CG5 GoTo Blues... [Archive]

g__day

17-06-2006, 11:07 PM

Well I'm up to day four with this my first GoTo mount. Accuracy is variable and lacking - at present its like daylight saving has confused things and its pointing an hour behind where everything currently is or something, plus more pointing errors.

Just some initial observations about the mount and manual.

1. The mount arrives with the Alignment peg placed between two legs rather than over one, against Celestron's advice - increasing its turning moment and chance of making a nasty whoopsie all the more likely.

2. The manual probably should suggest the following:

Understand where 20 or so most prominent alignment guidestars are, else if the set up GoTo is wrong you will not have the knowledge to align the scope to the correct stars
realise the design we choose means the dec motor can often knock into the RA motor housing - possibly stuffing up alignment? whenever you get to close to Alpha Centuari.
in fact about a third to half my GoTo attempts failed outright to complete due to the motors colliding, is this a dud design like a car that can go forwards or back, right in either direction but left only in reverse? I'm wondering if this lack of clearance is simply a fatal design flaw doomed to kill half the GoTos you could issue.
the scope doesn't understand this last point, and if there are two options to get to a new Goto point - bet your bottom dollar that it chooses the one that causes Dec motor housing to have a clunk and stop rather than take the obstruction free route
same with the the 90 degree prisms hitting the tripod leg on some viewing angles cause of the travel route it favours3. If you point to an incorrect wrong star as one of your three alignment stars you can't really undo, you have to re-boot and start from scratch again.

4. About 50% of the time on goto first alignment star it points below the horizon which is just plain wierd!

5. Accuracy - well its about three finger knuckles behind where it should be on Spica and Jupiter.

6. Quick align on Jupiter then move teh scope and search for Jupiter again fails. With a small move doesn't the mount is unable to find Jupiter - the one alignment star that you choose 30 seconds earlier.

7. The manual has no trouble shooting section

8. The manual has no first use diagnostic to give feedback on how to check your scope is functioning correctly (no benchmark diagnostic tests)

So right now I don't know if its a lemon, operator error and/or a setup fault

Here I go again - attempt 8 tongiht at a alignment that is accurate enough to then get within even the 8 * 30 finderscope for Jupiter.

Any help or suggestions would be greatly appreciated guys. I had such high hopes and desires and now I am left feeling very flat. Simply follwoing all directions to the best of my ability is producing very mediocre results at best.

PS

Test 10 - some better luck, changed the location from Google Earths GPS coordinates of my backyard to just the manufacturer defined Sydney and suddenly GoTo is a whole lot better. This time Jupiter was in the wide angle scope about halfway in. Still though half my GoTos fail with one of the motors hitting some the other.

PPS

Can anyone else here who uses a CG5 mount validate or refute my worries?

Set up properly does it Goto things quite accurately?

Can it be commanded to GoTo and object along a route that won't involve it briusing itself most of the time?

Many thanks guys,

Matt

Dennis

18-06-2006, 07:12 AM

Mate – that sounds awful!

I suspect the peg between the legs should mean fewer tripod collisions compared to the peg over a leg?

An American work colleague once came to one of our meets with a Celestron GoTo ‘scope and for the alignment, he had to point the OTA N (not S) and use Time Zone 14 in the Celestron Manual, although he had a Alt/Az Nexstar5 which may be a different hand controller/protocol than yours?

When he accidentally pointed the OTA S as the initial position, he got weird slews.
When he correctly pointed the OTA N but used the incorrect Time Zone he also got weird slews.

When he finally read the manual, pointed the OTA N and used Time Zone 14, everything appeared to work quite well.

Not sure if that really helps?

Cheers

Dennis

g__day

18-06-2006, 11:33 AM

Thank you.

No the peg position between the legs means the centre of weight is about 4- 6 inches further away from the tripods centre of suspension. This means to tip it over accidentally you have to bump the scope 4-6 inches less than is the centre of weight is closer to the point of balance.

Not sure which controller I have other than its the flash upgradeable one - with no documentation supplied on how to do this!

I just wished there was a diagnostic test documented to confirm it is working or not.

Still anyone else have data on this mount or know of a url where test matters are discussed?

Taa guys!

