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New (to me) Mach2 poor tracking

Marc Blank
 

So this is the second night I've tried the 2021 vintage Mach2.   The first night, guiding was awful, but the RA axis was loose, a problem I fixed with help from A-P.

Tonight, I'm seeing poor tracking (not guiding) in RA, so I did what I suppose Roland would suggest and let the Mach2 run for 10+ minutes unguided.   Here's what I see - note peak-to-peak RA is over 7 arc-seconds (although in fairness, it just keeps running away in RA).  Guiding is also pretty poor, though the skies look "ok" to me (around .7" overall, around .5" on each axis).   As far as guiding goes, I'm using Brian's recommended settings per the video.

It's pretty disappointing, honestly; not really sure what's going on, but I don't think I've ever seen numbers this bad when I had an 1100 without encoders.   All help appreciated.
Marc Blank
 

Here's a screenshot of unguided...

Mach2Unguided.png

Marc Blank
 
Edited

And the guide log...    I should add that the Mach2 is in good balance, I guess.   Let me know if other info would be helpful!

PHD2_GuideLog_2023-03-29_175336.txt

PHD2_GuideLog_2023-03-29_175336.txt

Roland Christen
 

You have the same amount of star motion in Dec as you have in RA. You should be disappointed in your skies, not the mount. Do you understand that when you do this test the DEC axis is standing perfectly still and the motors are not moving even a micron? So the Dec shows more than 2 arc seconds of star motion which is 100% due to atmospheric seeing in the sky above your location. Is there something you don't understand about atmospheric seeing and how you determine this? The mount is contributing zero to this tracking error.

Roland Christen
Astro-Physics Inc.


-----Original Message-----
From: Marc Blank <marc.blank@...>
To: main@ap-gto.groups.io
Sent: Wed, Mar 29, 2023 5:50 pm
Subject: Re: [ap-gto] New (to me) Mach2 poor tracking

Here's a screenshot of unguided...

--
Roland Christen
Astro-Physics
Marc Blank
 
Edited

Thanks for the response, Roland, although it seems a bit harsh.

Of course I know that the DEC motion is entirely seeing; it’s not what I was concerned about. 

I wanted to know about the pronounced RA drift, and whether it was expected given the encoders.  That’s what I don’t understand and was hoping for guidance on.  

Marc
Roland Christen
 

RA drift is strictly a function of polar alignment and where in the sky you are shooting. The mount's primary tracking rate is sidereal. The stars move at sidereal only at the zenith. Everywhere else in the sky they will move anywhere from 5 to 150 arcsec per hour. That is fundamental for stars moving across the sky. If you have perfect polar alignment the sidereal tracking rate will work fine within a circle of about 15 degrees around the zenith for typical 5 - 10 minute exposures. This is also fundamental. 

However, perfect polar alignment will NOT eliminate RA drift over the whole sky, especially East, West and South of the zenith. This is also a well-known fact and many papers have been written that allow calculation of the drift rate at various parts of the sky. Look up Publications of Brayebrook Observatory, which has very detailed calculations for figuring out star drift across the sky.

If you want no RA and no Dec drift, you will need to model.

Roland Christen
Astro-Physics Inc.

-----Original Message-----
From: Marc Blank <marc.blank@...>
To: main@ap-gto.groups.io
Sent: Wed, Mar 29, 2023 8:43 pm
Subject: Re: [ap-gto] New (to me) Mach2 poor tracking

Thanks for the response, Roland.  Is the pronounced RA drift expected given the encoders?   That’s what I don’t understand.  
Marc

--
Roland Christen
Astro-Physics
fernandorivera3
 

Call George Whitney in AP technical support after they open in the morning, he should be able to help you. Perhaps Howard also if he has returned back to AP already. 

Fernando

Andrea Lucchetti
 

Hi Marc,
Probably you mentioned before,
Are you 100% sure that Ra & Dec are mapped on x&y?
Basically, are you sure the drift is in RA and not in DEC? 
You know, sometimes we need a third eye to spot the simplest issues because we are so convinced.
In case just move the mount and check real  displacement.

