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Nexstar 8se mount tracking issues

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#1 Rostokko

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Posted 13 April 2024 - 08:35 PM

I have a Nexstar 8se. I have had continuous tracking issues with the mount - since I have been gifted the scope in December 23.
I initially thought these issues were due to me doing something wrong, but at this point I don't think that's the case anymore.

 

Just the other night I was out for a viewing session; tripod/mount were level, alignment was good; I pointed to M81, and I was happy to notice that the mount kept a steady, stable tracking for a good 30 minutes; great!

Then I slewed to M51 (not that far away), and the mount started mis-behaving as usual for me: the target would keep moving fairly dramatically in and out of the 35mm eyepiece, and I couldn't find a way to stabilize it - even repeating the "goto" operations. At the end of the goto, M51 was always perfectly centered, but it would start drifting in one direction or another fairly quickly.

 

I checked all obvious things: power was stable; mount still level; tracking enabled and set to sidereal in the hand control; date and time checked out.
I tried to slew back to M81; and, to my surprise and disappointment, I noticed that now even M81 was drifting out of the eyepiece - no more stable as it was just about one hour earlier.

At this point, I am at a loss; I don't really know what else I can do or try - short of changing mount; a few weeks ago I even tried testing the StarSense AutoGuider, but results were abysmal. I could see the AutoGuider trying to correct the drifts, but even that would eventually fail. I gave up on it and returned it.

I do occasionally try some photography with this telescope and mount, and these kind of tracking issues, while annoying in visual sessions, they are killers when I do even 2-5 seconds exposures...

 

Am I missing something obvious? Do I have a defective mount? Is it just that the Nexstar mount is not able to keep a target *stable* in the FOV even for a handful of seconds? Is the mount just very limited, and known for this kind of behavior? If that's the case, at least I would know I need to start planning for a future investment in a better mount.

 

This is just getting frustrating and it's kind of ruining a new experience that I otherwise like very much. Thanks for letting me vent.


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#2 enigma-2

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Posted 13 April 2024 - 09:31 PM

My (uneducated) suspicion leans towards the power supply. Works great for 30 minutes, extra power required for slew, then tracking problems.

How are you powering the setup?

#3 Rostokko

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Posted 13 April 2024 - 09:44 PM

I have a battery bank which powers the mount - including the dew heater ring. So, yes, that suspicion has popped up in my mind as well - but on the other hand the voltage monitor on the power doesn't report any fluctuations...

That is my next test though, powering the mount through a dedicated power source - so that at least I can eliminate this as a possible cause of the problem.

#4 Ed L.

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Posted 13 April 2024 - 11:23 PM

Regarding power banks, you might want to check out this topic and the linked video in the first post.

https://www.cloudyni...-you-read-this/

 

If you use an AC to 12v DC power supply make sure that the plug that goes into the mount is 2.1/5.5mm and NOT 2.5/5.5mm.

 



#5 Rostokko

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Posted 14 April 2024 - 05:45 AM

Regarding power banks, you might want to check out this topic and the linked video in the first post.

https://www.cloudyni...-you-read-this/

 

If you use an AC to 12v DC power supply make sure that the plug that goes into the mount is 2.1/5.5mm and NOT 2.5/5.5mm.

Thanks for the tips.

Voltage is constant, as far as my voltage meter can measure it - between 12 and 13 volts; the dew heater controller confirms that. In fact, in the past I tried to use an AC/DC adapter I had in the house, but its output was actually below 11V or so, and the dew heater refused to work. Now, I can't exclude there is something going on there, like a reduction of a couple of decimal points in voltage during the night - which is why one of the next experiments will be to run power separately to the mount. But I don't hold many hopes about that test.

About plug size, I don't think I have seen a 2.5/5.5mm plug around in my recent past; but I am indeed using all 2.1 ones.



