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Unwanted movement on my Celestron 8SE while tracking.


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Hi all,

I was wondering if someone might be able to answer a question for me ? I set up my scope tonight (I have a Celestron 8SE) to have a look at Saturn. Successfully did a 2 star alignment on Arcturus and Dubhe. Slewed to Saturn. When I centered Saturn in the scope and let the scope track it, it seems to drop a very slight amount at equal intervals. Maybe 4 or 5 seconds apart. I have tried different setting of anti-backlash to no avail. It seems like the front of the scope is dropping straight down, as the image moves up. It's an SCT so tell me if that is correct. Is there an adjustment on the clutches that can be done by me or does it need service or am I just a Newbie... I'm hoping for the latter. Thanks for any advice or suggestions that anyone might lend.

Gordon

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I bought a celestron NexStar SLT a couple weeks ago. It's a different model than what you've got but it's still a celestron motorized mount. Mine started to do that with the left and right motor (azimuth) and unfortunately after about two nights of it, the motor completely seized up. I looked around online and read a few complaints of this happening with various Celestron models, the SE was among them. I had to send it back to Celestron and am waiting to see what they do about it. The service rep said it sounded like a motor problem and that I qualified for a full replacement. Still a pain in the ass.

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I bought a celestron NexStar SLT a couple weeks ago. It's a different model than what you've got but it's still a celestron motorized mount. Mine started to do that with the left and right motor (azimuth) and unfortunately after about two nights of it, the motor completely seized up. I looked around online and read a few complaints of this happening with various Celestron models, the SE was among them. I had to send it back to Celestron and am waiting to see what they do about it. The service rep said it sounded like a motor problem and that I qualified for a full replacement. Still a pain in the ass.

Unfortunately I bought it used, so I doubt there would be any warranty. I'm very frustrated about it. I'm thinking about buying a new goto alt/az mount and putting the OTA on it. My brother is a machinist, so I think so making a dovetail for it wouldn't be a problem. At least then I would be able to do astro photography too. It would probably cost me nearly as much to have it repaired.

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If its dropping is there any way of balancing the OTA, maybe its a balance issue?

I have tried to balance the OTA using bb's (don't know if you call them that) small ball bearing like things for shooting from an air rifle.

I went so far as to weighing the optics / camera and made counterweights accurate to the gram. It really doesn't seem to make that much difference. I've also tried changing the backlash setting and it didn't seem to change it that much. It also seems to change with the outing, as I have set it up on some nights and it doesn't seem to happen, at least not as much. Other nights a lot worse. I think I need to pay attention to the alignment of the goto base. Maybe that will make some difference. You know maybe one of the motors has to work more if the base is aligned a certain way. Thanks guys for the input.

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I read somewhere that celestron sells replacement motors for as little as 16 bucks but I couldn't find them for sale anywhere. It may be worth a shot sending them an email asking if they sell them... It may be a total load. Good luck to you.

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OK I don't know the details of this scope/mount, so I may be talking rubbish.

If the drop seen at regular equal intervals, this sounds like a periodic error problem.

Possibly a mishapen (damaged) gear tooth somewhere in the drive train?

Possibly a loose gear on a shaft?

Dismantling the drive will identify the cause.

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If it's not happening with every session, then it maybe an alignment issue. Check that the date and time are accurate (some say to within 10 seconds), daylight saving is set to on and your location is reasonably accurate (some reports state to within 50 miles)

Also, when aligning, centre the alignment star using a finder eyepiece (25mm or so) and then do the actual alignment centering using a shorter focal length, 9 or 10mm or thereabouts. Also ensure that your approach to each star is consistent... meaning, if you approach to the first alignment star is by moving the scope to the left and upwards (during the alignment step) then make sure you approach each alignment star in that direction. This apparently minimises backlash between stars (although the best direction to approach depends on settings in the scope setup, but I don't recall exactly which)

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I have a Celestron 6se, same mount/motor as yours.

Mine also seems to move around, but not always the same direction. What i've read it's just the down side the the mount/motor that Celestron uses. It can sometimes keep objects in view sometimes not. The movement on mine is the telescope adjusting to track the object but its not a uniformly fluid motion. The gears skip and lug ect. There are lots of tips on setting it up correctly depending on what side of the meridian the object is on. Thats really all that can be done (if its not a broken motor)

Also, doesn't the 8se already have a dovetail? the 6se certainly does. You should be able to just buy an EQ mount and throw it on there. Maybe it's different outside the US?

