporting it's at an incorrect position? If you are tracking at sidereal rate for about an hour, the mount will move about 15 degrees in the sky. 

I can't really say much about the initial runs because you didn't include the calibration at the start, but the unguided (GA) run shows a p-p error of 12", slightly over the 10" p-p which is the spec of the G11. It sounds like it's an older mount, so you will probably want to look at the losmandy youtube channel for adjustments to the worm blocks or worm preload. Otherwise it looks somewhat unremarkable

Your last run showed a total RMS of 1.15", RA is running higher than Dec, with the primary period being the biggest contributor

using the PPEC algorithm set to the period above and disable auto backlash compensation should help here. i would reduce the exposure time to around 2sec

Your Dec backlash is manageable, but you might be able to tighten up the Dec axis worm to reduce that. Backlash here is around 0.5" total RMS

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[wave...@talktalk.net]

Hello again Paul and Brian,
Here's the Fourier Analysis curve from the extended GA run Brian refered to.

This 12" P-P worm primary error is 90% reduced by PHD2, so good signs.
The Dec drive has backlash, so the guide pulses are labouring to execute a change in direction.
This shows a typical section of the 46 minute guided run. Note how many pulses are sent before the Dec responds.

A way to accomodate this is to set PHD2 for unidirectional Dec guiding.

Cheers,

- Jack

[Dawn, Paul, and Elizabeth Romero]

Thank you Jack and Brian, I think I have a great start on learning from your posts. In fact I have them printed out for next time!

Brian,

My mount is 21 years old, maybe 22. It has the latest G2 controller with it's great driver. 

After reading your post, I thought that maybe my mount was losing power intermittently and thus losing it's position, so I replaced the "cigarette lighter" connector with a direct hard wire connection to my 7.5 amp 12v Power Supply.

However, in operation, I still get unmanageable guiding, unless I calibrate and apply the GA suggestions. Other times,  the mount loses it's position, or "slips" enormously on rather mundane slews. I have tightened the clutches tight. The MI-250 mount is hefting about 60 lbs payload and 85 lbs counterweights (I might not be accurate wrt the Counterweight amount).

You asked how I am able to know the mount is reporting an incorrect position. I know that by observation, the mount is pointing near the meridian and celestial equator, but PHD2 reports it is far from that location. A platesolve will often fix this.  Also, in NINA, I often see huge errors in RA after tidly moves or bumps against the physical limits (which for my mount is very close to 90 degrees vertical for RA).

For example, here is a platesolve from the mount before and just after a small slew:

This occured as I was nursing the scope around from the West side to the East side, as the mount (or G2 unit) refused repeated commands to perform a meridian flip, when commanded on the "hand controller".

I cannot physically move the scope when the clutches are tight (at least not without a fight). There is a worm gear in this mount that is probably similar to the G11, where it surrounds a central "core". Perhaps this "ring" of a worm gear is slipping from the RA axis. That would explain the "long time" of this problem. Perhaps you might be willing to look at it with a second set of eyes, as this mount's gearing is probably very similar to the G11 or Titan and I am willing to travel to Sacramento area.

Clear Skies,

Paul

[Dawn, Paul, and Elizabeth Romero]

Update a month later...

Hi Jack and Brian,

I've gone back and forth 3-4 to my DEC and RA worm gears...adjusting and learning. I believe my guiding is getting better, as it needs to be for a 2032 mm focal length scope. Could  you take a look at the log file created tonight? I do not know why the orthogonal error is so great on my calibration, as it has been much better in the past. I am using the predictive pec algorythim now, as it was recommnende by Cuiv the Lazy Greek Youtuber. The log file can be found at:

https://openphdguiding.org/logs/dl/PHD2_logs_A5q2.zip

Clear Skies,

Paul

[wave...@talktalk.net]

Hello again Paul,

I'll take a stap at it, but I'm sure Brian or Bruce will give you a far better assessment than I can.

Anyway, the following grabs give a reasonable picture of where it stands right now.

As to why the calibration orthog error was disappointing, my guess is your settings and/or technique contributed to it.

The calibration required around twenty moves when the wizard should give settings for about twelve.

You appear to have increased the move distance somewhat and maybe didn't clear all the Dec backlash before starting (?)

The first screen grab show the 28 minute Guiding Assistant run to illustrate the typical PE effect of the RA drive (in blue) and the drift effect (I think) of 4.5 arcmin PA error.   I moved the output data from the right hand side so it all fits in view.

The next one shows the Frequency Analysis of the native PE from the RA worm drive.

I guess this is typical of a vintage mount with no PE training. My old LX200 Classic is similar, maybe worse.

Here's the same analysis on the 47 minute guided run.

The PPEC algorithm appears to be doing a quite reasonable job.

Whether this can be improved I couldn't guess, so any deeper insights/suggestions from the experts will be of interest to us both.

Cheers,

- Jack

[Dawn, Paul, and Elizabeth Romero]

Hi Jack,

Thank you for taking the time to respond to my long term update. I think what this shows is that the software can smooth out the errors in the worm drive. I think I can get round stars with looser gears and a little more backlash because of PHD2! The future for me will be a looser worm gear mesh from here on out, so I can avoid some of the other issues like RA Stalls etc. Again thank You and clear skies!

Paul