Pier Flip, AWR drive system & ASCOM

I’m guessing this will mainly be a question for one of the Developers.

I use an Alter D6 GEM mount fitted with an AWR drive system together with the driver supplied by Tigra Astronomy.

I’m fairly new to SGP but I’ve been unable to get an automatic meridian flip to work.

Both AWR & Tigra have been extremely helpful & supportive but I need some technical information in deeper detail than that provided in the SGP help files.

My system cannot support a time set before the meridian & SGP correctly warns me of this if I try to do this. In practice I need to set a post meridian delay of say 30 minutes.

The pier flip routine does begin, take an image, stop the guider, complete the JNOW\J2000 conversion etc. I can see it all in the log file. But the mount never actually slews. In the event log it tells me the procedure has failed because the starting side of the pier & the ending side of the pier are the same.

Here is an extract from the uploaded log file:

[10/09/18 21:57:39.415][DEBUG] [Pier Flip Thread] PHD2 GetPhdStatus - Post-Wait: Stopped
[10/09/18 21:57:39.415][DEBUG] [Pier Flip Thread] PHD2: Successfully stopped PHD2…
[10/09/18 21:57:39.415][DEBUG] [Pier Flip Thread] Meridian Flip: Sending Telescope command to execute meridian flip
[10/09/18 21:57:39.454][DEBUG] [Telescope Thread] ASCOM Telescope: Pier side is West
[10/09/18 21:57:39.454][DEBUG] [Telescope Thread] ASCOM Telescope: attempting pier flip using slew
[10/09/18 21:57:39.609][DEBUG] [Telescope Thread] Telescope: Slewing to J2000 RA: 18.8922030571624 (18h53m31.93s) Dec: 33.0155083437973 (33°00’55.83")
[10/09/18 21:57:39.609][DEBUG] [Telescope Thread] Telescope: Slew received J2000 coordinates, mount requires JNOW, converting…
[10/09/18 21:57:39.609][DEBUG] [Telescope Thread] Telescope: Slewing to JNOW RA: 18.9036111111111 Dec: 33.0452777777778
[10/09/18 21:57:43.479][DEBUG] [Telescope Thread] Scope reports it is done with synchronous slew, verifying…
[10/09/18 21:57:43.480][DEBUG] [Telescope Thread] Telescope: Slewing has completed
[10/09/18 21:57:43.480][DEBUG] [Telescope Thread] Telescope: Settling for 3 seconds
[10/09/18 21:57:46.480][DEBUG] [Telescope Thread] Telescope: Settling has completed
[10/09/18 21:57:47.000][DEBUG] [Telescope Thread] ASCOM Telescope: Failed to flip because starting pier side and ending pier side are the same!
[10/09/18 21:57:47.327][DEBUG] [Pier Flip Thread] Meridian Flip: Telescope command to meridian flip has completed
[10/09/18 21:57:47.327][DEBUG] [Pier Flip Thread] Meridian Flip: Telescope failed to perform meridian flipsg_logfile_20181009213158.txt (537.1 KB)

How can this be I ask? When it clearly is not?

I decide to run the ASCOM conform tool which exercises your mount & among many other things conducts side of pier tests as described in the following links to the relevant ASCOM standards documentation:

The subject is quite confusing, if you follow the links you’ll see there are historical reasons why the sideOfPier property name does not reflect it’s true meaning. My personal conclusion is that there may even be a mistake in the ASCOMSideOfPierBehaviour.pdf paper?

Anyway, the result of my conform test was that my mount reports the physical side of pier rather than the pointing state - which is flagged up as an issue at the end of the report.

Tests I’ve carried out using a terminal application to poll the mount (:GSP#) returns E when my scope is on the west side of the pier pointing east but this does not change when the scope crosses the meridian - which is not what I expected. It only changes if I perform a GOTO or a slew over the pole.

This is why I think I see the failure message “Telescope: Failed to flip because starting pier side and ending pier side are the same!” in the SGP log file.

I’m currently liaising with AWR & Tigra who are both give fantastic support but regarding SGP I’d like to ask the following questions:

  1. How do the developers view\interpret the sideOfPier property?

  2. Do you consider the ASCOMSideOfPierBehaviour.pdf paper is correct?

  3. Does SGP specifically require the mount to return it’s pointing state or can the automatic pier flip be made
    to work with mounts that only report the physical side of pier?

  4. How does SGP actually instruct the mount to flip? Does issue a GOTO\slew to the current coordinates?

  5. Perhaps an obvious question but if the scope is on the west, pointing east & mount tracks across the
    meridian naturally from east to west (the weights now point up), scope is on the west but now pointing
    west would SGP expect to see a change in the sideOfPier property? I.E should the flag change from E to W?

PS
I’d also be interested to hear from anyone else who uses an AWR drive system.

