Slewed to target in post-meridian flip position (before transit time)

Improve101

This occurred on Wednesday night, where my target was going to transit at 12:06am, i slewed to target at 11:36pm (30 minutes or around 7 degrees prior to transit) and was surprised to watch the mount (EQ6R Pro in EQMod Mount mode on the asiair) slew to the target in a post-meridian flip (post-12:06am) orientation, and by doing this, the camera almost collided with the tripod legs. At 12:06am, Autorun tried to do the Meridian flip however the mount didn't move, it just checked it's position, refocused (based on my setting to do that after each meridian flip) and continued on as it was already in a post-meridian flip position.

This could have been an expensive error and I'm glad i was there watching it.

Any idea how this might have happened? Anything i need to do to prevent it from happening? Can we have more control over a meridian flip, like 'only start in a post-meridian flip position when target within X degrees from the transit line, else start in pre-meridian flip position'.

Thanks & keep up the great work!

wvreeven

Improve101 What probably helps for you is to understand that the mount is in control of meridian flips and how it points to objects and not ASIAir. All ASIAIr does is issue a goto command with specific sky coordinates. In case of an equatorial mount those coordinates are Ra and Dec. The mount then decides how it slews and points to those coordinates. As soon as a meridian flip is due, ASIAir sends yet another goto to the mount with the same sky coordinates. Again, it is up to the mount whether it performs a meridian flip or not.

Unfortunately the SkyWatcher SynScan manual doesn't indicate anything related to "pointing east of the meridian with the counter weight up" limits so this may be a hidden feature of your mount. I have an EQ6R Pro as well and never observed this behavior but as far as I remember I never willingly pointed at a target so close to the meridian and if I did it was so long ago that I don't remember it.

darkmatter

I had a similar issue this weekend, the Asiair tried to steer the scope through the tripod leg but in my case it can't be blamed on the mount. I use an Avalon Linear and by itself the mount is pretty dumb: no encoders, no goto, no meridian flip, nothing. With the plastic-fantastic hand controller you can set slew speed and then slew the mount but for anything more than that it relies entirely on external devices. The benefit of this is that there's never a conflict between the external device and the mounts internal system. In my case it also means that anything going wrong with the meridian flip is entirely the Asiairs fault. If you have a big filter wheel sticking out at the end of a long scope you're going to need some extra margin. Thankfully there's a very simple solution to this: give us the option to set the meridian flip to happen something like 5 or 10 minutes BEFORE reaching the meridian. Or better yet, if the meridian flip has to be done within a certain amount of time (20 or 30 minutes or so) after the start of an autorun sequence, ask if the flip has to be done first. And finally, I would like to have a simple "do meridian flip now" option. All these should be fairly simple to implement.

Jarno

w7ay

darkmatter no meridian flip

Wait, Jarno. If the Linear has no Meridian Flip ability, then you are out of luck.

Except for the EQMOD library, ASIAIR depends on the mount to execute a Meridian Flip (by asking the mount to perform a GOTO after the target is known to have passed the meridian). With EQMOD, the meridian flip path is in the EQMOD library.

Are you sure the Linear does not have Meridian flip? Perhaps it depends on ASCOM to do it (ASCOM has the smarts that ASIAIR does not).

You can check by doing a GOTO a star (target) high ahead, just east of the Meridian. Just let it track with auto guiding turned off. After perhaps 5 minutes after the star has transited, send another GOTO to the same star. Does the Linear execute a Meridian Flip? If not, wait another 5 minutes and try again, just in case you mount is not east-west leveled. If there is no Meridian Flip after a good amount of time, the Linear indeed does not have Meridian Flip ability.

Best thing is you can test this in the day time, since no plate solving is involved.

Even my EM-11 with its very dumb Temma 2 controller has Meridian Flip (Takahashi lives in the 20th century -- that is why there is good craftsmanship and optical precision; but they are not known to be cutting edge).

Chen

w7ay

darkmatter

Jarno, are you using the StarGO in conjunction with the Linear?

This is what the StarGO manual says:

In the case the object to mount is located in the other side of the Meridian the GOTO will cause a Meridian Flip to avoid mechanical interferences between the telescope and the tripod or the column.

https://www.swagastro.com/uploads/2/3/3/7/23377322/stargo_user_manual_rev1.7.2.pdf

So, indeed, it should have Meridian Flip built in.

Most mounts (in fact, almost all of them) do not even have a "perform Meridian Flip" function. The Meridian flip for all the German mounts are implicit -- when you command a GOTO after the hour angle of the mount has gone past zero (i.e., past what the mount considers to be the Meridian). Do the experiment that I suggested in my prior reply and you should see it do a Meridian flip.

