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CG5 meridian flip & other challenges to alignment

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#1 A. Viegas

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Posted 31 December 2012 - 10:28 AM

Just wondering if anyone else has this problem, namely GOTOs are just fine until a GOTO sends a very long slew, usually this happens when I am close to the meridian and we spin all the around, post this point alignment is toast and needs to get totally redone. Additionally another challenge is when remote controlling and close to zenith there is always the risk of DEC housing bumping into mount head an again ruining alignment. I am usin 5.20. Anyone have any advice on these challenges?


Al

#2 RTLR 12

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Posted 31 December 2012 - 10:58 AM

You can set your "RA Limits" so that the mount won't rotate that far in RA. The "RA Limits" function is located in the "Scope Setup" menu.

Stan

#3 SkipW

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Posted 31 December 2012 - 02:10 PM

Are you doing the four-star calibration after the initial two-star alignment? Is a clutch slipping due to balance problems, perhaps?

My CG5's gotos are accurate on either side of the meridian all over the sky, no matter how many meridian flips, after careful balancing, two-star alignment and calibration with four stars. Usually when setting up, the first cal star (on the other side of the meridian from the alignment stars) is somewhat off, but by the third it's almost always perfect or near perfect.

In addition to the RA limits, another possibility for fixing the dec housing clash is to experiment with the index mark alignment at start up. I think the only time I had a problem with that was when I intentionally started with the indexes not aligned; it was a while ago, but I do think that was a side effect.

#4 A. Viegas

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Posted 31 December 2012 - 09:48 PM

Hi Skip,

Sure do, 2+4 and polar alignment routine. My initial star and 2nd alignment star are usually 10-20 degrees off, but first and definately 2nd calib stars are spot on. I start at RA index marks, i lost the DEC index marks but made a tape indicator. Clutches slipping i dont think so, but maybe possible. E-W balance is good, maybe N-S or DEC balance maybe not so great, but that is only possible problem...

I think your startup Index mark alignment issue is maybe a worry for me also, as i dont understand why my first star alignment is always 10-20 degrees off in RA. I have done the RA index calibration after aligning many times, but it has not fixed it...

hmmm

Al

#5 SkipW

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Posted 31 December 2012 - 10:18 PM

My first alignment star is also often off by 10° or so, mostly in RA, and that was why I tried starting "off the mark". I think it did help, but the mount seemed to be confused in other ways, causing the dec housing to jam trying to point to some locations, so I didn't pursue further.

The best it did with the first alignment star was when I visited my brother who lives about 12° east and a little south of me and I forgot to reset the location; the first alignment star was much closer than usual! Unfortunately, it thought some things were still up when they weren't actually, because of the error. Oh, well.

I don't know why you're having problems with goto after long slews. I don't have that problem. It may be something as simple as a slipping clutch, but it doesn't seem to be a design flaw with the mount since mine works. Keep looking!

I'm using version 4.16 HC software (I think).

#6 rockethead26

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Posted 01 January 2013 - 06:31 AM

Are you sure you have the time set correctly? Sounds like an issue I had when I set the daylight savings time wrong.

#7 rmollise

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Posted 01 January 2013 - 09:04 AM

Just wondering if anyone else has this problem, namely GOTOs are just fine until a GOTO sends a very long slew, usually this happens when I am close to the meridian and we spin all the around, post this point alignment is toast and needs to get totally redone. Additionally another challenge is when remote controlling and close to zenith there is always the risk of DEC housing bumping into mount head an again ruining alignment. I am usin 5.20. Anyone have any advice on these challenges?


Al


This is not at _all_ normal. The problem might be your alignment, or it might be mechanical issues, but this should not happen and certainly doesn't happen to me.

#8 rmollise

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Posted 01 January 2013 - 09:05 AM

You can set your "RA Limits" so that the mount won't rotate that far in RA. The "RA Limits" function is located in the "Scope Setup" menu.

Stan


Shouldn't matter if it "rotates" that far or not.

#9 rmollise

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Posted 01 January 2013 - 09:07 AM

Hi Skip,

Sure do, 2+4 and polar alignment routine. My initial star and 2nd alignment star are usually 10-20 degrees off, but first and definately 2nd calib stars are spot on. I start at RA index marks, i lost the DEC index marks but made a tape indicator. Clutches slipping i dont think so, but maybe possible. E-W balance is good, maybe N-S or DEC balance maybe not so great, but that is only possible problem...

I think your startup Index mark alignment issue is maybe a worry for me also, as i dont understand why my first star alignment is always 10-20 degrees off in RA. I have done the RA index calibration after aligning many times, but it has not fixed it...

hmmm

Al


It doesn't matter at all how far the first star is off, nor does it matter where the alignment marks are as long as you set the scope on them. It I were having this problem, the first thing I'd do would be to do a Reset to factory defaults in the HC, and then look for mechanical issues in scope/mount.

#10 A. Viegas

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Posted 01 January 2013 - 09:47 AM

I will test it next weekend with less weight. I may be overdoing it, had the C8 + C80ED and cameras and whatnot, weighing in at 27 lbs. I did a factory reset last week, but now that you mention it I think I did put it in daylight savings time, which it most certainly is not... hmmm... maybe thats it?

