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G-11 tracking issues

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#26 APshooter

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Posted 18 October 2013 - 11:00 PM

Correct. My mount was made before Gemini, it's the standard G-11 mount. I'm waiting out the clouds in hopes of testing under the stars before it gets too cold here.

#27 Joe Bergeron

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Posted 18 October 2013 - 11:35 PM

A few days ago I examined my G11 to try to figure out why I was getting such bizarre guiding results. I made a few changes:

Added more lube to the RA worm

I found that the coupler was not correctly seated on the flat part of the stepper motor output shaft for some reason. Fixed that.

I noticed that this shaft could slide in and out of the motor gearbox a little bit. I arranged the coupler so that can't happen any more.

I loosened the RA setting circle so it can turn more freely.

Well, one or more of those things made a big difference. Tonight I set up beneath the full moon solely to try things out. Guiding was much better. The PHD graph was much gentler, with an RMS around 0.20 or slightly better. Stars are still a tiny bit elongated E-W…not sure why. Could be an issue with the PHD settings.

#28 APshooter

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Posted 19 October 2013 - 12:19 PM

Interesting. Good to hear things are improving. I did not check my couplers to see if they were seated on the flats. I did tighten them however. Still raining here, weatherman says clearing by Sunday night! I'll try a shot or two then to see if the changes took, I'll post the results either way.

#29 powerstroke01

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Posted 19 October 2013 - 03:51 PM

Well after going through double stars and elongated stars for about a year I finally sent the mount off to have it hypertuned. It came back looking brand new. After some careful balancing it now performs on par with much more expencive mounts.

#30 APshooter

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Posted 19 October 2013 - 10:53 PM

Your gallery of shots using the G-11 are impressive to say the least. I hope I can get mine up to speed soon.

#31 APshooter

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Posted 21 October 2013 - 10:45 PM

As promised, I have some shots from the previous night. These are quick and dirty without very much processing, but you can see the results of the tweaks. 5 subs stacked, 588 secs each. No flats or dark frames. Imaging source DMK 41AU02.AS camera.

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#32 APshooter

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Posted 21 October 2013 - 10:47 PM

And another shot:

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#33 APshooter

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Posted 21 October 2013 - 11:08 PM

Many thanks to all who contributed info to help beat back the gremlins! I'm pleased with the results from a mechanical standpoint...it looks like the Ovision worm is a success, as were all the tweaks:
1. Swapped the Dec motor with the RA drive.
2. Readjusted the backlash on the Ovision worm.
3. Checked and tightened the Oldham couplers.
4. Put three thumbscrews in the guidescope tailpiece instead of one to hold the ST-4.
5. Balanced the mount east heavy.

Surprisingly, the biggest change came when I started shooting. I had set the backlash compensation setting in the ST-4 to 5; reducing it to 0 made the stars round. The ST-4 may have been over guiding out what was really only a small error to begin with. In any event, I'm sure the other tweaks helped the situation as well. I'm hoping to reproduce these results the next clear night. If that works I may have to start saving up for another camera :)

#34 pfile

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Posted 22 October 2013 - 12:32 AM

how much backlash do you have on step #2? i assume you tested it by turing the worm gear with your fingers?

thanks

rob

#35 APshooter

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Posted 22 October 2013 - 01:22 AM

2mm side to side as measured at the end of the counterweight shaft. I used two .050 allen wrenches to act as spacers between the block and the RA housing. That gave me the recommended amount of backlash.

#36 pfile

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Posted 22 October 2013 - 02:05 AM

2mm! surely i have more than that based on the worm play somewhere between 1/8 and 1/4 of a turn.

its a story for another thread but apparently the worm was too close to the wheel. i can't believe this.

rob

#37 Raginar

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Posted 22 October 2013 - 08:58 AM

Rob I'm really sorry about your trials. It's important to check the full motion under load when you adjust your worm mesh. Otherwise, what you describe does happen.

Have you thought about a hyper tube from Ed? I think it might behoove you to get it adjusted professionally.

#38 pfile

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Posted 22 October 2013 - 09:42 AM

I think I'm just going to sell it for parts if the RA motor is burned out. this particular mount has seen too much trauma.

