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PlanetGazer

Help with GoTo Dob mount slipping/dropping of the scope

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Long storey short :

the OTA slips dramtecly when vewing an object to 0 altitude.

Details:

So I bought the Skywatcher GoTo flextube 10 inch a year ago. It was nothing but great, until yesterday when I was just starting the session to level up the scope on the mount for alignment. I Went to get some equipment and when back noticed the scope has declined to a minus reading on the altitude! With no attachments on the OTA. 

I re-leveled it to the horizon and it held itself, put on the nothing but stock attachments as usual. Switched on the GoTo and started aligning, when alignment is successful, I chose an object and notice the object is far off.  I check the battery voltage and it's 12.5 volts, which indicates it's not a battery issue.

I turn it off to re-align again, this time when I press the up arrow to align to an object I notice the GoTo gears struggle to move the OTA upwards, but eventually the speed increase to normal and manage to points upwards to the object. I pick a second object which happens to be near the zenith and the GoTo goes out of control straight to zenith and carrying on above 90+ degrees on the altitude bearing. I try to stop the scope with the handset before the base of telescope hits the wood in the base, only to notice the handset is not showing light or responding. I turn the GoTo off.

Start to align for the third time, this time aligns but still off target. I ignore and start viewing Jupiter which happens to be 40+ in altitude , after few minutes of viewing, the scope drops slowly to zero altitude with no hand or handset movement! Handset is still showing that the viewed object is still Jupiter!

Note: I did notice weird sounds of the gears when trying to increase altitude. Not the common sound.

Has anyone faced this issue and fixed it, should I return under guarantee? Is this a gear slippage? Or clutches not engaged? Your help will be much appreciated!

 

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I would still suspect the power supply as many of your symptoms can be due to this.  12.5 volts may not be quite enough for the task, a fully charged battery would be over 13v, doesn't sound much difference but the drives are very sensitive to power supply. easy enough to try a full charge.  Connections are another potential source of problems.     🙂

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Posted (edited)

Battery works very well, it was perfect the session before. The battery was fully charged for last session. 12.5 is max I usually get.

 

Regardless, battery issue doesn't explain why OTA slips before turing it on, it should hold it self without switching on the system

Edited by PlanetGazer
Adding more detail

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Far be it for me to intercede in this conversation, but are you sure about the balance point of the telescope tube?
I'm a martyr to changing balance of my OTAs. It's a constant uphill battle!
I think little people must sneak in and mess about in the middle of the night. :wacko:

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1 hour ago, Rusted said:

Far be it for me to intercede in this conversation, but are you sure about the balance point of the telescope tube?
I'm a martyr to changing balance of my OTAs. It's a constant uphill battle!
I think little people must sneak in and mess about in the middle of the night. :wacko:

You're more than welcome to participate in the discussion!

If you mean balance point for equatorial mounts, then this does not apply in my case. My scope sit on a dobsonian mount which designed in such a way that it doesn't require balancing, unlike equatorial mounts. 

 

Here is a link showing a picture of my scope:

 

https://www.firstlightoptics.com/dobsonians/skywatcher-skyliner-250px-flextube-goto.html

 

 

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If as you say it is still under warranty then I would not hesitate to return it and get it checked out.

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18 minutes ago, PlanetGazer said:

You're more than welcome to participate in the discussion!

If you mean balance point for equatorial mounts, then this does not apply in my case. My scope sit on a dobsonian mount which designed in such a way that it doesn't require balancing, unlike equatorial mounts.

Here is a link showing a picture of my scope:

https://www.firstlightoptics.com/dobsonians/skywatcher-skyliner-250px-flextube-goto.html

Every mounting needs the OTA to be balanced.

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Yes, balancing is most important.  I presumed, due to the fact that it was a driven Dobsonian, it would have been balanced being as it had been used.  If possible, disconnect the drive system and check that the optical tube assembly is balanced in the altitude axis.    🙂 

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2 hours ago, Peter Drew said:

Yes, balancing is most important.  I presumed, due to the fact that it was a driven Dobsonian, it would have been balanced being as it had been used.  If possible, disconnect the drive system and check that the optical tube assembly is balanced in the altitude axis.    🙂 

How do you check that? Do you mean leveling the OTA on the mount to the horizon before starting it up?

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If you are using it in Goto mode and the clutches are tightened up fully then there is no way the scope can "slip" down on its own, you would have to physically push down on the front of the scope to do that. It sounds certain to me as the owner of a similar scope that yours has a fault that needs repairing, particularly as you say it is making strange sounds.

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10 hours ago, Geoff Barnes said:

If you are using it in Goto mode and the clutches are tightened up fully then there is no way the scope can "slip" down on its own, you would have to physically push down on the front of the scope to do that. It sounds certain to me as the owner of a similar scope that yours has a fault that needs repairing, particularly as you say it is making strange sounds.

So how do you correctly tighten clutches in a goto dob system? I assume they are not easily accessible.

Initially I thought I would have to use a wrench to tighten this part in the altitude motor box, but wanted to ask here first.

 

Screenshot_20200815-131346__01.jpg

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If your model is the same as mine this is the altitude cluch handle that you have to tighten by hand quite firmly, otherwise the goto motion will not work...

20200815_203909.jpg.7c6de6782d1e4783cd68bd23df91df0c.jpg

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4 hours ago, Geoff Barnes said:

If your model is the same as mine this is the altitude cluch handle that you have to tighten by hand quite firmly, otherwise the goto motion will not work...

20200815_203909.jpg.7c6de6782d1e4783cd68bd23df91df0c.jpg

Oh that's the first time I see such a model. Which makes me think that such a handle should be there for all models. Mine doesn't have it, but the thread i showed in the earlier picture is on the same level, but from the other side. Your scope look 12 inches or more, right?

 

This is how my base looks, but I have a different handset model:

 

 

 

 

Screenshot_20200815-175342.jpg

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Mine is the 12 inch model. The altitude clutch for yours will be under the black plastic cover that your handset sits on.

You will have to remove that cover to gain access to the clutch to adjust the tension. Might be worth contacting Skywatcher for advice regarding the procedure for this.

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