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Terrible RA drifting with a Celestron AVX

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58 replies to this topic

#51 Darrenlh


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Posted 19 September 2017 - 07:40 PM

Get the unified Celestron driver from the ASCOM site. It will make calibration a one time process per session, and can allow software to be aware where the mount is pointed at all times. Calibrating once per session is really sweet. 




I don't think the pixel size is correct, you should override this to 3.75. My SSAG has 5.2 x 5.2 micron pixels unbinned, and that's exactly what appears in my equipment profile (5.2). This could actually have a massive effect on the guiding. Maybe someone made a typo in the driver.

Edited by Darrenlh, 19 September 2017 - 07:42 PM.

#52 Genryuu111


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Posted 20 November 2017 - 12:03 PM

A final update to this thread.


I give up.


The mount is too **** up (and I evidently lack the knowledge/skill to actually fix it myself).


The sky was crappy until recently, but I managed to try again a few times, and nothing worked (not even getting close to have any decent result).


After storing everything for almost two months, now that the sky is decent fairly often, I tried taking a moon picture (using the toupcam I bought for star tracking), and the result was amazing, especially compared to my last best moon picture.

On a side note, the mount is making a weird noise now when moving in RA.


I agonized for months because of the issues I had, spent a lot of time and money trying to fix it, and trying star tracking, but nothing worked. I started to hate the hobby.


Luckily this moon shot brought back the happiness of taking pictures of the sky. I will be waiting for the planets to be visible at decent times (for now only mars is out during night, and I'm not having much luck trying to image it), and focus on our solar system for now.


I will probably upgrade the telescope fairly soon, and if I can, I'll try to sell the mount and buy a new one.

In hope I won't have the same problems, and that I'll be able to use everything for DSOs too.


Anyway, thanks everyone who tried to help here.

#53 denny-o


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Posted 20 November 2017 - 05:10 PM

It is a real pain to have those kind of problems. I have followed along without posting because I did not have anything useful to add. Now that you have something to image with is it possible to get help from an astronomy club or someone who has experience with mechanical gearing and small motors. We all have different skill levels of different kinds and there are people who have the experience and ability to strip down an AVX and solve the mechanical problems. You live in one of the major manufacturing countries so there might be people with skills in your area.  Maybe retired and looking for a challenge.

#54 xiando


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Posted 20 November 2017 - 05:15 PM

Are you balanced and are you properly polar aligned? If not and/or if not, you can expect lower than normal RA performance, since the mount won't be able to overcome the errors introduced by a heavy imbalance and/or poor polar alignment. At least that has been my experience with my own (Not AVX) mount.

Edited by xiando, 20 November 2017 - 05:16 PM.

#55 astrogeek64


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Posted 20 November 2017 - 05:26 PM

I'm in the same situation last night I had a very hard time getting a stable alignment. Once I finally did, things were great, everything would line up, dead center..... Until I slewed to an object in the SW, then everything went down the toilet. I'm just about done with it, ready to start searching for a mount that just works at leat most of the time......

#56 Stelios


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Posted 20 November 2017 - 05:42 PM

I also had a bad AVX, which I sent back and got a new replacement (haven't tested it yet).


But you had several issues with your PhD2 setup which could account for a fair share of the problems (the pixel size for one). 


I can well understand your not wanting to fiddle with the mount (I got a Mach1 exactly because I got sick and tired of fiddling). But my problems were very different, and unfixable. Your problems look fixable--your graphs look normal, it's just that the swings are too high. 


So I'd say, give it one more try, and this time be methodical about it. 


0) Polar align well, and balance well (to start--see also below).

1) Put in the correct pixel size.

2) Use ASCOM rather than ST-4. Calibrate on a star near Meridian and Equator (a bit north of equator). That calibration will be good sky-wide (if using ASCOM), don't recalibrate. 

3) Use a 2" refresh interval in PhD2. 

4) Use 75% aggressiveness.

5) Run guide assistant and set the MinMo it tells you, but *no more than 0.15*.

6) Set MaxRa and MaxDec to 1000.

7) Pick a target somewhere between 30 and 70 degrees in elevation.

8) Mount should be slightly east-heavy, and *very slightly* camera-heavy. Emphasis on slightly, and why you have to have balanced well.

9) You may want to only guide in one direction in DEC, but if so, you'll need to switch to Auto as you approach the Meridian and to the other direction once past it (or if on a target on the other side).

10) If you are on concrete, *don't step around your mount or do it lightly*.


Do all those things. Give it some time. If you *must* change a setting, change only one, then restore it before changing another (else you can never tell what works and what doesn't). 


If it is better, consider also doing PEC (AVX can load and replay PEC natively, it's not a hard process at all). 


If it's not, send it back for a replacement or repair. 

#57 Genryuu111


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Posted 20 November 2017 - 11:18 PM

Thanks Stelios for your inputs, I will keep your post in mind in case I decide i want to start hating the hobby once more ahah lol.gif

Jokes aside, I appreciate it, but this has been a very long journey that led me to almost quit.


While I understand part of the problem comes from my inexperience, it's too clear that the mount has serious issues (that I have worsened by fiddling with it).

Like I said in my first post, the FIRST time I tried doing DSO, just for fun, after an approximative polar alignment, unguided, I was taking 2 minutes subs (that looked like crap for other reasons, but without trails).

After that, something must have gone wrong with the mount. Could have been my fault with bad handling or not. But now I can't take 20 seconds subs without trails.

And even if I could somehow make things better with star tracking, it feels like trying to fix a broken wall with tape.

Now it is also making a weird sound when moving in RA after staying still for 2 months.


I thought about getting it fixed somewhere.

While they sell telescopes literally everywhere here in Japan, specialized stores are really rare.

There is no actual Celestron support centre here. The only place that handles Celestron stuff semi-officially told me that "they don't fix stuff bought outside of Japan because if they did, people wouldn't buy stuff in Japan anymore (here everything costs at least 50% more)". The idiotic stuff they come up with in this country can be amazing.


I really think my best bet would be trying to sell this unit for half the price, and buy something new.

Lesson learned, no more Celestron mounts (both for the issues, and the fact I'm basically screwed because of where I live), and no more trying to fix expensive stuff myself. wink.gif


Thanks everyone for your support!

#58 Whuppy


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Posted 21 November 2017 - 10:52 AM

"I had PHD detect the pixel size (it's set on 7.5, and on amazon it says 3.75 x 3.75...is it ok?), and set 240mm as focal lenght."

Your focal lenght is okay but your pixel size of 7.5 could be a problem. Set it to 3.75, I'll bet that helps big time.

#59 Genryuu111


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Posted 21 November 2017 - 09:14 PM

I didn't bother updating about that, but I tried, and nothing changed.


Yesterday I tried to open the mount one last time to see what was the weird sound, and it comes directly from the motor.shocked.gif

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