#6 mclewis1

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Posted 14 April 2024 - 08:06 AM

Assuming the usual - a good setup (level, snug clutches, etc.), good stable power, and good data. Then with reasonably good gotos but the object drifts in and out of the wide eyepiece's fov over a period of a few minutes, and over a longer period of time the object generally remains in the field of view?

 

That sounds very much like a reduction gear problem on one of the motors. There are small gear boxes on each motor and it's not unheard of having a gear start to come loose from an axle or have lost a tooth. It doesn't sound like an encoder problem since the initial gotos and the tracking over the longer term don't appear to be an issue. 

 

Can you determine if the drift of the object is in one axis vs. just a random movement? That will tell you which motor/axis is the problem.



#7 mlord

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Posted 14 April 2024 - 09:19 AM

My (uneducated) suspicion leans towards the power supply. Works great for 30 minutes, extra power required for slew, then tracking problems.

Good thought. A related possibility may be that the wiring is too skinny for the peak currents needed.  One might measure the voltage and say "Fine", but unless it is logged in real-time one would never know for sure about voltage dips under current spikes.
 



#8 Rostokko

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Posted 14 April 2024 - 10:43 AM

Assuming the usual - a good setup (level, snug clutches, etc.), good stable power, and good data. Then with reasonably good gotos but the object drifts in and out of the wide eyepiece's fov over a period of a few minutes, and over a longer period of time the object generally remains in the field of view?

 

That sounds very much like a reduction gear problem on one of the motors. There are small gear boxes on each motor and it's not unheard of having a gear start to come loose from an axle or have lost a tooth. It doesn't sound like an encoder problem since the initial gotos and the tracking over the longer term don't appear to be an issue. 

 

Can you determine if the drift of the object is in one axis vs. just a random movement? That will tell you which motor/axis is the problem.

Potential issues with gears is my main fear. I would say that by far DEC is the main axis on which I see the drift (in either one direction or the other...), but there have been multiple times when I also noticed that DEC was decently stable, and RA would start moving...



#9 Rostokko

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Posted 14 April 2024 - 10:48 AM

Good thought. A related possibility may be that the wiring is too skinny for the peak currents needed.  One might measure the voltage and say "Fine", but unless it is logged in real-time one would never know for sure about voltage dips under current spikes.
 

It's also true that we are not talking about high power here though; these are still quite small motors... Anyway, I hear what you guys are saying: power is a potential culprit; I will dig down deeper in that direction.

 

The overall feedback I see here is that what I am experiencing is *not* normal for a Nexstar mount; and, in a sense, that's encouraging, as it gives me hope that eventually I will be able to identify the problem. I would love to be able to test a different Nexstar mount, same model as mine; I even looked on ebay to see if I could find one used; that would make investigation much easier. I have submitted a help request with Celestron; who knows, maybe they will be so nice to swap my mount with a new/refurbished one...



#10 mlord

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Posted 14 April 2024 - 11:14 AM

I slewed to M51 (not that far away), and the mount started mis-behaving as usual for me: the target would keep moving fairly dramatically in and out of the 35mm eyepiece, and I couldn't find a way to stabilize it - even repeating the "goto" operations. At the end of the goto, M51 was always perfectly centered, but it would start drifting in one direction or another fairly quickly.

Back to the original report here.  Is it accurate that, within a single session. after a single alignment, you can repeatedly go-to an object (eg. M51) and it will be centred each time.  Then later drift quickly out of view?   And another go-to, without redoing alignment, puts it back in centre?

 

That could be a power issue, or a loose clutch  -- No, not a loose clutch, as that would throw the encoders off and go-to would no longer centre things.


Edited by mlord, 14 April 2024 - 11:15 AM.


#11 Rostokko

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Posted 14 April 2024 - 12:37 PM

Back to the original report here.  Is it accurate that, within a single session. after a single alignment, you can repeatedly go-to an object (eg. M51) and it will be centred each time.  Then later drift quickly out of view?   And another go-to, without redoing alignment, puts it back in centre?

