My (niggling) HEQ5 "wandering" Problem

[Macavity]

My (niggling) HEQ5 "wandering" problem. Now I have (semi-infinite?!? lol!)
time to try to fix this, I wondered if anyone had ideas, given the symptoms? 😛

In a nutshell, I am (still!) Video Imaging with a Watec Camera, so the mount
only has to track "well" for say 10s maximum. I control the mount *remotely*
via (now reliable) USB2 link / EQMod from the comfort of my "lounge" etc. 😎

BUT! Over my typical data acquistion time of FOUR minutes, my 8"/F4 Newt
30'x20' field wanders around by *minutes of an arc* from a setup position! 🙄

Question: This cannot be GOOD?! 🤔 But what should my *expectations* be
for the tracking accuracy for HEQ5 without autoguiding? I would prefer not
to go down THAT (more complex) route for my "simple" Video Astronomy...

I had suspected this to be a "backlash" problem? The collars (under bungs)
are tight? I cannot "jiggle" the mount physically on *either* axis? Maybe a
complete stripdown of the mount again? I TOO praise "Astro Baby" for her
guide, but one axis resisted all my attempts to "gently tap" it appart?!? lol

I should (finally!) give this go? Something to do during self-isolation?!?! 😛

Edited April 23, 2020 by Macavity

[carastro]

I could never get my mount to track accurately for very long without trailing.  But if you are doing video Astronomy, is it that necessary to be spot on?  Long exposure imaging it is a must.  Good Polar alignment will make this more accurate. 

With an 8" Newt it is bound to be more obvious. 

If it really bothers you, guiding is the way to go.  I used to guide even doing video Astronomy otherwise I would eventually lose the target.

Carole   

Edited April 23, 2020 by carastro

[Macavity]

31 minutes ago, carastro said:

I could never get my mount to track accurately for very long without trailing.  But if you are doing video Astronomy, is it that necessary to be spot on?  Long exposure imaging it is a must.  Good Polar alignment will make this more accurate. 

With an 8" Newt it is bound to be more obvious. 

If it really bothers you, guiding is the way to go.  I used to guide even doing video Astronomy otherwise I would eventually lose the target.

Carole   

Thanks for that, Carole! To be honest, I have NO idea how much the "wander" should be?
Even in worst case, AS!3 is capable of stacking many (sharp) Watec internal integrations.
I tend to crop 800x600 frames to 640x480 to avoid edge (Watec "electronic heat") etc. 😏

I have *not* entirely rejected the idea of some sort of (modest technology) "guiding"...
These days, I have a permanent aluminium "cross bar" on the MOUNT, plus EVOGuide
"Video finder" etc. Maybe I could become a convert to "Classical imager" techniques? 😎


 

[MarkAR]

I had a bit of drift last night again, after the meridian flip and plate solve it seemed only to drift half as much.

So I'm just wondering if it might be something like cone error, do you do a 3 star alignment first ?

In Ekos there is a mount model function, haven't investigated it yet but it sounds like it fine tunes things. 

[FaDG]

1 hour ago, Macavity said:

had suspected this to be a "backlash" problem

If you're just tracking in RA, then backlash has no effect whatsoever: the motore runs in a single direction, so that's not your problem. 

When you write: "moved by arcminutes", is it always in the same direction? 

If so it could be that the sidereal rate is wrongly configured, or you might have selected a different (lunar, solar) tracking rate. 

As most other mounts, the HEQ5 exhibits Periodic Error, over a cycle of about 10 minutes. But this type of mount is quite well behaved, and the effect shouldn't be major: not arcminutes for sure! 

Edited April 23, 2020 by FaDG

[Macavity]

26 minutes ago, FaDG said:

If you're just tracking in RA, then backlash has no effect whatsoever: the motore runs in a single direction, so that's not your problem. 

When you write: "moved by arcminutes", is it always in the same direction? 

If so it could be that the sidereal rate is wrongly configured, or you might have selected a different (lunar, solar) tracking rate. 

As most other mounts, the HEQ5 exhibits Periodic Error, over a cycle of about 10 minutes. But this type of mount is quite well behaved, and the effect shouldn't be major: not arcminutes for sure! 

