Sidereal tracking motion during star-cross test?

[gerrit...@gmail.com]

Hello everyone,

I used PHD2 for the first time last night, with a Celestron OAG and ZWO ASI120 guide cam on my Meade 102ED (920 mm focal length f/9).  It was generally successful -- everything played together and I got good star images in PHD2, plenty of SNR and good star profiles at 2 s exposure.  I ran a star cross test with the default settings and got something vaguely resembling a cross, but it looks like my mount's sidereal tracking (I'm not sure if that's the right term) might have been overriding the E/W legs of the cross.  N is up in the image below, and polar alignment was not the greatest:

Is it generally necessary to turn off the mount's sidereal tracking before doing a star cross test in PHD2, or have I just got huge RA backlash?

Judging by the rattiness and open loops of the cross I'll want to get in and tune up my gears & backlash anyway, but I want to make sure I'm running the star cross test properly.

Thanks for any help,

Gerrit

[bw_msgboard]

Hi Gerrit, welcome to the group.  Comments below…

 

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From: open-phd...@googlegroups.com [mailto:open-phd...@googlegroups.com] On Behalf Of gerrit...@gmail.com
Sent: Monday, April 23, 2018 2:05 PM
To: Open PHD Guiding
Subject: [open-phd-guiding] Sidereal tracking motion during star-cross test?

Hello everyone,

 

I used PHD2 for the first time last night, with a Celestron OAG and ZWO ASI120 guide cam on my Meade 102ED (920 mm focal length f/9).  It was generally successful -- everything played together and I got good star images in PHD2, plenty of SNR and good star profiles at 2 s exposure.  I ran a star cross test with the default settings and got something vaguely resembling a cross, but it looks like my mount's sidereal tracking (I'm not sure if that's the right term) might have been overriding the E/W legs of the cross.  N is up in the image below, and polar alignment was not the greatest:

 

Is it generally necessary to turn off the mount's sidereal tracking before doing a star cross test in PHD2, or have I just got huge RA backlash?

 

No, you need to leave tracking on or the star is just going to whiz out of the field of view.  You’re basically trying to emulate what really goes on during guiding, moving the mount in all four directions while tracking at the sidereal rate.  Assuming the guide rate in your mount is at 1x sidereal or less, backlash in RA is irrelevant – it will have no effect on guiding.  Bottom line, I think you ran the test correctly.

 

Judging by the rattiness and open loops of the cross I'll want to get in and tune up my gears & backlash anyway, but I want to make sure I'm running the star cross test properly.

 

This is a pretty odd-looking result, especially if RA is left-right in the image.  You probably have large amounts of both Dec backlash and periodic error in RA.   If you want to post your guide log including the calibration, we can get a different perspective on what’s going on.

 

Cheers,

Bruce

 

Thanks for any help,

Gerrit

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[gerrit...@gmail.com]

Thanks for the quick reply and feedback, Bruce.  I see two log files from last night, not sure why, but I've zipped them together here.  I was fiddling around with several things, so you'll see some GA actions etc.  I was trying to take a look at RA PE, but haven't analyzed the result.  Is the calibration found elsewhere, or included in the log?

Gerrit

[bw_msgboard]

Hi Gerrit.  PHD2 produces two log files with each session – a debug log and a guiding log.  Those are described in the help file and partly here:

 

https://openphdguiding.org/getting-help/

 

Now that I see the guide log (which contains the calibration), I see you’re using on-camera guiding with an ST-4 guide cable.  There’s something wrong with the ST-4 cable, so guide commands to move the mount east don’t work at all.  That explains the odd star-cross test you got.  This is a fairly common problem and is one of many reasons we urge people to use ASCOM pulse guiding.  Your mount has a capable ASCOM driver so that’s the way you should probably go.  It will also give you many other benefits because PHD2 will know where the scope is pointing.  Here’s some more info:

 

https://openphdguiding.org/phd2-best-practices/

https://openphdguiding.org/manual/?section=Basic_use.htm#Equipment_Connection    (scroll down to mount-selection)

 

Since you’re at the stage of wrestling with the equipment to get it to behave, you should also upgrade to our latest development release, here:

https://openphdguiding.org/development-snapshots/

 

While you’re at this stage, you should probably disable Dec backlash compensation despite what the Guiding Assistant recommended.  It’s better at this point to get a clean look at the capabilities of the mount before trying to deal with its warts. J

 

Good luck,

Bruce

[gerrit...@gmail.com]

Thank you!  I am indeed using ST-4 from my ZWO guide camera, with the cable which came with the camera.  I bet the cable is bad.