Dave47tuc

18-06-2006, 12:01 PM

Hi Matt,
Here a few links that you should look at which you can join and will help you immensely.
The CG5 mount is a very good “Go To” type mount and once you work it all out will give you many enjoyable viewing nights.

http://groups.yahoo.com/group/nexstar/

http://groups.yahoo.com/group/Celestron_AS/

http://www.cloudynights.com/ubbthreads/postlist.php/Cat/0/Board/lxd55

http://www.nexstarsite.com/

Good luck.:)

g__day

18-06-2006, 12:13 PM

Dave,

Your a God send with those views and links. Hugely appreciated, off to browse.

Matt

PS

I noticed on first alignment slew last night it was about 70 degrees off, pointing at horizon rather than high in the sky - shows some sort of offsite.

PPS

Annoyance - the Yahoo Celestron group takes a week to join before you can read it even, arggghhh!!!

sheeny

18-06-2006, 12:43 PM

Oh Matt! I hear ya mate! Major frustration! Let me just try to address each point in turn...

I have found with mine (prior to fitting the GPS module) that despite setting the time accurately (as wellas location, etc) the drive was always behind in RA. The amount it was "behind" varied, and since fitting the GPS module, this error has gone, sine the drive is always up to date (time?) from the GPS signal. I suspect the drive does not start the clock when you enter the time, but after you have completed your alignment.:mad2: Other than that, my drive is reasonably accurate... provided you put accurat info into it. Its the old GIGO problem (garbage in, garbage out).

Hmmm. I have my alignment peg between the legs, as delivered. I have not had a problem with this. Given the location of the counterweight and scope this should be the most stable position. I could see that with some OTAs it might be necessary to move the peg to the other side to avoid a crash between the OTA and the tripod leg, but otherwise I would be concerned about it.

This is a worry... If the housings are clashing I suggest either the drive is faulty, or the alignment marks are not properly aligned during the start up alignment procedure, or the RA and Azimuth limits in the drive are not set. They should be set from the factory but can be changed.

[/LIST]Are you talking about your star diagonal? What OTA are you using? I can't imagine this with my C8.:shrug:

Actually it lets you correct 2 out of 3... but I share your frustration with this one!

Way below? A reasonable amount of time the drive will try to find a star that theoretically visible but it might be below your local horizon. If it's pointing below horizontal, though, something is wrong. Either the alignment marks not aligned during the start up alignment procedure, the database filter is disabled, etc.

Yup! This, I believe is a timing issue which the GPS module fixes.

In a Quick align, the sky is just modelled from the time and location data you enter. It doesn't take any notice of where the scope is pointing... so it still goes to where it thinks Jupiter is.

What was the difference? The difference in position should be small, but obviously something about the way you've entered the data must be different???:shrug:

Definitely more accurately than you are describing!:P

The accuracy is only as good as the alignment and data entered. If your initial alignment is out by a couple of degrees (you won't neccessarily do any better by compass) then everything is out by a couple of degrees until you drift align.

The biggest inherent accuracy issue I have found with my CG-5 is the timing issue, which the GPS module fixes. Prior to the GPS I would set the time accurately, but I suspect the clock in the drive didn't start running till after the alignment procedure was finished. So if it took 20 minutes to muck about with the alignment (and maybe a collimation as well) then the scope is out 5 degrees in RA.:(

Since I have installed the GPS, the goto is reasonably accurate. The night before last for instance, I did a rough align only (compass alignment of tripod followed by 3 star auto align) and it slewed to about a dozen different DSO's and everytime the DSO was well within the FOV of a 30mm EP in the scope. I changed to a 13mm Nagler and some were inside the FOV and some were just outside. If I had bothered to drift align, I would expect all objects to be inside the FOV of the 13mm Nagler.[/quote]

I dunno what's happening here. Only once I've had this issue, and I didn't get to the bottom of it. I switched it off before it did any damage, so then I couldn't see what data it had wrong in it to make it do what it did. In my experience this just isn't an issue in normal operation. You could muck about with the RA and Dec limits in the drive, but I think you'll find that too limiting. I suspect something is not right to be causing the crashes. Have you sought advice from the dealer you bought the scope from?

JohnG

18-06-2006, 01:09 PM

Hi

First off, I must admit that I don't know anything about a CG Mount so this might be wrong.

Is your date and time inputted in the correct format? especially date, is it required to be entered in the American format ie mm/dd/yy? is time required in UT format?