Once it is determined that the Linear can Meridian Flip, all you need to do is to set the two times in the auto meridian flip setup in ASIAIR to choreograph the whole thing (i.e., first turn off autoguiding and tracking, then wait for the second time parameter to arrive before sending a GOTO -- that then should make the Linear go through a Meridian flip).

(That said, I rarely use the ASIAIR auto meridian flip function -- for me astronomy is a technical hobby, not a selfie taking machine, and I enjoy controlling the telescope myself. Same thing with the ASIAIR auto focus; I compute my own V curve, and when it is not cold outside, use a Bahtinov mask for the fastest focusing and most precise process there is; even under poor "seeing" conditions.)

By the way, this article describes the Frauhofer mount (which is unfortunately called just "German" mount today, instead of after its inventor -- many other contributions including spectral lines, lenses, etc), and it mentions Meridian Flip :-)

http://www.astrosurf.com/re/fraunhofer_great_dorpat_refractor.pdf

As noted in the article:

Some regions of the sky are only accessible after performing a meridian flip of the mount (by reversing the telescope about its polar axis).

Chen

darkmatter

Hello Chen, I know it's hard to imagine in this day and age but without an external device such as a laptop, tablet or Asiair, the Linear, M-Zero and M-Uno mounts do not have any smart functionality whatsoever: no goto, no polar alignment, no meridian flip - nothing. The StarGO software does not run on the mount itself but strictly external to the mount. This is the StarGO PCB: https://www.avalon-instruments.com/media/kunena/attachments/1421/stargo-wifi-board-retro-02.jpg and as you can see there is no processing capacity at all, it's just a hardware interface. And speaking of interface: there is also no display of any kind on the StarGO control box or the keypad, nor any way to enter commands or object names. This is why step 5 of the quick start guide on page 3 of the manual states: "Launch StarGO program on the PC, connect the mount... " and the system description on page 5 says: "The StarGO software, entirely written inside Avalon Instruments, allowing the performing, with a computer, all the setup and management operations..."

So without an external device you're left with manual mount that's not just dumb but totally brainless, and you can do precisely two things: 1) slew the mount and 2) control a Steeldrive focuser or similar. The external device (in this case, the Asiair) is what's controlling the goto commands and also the meridian flip. The good part is that can be no software conflicts, the bad part is that you're stuck with ZWO's implementation of the meridian flip which -ahem- clearly has room for improvement.

But apart from that, doing the meridian flip after the target has crossed the meridian may already be too late. If you have a long scope with things like EAF, OAG or filter wheel sticking out of it you may have to flip some time before the meridian crossing and move the mount in such a way that it stays well clear of any tripod legs.

Jarno

w7ay

darkmatter But apart from that, doing the meridian flip after the target has crossed the meridian may already be too late.

This is what that first Auto Meridian Flip parameter in ASIAIR is for. It is the time before transit when ASIAIR stops taking images, stops autoguiding, stops tracking. I.e., no movement of the mount N minutes before transit (user gets to choose N).

Do you know if anyone has written a StarGO implementation for Raspbian? If so, just run an extra Raspberry Pi box in between ASIAIR and the Linear.

EDIT: I see Avalon has a Raspberry Pi based StarGO2 that has some brains and emulates the LX200 protocol. However, it seems to talk to a host only through wireless or Ethernet. Unless ASIAIR can connect that way (instead of a serial/USB port), it still won't work for you.

EDIT2: with StarGO2, you won't even need ASIAIR; have you considered that option? It will work with better cameras and focusers, too.

Chen

darkmatter

Hi Chen, I'm aware of that setting but it's very wasteful in my opinion. Let's say you stop tracking 10 minutes before the meridian, why would you have everything sitting idle until the target finally crosses the meridian? Why not give the user the option to initiate the flip at that moment? Or even better, if the target is expected to cross the meridian within X minutes of starting a sequence, have a message appear: "Target crosses the meridian in X minutes. Do meridian flip now before starting sequence?"

As for the StarGO2, I don't see an option to retrofit it to existing mounts (yet) and I would strongly prefer it to be integrated into the mount as is the case with the M-Due. It's also expensive, costing 6 times as much as an Asiair. I haven't read the manual carefully yet but at first glance the user interface seems less intuitive than the Asiairs. When I'm under the stars I want everything to simply work without having to troubleshoot things like drivers or communication protocols. Time will have to prove whether or not that's the case with the StarGO2.

Jarno

wvreeven

darkmatter I agree that 10 minutes being idle is a complete waste of time. However, most mounts will not perform a meridian flip before the target culminates but only after and then very often also only several minutes after culmination. So my preference for ASIAir would be to continue imaging until the meridian flip can be done, just like Ekos does.