Andrea


Il giorno gio 30 mar 2023 alle 09:28 Roland Christen via groups.io <chris1011=aol.com@groups.io> ha scritto:
RA drift is strictly a function of polar alignment and where in the sky you are shooting. The mount's primary tracking rate is sidereal. The stars move at sidereal only at the zenith. Everywhere else in the sky they will move anywhere from 5 to 150 arcsec per hour. That is fundamental for stars moving across the sky. If you have perfect polar alignment the sidereal tracking rate will work fine within a circle of about 15 degrees around the zenith for typical 5 - 10 minute exposures. This is also fundamental. 

However, perfect polar alignment will NOT eliminate RA drift over the whole sky, especially East, West and South of the zenith. This is also a well-known fact and many papers have been written that allow calculation of the drift rate at various parts of the sky. Look up Publications of Brayebrook Observatory, which has very detailed calculations for figuring out star drift across the sky.

If you want no RA and no Dec drift, you will need to model.

Roland Christen
Astro-Physics Inc.

-----Original Message-----
From: Marc Blank <marc.blank@...>
To: main@ap-gto.groups.io
Sent: Wed, Mar 29, 2023 8:43 pm
Subject: Re: [ap-gto] New (to me) Mach2 poor tracking

Thanks for the response, Roland.  Is the pronounced RA drift expected given the encoders?   That’s what I don’t understand.  
Marc

--
Roland Christen
Astro-Physics

Roland Christen
 

Regardless of which axis is showing drift, the mount itself is not producing drift. It is either polar misalignment or atmospheric refraction drift, neither of which is caused by the mount's tracking. The Mach2 especially cannot drift, it has high resolution encoders maintaining a steady sidereal motion to the RA axis. The Mach 2 mount maintains a very rigid and accurate tracking rate within 1/4 of a arc second, and that's hour after hour. No cheap guidescope can measure this level of accuracy, even for a few minutes.

One problem a lot of setups have is a small guide scope held in place by flimsy 3-point screws. This is then attached to the rings which hold the main scope. As the main scope flexes slightly inside the rings, the rings then impart a small motion to the guide scope. I've seen people trying to guide a 140mm refractor with a 30mm F5 guidescope. This is a total disaster if you want to guide accurately. Even measuring the basic guidestar position is nuts - it's like trying to measure the thickness of gold leaf with a wooden yardstick. Then trying to explain the the mount is doing the job correctly is a fool's errand. Nobody believes the manufacturer these days. 

Roland


-----Original Message-----
From: Andrea Lucchetti <andlucchett@...>
To: main@ap-gto.groups.io
Sent: Wed, Mar 29, 2023 9:49 pm
Subject: Re: [ap-gto] New (to me) Mach2 poor tracking

Hi Marc,
Probably you mentioned before,
Are you 100% sure that Ra & Dec are mapped on x&y?
Basically, are you sure the drift is in RA and not in DEC? 
You know, sometimes we need a third eye to spot the simplest issues because we are so convinced.
In case just move the mount and check real  displacement.

Andrea


Il giorno gio 30 mar 2023 alle 09:28 Roland Christen via groups.io <chris1011=aol.com@groups.io> ha scritto:
RA drift is strictly a function of polar alignment and where in the sky you are shooting. The mount's primary tracking rate is sidereal. The stars move at sidereal only at the zenith. Everywhere else in the sky they will move anywhere from 5 to 150 arcsec per hour. That is fundamental for stars moving across the sky. If you have perfect polar alignment the sidereal tracking rate will work fine within a circle of about 15 degrees around the zenith for typical 5 - 10 minute exposures. This is also fundamental. 

However, perfect polar alignment will NOT eliminate RA drift over the whole sky, especially East, West and South of the zenith. This is also a well-known fact and many papers have been written that allow calculation of the drift rate at various parts of the sky. Look up Publications of Brayebrook Observatory, which has very detailed calculations for figuring out star drift across the sky.

If you want no RA and no Dec drift, you will need to model.

Roland Christen
Astro-Physics Inc.