I was afraid to test under load thinking that the worm could be damaged. i did run it through a pretty wide range of angles and figured that the wheel should be mostly centered and in-round, but lesson learned for sure.

rob

#39 dragonslayer1

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Posted 22 October 2013 - 10:54 AM

I have a post on getting a heavier mount (favoring the CGEM or DX) and was looking at G-11. A couple posted there that really look into the G-11 before leap,, I don't know if was a control issue or bad material batch. One specifically pointed to the 2011/2012 batch I think... Hope this helps, Kasey

#40 pfile

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Posted 22 October 2013 - 11:19 AM

it is possible that there was a bad run, because my experience does not match at all what i read prior to purchasing. i like to think that i researched everything and concluded that the value was there for the money, but i may have succumbed to magical thinking. i've had a lot of trouble with this mount, but i take responsibility for all my problems. i think i overestimated my ability to handle mechanical problems.

the firmware problems i've had with the G2 are another story, however :)

i think the bottom line is that if you own one of these and intend to use it for imaging, you need to be comfortable becoming a G11 mechanic. at the very least most people want the one-piece worm block or the ovision one-piece block. what i just learned is that you better run the worm wheel through 360 degrees of travel after replacing the worm, because there might be some high spots. to be fair we're probably talking about a tiny difference between "meshes great" and "locks up".

rob

#41 Tonk

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Posted 22 October 2013 - 12:32 PM

you need to be comfortable becoming a G11 mechanic


Same for the GM-8.

I've had a good run for 10 years with mine, but eventually the annual mechanics sessions got too much. One season I could have superb performance which gradually degraded over a year or so, so a strip down and rebuild was required. Sometimes this excercise would yield nothing but frustration for weeks trying to get the mount to track accurately again.

I suspect it was due to a build up of grit in the grease on the worms, and my comparative lack of good skills in realigning the worm block afterwards.

Once I had the mount in the hall while building work (and a lot of dust) was going on elsewhere in the house and it took a number of stripdowns and relubing and worm block reseting to get the performance back. Its never really got back to the top unguided performance I got 2005 - 2008.

My new mount is sealed and does not allow user mechanics to be done! (has "void if broken" stickers on it!). And it does not require servicing for 10 years (heres hoping this turns out true - only time will tell).

Losmandy mounts are good but do require considerable fettling IMHO

#42 APshooter

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Posted 22 October 2013 - 11:59 PM

Rob:
I totally agree with the statement about becoming a G-11 mechanic. Those who have followed me since I got the mount in '97 know I've fought with flexure and tracking issues for many years. I have tinkered with my mount since day one. Some of the fixes came right out of forums like this one, others I kind of made up as i went along. For instance, I took the nylon friction clutches out years ago and replaced them with automotive head gasket material, because the nylon ones slipped in the cold, no matter how hard I tightened the clutches. I modded the mount to have power taps mounted on a steel plate bolted on the bottom of the tripod base. I've had problems with broken hand controllers and faulty drive boards. All fixable, but at the cost of hair pulling and lost time under the stars. As a visual mount it performs just fine, it's imaging that really pushes it to the limit. Thank goodness the Ovision mod worked for me. It's a shame that they stayed with that two block assembly for so many years. It would have been a whole different ballgame if they kept modding and improving the mount for imaging over the years.

#43 blueman

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Posted 23 October 2013 - 01:02 AM

I used the G-11 for quite a while. I was the first to put McLennan gear boxes in one and one of the first to get the OVision for the RA.
I had it working pretty well, but then sometimes it would just get touchy and need a tweak. I sold it and got an MI-250 and it was a step above, but it still was not exactly without issues.
Finally I bought an AP900 and it is very nice. Perfect? No, but it is easy to operate and is much more stable.
Imaging is tough no matter what you do. But the mount is the heart of the whole operation and if the heart is not strong the rest of the system is weak too.
Blueman

#44 APshooter

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Posted 23 October 2013 - 01:44 AM

So true.

#45 APshooter

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Posted 28 October 2013 - 09:34 AM

Just an updated M27 shot from the mount last night.

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