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http://www.cloudynights.com/ubbthreads/showflat.php/Number/3623862

Hi Gordon, Try the link above, I've been searching the net for a possible cause and fix for you - not sure if this is the same problem your having, but it sounds the same - have a read of the article and remember these mounts are portable and light so the components that are used in their construction are on the flimsy side - as with all construction now a days - so be careful when tightening and use the least amount of force - hope this helps Gordon.

Regards Paul.

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http://www.cloudynig.../Number/3623862

Hi Gordon, Try the link above, I've been searching the net for a possible cause and fix for you - not sure if this is the same problem your having, but it sounds the same - have a read of the article and remember these mounts are portable and light so the components that are used in their construction are on the flimsy side - as with all construction now a days - so be careful when tightening and use the least amount of force - hope this helps Gordon.

Regards Paul.

Wow Paul,

That looks very straight forward and pretty simple. I think I may even have a socket that will work. For sure an adjustable wrench that will make it. This forum is the greatest and I REALLY appreciate you taking the time to give me this information. It's really nice to have so many new friends (even though they're about 6000 kilometers away) that are so passionate about this fantastic hobby. Thanks a lot Paul, I really do appreciate it.

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To all my friends on SGL,

I would really like to personally thank all you guys for all your help with this problem. I'll make sure that I keep you all informed as to the outcome. It's really inspiring to come to this site and glean so much information in such a short time, provided by so many intelligent and passionate people. I feel like people I have never even met, care about the little problems that crop up for me.

Thanks again everyone

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I have a Celestron 6se, same mount/motor as yours.

Mine also seems to move around, but not always the same direction. What i've read it's just the down side the the mount/motor that Celestron uses. It can sometimes keep objects in view sometimes not. The movement on mine is the telescope adjusting to track the object but its not a uniformly fluid motion. The gears skip and lug ect. There are lots of tips on setting it up correctly depending on what side of the meridian the object is on. Thats really all that can be done (if its not a broken motor)

Also, doesn't the 8se already have a dovetail? the 6se certainly does. You should be able to just buy an EQ mount and throw it on there. Maybe it's different outside the US?

I have a Celestron 6se, same mount/motor as yours.

Mine also seems to move around, but not always the same direction. What i've read it's just the down side the the mount/motor that Celestron uses. It can sometimes keep objects in view sometimes not. The movement on mine is the telescope adjusting to track the object but its not a uniformly fluid motion. The gears skip and lug ect. There are lots of tips on setting it up correctly depending on what side of the meridian the object is on. Thats really all that can be done (if its not a broken motor)

Also, doesn't the 8se already have a dovetail? the 6se certainly does. You should be able to just buy an EQ mount and throw it on there. Maybe it's different outside the US?

Goolosh,

First off, check this link out. Northern Soul Man gave me this link which I think will address the problem (hopefully) http://www.cloudynights.com/ubbthreads/showflat.php/Number/3623862

Secondly, I don't know if the 8SE has a dovetail. It really doesn't look like it. There is a bar from the front to the back of the OTA that looks like it's fastened to the center of the drive. I haven't done any research yet to know if it is adjustable. If this fix Paul posted doesn't fix it, I might look into an EQ mount. I have looked into a few, but haven't really done any deep searches.

I'm from the Chicago burbs and I see that you're from California. Where abouts ???

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If it's not happening with every session, then it maybe an alignment issue. Check that the date and time are accurate (some say to within 10 seconds), daylight saving is set to on and your location is reasonably accurate (some reports state to within 50 miles)

Also, when aligning, centre the alignment star using a finder eyepiece (25mm or so) and then do the actual alignment centering using a shorter focal length, 9 or 10mm or thereabouts. Also ensure that your approach to each star is consistent... meaning, if you approach to the first alignment star is by moving the scope to the left and upwards (during the alignment step) then make sure you approach each alignment star in that direction. This apparently minimises backlash between stars (although the best direction to approach depends on settings in the scope setup, but I don't recall exactly which)

Dunkster,

I have an older 8SE and the software only allows 2 star alignment and the time only is settable to the minute. I will certainly make sure that I approach each star from the same direction to avoid any further problems... Thanks for that. I'll also try the multiple EP trick too. Right now I only have a 22, 13, and a 5mm EP. The 13 and 5 should work.

Thanks again

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I find this site absolutely amazin!!!!!! - no matter what problem arises you guys and gals on here have either suffered with the problem or "knows someone who has". All mounts now seem to be ok to use just with the original add ons - but as you know on here, the hobby becomes a passion, and before you know it, you have massive 2" eyepieces, star diagonals, up graded finders hangin off the back of the scope and great big dew shields and heaters hangin off the front - not to mention cameras.