-----Original Message-----
From: Marc Blank <marc.blank@...>
To: main@ap-gto.groups.io
Sent: Wed, Mar 29, 2023 8:43 pm
Subject: Re: [ap-gto] New (to me) Mach2 poor tracking

Thanks for the response, Roland.  Is the pronounced RA drift expected given the encoders?   That’s what I don’t understand.  
Marc

--
Roland Christen
Astro-Physics

--
Roland Christen
Astro-Physics
Ray Gralak
 

Hi Marc,

Tonight, I'm seeing poor tracking (not guiding) in RA, so I did what I suppose Roland would suggest and let the
Mach2 run for 10+ minutes unguided. Here's what I see - note peak-to-peak RA is over 7 arc-seconds (although
in fairness, it just keeps running away in RA). Guiding is also pretty poor, though the skies look "ok" to me (around
.7" overall, around .5" on each axis). As far as guiding goes, I'm using Brian's recommended settings per the
video.
In addition to refraction, the RA tracking error could be caused by flexure changes in the telescope while tracking. Also, tugging cables and ground settling can contribute. To get the best tracking performance you should create a dense pointing model with APPM and use APCC's Dec Arc Tracking option.

-Ray
ROBERT WYNNE
 

Reminds me of the first day reporting as an apprentice machinist with what I thought was the minimum set of tools. I had bought a wooden rule which I thought was consistent with the rule requirement for a basic set of tools. The shop foreman came over to check the completeness of my set and found the wooden rule. He picked it up and tossed it in the garbage can at the same time said, "What do you think we are here, carpenters"? -Best, Robert

On 03/30/2023 1:37 AM Roland Christen via groups.io <chris1011@...> wrote:


Regardless of which axis is showing drift, the mount itself is not producing drift. It is either polar misalignment or atmospheric refraction drift, neither of which is caused by the mount's tracking. The Mach2 especially cannot drift, it has high resolution encoders maintaining a steady sidereal motion to the RA axis. The Mach 2 mount maintains a very rigid and accurate tracking rate within 1/4 of a arc second, and that's hour after hour. No cheap guidescope can measure this level of accuracy, even for a few minutes.

One problem a lot of setups have is a small guide scope held in place by flimsy 3-point screws. This is then attached to the rings which hold the main scope. As the main scope flexes slightly inside the rings, the rings then impart a small motion to the guide scope. I've seen people trying to guide a 140mm refractor with a 30mm F5 guidescope. This is a total disaster if you want to guide accurately. Even measuring the basic guidestar position is nuts - it's like trying to measure the thickness of gold leaf with a wooden yardstick. Then trying to explain the the mount is doing the job correctly is a fool's errand. Nobody believes the manufacturer these days. 

Roland


-----Original Message-----
From: Andrea Lucchetti <andlucchett@...>
To: main@ap-gto.groups.io
Sent: Wed, Mar 29, 2023 9:49 pm
Subject: Re: [ap-gto] New (to me) Mach2 poor tracking
Hi Marc,
Probably you mentioned before,
Are you 100% sure that Ra & Dec are mapped on x&y?
Basically, are you sure the drift is in RA and not in DEC? 
You know, sometimes we need a third eye to spot the simplest issues because we are so convinced.
In case just move the mount and check real  displacement.

Andrea


Il giorno gio 30 mar 2023 alle 09:28 Roland Christen via groups.io <chris1011=aol.com@groups.io> ha scritto:
RA drift is strictly a function of polar alignment and where in the sky you are shooting. The mount's primary tracking rate is sidereal. The stars move at sidereal only at the zenith. Everywhere else in the sky they will move anywhere from 5 to 150 arcsec per hour. That is fundamental for stars moving across the sky. If you have perfect polar alignment the sidereal tracking rate will work fine within a circle of about 15 degrees around the zenith for typical 5 - 10 minute exposures. This is also fundamental. 

However, perfect polar alignment will NOT eliminate RA drift over the whole sky, especially East, West and South of the zenith. This is also a well-known fact and many papers have been written that allow calculation of the drift rate at various parts of the sky. Look up Publications of Brayebrook Observatory, which has very detailed calculations for figuring out star drift across the sky.

If you want no RA and no Dec drift, you will need to model.

Roland Christen
Astro-Physics Inc.

-----Original Message-----
From: Marc Blank <marc.blank@...>
To: main@ap-gto.groups.io
Sent: Wed, Mar 29, 2023 8:43 pm
Subject: Re: [ap-gto] New (to me) Mach2 poor tracking
Thanks for the response, Roland.  Is the pronounced RA drift expected given the encoders?   That’s what I don’t understand.  
Marc


--
Roland Christen
Astro-Physics



--
Roland Christen
Astro-Physics

steve.winston@...
 