Al

#11 RTLR 12

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Posted 01 January 2013 - 10:26 AM

As usual the Great and All Knowing 'Oz' is rather penurious with his wisdom...But as he/we know, he is always right.

#12 LTE

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Posted 01 January 2013 - 01:29 PM

I have been using a CG5 for the last six years and have had only one bad slew in hundreds. I always do the 2+4 stars to setup the alignment and have mainly used the light 6in F5 Newtonian it came with, though I will use an 8in Meade SCT in future. My only worry is that the motors and gears have a hard time with the sticky "lubrication". Tom.

#13 rmollise

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Posted 01 January 2013 - 01:50 PM

As usual the Great and All Knowing 'Oz' is rather penurious with his wisdom...But as he/we know, he is always right.


Whatever. How far it goes in RA still doesn't mean pea-turkey. :lol:

#14 RTLR 12

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Posted 01 January 2013 - 02:23 PM

Sorry, I don't know what pea-turkey is, but I was giving you a compliment, Rod. Maybe there is a language barrier.

Stan

#15 SkipW

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Posted 02 January 2013 - 07:45 PM

There were two issues in the OP: one regarding the loss of accuracy after long slews, and a second about the dec housing hitting the mount head.

The consensus is that the former is not normal and some avenues to investigate were suggested - I'd start with weight and balance. For the second, there were also some suggestions. How far the mount rotates past the meridian certainly does matter; in some positions the motor cover can hit past the meridian. Loosen the clutches and try it some time with no scope or CW. I don't recall any times myself when the dec motor housing hit the RA housing while executing a GoTo, except for the time I intentionally skewed the initial index-mark alignment, so that might be something for the OP to look at - his index marks may start the mount at an incorrect position.

While the initial pointing makes no difference for GoTo accuracy once alignment is complete, if it's more accurate to start with it's easier to find some alignment stars while the sky is still relatively bright (you would be surprised how early you can see a bright star like Vega if you know exactly where to look). This allows you to get fully aligned, ready, and finding stuff before it's very dark.

In my case, the time, time zone and daylight settings are correct, and I'm still off on the first star, even when close to correctly polar aligned. I'm sure the mount isn't an hour (or more) off because slews to the moon, once aligned, are always spot on. The moon moves its own diameter in about an hour, so while, after alignment is complete, a TZ/DST error wouldn't be significant for anything else, I believe the moon would be way off. I'll have to try this to see if that's right.

#16 SkipW

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Posted 02 January 2013 - 08:11 PM

"doesn't mean pea-turkey" is an idiom that means "doesn't matter" even though it literally says exactly the opposite: "does not mean nothing", which, of course, is the same as "does mean something". Idioms mean what they mean no matter what they say.

Friends don't let friends use idioms on international message boards.

#17 WadeH237

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Posted 02 January 2013 - 09:44 PM

It doesn't matter at all how far the first star is off, nor does it matter where the alignment marks are as long as you set the scope on them.


I agree that the alignment marks have no effect on star alignment, goto, etc.

The alignment marks do have an effect, though, on the mount's slew and tracking limits. By this, I mean that the mount does not have any way to know the actual position of either axis directly. It establishes this reference by assuming that the assuming that the axes are in the correct position at initialization time. And by "correct position", I mean that the counterweight shaft is pointed down, and the scope is perpendicular to the plane in which the RA axis rotates. I would go so far as to say that it's fine to ignore the alignment marks completely and just make sure that the scope is set up this way at initialization time.

Using the RA axis as an example, when you initialize the mount, it assumes that it's pointed at the meridian when it moves 90 degrees in either direction from there. If your alignment mark is way off, the mount could easily crash into itself instead of stopping at the configured limit.

Also, if the clutches are released and the scope moved, or if the clutches slip after initialization, it would mess up both star alignment and the mount's physical reference. In that way, this could account for what the OP is seeing.

Another thing that I've seen personally on my CG5 is that if you are running a recent hand controller version, with an older motor controller firmware version, there is a bug that prevents the slew and tracking limits from working properly. I had a problem with both of my CG5s where they would crash into themselves instead of stopping tracking at the meridian. Updating to the latest motor controller firmware fixed this, and now they stop tracking properly (and won't slew into themselves either). Note that this is not the OP's problem because star alignment was not a problem. I just wanted to mention it here for completeness.

-Wade

#18 rmollise

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Posted 03 January 2013 - 10:02 AM

Sorry, I don't know what pea-turkey is, but I was giving you a compliment, Rod. Maybe there is a language barrier.

Stan


Sorry Stan. I thought I was kidding around having a little fun...the PEA TURKEY is, I guess, a southern thing only... (?)

#19 RTLR 12

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Posted 03 January 2013 - 12:06 PM

Rod,

I'm just a city boy from a Southern California beach town. When I was in the service I received my training in North Carolina, Georgia, and Oklahoma. I'm not sure what language they were speaking, but I didn't understand most of what was said down there. I asked for an English to Dixie dictionary, but I never got one. I asked for directions once and had to have someone explain the difference between "Ritech Yonder", Down the Road a Piece" and "A Considerable Distance". I never got to where I was trying to go.

Stan

#20 rmollise

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Posted 03 January 2013 - 12:32 PM

You mean, you didn't get told they would give you instructions "directly"--which for us can be anywhere from the next minute to the next year... :lol:






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