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Is this performance typical of G11?

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#76 EFT

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Posted 30 January 2013 - 08:16 PM

Probably the only good way to check the worm wheel is to remove it, clean it, and then look at it under magnification. That is obviously a lot of trouble, but the wheels are interchangeable and not terribly difficult to get at, so you could try trading them out as well.

#77 korborh

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Posted 30 January 2013 - 08:42 PM

The deviations appear to be periodic, on the order of every 120 seconds or so which corresponds to half the worm cycle. But this is with a completely different worm than before! I honestly don't know what could even cause such behavior. I am out of ideas, other than return the silly thing. But I don't know what part of it is defective.

Any suggestions?

Jeremy


It could also be due to the worm bearing runout. That can cause periodic glitch in tracking as the worm wobbles about the bearing.

#78 JoseBorrero

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Posted 30 January 2013 - 09:46 PM

I don't know at which focal lenght are you guiding, but It became easy to me to autoguide with the miniguide scope even than OAG.


OK, finally had some clear skies last night to test things out.

The short version: I am ready to throw this thing in a lake. My CGEM tracked better than this.

After changing the RA worm, gearbox, and bearings, I continue to get trash results with RA tracking. Deviations were on the order of 10-15 arcsecs, and they were quick (unable to guide them out). I tried guide exposures anywhere from 0.5 secs to 4 seconds in an effort to get in front of whatever is causing the problem, but no luck.

The deviations appear to be periodic, on the order of every 120 seconds or so which corresponds to half the worm cycle. But this is with a completely different worm than before! I honestly don't know what could even cause such behavior. I am out of ideas, other than return the silly thing. But I don't know what part of it is defective.

Any suggestions?

Jeremy



#79 powerstroke01

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Posted 30 January 2013 - 11:31 PM

OK, I've been watching this thread. I had the same issues. Even worse!
Sent the g11 to ed Thomas got it back and it was flawless.

#80 orlyandico

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Posted 31 January 2013 - 01:04 AM

i am in no way questioning Ed's service.. but i'd be pretty upset if a $3600 G11 G2 needed a hypertune right from the store...! now if it was an old $1200 non-Gemini G11, or a Synta mount, then it's expected..

#81 EFT

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Posted 31 January 2013 - 09:48 AM

OK, I've been watching this thread. I had the same issues. Even worse!
Sent the g11 to ed Thomas got it back and it was flawless.


Thanks Jarrod. I'm glad that it is working now.

#82 EFT

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Posted 31 January 2013 - 09:51 AM

i am in no way questioning Ed's service.. but i'd be pretty upset if a $3600 G11 G2 needed a hypertune right from the store...! now if it was an old $1200 non-Gemini G11, or a Synta mount, then it's expected..


I would agree with this. When a mount clearly doesn't work out of the box because of a problem with the mount (as opposed to user error or incorrect expectations), then it is time for a return.

#83 Startraffic

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Posted 31 January 2013 - 09:53 AM

orlyandico,
I think if I had Jeremy's or Hilmi's mount, we wouldn't have to worry about seeing the sky. The glow from my head becoming a supernova would blot it out. Their frustration is understandable, & their patience is far greater than mine.

From the pic Jeremy posted of his worm, it is toast, & needs to be replaced, same for the coupler. There is no reason for it to fall apart or be mis-assembled.
My venerable G11 (ca'92?) was able to do 10-15 minute B/W SLIDE FILM exposures of M42 through an 8" F4 Vixen R200ss without smearing running on a Digital Drive System & a Sky Commander. I KNOW a G11 can perform & do it well.
Since Jeremy has found these problems I feel that he would be well within his rights to call up OPT or Losmandy & seek a replacement G11. At this point I would suspect everything with the mount.
Hilmi's mount is also a problem and there was yet another guy that got one recently, Charlie Bradshaw maybe. He lives sort of near me up in Belair Md. I was going to get together with him & see if we could sort his mount out but have lost touch with each other. That is 3 mounts that we know of that are possible from the same batch that have problems. I ownder if maybe a bad run has gotten through?
Jeremy & Hilmi what are the serial #'s of your mounts? It should be on the bottom of the head. If they're from the the same batch then that is a whole new ball of wax & Scott Needs to be brought into the loop. If it is indeed a bad run, then I'm sure that Scott will make things right.