I only ask this as the Gemini is required in this format, maybe that is what is wrong !!!!!!!!!!!! only a guess. It is rather strange behaviour. :shrug:
Cheers

JohnG

anthony2302749

18-06-2006, 01:12 PM

I am not sure whether is will be any help now after all the other comments:D , but may be useful. Sheeny comment about setting the time is an interesting conundrum indeed.

Welcome to the world of Synta (the real manufacturer of this mount) Skywatcher/Celestron CG5

First of some basic question.

Is the tripod level prior to placing the EQ Head on top?
Is the polar axis pointing due south (counter weight on the southern side of the mount) and set to the correct elevation?
Does the mount have a polar alignment scope and if so can this be used to accuracy align it with the constellation of Octans which is located near the SCP and if the scope did not come with one ask the supplier why?
Is the mount/scope balanced properly?If you’re southern view is obstructed by housing use a compass to find magnetic south and then adjust for magnetic variation to find true south. Mark it on the ground so that you can use it for later reference.

What I have done is gone through some of the basic set for an EQ mount.

Time to set up the GO-TO, I would recommend that you do a factory reset and set your location for Sydney. We will worry about enter your location data later, mainly because the software is written for the northern hemisphere e.g. the good old USA.

Now for the alignment process, ensure that the index marked in both R.A. and Dec are aligned. This is very important as the mount need to know were it is starting from. Go to the Two Star Alignment Menu, now you are going to choice two alignment stars it the Eastern part of the sky. There is an obvious reason for this and that is Meridian Flip. We are keeping things simple.

Choice two stars that lie about 45 to 90 degrees apart. Choose the first alignment star and allow the mount to slew to it. Align on the first star press enter to accept the alignment select the second alignment star and allow the mount to slew to it. Align on the second star; press enter to accept the alignment. Job done, the scope should point accurately enough to find most object in the eastern part of the sky (most objects will end up in the FOV of a standard 26mm Plossl EP). When you flip over to the western part of the sky you should be able to locate a know object and from the software menu you may have some this like “Align on Object or Sync” this should sync the scope for operation in the western part of the sky.

Finally go back to the manual and have another read. Remember it is written for the northern hemisphere.

P.S. I will get back to you about setting your location data later.

sheeny

18-06-2006, 01:25 PM

Yeah, I agree John. Something simple like that would seem the simplest explanation for the behaviour.

Alignment marks?
Date wrong format?
Wrong Time zone?
Wrong time (am/pm)?

Matt, I assume your electronic compass works by detecting magnetic field. Are there any magnetic anomalies around you that could affect your compass? EG concrete building(reo), power lines, etc. That could have a big effect on your alignment (but not big enough to have it looking for stars underground!)

Also are you still using you PC to drive it or have you gone back to the hand controller? I suggest going back to the hand controller until you get it sorted, just so any complications from the PC system are not introduced.

Hang in there mate! It would be nice to put two drives side by side to see the differences!

Al.

g__day

18-06-2006, 07:39 PM

Guys a huge thank you!

I ponder the internal clock issue because on a reset the last time it knows about is the clock when alignment started, not the time when it was powered down - which implies the clock wasn't running, which would definetely contribute to the problems I encountered - and as my first alignment took 20 - 45 minutes would say why my GoTo errors were so large. By the end of the night alignment took < 20 minutes - so pointing accuracy on Jupiter was far better.

Alignment marks checked on both axis on each power down reset. Also checked vs the handcontrollers query - and the DEC alignment marks are spot on, but the RA is about 3 degrees out - the RA alignment marks should be a bit to the left of the marked position to get a 0 00' 00" reading so I countered for this later in the night.

Date wrong - well its MM/DD/YY so it wont accept 17 as a valid month, so I set 06/17/06 yesterday, only had a date error on my very first set-up.

Time zone is 10 for Sydney (and I pretty sure it was +10) checked this twice.

Time was entered both as pm but normally using 24 hour miltary time. I've been round the world 15 times now and can kinda do it in my head.

I used two compasses, both gave readings for 170 (I treat Celestial South in Sydney as 11 degrees East of magnetic South). I also roughly checked where the crux and two points intersect as a rough double check, and did a 20 mintue drift track on Jupiter and adjusted to improve. It wasn't perfect but it should be within 5 degrees.