On Wed, Mar 29, 2023 at 11:43 PM, Marc Blank wrote:
I wanted to know about the pronounced RA drift, and whether it was expected given the encoders.  That’s what I don’t understand and was hoping for guidance on
I think you mean the reported RA PE here, not "drift"?    The reported PAE is only 0.1 arc-mins, so drift does not appear to be a problem :).   The reported PE however is almost 12 arc-s, which is very unusual for a Mach2.  My AP1600AE has LEDs on the mount that indicate whether the encoders are enabled and working - I assume the Mach2 has the same? - what color are these LEDs when your mount is powered up?

Overall, your 8 minute guiding session looks like it is guiding within your local seeing conditions, and the constraints of your guide set-up. Your guide star has a HFD of 5" and you're guiding at 0.6" RMS, so that's guiding within 1/8th of a pixel, which is probably as good as it can guide..  If possible, I'd suggest increasing your guide scale and / or waiting for a night of good seeing to redo your tests.  And checking that your encoders are working and enabled (which even from your short guiding results, they appear to be).
Brian Valente
 

>>>The reported PE however is almost 12 arc-s, which is very unusual for a Mach2

I have a different interpretation of this data

the Polar alignment error is calculated from the Dec drift, so that is independent of any RA measurement or RMS

If we rotate the RA to get rid of the apparent drift, you can see the peak-to-peak is not 12" but more like 1-2"

image.png

Looking more closely, these 'peak to peak' values are not periodic but rather exposure to exposure (i.e., this suggests seeing conditions to me)

image.png



On Fri, Mar 31, 2023 at 6:39 AM <steve.winston@...> wrote:
On Wed, Mar 29, 2023 at 11:43 PM, Marc Blank wrote:
I wanted to know about the pronounced RA drift, and whether it was expected given the encoders.  That’s what I don’t understand and was hoping for guidance on
I think you mean the reported RA PE here, not "drift"?    The reported PAE is only 0.1 arc-mins, so drift does not appear to be a problem :).   The reported PE however is almost 12 arc-s, which is very unusual for a Mach2.  My AP1600AE has LEDs on the mount that indicate whether the encoders are enabled and working - I assume the Mach2 has the same? - what color are these LEDs when your mount is powered up?

Overall, your 8 minute guiding session looks like it is guiding within your local seeing conditions, and the constraints of your guide set-up. Your guide star has a HFD of 5" and you're guiding at 0.6" RMS, so that's guiding within 1/8th of a pixel, which is probably as good as it can guide..  If possible, I'd suggest increasing your guide scale and / or waiting for a night of good seeing to redo your tests.  And checking that your encoders are working and enabled (which even from your short guiding results, they appear to be).



--

steve.winston@...
 

Hey Brian,

So you're saying PHD2 is not removing RA drift when calculating PE?   I can't say I've ever noticed my measured PE change based on changing PAE or RA drift.   Maybe a question for the PHD2 forum.

Steve
Ray Gralak
 

Hi Steve,

Hey Brian,

So you're saying PHD2 is not removing RA drift when calculating PE? I can't say I've ever noticed my measured
PE change based on changing PAE or RA drift. Maybe a question for the PHD2 forum.
It is very confusing for PHD2 to have chosen that label. There is no way that the graph shown indicates a periodic error of 12 arc-seconds. It looks like PHD2 may have used the minimum and maximum pixel coordinates to calculate peak to peak. In this case, there is RA drift which produced the misleading result. There is no PE in the data nor in the Mach2.

-Ray
Brian Valente
 

Hi Steve

>>>So you're saying PHD2 is not removing RA drift when calculating PE?   I can't say I've ever noticed my measured PE change based on changing PAE or RA drift.   Maybe a question for the PHD2 forum.

No, sorry I probably wasn't clear. 

We were talking about the peak-to-peak being 12.5" but that is misleading in this case because of the drift and certainly not an indication of periodic error. If you correct for the drift then peak-to-peak is more like 1-2". 

image.png

The PHD2 analysis of periodic error from the unguided results here put everything < 0.15"
image.png
 

On Fri, Mar 31, 2023 at 7:44 AM <steve.winston@...> wrote:
Hey Brian,

So you're saying PHD2 is not removing RA drift when calculating PE?   I can't say I've ever noticed my measured PE change based on changing PAE or RA drift.   Maybe a question for the PHD2 forum.