I tried using ASCOM during daytime testing a few days ago and didn't see any effect so I assumed my ancient mount didn't support it (it's from the mid-90s, and I've recently inherited it so I don't know its provenance).  I was going through the ASCOM POTH hub, since I have a few other things communicating with the mount which use POTH.  Should the ASCOM interface convert PHD2 guide pulses to something even my old mount will recognize?  There may be something I need to do to make that happen, because I didn't see any PHD2 effect through ASCOM POTH a few days ago but I did using ST-4.

I'll try disabling the Dec backlash too.  Is the development release stable enough for a green newbie like me?

Gerrit

[Andy Galasso]

On Mon, Apr 23, 2018 at 6:04 PM, <gerrit...@gmail.com> wrote:

I didn't see any PHD2 effect through ASCOM POTH a few days ago but I did using ST-4.

It can be very difficult to observe the effect of guide pulse commands during the daytime. Did slews work with ASCOM?  Did the sending the guide pulses cause any error messages to pop up?  If you didn't see any error messages then ASCOM was probably working and it would be worthwhile to give it a go at night with actual stars.

BTW, the Celestron ASCOM driver allows connections from multiple applications at once (e.g. PHD2 and a planetarium app and an imaging app) so there is no need to use the ASCOM POTH hub and you can remove that from the mix as it is just an unnecessary complication.

Andy

[gerrit...@gmail.com]

Hi Andy,

Thank you for the help.  Yes, it is difficult to see PHD2 movement in the daytime.  I was using Manual Guiding with 5000 ms pulses, though, and I could definitely see movement using ST-4 but not when using ASCOM pulses.  I didn't see any error messages when doing ASCOM pulses.  I'm setting up right now (6 PM local) to run the test again.

I didn't do any slewing with PHD2 -- I didn't know that was possible.  But I'm using Stellarium Scope and APT to slew the scope through ASCOM so I know that interface is working.

My scope is a Meade.  Can I use a Celestron ASCOM driver?  I'm really hazy about the whole ASCOM concept...  I find the software and UI unintuitive and the help unhelpful.  I've managed to cobble something working together by telling POTH that I have a Meade Classic and that seems to work, but if I can use a Celestron driver and jettison the POTH I'll try that.

Gerrit

[Andy Galasso]

On Mon, Apr 23, 2018 at 9:11 PM, <gerrit...@gmail.com> wrote:

My scope is a Meade.  Can I use a Celestron ASCOM driver?  I'm really hazy about the whole ASCOM concept...  I find the software and UI unintuitive and the help unhelpful.  I've managed to cobble something working together by telling POTH that I have a Meade Classic and that seems to work, but if I can use a Celestron driver and jettison the POTH I'll try that.

oops, my bad, I thought it was a Celestron mount.  Nope, you can't use the Celestron ASCOM driver for the Meade mount.  And I'm pretty sure the Meade ASCOM driver only allows a single app to connect so you do need to use POTH to support multiple apps.  Sorry for the confusion.

Andy

[gerrit...@gmail.com]

No problem!  I did mention that I'm using a Celestron OAG, so that probably planted the seed.

I'm using PHD2 and APT with my imaging camera on LiveView right now, looking at a distant tree, and I sweartagod that ASCOM guide pulses are not moving my scope.  I'm using 5000 ms manual guiding, and repeating the same direction multiple times to make sure backlash is taken up.  I don't see any movement, but when I switch to On-camera mount and use ST-4 and the same test I can clearly see movement (esp N/S).  I can see backlash when I reverse direction, too.  I have to believe my old scope just doesn't accept guide pulses over ASCOM.

I found a little shard of plastic over one of my ST-4 connector pins, so I think that might have been the reason I wasn't seeing proper E/W movement in my star cross test last night.  I cleaned it off and I can see that sidereal motion stops when I manually guide E repeatedly (with ST-4), so I think maybe my star cross test will look better next time.

I'd love to use ASCOM guide pulses, so please let me know if you know of a way I can convert.