Backyard has no concrete buildings or powerlines within 50 yards.

I thought modelling 3 points give you a complete sky picture - PLUS compensation for the drives not being properly polar aligned. I assumed the software was specifically looking to estimate and conteract this.

Mount stability - rock solid and not bumped all night.

Tripod base level - yes according to both my spirit levels and the internal bubble on the mount.

Scope as perfectly balanced as I could get it.

I have gone back to the Hand controller to drive it while its in the back patio.

No Polar alignment scope - probably the next thing I buy.

GPS - YES I think its my next major buy, from Andrews again if I can - that way its one supplier fixing all the issues and no finger pointing to somebody elses problem, and if doesn't work in the end its a warranty call.

Factory reset - very temped too.

* * *

Questions on the GPS option. I presume it plugs into the hand controller, and is only present at the start-up time (otherwise you couldn't computer control the mount, unless the PC plug goes into the GPS? Or is it GPS or PC but not both in one viewing session?

* * *

On the drive housings bumping. They are not round with a clear gap in all positions / rotations, they are horseshoe shaped and if you are looking close to SCP there are many positions which they will hit each other.

Similarily both the guidescope and the 90 degree diagonal can hit the tripod in the wrong positions looking near the SCP.

This is simply because the drives are too close to each other and the mount is not tall enough to rotate fully and not position the scope to collide with the mount or tripod.

* * *

Well rather than viewing again tonight I'll likely just spend teh night websurfing trying to find a diagnostic or a fix. :(

Keep the advice comming guys - especially if you know of a suorce that has experienced and solved this problem.

sheeny

18-06-2006, 09:02 PM

Matt,

Hang in there mate! I know its frustrating, I've been there myself (just not as deep I think!:P )

The GPS option, FYI, includes the GPS receiver and an accessory module. A cable joins the GPS module to the accessory module and another one joins the accessory module to the hand controller port on the RA housing. There are two other ports on the accessory module - one will take your hand controller, and the other is for your PC connection. So it's all hooked up and available 100% of the time if you want it! The GPS runs continuously so the time in the scope is accurate... always!

It would be nice if the GPS option was cheaper (of course!) but I am SOOOO glad I got it!:thumbsup:

Al.

g__day

18-06-2006, 10:07 PM

Al

That's very pleasing to hear! How is the GPS powered? What voltage / ampage does it need?

Where did you get it and how much? I've asked Lee of Andrews to price one for me, they are trying to help me but its a new issue to them and they are in the process of refering me to a collegue with greater specific mount knowledge.

* * *

I finally got into the yahoo CG5 forum and the faq states something interesting

For alignment to work, the GoTo Electronics require that you use two stars to the West of the Meridian and one star to the East of the Meridian.

Well with my limited knowledge of stars I simply chose alignment stars in the alignment catalogue whose names I knew - no idea what side of the Meridan they were on, nor if that is a Northern Hemisphere restriction only!

sheeny

19-06-2006, 01:07 PM

G'Day Matt,

I got my GPS module from AstronomyOnline for $680 I think (from memory!). It draws it's power from the scope drive, no separate power supply required.

The standard auto align procedure is fine. Stick with that to start with. In the southern hemisphere (i.e. for us!) it will pick two stars in the eastern hemisphere and one in the west, than calculate cone angle errors etc.

If it picks a star that you can't see, just press the Undo button, and it'll go to the next one, etc until it gets the stars it needs. If it picks a star that you aren't sure about, you can "undo" that as well if you like. Once you get into it, it's pretty straight forward, it will lead you through.

Al.

anthony2302749

19-06-2006, 01:12 PM

Hi

The wording is correct it is my very rusty navagation skills. So you are correct by saying True South is 11 Degrees east of magnetic south.

Your understnading is correct about finding true south.

The magnetic delination or magnetic north in Sydney is moving in an easterly direction. Currently magnetic north is about 13 Degrees East of True North, therefore True north is 13 degrees west of Magnetic North. True south will be 13 degrees East of magnetic south. See diagram. If I am wrong "OOOOp's" which I was before correcting the post:doh:so sorry for the confusion :confuse3: .

Using Crux and the Two Pointers to find due south is a very good way to get rough polar alignment. Using drift is also a good idea as well.

g__day

19-06-2006, 02:27 PM

Al,

Lee from Andrews has now got Steve Boyle (the Celestron guru in Oz) in the link trying to sort this with Celestron in the USA, so my peace of mind has risen substantially!