 

That could be a power issue, or a loose clutch  -- No, not a loose clutch, as that would throw the encoders off and go-to would no longer centre things.

Right - that is what typically happens to me. I did tighten the alt clutch a few weeks back, as the scope would very easily move up or down when I touched. Unfortunately that didn't change anything. Goto does consistently work quite well for me.



#12 Mike Mc

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Posted 14 April 2024 - 01:19 PM

Power supply sure seems to be the culprit. Another test to try would be to turn off the dew heater and see if the scope then tracks correctly. The heater is probably your big power user. 

 

Good luck.



#13 Rostokko

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Posted 14 April 2024 - 01:25 PM

Thanks all, excellent feedback.

It looks like we are going to have 2-3 suitable nights here in New England this coming week, and I will take the opportunity to run more tests. I'll report back if I discover anything.



#14 Notdarkenough

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Posted 14 April 2024 - 11:56 PM

The SE mount has a known problem with AA battery packs. Known and well documented. If that is what you are using, it is what it is. Best information and tips for NexStar mounts is here:  https://www.nexstarsite.com/



#15 Rostokko

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Posted 15 April 2024 - 05:33 AM

The SE mount has a known problem with AA battery packs. Known and well documented. If that is what you are using, it is what it is. Best information and tips for NexStar mounts is here:  https://www.nexstarsite.com/

Yep, no AA batteries for me; I remember I tried and gave up on those 12 hours after setting up scope and mount for the first time... I can't really understand how Celestron would ship a scope and mount worth >$1K without any reliable built-in way to power it... Anyway, that's not the problem here for sure.



#16 mlord

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Posted 15 April 2024 - 08:16 AM

They do the same as everyone else.  Some Sky-Watcher mounts also accept AA batteries, but the real way to power any mount is through the DC-input jack.  (or AC/DC jack on some).



#17 Rostokko

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Posted 15 April 2024 - 08:23 AM

They do the same as everyone else.  Some Sky-Watcher mounts also accept AA batteries, but the real way to power any mount is through the DC-input jack.  (or AC/DC jack on some).

...then include a $10 power adapter in the package?... I understand others may have the same approach, but that doesn't make it make more sense...

Anyway, we are drifting off-topic here :)



#18 mlord

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Posted 15 April 2024 - 08:28 AM

Yes off-topic.  So I'll end my part here:  I already have a box of suitable 12V power supplies, so I'm happy to pay $10-$30 less for a mount that doesn't include yet another one.  Those who need one, can get the right size/capacity version from Amazon quickly and cheaply.  And that may be a battery for them, rather than an AC brick.

 

Cheers


Edited by mlord, 15 April 2024 - 08:38 AM.


#19 speedster

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Posted 16 April 2024 - 02:00 AM

The mount runs on a 3A power supply but running dew heater in addition?  You might try a 5A power supply if you don't already have one.  Some others have solved their problem with a bigger brick.



#20 Rostokko

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Posted 16 April 2024 - 05:57 AM

Yesterday night I ran my setup with two separate power supplies, one for the mount (AC/DC 3A adapter) and the other one for the dew heater (battery bank).

 

Unfortunately, nothing changed; I tried tracking a handful of objects/stars, but each of them (to more or less degree) showed the dreaded tracking drift. That seems to eliminate power/electrical as the possible culprit.

 

It was a good, warmish night, and I decided to lose some sleep and run another big experiment: fully load the scope with my EAA setup - asiair, hyperstar, asi533 camera and guiding scope. I kept powering the scope by its own, and all the rest through the battery bank.

The results were *identical* to my visual observations; I would get perfectly fine 1-2s shots, but anything longer than that would have a high chance of capturing the drift blur.

I tried to turn on guiding, just to see how that would work. I did notice that setting fairly long DEC pulses, guiding would be able to at least keep the object of interest from drifting away from the fov. I also noticed through the asiair app that the main source of the drifts is *by far* DEC (at least, in this "loaded" setup). RA would be fairly easily controlled by guiding - with short adjustment pulses; but in order to keep DEC more or less under control, I had to increase the DEC adjustment time to the max (10s); and even then guiding at some point stopped when slew rate was set to 1x, complaining that DEC drifts were not manageable.