Gerrit

[Andy Galasso]

Sounds like you've pretty definitively proved ASCOM pulse guiding is not an option for that mount and ST4 will be the way to go. Good find on that plastic shard, you should be back in business for guiding.

BTW, I think Bruce may have mentioned this already, but you can gain back some of the benefits of the ASCOM connection to the mount by selecting the ASCOM mount as the Aux Mount in PHD2.  Guide pulses will still go through ST4 ("On-camera"), but PHD2 will have the benefit of knowing where the scope is pointing and which side of the pier it is on among other things.

Andy

[bw_msgboard]

Hi Gerrit.  Have you switched to the Meade ASCOM driver?  You can’t use a driver for a different kind of mount, that’s not going to work.  If you get the driver configuration right and are still convinced you can’t do pulse-guiding, you can use ST-4 guiding.  But by all means connect to the Meade ASCOM driver as the ‘aux-mount’ in PHD2.  That will save you a bunch of wasted time and will make it much easier for us to support you.  That said, even if the mount firmware doesn’t support pulse-guiding, it can be emulated by the ASCOM driver.

 

I don’t think I quite understand your comment about the ASCOM UI – there pretty much isn’t any. J  Once you set the driver properties and get squared away with which serial port you’re using, ASCOM becomes pretty much invisible.  If there are things that don’t make sense to you, we can probably help you out as long as you can identify specific questions.

 

Regards,

Bruce

 

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From: open-phd...@googlegroups.com [mailto:open-phd...@googlegroups.com] On Behalf Of gerrit...@gmail.com
Sent: Monday, April 23, 2018 7:15 PM
To: Open PHD Guiding
Subject: Re: [open-phd-guiding] Sidereal tracking motion during star-cross test?

 

No problem!  I did mention that I'm using a Celestron OAG, so that probably planted the seed.

--

[mj.w...@gmail.com]

Hi Gerrit

Just a thought, you do have the right Meade ASCOM driver se!ected ?

The list of drivers on the ASCOM site has several special LX200 Classic drivers before you get to the "LX200 Classic and Autostar 497........" driver.

Michael
Wiltshire UK

[gerrit...@gmail.com]

Thanks again to both of you.  I will definitely connect the mount as an ASCOM aux mount in addition to the necessary evil of ST-4 guiding.  I want to do drift alignment with PHD2 too, which look like it is better with an ASCOM connection.

Bruce, when I was experimenting with ASCOM pulse guiding I was using the PHD2 ASCOM POTH driver, since that's the way I would have to run it in conjunction with Stellarium and APT.  As I recall you tell POTH your scope type and comm details.  All that is working correctly; Stellarium and APT are communicating with the scope just fine using ASCOM POTH.  There wouldn't be a difference for PHD2 if I used the direct Meade ASCOM driver would there?

[gerrit...@gmail.com]

Hi Michael,

See my response to Bruce just below (our posts crossed in cyberspace).  I am able to control the scope just dandy with Stellarium and APT through ASCOM POTH configured for "Meade classic and Autostar 1".  I looked again at the ASCOM driver list just now and I don't see anything else which looks better.  This is a pretty old scope, from the mid-90s I think.

Thanks,

Gerrit

[bw_msgboard]

Hi Gerrit.  If the Meade ASCOM driver doesn’t support multiple concurrent client apps – and it may not if it’s really old – you should stick with POTH.  So from PHD2 you would use the aux-mount to connect to POTH, just like you do with the other two apps.  POTH will be the component that “owns” the serial connection to the mount.

 

One of the “evils” of ST-4 guiding is the potential routing headaches for the cable – it is probably the most common source of cable snags/drags/pinches.  It can be an awkward thing to route because it has to go from the very back of the guide assembly down to the rear plate of the mount controller.  One alternative that I used for years with my Meade mount was the Shoestring GP-USB device.  It’s still doing ST-4 guiding but the physical connection runs from the host computer to the base of the mount – so neither end is moving around as the scope is slewed.  It does require a separate USB port on the computer.  The devices are cheap and virtually bullet-proof in my experience.

 

Good luck,

[gerrit...@gmail.com]

Thank you for the tip, Bruce.  My cables are indeed getting a little snarly now.  I've tried to route them and tie them down in such a way that they don't bind for legal aiming positions, but it's starting to look like Medusa up there.  I'll look into the Shoestring gadget.