I now know the names and locations of about 10 alignment stars so set up is alot quicker now! And yes I know all about the UnDo buton and select alignment stars which you know!

Anthony,

Was that a major oops on my part? BinTel told me 11 degrees East of Magnetic South for Sydney, but if its 13 degrees West well that's a major stuff up! Anyone point us to the definite correct answer? What is the compass heading for the SCP, is it 169, 167, 191 or 193 degrees?

Various resorces seem to conflict

http://www.myastroshop.com.au/guides/polar-align-basic.pdf says its 12 degress 36 minutes East of South for Sydney

vs

http://www.geocities.com/magnetic_declination/

Says is 13 degress East of North

Location Lat. Long. Declination Incorrect Error
(degrees) Declination (degrees)
(angle between (degrees)
where a compass (angle between
needle points north magnetic
and true north dip pole and
pole) true north pole)

Sydney 34.0S 151.5E 13 E 13 E 00
Australia

anthony2302749

19-06-2006, 03:23 PM

Hi

My apologies, Myastroshop is correct with his compass direction. It's me, generally my navigation skill were spot on, obviously I am getting to old. Go with the second one, 13 degrees west of magnetic north. So on your compass true south should be 167 degrees from magnetic north.

Dennis

19-06-2006, 03:36 PM

Although I don't do this any longer, (as I have three fixed registration marks in the back garden), I used to align the polar axis with the green line in the attached image. This would place the four stars of Octans, one of which is Sigma Octans, in the FOV of my Polar Alignment Scope where I would then align more accurately by adjusting the Alt Az knobs of the GPDX mount.

Edit:
I have just added a scan of a Brisbane map, (coincidentally showing Cambroon, Ron's location) which graphically shows the relationship between Grid North (GN), True North (TN) and Magnetic North (MN).

This appears to indicate that when the compass needle is pointing N on the previous photo of the compass, (=0 deg), then we need to subtract 11 deg, which gives 349 degrees.

We then set this 349 deg at the “READ BEARING HERE” mark and let the compass point to N as shown by the rotating pointer at the “N” mark in the white outer bezel. Then, the True North line will be along the green line.

At least I think that is correct? Corrections welcome and gladly accepted!

Cheers

Dennis

Karls48

19-06-2006, 05:59 PM

Hi
Magnetic declination varies by 1 to 4 degrees between places only tens kilometres apart. For my place 33 45 S and 150 28 E it is12.27 degrees east.. You subtract East declination from your magnetic bearing. In other words your compass is pointing 12 27 degrees East from true North. If you don’t believe me, take your compass and point it on constellation of Octans.. You will read around 170 degrees. :)
Very good Web site to find Declination is http://www.ngdc.noaa.gov/seg/geomag/jsp/Declination.jsp (http://www.ngdc.noaa.gov/seg/geomag/jsp/Declination.jsp)
Karl

g__day

20-06-2006, 10:10 PM

Found the problem and a simple correction to the set-up fixed all the problems, the motors knocking and the pointing being simply crappy. Its was so easy when I figured it out. The thing that twigged me to it was I tried doing a 3 star align using Antares, Acturus and Spica - in under 5 minutes as the cloud cover started to roll in. Well Antares was star numer one and the scope pointed below the horizon. Then for star 2 I stopped it just before the motors went to hit. Spica was totally wrong. So got these entered in under 10 minutes and searched for Jupiter - again the motors went to collide and nothing I could do manual slewing to any position and then executing Goto when close to Jupiter could stop a motor collision. At this point I was think what a piece of total **** this mount was... I tried a factory reset and no joy there either.

Then it hit me. I re-powered and set the scope to its initial trangles pointing to each other on each axis position and stopped the set-up and checked the axes positions. Bingo - 0 00 00 and 90 00 00 - DEC was ninety degrees out as it had arrived from the factory. So I simply manually slewed back to a point where the mount axes said 0 00 00 and 0 00 00, then released the clutches and moved the DEC axis back to its alignment mount. I re-powered and what a difference! Initial set-up and slewing to the first 3 alignment stars was good. And the motor drives never clunked. I executed a few gotos - Antares, Spica, Jupiter, Alpha Centura and M4 - beautiful, absolutely beautiful. Close to centred even on my rough set-up and the motors moved very cleverly around each other and never touched once!

sheeny

21-06-2006, 07:31 AM

Well that is good news! :thumbsup:

...but I'm intrigued now... what was wrong from the factory? Is it:

the position of the alignment markers on the body of the dec axis housing?
the initial position in the software of the scope once the initial alignment was done?
the scope's home position?I'm not sure if the home position affects the alignment - I assume not, but I've never played with it. You can change it if you want to.