Peter Simpson and I spent a lot of time getting the ASCOM Pier Side documentation and Conform working correctly. As you say the name isn’t wonderful, Pointing State would be better,

If a mount is tracking an object to the SE then the pointing state should be West (looking East). As the telescope tracks through the meridian the pointing state should not change. This is what is expected, and is what a dome needs to be able to continue to be aligned so the scope can see out.

Now the mount has tracked past the meridian. The object is now slightly West of South and the counterweight is beginning to be higher than the scope. This can’t continue for long. Al this point a slew should move the hour angle axis through 180 degrees and the declination axis to the other side of the pole. You see the mount slew through the pole. This process changes the pointing state and it should now be East (looking West).

Your incomplete log doesn’t give all the information that’s needed because it doesn’t show the pointing state before the mount crossed the meridian but it looks as if the pointing state just before the slew is correct - West (looking East).
What would be expected is a long slew, 180 degrees in hour angle and 114 degrees in Declination but the slew is reported as only taking 4 seconds and that doesn’t seem long enough.
So it looks as if for some reason the mount didn’t change pointing state and so did not report a change. SGP doesn’t like that.

We don’t know why, largely because we can’t see the mount.
First what is the actual mount state before the slew? Is it with the Scope to the West of the mount and the counterweight to the east? That’s what is expected if the tracking was started well before the mount reached the meridian.
Second, is my speculation correct and the slew did not change this?
Third, how far past the meridian is the scope pointing? If it’s very close to the meridian then although SGP thinks it is past, the mount may think it hasn’t and so not do the long, pointing state change, slew. Log data from earlier in the process might have shown this.

Other things
The pointing state reported by the hardware may be different to the ASCOM state. Part of the driver’s duties is to convert the hardware state to the ASCOM state.
Conform does a good job at testing this and if it reports that the mount is reporting physical rather than the correct pointing state then it’s probably correct.

In the situation you describe in your point 5 if the mount spontaneously changes pointing state as it tracks past the meridian then that is physical pier side, not pointing state. The pointing state can only change as a result of a slew with the dec axis going through 90 degrees.

HTH

Chris

Hi Chris,

Many thanks for the prompt reply. Apologies I thought I’d uploaded the complete log – please find it attached to this email.

Apologies too, no offence intended, as I’m assuming from your comments you may be the ‘Chris’ mentioned in the Side Of Pier document? Oooops!

It’s just that for me I read in the ASCOM ITelescopeV3.SideOfPier Property documentation that Normal Pointing State is pierEast. But in the Side of pier pdf document I included in the post, Figure 2 shows the green east side is labelled as normal pointing state whereas in Figure 4 the blue west side is labelled as pierEast. So I figured this was a contradiction & it’s added to my confusion.

Now I read your comment regarding dome requirements I understand the need for the pointing state to remain unchanged as the scope tracks through the meridian. Dome slaving is on my To-Do list after this automatic pier flip has been resolved. So thank you for highlighting this.

With my mount tracking a SE object, so my mount is on the West with my scope pointing EAST, then my hardware returns E# in reply to :GSP#. This does not change as the mount tracks through the meridian. Nor does it change if I manually slew in RA through the meridian. It will only change if I manually initiate a meridian reversal from my hand controller or from planetarium software which causes the mount to slew over the pole. Now my mount is on the East (looking West) & my hardware returns W# in reply to :GSP#. I’m not sure how I could independently compare this to what the driver’s reporting though?

Hopefully the attached log will fill in a few gaps.

From you final comments under “Other things” it sounds like my hardware reports pointing state - but, I’m guessing the driver does some kind of conversion as conform flags a pointing issue. I’ve attached the conform report.

So to return to one of my original questions :- can SGP’s automatic pier flip work with a mount driver that reports physical pier side instead of reporting the pointing state?

Many thanks & regards

Martin

sg_logfile_20181009213158.txt (537 KB)

ASCOM.AWR.Telescope.Validation3.txt (511 KB)

Yes, I’m the Chris involved with the ASCOM pointing state stuff, no apologies needed.

I must defer this to Ken and Jared and the AWR driver developer, the logs should help a lot.

What I can see is that the start of the sequence is a very short time before the pointing state change was attempted and that the position seems to be a long way past the meridian. Was the mount already aligned before the start of SGP?

I very much doubt that Ken and Jared will implement any pointing state behaiour other than what is expected, ddefinitely not using physical pier side (whatever that is).

I’m guessing that your mount is reporting the incorrect SideOfPier for some reason or another. It could be bad setup (date/time/Lat/long) in the ASCOM driver or mount. It could be a bad sync, or it could just be incorrect behavior from the ASCOM driver.

This is generally ok and only presents a problem when you’re imaging below the pole. Which for most of us is rare.

It should not change when you cross through the meridian. Also keep in mind that what the serial commands say and what the ASCOM driver says can be two different things. The ascom driver may be interpreting things for you. However the document does address this state.