How would I tell PHD2 to send guide pulses to the GP-USB?  "On-camera" already mysterious enough to me -- PHD2 must be sending guide pulses to the USB guide camera which then translates them to ST-4.

Gerrit

[bw_msgboard]

 

 

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From: open-phd...@googlegroups.com [mailto:open-phd...@googlegroups.com] On Behalf Of gerrit...@gmail.com
Sent: Tuesday, April 24, 2018 11:38 AM
To: Open PHD Guiding
Subject: Re: [open-phd-guiding] Sidereal tracking motion during star-cross test?

 

Thank you for the tip, Bruce.  My cables are indeed getting a little snarly now.  I've tried to route them and tie them down in such a way that they don't bind for legal aiming positions, but it's starting to look like Medusa up there.  I'll look into the Shoestring gadget.

 

How would I tell PHD2 to send guide pulses to the GP-USB?  "On-camera" already mysterious enough to me -- PHD2 must be sending guide pulses to the USB guide camera which then translates them to ST-4.

 

From the help file:

The "Guide-port" (ST-4) interfaces use a specialized, hardware-level control port available on most mounts.  To use this type of interface, there must be another device in the link between PHD2 and the mount:

1.      Any of the guide cameras which have an ST-4 compatible "on-camera" guider interface. Use the 'on camera' mount choice for these setups.

2.      Any of the Shoestring GP-xxx devices

3.      A supported AO device with a guide port interface

With this style of interface,  PHD2 guide commands like "Move west 500 mSec" are translated by the intermediate device (camera, Shoestring box, AO) into electrical signals necessary to drive the mount motor for the correct length of time.

 

The ‘mount’ interface in PHD2 will include an entry for GPUSB – you would choose that one.

 

 

 

Bruce

[gerrit...@gmail.com]

Oh, man, I'm trying not to ask questions already in the excellent PHD2 documentation -- sorry about that!  I'll re-read.  It's perfectly clear how to use GP-USB, thank you very much.

Gerrit

[bw_msgboard]

No worries, Gerrit, I wasn’t intending to gouge you. J  Truth is, most of our users probably never look at the docs, so we will sometimes nudge people in that direction.  Plus, you might have come back with “yes, I read that but it was incomprehensible”, in which case we’d have to make another try at it.  

 

Good luck with the guiding,

[gerrit...@gmail.com]

The good news is I'm getting nice star-crosses now:

I discovered that “use newer pulse guiding” in ASCOM POTH was the main culprit.  When I switched that off, guiding through my ZWO ST-4 port became much better.

I also did a periodic-error calibration on my mount.  There is just a slight wobble visible on the N arm (toward the top) now.

With this tremendous improvement I was hoping for good PHD2 performance, but it's still a mess!  It won't calibrate or detect Dec backlash, and I can watch stars drifting around randomly.  I will post a new query about this shortly, but wanted to close the loop on this star-cross problem.

[bw_msgboard]

 

 

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From: open-phd...@googlegroups.com [mailto:open-phd...@googlegroups.com] On Behalf Of gerrit...@gmail.com
Sent: Monday, May 14, 2018 11:44 AM
To: Open PHD Guiding
Subject: Re: [open-phd-guiding] Sidereal tracking motion during star-cross test?

 

The good news is I'm getting nice star-crosses now:

I discovered that “use newer pulse guiding” in ASCOM POTH was the main culprit.  When I switched that off, guiding through my ZWO ST-4 port became much better.

Hi Gerri.  This part doesn’t make sense to me.  If you’re guiding with the ZWO ST-4 cable, you aren’t using ASCOM at all.  If you want to use ASCOM pulse guiding (recommended), you need the ‘mount’ connection to be the ASCOM driver for your mount – or POTH.  Not “on-camera”. And if you’re using pulse-guiding, you should disconnect that ST-4 cable entirely – it will just cause problems.

If you post your log files we’ll probably be able to tell you more.

Bruce

 

I also did a periodic-error calibration on my mount.  There is just a slight wobble visible on the N arm (toward the top) now.