You can check No 1 visually when it's set up. With the mount setup and aligned to the SCP the motor bulge in the dec housing points to the west when the alignment marks are lined up. Do yours?

I guess if it's neither of those things i has to be No 2. Which I would think is weird!:shrug:

Let us know... you've got me intrigued now!

Al.

anthony2302749

21-06-2006, 09:42 AM

Hi

Glad to see that you have got it worked out and the fix turned out to be a simple. I can also see why your pointing accuracy is way off. In the manual it describes following;

Before any of the described alignments are performed, the telescope mount needs to be positioned so that the index marks are aligned on both the right ascension and declination axes (see Fig 2-8).
Once the index position has been set, the hand control will display the last entered date and time information stored in the hand control. Once the telescope is powered on:

What Celestron should say is “Before powering up the hand controller, the mount needs to be positioned so that the index marks are aligned on both the right ascension and declination axes”. If the hand controller is power up before the index marks are aligned the hand controller will accept that as the home position.

So just looking a one axis, the declination, if the index marks are not aligned, say by about 10 to 15 degrees, and the hand controller is powered up there will be an error of 10 to 15 degrees in declination. Moving the mount to the index marks after powering will not correct for this error. The same will occur in RA if the index marks are not aligned before powering up.

Putting in simply, the index marks must be aligned before the hand controller is powered up. The hand controller need to know the home position e.g. index marks, so that it can calculate were the first alignment star is and so on. If the mount is powered up before the index marks are aligned there will always be an error in pointing.

g__day

21-06-2006, 09:53 AM

The position of the alignment marks were fine, as is the software, but the data wasn't. The encoders weren't storing a correct set up value on both axes for the alignment position - meaning:

1) On alignment each star looked like it was 90 degrees out of position and
2) Each motor was almost guarannteed to knock into each other on half of all gotos

So in alignment position I assummed each axis should read 0 00 00 or 90 00 00, but one on 90 and one on zero seemed confused.

What did surprise me last night when I finished up and went into hibernation I read the axes and they said 90 and 90, even though I'd adjusted them to be 0 and 0 on set-up.

So once the weather clears I will try them again.

Oh and I fixed up a really annoying DEC backlash - somehow the settings had moved from 0 to 18, setting it back to 0 fixed everything.

anthony2302749

21-06-2006, 03:45 PM

The first set of digits represents Right Ascension (HH:MM:SS), the second set of digits represent Declination (Degrees:Minutes:Seconds).

I suppose when you first power up the hand controller after aligning the index markers you may get a reading of 00:00:00 for RA and 90:00:00 for Dec. Remembering when using celestial coordinate’s declination is measured in degrees north and south of the celestial equator. The South Celestial Pole is at 90 Degree Declination and would be written as -90 degrees, the minus denotes south of the celestial equator (0 Degrees).

Now remember at power up, the telescope does not know were it is and may give a reading of 00:00:00 for RA and 90:00:00 for Dec (This is the home position). The things in need to know is its location, date, time and the location of one, two or three star. Once it has all this information it can then compute the location of any object with in the data base of the handset and find them. The hand controller will give you the correct coordinates for any given object as well.

Still work on the other problems you are currently experiencing.

Just been reading the manual, very confusing chinglish, it should be re-written so that it will make sence.

sheeny

21-06-2006, 04:43 PM

Hmmm. Interesting Anthony! Generally I align the marks prior to powering up as you suggest, even though the program prompts suggest you can align the marks after powering up... if you are right you might have shed some light on the one or two times my drive has done some screwy things!:thumbsup:

Thanks,

Al.

g__day

21-06-2006, 05:13 PM

Hmmm,

My process was

1) Put axes markers in start position
2) Power on
3) Abort alignment by pressing menu
4) Read axis position in Utilities menu
5) Adjust scope using RA and DEC until ALt and AZ both read 0 00 00
6) Unlock clutch and manually move scope back on alignment marks

7) Not sure if I powered down or not

8) Start alignment - setting time and date

Three stars latter all is well and no motor housing clunks whilst operating

9) Slew back to alignment marks at end of night
10) Read Alt and AZ - now 90 00 00 and 90 00 00 (I expected 0 and 0)
11) Hibernate and power down.

