Meridian Flip twice? EQ6R-Pro

dhess62@hotmail.com

Everything running normally the other night, it did the meridian flip right on time, then it immediately did another meridian flip back to the previous position it was in before the flip. Has anyone seen this happen?

Byrdsfan1948

@dhess62@hotmail.com#54379 Only in the Olympics........ Seriously, I have an Ioptron CEM25EC mount paired with the ASIair Pro using the latest FW update. Honestly with all the other issues, and problems I have encountered with my ASIair Pro, doing a MF has been the least. Actually I cannot even remember any problems ever......... What still perplexes me while we are on this subject however, is why my guiding becomes so much more precise, AFTER a flip than before??

dhess62@hotmail.com

Byrdsfan1948 I'm not sure what's going on. I think it all comes down to firmware. I haven't noticed any difference is guiding after the flip, my numbers have always looked about the same. I'll pay more attention to that next time.

ckoos

Often a difference in guiding from one side of the pier to the other is caused by:
RA balance.
Cables dragging on one side, but not the other.
Something is loose that only becomes a problem when the orientation changes.
Or, one of a hundred other possibilities I haven't (but probably will) run into yet.

w7ay

@dhess62@hotmail.com#54384 I'm not sure what's going on. I think it all comes down to firmware.

Keep in mind that the ASIAIR does not really know how to perform a Meridian flip. You mount is the one that computes the motor's movement to perform the meridian flip when it discovers that the target is on the same side of the pier.

The ASIAIR simply sends a GOTO to the mount when it thinks the target has moved past the mount's meridian (i.e., target is now on the same side of the pier as the OTA).

After a meridian flip, the ASIAIR does a plate solve to confirm that a flip has occured. And it sends a Sync and GOTO if you had also set the "GoTo Auto-Center."

To get a meridian flip, followed immediately by another Meridian flip probably means that there is sufficent inconsistency between the ASIAIR plate solve and the mount's coodinates (i.e., if it is perfectly level, and perfectly polar aligned). After the first flip, the mount again thinks that the plate solved location shows that the OTA is again on the same side as its pier.

If you can't get your mount perfectly leveled and perfectly polar aligned, increase the "DO AMF x min after Meridian" parameter in the Meridian Flip Settings to compensate for any inaccuracy.

If you don't want to waste time waiting for the ASIAIR to issue a GOTO for the meridian flip, just level your mount accurately in the East-West direction, then do a good star alignment if your mount does not have an absolute encoder (or a relative encoder that is calibrated), and make sure polar alignment is precise.

You could of course avoid the double meridian flip by turning off auto-center.

For what its worth, ASIAIR could have avoided this double flipping if it had checked the pier side of the mount before issuing the auto-centering GOTO. But with my various experiments with my mount simulator, I have never seen the ASIAIR request the pier side from the mount.

For any given target, you should only get Meridian Flips that are 12 sidereal hours apart (two Meridian flips per day).

Chen

stevesp

Chen maybe the pier side is not available in all mounts as output info

w7ay

stevesp maybe the pier side is not available in all mounts as output info

But that does not preclude the use of pier side for mounts that do support it.

Chen

stevesp

Skipping the feature is easier to program

Byrdsfan1948

@dhess62@hotmail.com#54384 I'm sure you've read Chen's comment below by now..... As usual what he suggests makes a lot of sense. In particular to my simple mind, increasing the time to DO AMF after the Meridian. As I mentioned I have NEVER had any problems like you have this way. However I set up in a location that allows for very solid and good leveling. Since I have the tripod locations precisely marked on my patio I am also always able to get my PA under 10" every night before I start imaging. Of course just how accurate that really is I don't know. In my case I have my ASIair set to: DO AMF 2 minutes after the Meridain. I used to have it set 5 but lowered it to 2 without any issues like your having. Still however if you have not tried it yet, I'd try increasing yours from where ever you are currently set to if that helps.
Just for laughs if I can tonight I will try lowering mine further to see if I can simulate your problem. I'll post my results here hopefully tomorrow if the clouds co operate tonight. Al

w7ay

Byrdsfan1948 Just for laughs if I can tonight I will try lowering mine further to see if I can simulate your problem.

