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NexStar GoTo Wandering

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#1 O-Ryan

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Posted 22 February 2013 - 12:24 PM

Hi all - I purchased an 8SE a couple weeks ago and am largely getting the hang of it. One issue I'm running into (usually once a night) is the GoTo wandering off when trying to find a target. I'll have the telescope configured properly using Sky Align to where I can have it slew to Jupiter or M42 almost dead-on (so it's seemingly configured right). Then a little later I'll try to slew it to another object in the observable sky and it will do something like pivot upside-down on its axis and wander off in some random direction. When this happens I usually have the diagonal still on so it runs into the mount, and at this point I panic and shut the thing off real quick so I don't do any damage, but then I've got to turn it back on and realign it.

Has anyone else run into this? Thoughts on the issue? I was thinking it could be a battery issue, but it's done it after only an hour or so on fresh batteries.

#2 Doug Michel

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Posted 22 February 2013 - 12:27 PM

Be sure to set some slew limits especially for objects nearly directly overhead as the diagonal will hit the base unless you have the OTA slid far enough up, which makes the tube out of balance however. I think I set my slew limit to 80 degrees or something. If I want to view something that high up, I go manually there so as to not damage anything.

#3 ben2112

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Posted 22 February 2013 - 12:44 PM

It sounds like batteries to me. I went out a couple of times on batteries. Maybe 2hrs with each viewing. I then setup the scope to play with controlling it with Stellarium. It was acting really strange. I then plugged in my AC adapter and it went back to normal. The 6/8SE will eat batteries.

#4 O-Ryan

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Posted 22 February 2013 - 12:53 PM

It sounds like batteries to me. I went out a couple of times on batteries. Maybe 2hrs with each viewing. I then setup the scope to play with controlling it with Stellarium. It was acting really strange. I then plugged in my AC adapter and it went back to normal. The 6/8SE will eat batteries.


I'm planning on getting an AC adapter because I knew it chewed through batteries; just didn't think it would go through a new set that quickly. Thanks!

#5 ben2112

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Posted 22 February 2013 - 01:00 PM

That is why I got an AC adapter when I got the scope. Very well worth it. But I would keep new batteries in it even while you are using the AC adapter. So if it comes unplugged, you won't loose your alignment.

#6 hopskipson

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Posted 22 February 2013 - 01:10 PM

Sounds like a power problem.

#7 Arctic_Eddie

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Posted 22 February 2013 - 01:19 PM

An external battery pack that rides with the scope is a good solution.

http://www.onlybatte...ItemID=11728.37

And charger.

http://www.onlybatte...ItemID=11862.12

Select your connectors at order time. You will need to make up one cable from the battery to the scope external input. Use a 5.5mm x 2.1mm x 10mm plug.

#8 Tel

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Posted 22 February 2013 - 01:21 PM

Hi O-Ryan,
Welcome to CN and to this forum ! :bow::bow:

As Ben has already advised, I'd certainly second the battery failure theory. It's all but a classic case.

It does however seem that there happens to have been a very short period of operation before the onset of the erratic behaviour associated with this failing power, but then who can guarantee how long these batteries will last ?

Again though, and as Ben has advised, invest in either a mains AC/DC transformer with an output current of ca. 1200-2000mA, or alternatively, a large capacity (e.g. 20Ah) battery: an automobile "JumpStart" being ideal.

Best regards,
Tel

#9 Midnight Dan

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Posted 22 February 2013 - 02:05 PM

All I can do is add my voice to the chorus :grin: - very typical behavior for low power. Normal AAs only last 2-3 hours, less in cold weather. Most people use a 12V jump starter as a rechargeable power supply.

Also, be sure and move your OTA (optical tube assembly) forward on the dovetail clamp so that if it does go all the way up, the diagonal won't hit the base.

-Dan

#10 O-Ryan

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Posted 22 February 2013 - 03:05 PM

Great, thanks everyone!

#11 Bob Griffiths

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Posted 23 February 2013 - 10:17 AM

No need to power the scope off if you think the OTA will hit the base...just hit one of the direction buttons and the scope will stop slewing...

BUT I too think you have a power supply problem (actually a good 90 percent of the problems you will run into with these scopes can be directly traced back to a power problem)...

I however refuse to power my scope with an AC adapter... because these scopes do not have any fuses etc to protect them from a voltage surge ..one voltage spike and you could fry your scopes electronics in a millisecond..! Get yourself a good external power supply and be happy and keep a set of RECHARGEABLE AA's in the base to act as a backup power supply because you know darn well that you will pull the power cord out of its connection sometime......

Just my own opinion...

Bob G.

#12 jturie

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Posted 23 February 2013 - 10:31 AM

Yep, this happened to me the other night. All of a sudden, scope acted wonky and would miss its targets. Turned out the various slews pulled out the AC plug enough to turn it over to the batteries. They definitely didn't last long. Reattached the plug, and all was well.

#13 ben2112

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Posted 23 February 2013 - 10:48 AM

Yep, this happened to me the other night. All of a sudden, scope acted wonky and would miss its targets. Turned out the various slews pulled out the AC plug enough to turn it over to the batteries. They definitely didn't last long. Reattached the plug, and all was well.


That is why I use velcro straps or zip ties to keep the plug in. :waytogo:

#14 butsam

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Posted 23 February 2013 - 02:02 PM

I agree it sounds like low-power condition, but let me add in something that could happen, which makes sense if you think of it in 3-D, but seems counter-intuitive at first blush.

I have noticed that sometimes, the NexStar doesn't take what I think is the most direct route...but what with more thought actually is faster.

For example, say you are viewing something at 60* elevation, due South, and choose to view something at 60* elevation, due North. You may expect the 'scope to simply rotate 180* horizontally, but it is actually faster to slew up to a steep angle, then slew clockwise (or CCW) 180* in this new orientation, where 180* requires less actual movement, then slew back down to 60*.

If you have set slew limits (especially the elevation slew limit), though, then it will stop at that upper bound, keeping your equipment safe.

Alternatively, you can mount the 8SE higher on the fork-arm to avoid the possibility of hitting with the diagonal. I know it is possible with the 8SE and star diagonal...but even then, I recommend setting slew limits just to be on the safe side.

So, even though it sounds like it was power in your case, everyone should set an upper slew limit. Mine is at 80* as well, and I have had no issue.

Also, keep in mind the NexStar has settings for an "Approach". It will always overshoot (or undershoot) a target in both Alt and Az so it approaches a target with the same final movement. I believe the default is for final approach to be right and down. This is done because of the gear system...others know more about the details than me, but basically, the gears navigate best if final approach is always the same. (By the way, you should use this final approach whenever navigating to your setup stars, too.) So, sometimes your 'scope may appear to overshoot, but then will correct it.







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