CG5-GT accuracy help please!!!!

[spaceboy]

Hi All

After another hunt for objects I am to admit defeat and ask the wise members of SGL for humble advice.

I have a Celestron CG5 GOTO mount on a fixed pillar. My polar alignment is only a tad off but still giving me at least 6-10 minutes tracking at high powers. I have with success aligned 2 stars and calibrate 3-4. The GT is for 7-8 objects right on the money. BUT as I choose different objects some of them get further and further out of alignment while others are only minimally off. I have noticed some slop when you use the direction keys. Not in the worms (backlash has been adjusted) as such but the image once a direction key is used will take a little while for the object to come to a stop. Any help would as alway be greatly appreciated but on this occasion more so as these mounts aren't cheap and I'm finding myself having to manually search for objects most of the time. I often feel the need to have to carry out alignment every time I observe which defeats the object of having the scope permanently mounted.

SOMEONE PLEASE HELP

SPACEBOY

[Peter Drew]

With some mounts, my C8 SE, for example, the manual recommends that the same motions with the same directional keys are used as those which you initially aligned the scope. This ensures that takeup in the motors and the gears has been compensated for. Hope this might help. .

[glowjet]

If your scope is pillar mounted I believe the most positive accurate way to align the scope is to drift align it, there is much written about this black art without going into detail, if you look into the imaging section, Peter is also right when approaching your target in the same manor with the direction keys such as : come in from the right move up or down, it does not matter which, so long as you repeat what you have done each time

[spaceboy]

Thanks guys. I did read a little about goto approach & setting up direction buttons to suit but it all went over my head TBH.

From what I gather drift alignment requires a view of the horizon which is impossible where the scope is setup. At best I can see from 20 degrees to zenith.

What I don't understand is the alignment and calibrations all goes well. But after only a several selections I find some objects drop in the cross hairs and others barely make it with in the view of the finder scope. I can put it in hibernate, come back the next day and it starts of OK and then it happens again. Driving me nuts now but I guess this is a consequence of including technology in to the mix.

[Sparrow]

It's only a thought, but it's not slipping on the clutches is it? - I generally only target two or three objects in a night as I'm imaging, but I'm using quick alignment that I set up months ago and my CG5 GT still puts the objects in the finderscope. I do use precise goto, but the initial star for the precise goto is always in the FOV which is why I'm thinking it might be slipping on the clutches.

Regards

John

[spaceboy]

I had an unfortunate DUMB *** first experience using the GT mount where the mount wanted to find the double cluster and ran in to the pillar. After stripping the mount apart to check gears etc hadn't stripped I put it back together adjusting the worm gears but I had no idea there are clutches. I assume you are referring to the RA/DEC locking knobs ?? These are always done up tighter than tight. I have no doubt there is slack some where that is slowly letting each target slowly out of view but I'm aware of the consequences of over or under tightening worm gears and the GT motor gears mesh well. The locking knobs tighten down strong so I cannot imagine where the slipping is occurring. I know when manually slewing there is a small amount of movement in the image after the slewing has stopped but I also had this when I used standard tracking motors so assumed this to be normal settling of the drive train.

[Uranium235]

Sounds like your PA is still off, try 2 or 3 iterations of the PA routine in the handset to get it as close as poss without having to do drift alignment.

Usually, by the end of the evening (after much changing of filters, ep's etc) I always end up doing a precise goto in order to get other targets in the centre of FOV. All those little knocks and nudges add up after a while.

Oh, another thing i remember from tuning my CG5, when you lock either axis - is there any "give" in either of them? If there is then it might be an indication of it not being meshed enough, it just needs a little tweak (1/4 turn maybe). Though it can take some trial and error to find a happy medium.

[spaceboy]

Thanks U235 But for some reason my handset doesn't allow PA and it is all done manually through the mount. My instructions show that the hand set should have this option but it's not on the handset where it should be. Should I see about upgrading the firmware?? I will have a look at making some adjustments today.

[ollypenrice]

You dopn't need a view pf the horizon to drift align. In the south you need to be close to the celestial equator, which is well up, and in the East a 20 degree horizon is fine.

I don't know that handset or mount but usually you can re-synch each time you are at an object, thereby keeping the map of the sky up to date in the scope's computer.

Another issue might be Cone Error whereby the OTA is not parallel with the mount's polar axis. Most software can use a 3 star alignment to compensate for this, though.

OLly

[spaceboy]

I think my biggest problem is the manual all seems a bit vague to me. Is there a web site that would better explain all the tweaking needed? I also think that the guy who had the mount before me will have had all the settings tweaked for his location. Would it be worth doing a factory reset on the hand controller and starting from fresh???

[Glider]

Doing a factory reset helped me as it clears any tweaks the previous owner might have made to suit his setup but which might not suit yours.