Perhaps the Dec should be 90 at start up but the alignment marks should be 90 degrees further around?

anthony2302749

21-06-2006, 07:58 PM

Hi Al

I have been reading the manual to nut this problem out and find It is a bit screwy in places.

1. Before starting the alignment procedure the manual ask you to aligned the index marks on both the right ascension and declination axes. I would assume this is done before powering up the mount.
2. The manual then repeats the same set of instruction in Step 2 on page 19. If it was done as per paragraph one, page 19 why repeat the instructions. Step 2 to should real say "If you have not aligned the index marks on the mount the hand controller will prompted you to do so, and then suggest ways to correct the problem.

My suggest would be to align the index marks manually prior to powering up the mount.

3. Entering the time and date is not a problem, but location is, the manual is obviously written for the northern hemisphere in mind and gives no explanation of how to set the coordinates for locations in the southern hemisphere other then go look up appendix list.

4. The other thing I find strange is the alignment procedure. Reading "Auto Align" it states the following:

Once the telescope is finished slewing to your first alignment star, the display will ask you to use the arrow buttons to align the selected star with the crosshairs in the center of the finderscope. Once centered in the finder, press ENTER.

The display will then instruct you to center the star in the field of view of the eyepiece. When the star is centered, press ALIGN to accept this star as your first alignment star.

Why two key strokes, one would be enough no wonder it takes so long to complete a alignment proccess. The commonsence way of doing it would be to instruct the use to sight the alignment star with the finderscope first then center the star in the EP and then press ENTER. This is how you do it with the LXD75 mounts.

Anyway what I am trying to do is re-write the manual in regards to Alignment process so that it makes sense. Give me a couple of days.

anthony2302749

21-06-2006, 08:32 PM

Follow these instructions

Align the index marks on the DEC and R.A.
Power up the mount
Select Auto Align
Follow the instructions as outline in the manual, I think page 20.
If you have follow the instruction carefully you will have a Successful Alignment, and you are now ready to find your first object.Please do not take it the wrong way but your procedure is flawed. There is no requirement for the user to adjust the scope so that the RA and DEC read 00:00:00. after power up. See manual

The start postion for the telescope is the index marks. As I pointed out early the hand controller dose not know were it is until the time,date,location and 3 star alignment is complete. By moving the mount to RA 00:00:00 and DEC 00:00:00 will cause a lot of trouble as you have found out. Example if the Index Marks are line up correctly on the DEC (e.g. the front of the telescope is pointing south) and then you rotate the DEC in an Easterly direction so that the DEC reading on the hand controller reads 00:00:00 and then do a alignement you will more then likely be 90degress of your first alignement star. I think you have experienced the problem already.

So have a go at my procedure and follow the instruction in the manual and you will have success.

sheeny

21-06-2006, 08:51 PM

Yes.

Now that you mention it there was some doubt when I first fired up the mount... but I'm used to it now... well I should say I was... I don't have to do that anymore now that I have the GPS!;)

The CG-5 changes slew rate on the drive when you press the Enter key to make it easier to centre the star in the EP, that's all. Once you get the hang of changing slew rates on the hand controller, this wouldn't be an issue at all. When I was new to the drive I didn't mind it doing that... except when I hit the Align button accidentally instead of an arrow button and it aligned on nothing!:mad2:

But you're right, the procedure is slow and could be simpler! I would really like to understand the maths the drive does... how much does initial misalignment affect the so called cone error that it calculates?

I used to struggle through the auto align and then do a drift align... and it all becomes a bit tedious. These days, if I'm just doing some quick observing or some planetary imaging where some drift is not critical, I just do a compass alignment, then auto align. If I'm planning to some more accurate imaging and want to accurately drift align, I'll do the compass alignment, a quick align (the CG-5 just models the sky) then drift align. Then I'll power down and up again and do the auto align to calculate the cone error. Sounds messy doesn't it?