I think this is when we all need to think about mount up - grades, yeah I know - PRICEY and can run into the thousands.

Hope it works out for you Gordon - keep us posted and as you know on here the seats around this " table " in the Stargazers " lounge " are full of a wealth of knowledge "you only gotta ask!!!". Paul.

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Dunkster,

I have an older 8SE and the software only allows 2 star alignment and the time only is settable to the minute. I will certainly make sure that I approach each star from the same direction to avoid any further problems... Thanks for that. I'll also try the multiple EP trick too. Right now I only have a 22, 13, and a 5mm EP. The 13 and 5 should work.

Thanks again

The older software (from what I understand) is still as accurate as the newer software, only the newer software introduced "Sky Align" which allows you to pick 3 bright stars from the sky without knowing what they are. From what I've read, the "Sky Align" uses 3 stars to calculate the identify of each of the stars but then only uses 2 out of the 3 for the actual alignment. When I first got my scope, I used Sky Align all the time but now I'm getting more familiar with the sky I'm picking 2-star align.

What I do is pick Polaris as my first star, as this doesn't move much and for the second star I try to pick a star sort of south east (since my house blocks west) and more than 30 degrees above the horizon...for me at the moment, that is Altair. If your handset offers "Auto 2-star align" then when you pick the 2nd star from the list, it will slew there for you (the Auto part). If no Auto is available, you just have to slew to the 2nd star yourself. I find the 2-star alignment quicker to perform than Sky Align, so all things considered you're not missing much :)

Regarding the eyepieces... from the ones you have now, I'd try the 22 for centering and the 13 for the alignment... you could try the 5 but that might be a bit fiddly (5mm = 400x!). Once the star is in my field of view, I defocus it until it is a big donut as I find that easier to centre in the view than a dot.

Btw, I picked up most of this stuff from the guys+gals here :cool: (thanks everyone!)

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Goolosh,

First off, check this link out. Northern Soul Man gave me this link which I think will address the problem (hopefully) http://www.cloudynig.../Number/3623862

Secondly, I don't know if the 8SE has a dovetail. It really doesn't look like it. There is a bar from the front to the back of the OTA that looks like it's fastened to the center of the drive. I haven't done any research yet to know if it is adjustable. If this fix Paul posted doesn't fix it, I might look into an EQ mount. I have looked into a few, but haven't really done any deep searches.

I'm from the Chicago burbs and I see that you're from California. Where abouts ???

I didn't know you have the older 8se, maybe they didn't have the dovetail? the new ones do though (if you check out the pics http://www.telescopes.com/telescopes/catadioptric-telescopes/celestronnexstar8se.cfm that black bar is the dovetail mount, don't know if it's different than what you have)

I am in the San Jose area of California. It's been non stop clear skies here for weeks! i get out about 3-4 times a week! The moon has been my biggest sky watching enemy of late but we're going into a better phase so it's getting better out there! For me though to hit a Dark Site i have to drive at least 4+ hours :( but i have several mountain tops within 2 hours that offer better views than my back yard.

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Well guys,

Sorry to say that the Alt clutch tension was NOT the problem. Would have been such a simple fix if it were. The small gears, behind the plate, that is behind where the hand set hangs, is the problem. I'm attaching a link to a picture, though there was not as much light as it seemed there was when I took it. When I look down into the gears (in the picture) and gently move the scope (Alt) up and down, the shaft that comes out of the "gear set" ? on top of the drive motor moves quite a bit. Probably 1.5mm, I would say. For sure way more than the bearings should allow it I would think. I wish I would have found this site before I bought my used scope, not knowing a thing about it. Bad move on my part. Newbee mistake.

My next question would be: "Does anyone have a link to someplace on the "Interweb" where I can find parts to repair this problem. IE, motor, gear unit. Also I need instructions on how to do it, so I don't jack it up any worse than it already is.

Or should I just can the whole thing and buy an EQ mount and be done with it.

http://gordongreene.com/photogallery/displayimage.php?album=77&pid=3451#top_display_media

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I didn't know you have the older 8se, maybe they didn't have the dovetail? the new ones do though (if you check out the pics http://www.telescope...nnexstar8se.cfm that black bar is the dovetail mount, don't know if it's different than what you have)

I am in the San Jose area of California. It's been non stop clear skies here for weeks! i get out about 3-4 times a week! The moon has been my biggest sky watching enemy of late but we're going into a better phase so it's getting better out there! For me though to hit a Dark Site i have to drive at least 4+ hours :( but i have several mountain tops within 2 hours that offer better views than my back yard.