Steve



--

steve.winston@...
 

Hey Brian,

I think you (and Ray)  are both saying that the reported p2p for RA is not removing drift, and that is why it reporting such a high p2p.   And I agree, the log data seems to indicate that.

To Ray's point,  the "peek-to-peek" terminology used by PHD2 may just be confusing - I have personally always seen a very close relationship to the value reported here and the mounts measured PE (as confirmed by also measuring with PemPro), so my assumption has been that PHD2 is removing drift and not including it in the reported p2p for RA.

Anyway, the data in this log seems to indicate that drift in RA is not being removed.

Steve
Andrea Lucchetti
 

The phD log analyzer program is good at de-trending the data and separate drift and PE. In this case it is easy by eye to see that PE is small. Roland gave several reason to explain drift in RA. I can mention also a list of mistakes that I personally did that can produce the same ( wrong model in memory, wrong rate selection, custome rate , etc).
And my classic, reading DEC as RA 😂 with polar error. 

Il giorno ven 31 mar 2023 alle 19:05 <steve.winston@...> ha scritto:
Hey Brian,

I think you (and Ray)  are both saying that the reported p2p for RA is not removing drift, and that is why it reporting such a high p2p.   And I agree, the log data seems to indicate that.

To Ray's point,  the "peek-to-peek" terminology used by PHD2 may just be confusing - I have personally always seen a very close relationship to the value reported here and the mounts measured PE (as confirmed by also measuring with PemPro), so my assumption has been that PHD2 is removing drift and not including it in the reported p2p for RA.

Anyway, the data in this log seems to indicate that drift in RA is not being removed.

Steve
Brian Valente
 

>>>Anyway, the data in this log seems to indicate that drift in RA is not being removed.

yep, at least for peak-to-peak. using the tools in PHD Log Viewer will give a better understanding of the data

On Fri, Mar 31, 2023 at 10:05 AM <steve.winston@...> wrote:
Hey Brian,

I think you (and Ray)  are both saying that the reported p2p for RA is not removing drift, and that is why it reporting such a high p2p.   And I agree, the log data seems to indicate that.

To Ray's point,  the "peek-to-peek" terminology used by PHD2 may just be confusing - I have personally always seen a very close relationship to the value reported here and the mounts measured PE (as confirmed by also measuring with PemPro), so my assumption has been that PHD2 is removing drift and not including it in the reported p2p for RA.

Anyway, the data in this log seems to indicate that drift in RA is not being removed.

Steve



--

Roland Christen
 


 The reported PE however is almost 12 arc-s, which is very unusual for a Mach2. 
I think this statement is in error. PE in the Mach2 is zero for this mount. The Mach2 will not operate without encoders active and therefore cannot have PE. It can have drift of course, and that is strictly a function of polar alignment and atmospheric refraction. Neither one of those can be cured by encoders.

Roland Christen
Astro-Physics Inc.


-----Original Message-----
From: steve.winston@...
To: main@ap-gto.groups.io
Sent: Fri, Mar 31, 2023 3:39 am
Subject: Re: [ap-gto] New (to me) Mach2 poor tracking

On Wed, Mar 29, 2023 at 11:43 PM, Marc Blank wrote:
I wanted to know about the pronounced RA drift, and whether it was expected given the encoders.  That’s what I don’t understand and was hoping for guidance on
I think you mean the reported RA PE here, not "drift"?    The reported PAE is only 0.1 arc-mins, so drift does not appear to be a problem :).   The reported PE however is almost 12 arc-s, which is very unusual for a Mach2.  My AP1600AE has LEDs on the mount that indicate whether the encoders are enabled and working - I assume the Mach2 has the same? - what color are these LEDs when your mount is powered up?

Overall, your 8 minute guiding session looks like it is guiding within your local seeing conditions, and the constraints of your guide set-up. Your guide star has a HFD of 5" and you're guiding at 0.6" RMS, so that's guiding within 1/8th of a pixel, which is probably as good as it can guide..  If possible, I'd suggest increasing your guide scale and / or waiting for a night of good seeing to redo your tests.  And checking that your encoders are working and enabled (which even from your short guiding results, they appear to be).

--
Roland Christen
Astro-Physics

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