 

With this tremendous improvement I was hoping for good PHD2 performance, but it's still a mess!  It won't calibrate or detect Dec backlash, and I can watch stars drifting around randomly.  I will post a new query about this shortly, but wanted to close the loop on this star-cross problem.

--

[gerrit...@gmail.com]

Hi Bruce,

I agree it doesn't make sense.  I saw it first during daytime testing, where manual guiding from PHD2 caused "pulses" of guiding on ST-4, separate from the guide pulse length.  I watched it on the scope and in Stellarium.  There were typically long pauses at the beginning of a PHD2 Manual Guide pulse, and gaps during long guiding pulses.  Manual guide pulses of 1 s or so often weren't seen at all.  When I switched off “use newer pulse guiding” in my ASCOM Meade driver (technically not POTH as I called it before) the problem went away.  Visually and in Stellarium I verified that manual guiding now reacted immediately, did the guide pulse length as selected, and did not do the long pauses.

(Since Stellarium seems to sample scope position only about every 1 s and interpolate movement between samples, the Stellarium movement was still halting.  But visually I could see that manual guiding was now as continuous as it could be considering geartrain backlash.  I also listened to the motors.)

As near as I could tell, PHD2 star-cross pulses were being lost or truncated, and now they aren't.

And I'm kind of stuck with ST-4 guiding.  My old Meade mount just won't guide with ASCOM pulses.  I have ASCOM as my Aux mount in PHD2 though.  (Hmm, I just had a thought.  I don't believe I have re-tested ASCOM guiding after turning off “use newer pulse guiding”.  I will try that tonight.)

I want to re-try PHD2 calibration and make sure I'm near the celestial equator and meridian before I start whining about poor cal and Dec backlash detection again.  I can't swear that's where I was last time.

Gerrit

On Monday, May 14, 2018 at 12:02:03 PM UTC-7, Bruce Waddington wrote:

 

 

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From: open-phd...@googlegroups.com [mailto:open-phd...@googlegroups.com] On Behalf Of gerrit...@gmail.com
Sent: Monday, May 14, 2018 11:44 AM
To: Open PHD Guiding
Subject: Re: [open-phd-guiding] Sidereal tracking motion during star-cross test?

 

The good news is I'm getting nice star-crosses now:

(image removed) 

[gerrit...@gmail.com]

Just to close the loop on the ASCOM guiding: that now works, since turning off "use newer pulse guiding" in the ASCOM Meade Classic driver.  I can now remove the ST-4 cable from the guide camera and run PHD2 using ASCOM POTH Hub as my mount.  Nice!

But my latest star-cross test (near the meridian & equator) wasn't so rosy.  The cross didn't look as good as it did a few days ago, near the zenith.  I think I have some sloppiness happening somewhere. 

Gerrit

On Monday, May 14, 2018 at 1:50:05 PM UTC-7, gerrit...@gmail.com wrote:

Hi Bruce,

I agree it doesn't make sense.  I saw it first during daytime testing, where manual guiding from PHD2 caused "pulses" of guiding on ST-4, separate from the guide pulse length.  I watched it on the scope and in Stellarium.  There were typically long pauses at the beginning of a PHD2 Manual Guide pulse, and gaps during long guiding pulses.  Manual guide pulses of 1 s or so often weren't seen at all.  When I switched off “use newer pulse guiding” in my ASCOM Meade driver (technically not POTH as I called it before) the problem went away.  Visually and in Stellarium I verified that manual guiding now reacted immediately, did the guide pulse length as selected, and did not do the long pauses.

(Since Stellarium seems to sample scope position only about every 1 s and interpolate movement between samples, the Stellarium movement was still halting.  But visually I could see that manual guiding was now as continuous as it could be considering geartrain backlash.  I also listened to the motors.)

As near as I could tell, PHD2 star-cross pulses were being lost or truncated, and now they aren't.

And I'm kind of stuck with ST-4 guiding.  My old Meade mount just won't guide with ASCOM pulses.  I have ASCOM as my Aux mount in PHD2 though.  (Hmm, I just had a thought.  I don't believe I have re-tested ASCOM guiding after turning off “use newer pulse guiding”.  I will try that tonight.)

I want to re-try PHD2 calibration and make sure I'm near the celestial equator and meridian before I start whining about poor cal and Dec backlash detection again.  I can't swear that's where I was last time.

Gerrit

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