In all cases, even with guiding on, any exposure longer than 2-3s would miserably fail and capture the drifts and/or the constant attempts to adjust...

 

Considering that I have eliminated (at least, as far as I can tell) power/electrical as a potential issue, I am left with what I assume are mechanical issues here. And I can only think of 3 options:

  1. My expectations about the stability of the mount are just too high; maybe the Nexstar SE is just not designed/able to be perfectly steady for longer than 1-2 seconds.
  2. My setup overloads the Nexstar SE; but then I wouldn't expect to experience the same problem when going "light", with just the dew heater controller weighing on the scope - unless that by itself is enough to overload it (it's the "standard" Celestron dew heater controller with dew heater ring).
  3. I am dealing with a defective SE mount; and to verify that I would need Celestron to replace my current one - which likely won't happen.

I'm not in a happy place right now... somewhat sleep deprived for the day, and without a clear path forward.

But thanks all for your great help! It has really helped me finding the motivation to keep trying!



#21 mlord

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Posted 16 April 2024 - 06:04 AM

#3.  If under warranty, Celestron will tell you to ship it all back to them for analysis and repair.  In this instance, it sounds like the best action.



#22 Rostokko

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Posted 16 April 2024 - 06:16 AM

#3.  If under warranty, Celestron will tell you to ship it all back to them for analysis and repair.  In this instance, it sounds like the best action.

I did purchase it (well, it was gifted to me) in December 2023 - so, I suppose it is still under warranty. We will see when/how Celestron responds.



#23 mlord

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Posted 16 April 2024 - 06:29 AM

Before you send it back, remove that massive dew heater controller from it, and try again.  Just the tube, diagonal, original eyepiece, and red-dot finder.  If that still fails, there's definitely a defect for Celestron to handle.

 

Note that the 8SE, as shipped, is already AT the weight limit for accessories on the OTA.  Read the specs and get out the weigh scale.  People do manage to add stuff, but it's tricky to keep the weight balanced.  For lots of accessories, a mount rated for more weight capacity is advisable.

 

The SE mount was designed for a 6" OTA, which suits it well and leaves capacity for extras.  But they frequently sell it as a combo including the much larger/heavier 8" OTA..

 

Cheers


Edited by mlord, 16 April 2024 - 06:30 AM.


#24 Rostokko

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Posted 16 April 2024 - 06:49 AM

Before you send it back, remove that massive dew heater controller from it, and try again.  Just the tube, diagonal, original eyepiece, and red-dot finder.  If that still fails, there's definitely a defect for Celestron to handle.

 

Note that the 8SE, as shipped, is already AT the weight limit for accessories on the OTA.  Read the specs and get out the weigh scale.  People do manage to add stuff, but it's tricky to keep the weight balanced.  For lots of accessories, a mount rated for more weight capacity is advisable.

 

The SE mount was designed for a 6" OTA, which suits it well and leaves capacity for extras.  But they frequently sell it as a combo including the much larger/heavier 8" OTA..

 

Cheers

Good suggestion - I will try that. I must say the mount does look a bit flimsy for that big tube...

 

I do feel like we are getting closer and closer to the point where I will need to decide whether I want to keep exploring EAA/AP (which would involve a new/different mount), or if I can just be content of doing visual.



#25 mlord

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Posted 16 April 2024 - 06:55 AM

I missed that this setup had HyperStar installed.  So really, REALLY nose-heavy setup -- it's not going to track unless carefully balanced -- slide the OTA dovetail back into the mounting point until it stops tipping forward.  Might have to add a bit of extra counterweight on the rear, but only if it cannot otherwise be balanced.

 

Balancing the SE mount is tricky too, as it has no "release" clutches -- nearly all of the other Celestron mounts do have them. 




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