It is not just a matter of lowering the time to fo the flips, Al.

If you are perfectly leveled/star aligned, you can lower it to a fraction above zero, and it will still work. If you really want to test, just hack the polar alignment and the east-west leveling. I suspect that "the stars have to be aligned (so to speak)" for a double flip to happen.

Remember too that the system could also err in the opposite direction -- i.e., after the flip, the target is even further from the Meridian. It depends on so many factors.

To exacerbate the problem, you could also introduce a cone error by shimming the declination dovetail bar so that your OTA is no longer pointed directly at the pole when the declination is 90º. This will really change the coordinate systems between pier-east and pier-west (i.e., no longer just exchanging the signs of the hour angle).

Have fun with the experiments, Al -- to me, that is the fun part of astronomy. You can get pretty pictures from the Hubble web site, but short of working at an observatory, having hands-on with a mount is the only way to really learn how things work; just like when we took clocks apart when we were children. Heck, I had spent two sort-of-clear nights this past week to investigate the Beta ASIAIR's Bin2 guiding weirdness compared to be released version, and finally have enough evidence about the relation to guiding plate scales. That led me to use a 2.4 µm guide camera instead of a 2.9 µm camera -- I only have one 2.4 µmcamera that can gives me 2 FPS guiding at 0.5 sec exposure -- but sure enough, with it, I can get multi-star guiding at 2 FPS again with my current favorite guide scope [a frankenstein with the Borg 55FL objective in a Askar FMA230 tube]. If I could change their star detection algorithm, it could have been done with code changes rather than a camera swap. But it was worth the two nights to discover why the ASIAR Beta didn't work.

While you are experimenting -- just keep in mind that there are three spherical coordinate systems. One is the RA-Declination system of the sky. Another is the Hour Angle-Declination system of the mount with a pier-east configuration, and the third is the HA-Declination coordinate system with pier-west.

Chen

Byrdsfan1948

w7ay Hi Chen, I'm sure as kids we both dissected any toy or anything else we ever were given. It was never good enough to just play with it. In my case I always had to take it apart to see how it worked. Still do that today. As a mechanical/aerospace engineer you might have really appreciated some of the rockets I built back then....... I wish I had you as an electrical engineer to improve on our radio and other communications "technology" for those 'unguided missiles" :-).
BUT my favorite experiments always included something to do with high voltage even though unlike you I had no real idea what I was doing..
As usual I agree with your comments here. But as you well know to solve some problems with many possible culprits you need to first isolate the variables. Which would be my goal here tonight. Sometimes issues like this one are more fun to play with that the actual imaging. After all like you say if you want to see a great picture of anything Hubble has already made one. :-)) Al

Byrdsfan1948

As so often happens here in New England. Crystal clear deep blue skies all day. A forecast of a clear and near moonless night, albeit very cold. No problem getting my PA done in under 5 minutes, and within 9". The ASIair seemingly working fine, my PLAN set up and started, and a good stable WiFi signal. Unfortunately, the only part of the forecast that was correct was cold, and near moonless........ The clouds moved in shortly after I started imaging, SH2-274 and before my experiment with the DO AMF time which I had lowed to 1 minute after the Meridian. It would have passed the Meridian just before 9 PM but the clouds covered the entire sky well before then. GRRRRRRRR Next chance Monday evening. Al

w7ay

Byrdsfan1948 It would have passed the Meridian just before 9 PM but the clouds covered the entire sky well before then. GRRRRRRRR Next chance Monday evening.

Al, there is no need to wait for a known target to reach Meridian.

Just dial in (the GOTO panel) an RA that is just 3 minutes or so east of the Meridian assuming you are using the hemisphere towards zenith (remember that this Meridian's RA is simply the Local Sidereal Time). That will make you wait only 3+T minutes, where T is the delay that you have selected before auto meridian flip takes place. Try a declination close to the celestial equator, if you have visibility of the sky to do plate solves.

Plate solves don't need actual targets, they just need coordinates in the sky.

Chen