The "wanderings" in tracking are random. I am pretty well acquinted with varying speed
(deliberately!) via EQMod for special purposes. Wanderings can be stopped by giving a
quick "kick"  (click on EQMod Arrows!) in the *opposite* sense to the (random) drift. But
I *DO* welcome your feedback re.  "...it should not be arcminutes"!!! That is much what
I had thought? Give me an  *incentive* to really get to grips with the problem (finally)? 😛 

I sense the HEQ5 is a reliable and capable mount. It has served me well (outside) etc.
I tend to think it is "mechanical / hardware" related somehow...🤔 (Good to fix too)!

Edited April 23, 2020 by Macavity

[FaDG]

16 minutes ago, Macavity said:

Wanderings can be stopped by giving a
quick "kick"  (click on EQMod Arrows!) in the *opposite* sense to the (random) drift

Hang on... Does this only happen with EQMOD? Have you tried the Synscan handset? 

Unless it is caused by uncommonly high PE, I'd rather think of a SW issue more than a mechanical one. 

Just out of my mind: maybe you have a (now) invalid PEC table saved in EQMOD, which causes unwanted corrections to ruin your tracking? 😳 

Edited April 23, 2020 by FaDG

[7170]

Is it wandering in both axes or just one when tracking? Sometimes hard to actually tell given the angle of the camera but that would be useful to know.

How are you polar aligning it and how close is the PA if you use one of the software tools out there to check it, eg sharp cap (if you can use it with your camera).

If imaging I would not use the built in pole scope or drift, I use EKos polar alignment using the guide scope first and then main scope after.

I assume balance is very good? The other test is to turn your camera on and see how much movement there is in the mount when you give it a bit of poking. A common oversight is to have the top altitude bolt a bit loose, so things will start to move depending where the scope is pointed in the sky. You should be able to get >30s easily in my experience if it is well PA without tracking with an ED80 capturing as a comparison.

Edit - looking at the photo you have the cables dangling to ground level perhaps? I would bunch up and fix to the mount to reduce the weight on the end of the scope and improve the balance in all locations of the sky.

Edited April 23, 2020 by 7170
Cables

[Macavity]

Heheh. I still favour the "some sort of backlash" theory. But genuine thanks for all the above! (**)
If I track this down, I will update you!? If some far-future "thread archeologist" discovers this? 😛

Lots of useful points! Re. good balance. Yes it is... Can be moved in both axes with one finger. 😇
I tend to leave (lightwight) camera leads to "just dangle" - I never do unattended meridian flips!
Any residual imbalace (as is anecdotal) might help to cure remaining backlash? But I do accept
that my notion of polar alignment (Solar noon + decent digital level) are VERY hit or miss! lol 🤣

Ultimately THIS (many SGL threads) are a good *memory* jogger? Now I remember: Pushing
da "EQmod button" on ONE axis (I DO need to WRITE down which!) results in a "delay" before
the mount begins to move! Still d*mned if I can SEE anything obvious? But I feel determined...
Such can be (easily) seen / reproduced during daylight, so I have fewer excuses now. ☺️

** Appreciation for those who reply to queries... devote their TIME... look up references etc. 😎
Still "working up" to doing "astronomy stuff" in social isolation, but I sense this will come...

Edited April 24, 2020 by Macavity

[FaDG]

May I still suggest another test? 

Properly align your camera such that RA axis be either purely horizontal or vertical. Test this with manual motion and very short shots. 

Now, strongly misalign your polar axis wrt. to Polaris, let's say 10 or 15 degs higher or lower. This will induce a dec drift (and a small RA speed variation, take it into account). 

Point your scope eastwards or westwards, set ISO to minimum, centre a decent star, stop down your scope if you have any means for that or use filters, and launch a single 10-20 minutes exposure.

You should get a loong trail in the dec direction: ideally it should be purely a line, but if your scope tracked ideally you wouldn't have started this thread! 🤣🤣 

So, you'll rather see the PE curve superimposed to the line, and a possible drift shown by an oblique drift. Based in the system resolution (arcsec/pixel) it is possible to infer the error. Specifically, the curve should repeat every 10 minutes. 

Post the result here and we'll try to troubleshoot. I'll be surprised of any backlash during pure tracking. 

 

Edited April 25, 2020 by FaDG