I have found that my dec alignment marks are about 1mm inaccurate (checked by looking through the eyepiece while rotating round the RA axis).

Al.

anthony2302749

21-06-2006, 09:48 PM

Hi Al

Have you consider getting a polar alignment scope, it will give you a quick and easy method of polar alignment all the time with little of no error, I had one on my old EQ5 which worked very well. I would get accurate tracking up to 15min plus with minimal drift in DEC. The mount was only fitted with a simple dual axis drive. I would use the mount mainly for astrophotography and I got some very good results using film.

g__day

21-06-2006, 11:22 PM

Anthony when you said ""The start postion for the telescope is the index marks. As I pointed out early the hand controller dose not know were it is until the time,date,location and 3 star alignment is complete. By moving the mount to RA 00:00:00 and DEC 00:00:00 will cause a lot of trouble as you have found out. Example if the Index Marks are line up correctly on the DEC (e.g. the front of the telescope is pointing south) and then you rotate the DEC in an Easterly direction so that the DEC reading on the hand controller reads 00:00:00 and then do a alignement you will more then likely be 90degress of your first alignement star. I think you have experienced the problem already."

Actually my procedure corrected this and for the first time things just worked. When this orocedure wasn't applied the motor housings would always knock and alignment was nigh on impossible to complete.

I didn't try and complicate things for fun or sheer bloody mindedness, I need it for survival and it subsequentially brought me joy. Following the manual on page 20 over my first 16 attempts simply failed until the correction I gave above. I am still awaiting Celestron's response beyond the rather helpful (I kid you not) "doesn't this guy know how to use a GE mount?"

I am still very puzzled why when I set it to 0 00 00 manually for the star alignment position, then ended the in the same position - why it now read 90 00 00 and 90 00 00.

Perhaps its a bug in my mount?

PS

I need to re-test to see what I changed. I believe it was the RA and DEC settings, but what if it was the ALT and AZ readouts? My unfamilarity with the handcontrollers menu may have lead me to confuse the two. On the next clear night I'll be more exacting as to what I do and how cleanly it fixes the problems.

PPS

I noticed comming out of hibernation the scopes RA drive movement was jerking back and forth slightly on start up. This occurred yesterday to and when I looked at the setings for +ve and -ve RA and DEC backlash all four were set to 18. I re-set these back to 0 and all jerkiness went away again.

Why is this happening now and why must I reset this on every start-up?

sheeny

22-06-2006, 08:26 AM

The backlash settings in the drive are set to 18 from the factory. This probably correspnds to the average backlash they expect from the drive gears.

There is a procedure for adjusting the backlash. I don't have it with me to refer to at the moment. Unfortunately I suspect it is written in Chinglish as Anthony describes it, and it really takes some study to work out what you should be doing. I have worked through the procedure a couple of times (once with some success) but I note that do need to do it again since I have a significant jump in one change of direction.

There are two figures for each axis, one tells the drive how far to turn at high speed during a direction change to take up the slack in the drive gears... the other one I can't remember... It is in the manual. If you are thinking of doing any guided imaging work you'll need to sort this out.

Al.

sheeny

22-06-2006, 08:29 AM

PS. It doesn't sound right that you have to reset the backlash settings everytime. It should remember them.

Al.

g__day

22-06-2006, 11:09 AM

I concur! It wasn't doing this on the first 3 outings. Two days ago it was only DEC up that was jerky. This morning I powered on and both RA directions were jerky until I set backlash to zero. I wonder if there is an issue with problems caused when the motor housing were briefly clunking? Again setting backlash to zero fixes this, but I hear 18 is the factory default setting.

I hope this isn't a sign that they should be at 18, not zero, but some damage was done during motor housing clunks. I presumed real damage would be aborted as there must be a friction clutch which gives when the scope tries and impossible (blocked move).

Sigh, just one more thing to worry about.

Celestron say now they can't recreate the problem, have never heard of it, say the scope would be in a contorted position to view anything if it was used like this (fully agree there!) and don't know why it occurred and have asked for pictures. So I've sent them some and reminded them its the slew route, not the slew destination (well ultimately that too) that is trouble number 1. I will await their reply tomorrow.

Meanwhile I'm keen to get some clear viewing and try again to see exactly how my fix holds out for viewing experience five!