What versions of handset and motor controller software are you running? You can view these on the handset. There is an upgrade for both and a detailed pdf addendum to the manual to cover it all.

When you slew do you see a rotating progress indicator on the handset display? The slew isn't over until this disappears. The mount software should slew past your target, then reverse and approach again to take up slack in the gear train. This last stage is done at very slow speed and can take several 10's of seconds. It has caught me out a few times.

The slew accuracy will vary over the entire night sky. If you slew to a part of the sky and the target is off then;

Press escape.

Press the Align key.

Carry out a Sync.

Slew back to your target.

The slew will move off target and then slew back again.

Repeating the Sync proceedure when required will gradually improve the mounts model of the entire sky.

Something that confused me at first; each alignment, sync, etc is a 2 stage thing. Following the instructions on the handset display you first align through the finder whilst the mount automatically selects a high speed for you, then press Align. Then you Centre through the EP at a slower speed and press Enter to accept.

[Uranium235]

Glider pretty much covered the routine, but it should be in the handset.

But just to recap:

First, use "named stars" to slew to a star well away from the pole and away from the horizon (I used Aldebaran this eve).

Then, escape out back to the first screen and hit the "align" button.

Scroll to polar alignment, select, then scroll to align mount, select.

Then follow the onscreen instructions and youre sorted

[spaceboy]

Thanks guys I will give it a go once I've re-checked the worm gears

[carastro]

I've a CG5 GT and had problems in the past, particularly when the mount has got stuck on an obstacle as yours seems to have done

ran in to the pillar

. It tended to misbehave after that.

In the end I did a Restore to Factory settings (which I see some-one earlier did too), and after that it has worked fine.

Carole

[spaceboy]

Thanks Carole. I had the mount apart today and re-checked worm gears and took out any looseness. Checked the polar scope was well calibrated ready for re-aligning the NCP and done a factory re-set on the HC. Just need the skies clear tonight to get aligned on the NCP and star align to see if there is any improvements.

Thanks everyone for all the advice and I will keep you updated. Just have my finger crossed it works.

SPACEBOY

[spaceboy]

A quick update:

I'm not sure if it counts to actual goto accuracy but checking my polar alignment last night I found it to be a little way off. I assume after 2 star alignment and 4 calibration stars this would make no difference to pointing accuracy and only effect tracking ????? I had noticed at high magnifications it did stray a little so I was aware the PA wasn't right on the money.

Anyway my theory is after reading through the mounts manual is. It suggested if you need to make any adjustments if the object is a touch out that you adjust with the direction keys and make the final approach in the same direction as the mount... quote "up and right". Originally to much fiddling in my book I never paid much attention to how the mount settles on an object so I think this is where I am going wrong. I may look at 3-5 objects before I notice a little inaccuracy but on a planet the inaccuracy has to be adjusted to fit in the FOV and I do this with no regard to keeping the worm gears under tension so I can only assume after 2-3 objects this becomes more and more emphasized and so the accuracy of the GOTO is lost due to natural slack in the worm gears created by my adjustments to center objects????

I managed 5 objects last night with some what more accuracy than usual but as I did several things to the mount in preparation I am unsure which one may of helped??? After making adjustment to the worm gears my main concern is that I may now be mashing them up and it was the factory reset that fixed the accuracy issue. Should there be a slight run on as the mount slows from manual high speed slewing or should it stop dead ? The mount certainly sounds like it's making hard work of slewing in DEC now and so this is the reason for my concern.

SPACEBOY

[spaceboy]

Another update and to say thank you to everyone for your advice and help!!

Deciding the worm gear on the DEC was too tight I loosened it a bit. I also found that the RA worms also needed a little tweak and after doing another factory reset just to make sure, everything now appears fine. I purposely went from target to target to see if there was any inaccuracy growing but so far they always came in to near center view. There is still some issues with targets in certain parts of the sky but for the most all was acceptable and I am now doing a calibration every time the objects are slightly out of view. Fingers crossed this has now resolved the issues as to be frank I seemed to be spending more time messing with the mount than I did observing. One good thing came from it is that I now know the names of some of the bright stars I wish I could pin point what the problem was so if anyone else has the same issues it may help them but I made so many adjustments it would be hard to say which one worked.

Out of curiosity how far off are the mounts at finding the first alignment stars. I found it was more than the moons width but by the time I had finished the 4th calibration star it was almost spot on. I take it this is normal??

Thanks to everyone for you help.:icon_salut:

SPACEBOY

[carastro]

Despite having my CG5 GT on a pier and so the PA is always the same, the alignment stars are sometimes pretty close and sometimes not. I cannot see any logic for this but as I am not technical enough to sort it out I just live with it.

Carole