EXCEPTIONS TO THE RULE
Flip margins, slew limits etc. are tools that mount designers provide to allow the observer to override the basic design principle that the telescope should choose the pointing state that puts the telescope above the counterweights at all times. Conform deliberately avoids testing in sky areas where these conveniences are frequently implemented. It chooses hour angles well away from the meridian and wherever possible chooses declinations that keep observation points away from the horizon and the pole.

We take what the ASCOM driver reports as its SideOfPier, this is really up to the driver, not us. The one difference is the “under the pole” behavior which we need to account for. We do expect that the “Exception” mentioned above is in place (as every mount I have ever encountered implements this exception). Essentially If the scope is on the west side of your mount (normally called PierWest, aka looking East) and your mount tracks past the meridian, then you’re still PierWest. We do not expect it to change by tracking through the meridian (in most cases…see the “below the pole” exception)

Yes, we do. Since we’re implementing their interfaces they get to choose what is right and wrong and we just adhere to it. And I believe their implementation works well.

I guess it depends on how you differentiate the two. SGP will only automatically initiate a flip when the OTA is on the West side of the Pier ( driver reporting PierWest), that is assuming your mount can’t flip prior to the meridian.

If CanSetSideOfPier returns true then we explicitly set it. If it doesn’t we initiate a slew to the same coordinates once the hour angle and RA indicate that you’ve passed the meridian.

No, and just to clarify we would expect that it is reporting PierWest and that it stays reporting PierWest when it moves past the meridian.

To test things in SGP you should do the following:

  • make sure your lat/long/time are set correctly in your ASCOM driver or scope.
  • Slew to a bright star and sync your mount, or align it…whatever you normally do here.
  • Slew to a star near the meridian but east of it (OTA on the west side of the meridian)
  • Enable the “Use Auto Meridian Flip” and make sure that the “Minutest Past Meridian to flip”, in the Auto Meridian Flip Settings, is 0
  • When you move to the east you should then see the “Time To Pier Flip” counting down:
    image
  • If “Time To Pier Flip” shows “NA” then that means that SGP thinks you’re on the East side of the mount and it will not flip.
  • Now if you move your scope to the East side of the pier and the “Time To Flip” becomes something other than NA, then the driver is likely reporting the wrong time.

Hope that helps,
Jared

Hi Jared,

Many thanks for your very comprehensive & informative reply.

I can report that I’m very confident the sync is correct as GOTO’s are very accurate. I’m also very confident my date, time, lat, long, elevation & local sidereal time are correct. MY LST I can easily check using one of the independent on line tools & compare with my mounts hand controller, planetarium software & the ASCOM POTH. Likewise POTH reports my Hour Angle counting down from negative when my mount is on the West (scope pointing East) & calibrated in this quadrant (target between 0 & +90 deg declination). In POTH I can watch my HA go positive & my planetarium & scope cross the meridian at the same expected time. If I manually slew the scope towards either the East or West horizon it will automatically stop when the scope reaches the horizon - this is a feature of the AWR drive system & does not work correctly if the scope is wrongly calibrated or the date, time, lat or long is wrong.

Your reply has confirmed several things for me (thank you). I shall try the test\checks you suggest but is it possible to carry this out without engaging in a full imaging sequence? I mean with just the telescope selected. If I can check this without using the camera, autoguider, plate solving etc then I can carry out this check under cloudy conditions or even during the day just by observing what happens when the scope tracka through the meridian.

By the way my “Time to To Pier Flip” always shows “NA” I’ve never seen it display a time value.

I’ve not tried slewing East and seeing if “NA” changes to something else - I’ll try it & see what happens.

Many thanks & Regards
Martin

Yes, provided that your mount has a valid model you should be able to slew it to different locations (with the hand controller or otherwise) and see the results within SGP.

Thanks,
Jared

Hi Jared,

Thank you for your reply.

In the meantime I’ve had some fantastic advice from Alan at AWR & in particular some amazing customer support from Tim at Tigra Astronomy. Tim spent several hours with me in a couple of Team Viewer sessions debugging the driver, worked on the fix during his Sunday afternoon & issuing me with a new driver the same evening.

In amongst the clouds I’ve had a couple a few opportunities to test it for real. The sideOfPier() now returns the pointing state, SGP now displays the time to flip value & the mount flips right on cue. The time to flip then changes to NA after the flip when sideOfPier() returns East. In practice my mount has a minimum ‘Flip point’ of 30 minutes after the meridian. This seems to be down to a meridian reversal function built into the AWR drive system that is specifically available 30 minutes before or after the meridian (as a direct user instruction on the handset). So long as I enter a time after the meridian to flip >= 31 minutes then it works perfectly.

I’ve learned a lot over the last couple of weeks.

Many thanks to:-

Chris (ASCOM developer) for his initial advice & side of pier information.

Jared (Developer) for your very detailed reply to my questions. This was a big help.

Alan (from AWR) for his advice, product knowledge & understanding of my issue.

Tim (from Tigra Astronomy) for his tireless efforts, programming expertise & personal time.

A fantastic customer support effort by all involved.

Kind regards

Martin