Goolosh,

There very well could be a dovetail, as the bar that attaches to the OTA looks like the picture, but is covered by the plastic shrouds and I can't see a dovetail. Either way it doesn't look at all externally adjustable. You know, say like the rings attached to a dovetail, that would hold the OTA on some telescopes. I don't know if you read the other post, but the clutch was not the problem with my scope. It's the gear coming out of the motor on the alt drive. There is a lot of slop in it... a lot.

My "dark site" is at my brother's house about 2 hours west of me. He lives on 14 acres in the boonies. Pretty nice to go out there. At times the Milky Way looks like clouds. At my house there are times I can barely see Polaris and I'm not kidding. I live a little over a mile South of about 20 (no exaggeration) car dealerships that don't really care about how much light goes up. And about 1/8 of a mile North of a Park District facility that looks like a baseball stadium until after 10 O'clock. So suffice it to say, my place wouldn't be a first choice for an Astronomy club to meet. Ha Ha.

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The older software (from what I understand) is still as accurate as the newer software, only the newer software introduced "Sky Align" which allows you to pick 3 bright stars from the sky without knowing what they are. From what I've read, the "Sky Align" uses 3 stars to calculate the identify of each of the stars but then only uses 2 out of the 3 for the actual alignment. When I first got my scope, I used Sky Align all the time but now I'm getting more familiar with the sky I'm picking 2-star align.

What I do is pick Polaris as my first star, as this doesn't move much and for the second star I try to pick a star sort of south east (since my house blocks west) and more than 30 degrees above the horizon...for me at the moment, that is Altair. If your handset offers "Auto 2-star align" then when you pick the 2nd star from the list, it will slew there for you (the Auto part). If no Auto is available, you just have to slew to the 2nd star yourself. I find the 2-star alignment quicker to perform than Sky Align, so all things considered you're not missing much :)

Regarding the eyepieces... from the ones you have now, I'd try the 22 for centering and the 13 for the alignment... you could try the 5 but that might be a bit fiddly (5mm = 400x!). Once the star is in my field of view, I defocus it until it is a big donut as I find that easier to centre in the view than a dot.

Btw, I picked up most of this stuff from the guys+gals here :cool: (thanks everyone!)

Dunkster, thank for the info. I only have the 5mm for star collimation (which does a great job by the way) I put another post up that gives the real problem with my scope, which is the gear train on the Alt drive. Now I need to look for parts...

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http://www.cloudynig...5/o/all/fpart/1

Hi Gordon, sorry to hear that the fix didn't help, I've found another link entitled "Gear slop", quickly running through it - it mentions moving the bevel gears closer together by loosening an allen bolt on the gears thus taking up play on the shaft by eliminating the distance the shaft can move. Not knowing much about the internals of the gears/mount - there seems to be a step by step procedure to follow , not sure if you can either replace or repair, seems to have the links for all parts needed and may be cheaper than a new mount, but worth a look at - hope this helps Gordon. Paul

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Hello Gordon.

I have a 8SE which seems to have a similar ALT drive assembly. I noticed that the motor drive gear (the small one) was poorly supported and was likely to develop the problem you are experiencing which is caused by wear in the bush that the drive shaft runs in. I avoided this by adding a collar to the gear, which is over long, and supporting the collar with two ballraces at 120 degrees fixed to a bracket. This prevents the gear from deflecting downwards or sideways. A friend of mine refurbished a worn drive unit for a 6" by making a replacement bush for the shaft.

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http://www.cloudynig...5/o/all/fpart/1

Hi Gordon, sorry to hear that the fix didn't help, I've found another link entitled "Gear slop", quickly running through it - it mentions moving the bevel gears closer together by loosening an allen bolt on the gears thus taking up play on the shaft by eliminating the distance the shaft can move. Not knowing much about the internals of the gears/mount - there seems to be a step by step procedure to follow , not sure if you can either replace or repair, seems to have the links for all parts needed and may be cheaper than a new mount, but worth a look at - hope this helps Gordon. Paul

Soul Man,

Actually while looking at the gears that was the first thing that went through my mind. I tried it, to no avail. Reason being, the actual movement of the shaft with the slop in it is parallel to the OTA and the gear to which you refer is perpendicular to the OTA. Even with substantial pressure applied, when you reverse the direction of the gears, the shaft coming from the motor (the bad bearing) will just move back and forth across the face of the gear going to the alt drive. The gear to which you refer. I hope I explained that well enough to make sense. I just don't know if I should go ahead and fix this mount for $146 + shipping or buy a new mount... well I know I should just fix it, but am trying to justify buying a new mount in my big "kit filled head."

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