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#84 contraf15

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Posted 31 January 2013 - 11:27 AM

The only hesitation I have with a return at this point is that the mount is not exactly as I received it. Since I had to modify the Ruland coupler after I broke a steel tap in it there is some "user damage." The same tracking issues existed before and after the coupler mod, but it's not as if the mount is exactly as it was when it arrived from OPT. I guess I should call and explain the situation and see what they say about it.

Another part of me still thinks there must be something I am doing wrong to make this happen. This isn't exactly a complex machine and there are a limited number of things that could cause this behavior. Here is where I am right now:

-It's not the worm (tried 2 of them)
-It's not the gearbox (tried 2)
-It's not the motor (tried 2)
-I don't think it's worm to wheel spacing, as I get the same results with it very snug and backed off as far as the OPW will allow. I haven't measured spacing though because I don't have a feeler gauge.
-I don't think it is the worm bearings, as I swapped RAand DEC bearings with no noticeable change
-It's not software (same results with Maxim and PHD)
-It's not the OAG (same results guiding straight through a scope)
-It's not the SBIG STi (same results using the STF-8300 as a guide
camera)
-It's not seeing related
-It's not RF interference (I've disconnected dew heaters, separated cables, etc. with no change)
-It's not cable drag (I can post pictures later when I get home, but it's a very clean setup)

Remaining possibilities:
-ST-4 port: I can't get Maxim or PHD to guide through the Gemini ASCOM driver. This may indicate a software or other computer problem. All tests so far have been conducted using the guider relays.
-RA needle bearings: The axis seems smooth. At first I thought it was sticking, but it is just slightly tighter than DEC.
-Worm wheel: possibly a problem, but I get similar results in all parts of the sky. Unless the wheel has a defect all the way around, I don't think this is it. I need to try swapping the wheels to eliminate the possibility.
-Ruland coupler mod: The worm and gearbox turn smoothly (to my perception) with the coupling installed as-is, but it is possible that the way I rigged it has induced some sort of deviation that happens to mimic the way it performed with loose hex screws as it came from OPT. Not likely, but possible.
-Tracking rate. It occurred to me this morning that maybe the timing of my RA tracking is very slightly off. This would cause the guider to constantly fight the rate in one direction, and occasionally it would not be able to keep up, no? Anyone know how I might be able to test that?

What am I missing? If it is defective, I would like to identify specifically what about it is defective. I know I've asked this before and I appreciate the responses, but this is stream-of-consciousness troubleshooting at this point. Any flaws in my reasoning or other thoughts about what on the mount or in the electronics could possibly be causing this problem?

Jeremy

#85 D_talley

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Posted 31 January 2013 - 12:21 PM

I did not see it listed but what is the voltage and amp supply running the mount. My G11 sometimes acts strange if I drop down to 12.3 volts.

Also, do you have access to another Gemini controller or you could find someone with a digital controller and motors to test to see if the mount works.

#86 contraf15

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Posted 31 January 2013 - 12:36 PM

Thanks for the suggestions Dwight. The mount showed 12.9 volts last night.

I'll have to look into trying the mount without Gemini. Maybe I can get someone in the Austin Astronomical Society to help me try it out next month if I don't get to the bottom of it before then.

#87 Startraffic

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Posted 31 January 2013 - 12:51 PM

Jeremy,
I ran my G11 & run my HGM @ 15V through a power supply. When I ran the G11 with the Losmandy power supply (12VDC@5A) I did have some issues with Gemini shutting down during a 2 axis slew. I changed the PS & went to 15V & all is happy. I probably could've kept the original PS but I wanted to be able to feed a power distribution buss. The power supply I salvaged from a traffic signal controller, & has 1 variable 5-20VDC@20A, 1-9VDC@10A, & 1-5VDC@5A. More than sufficient for my needs & it has proven itself for at least 30Y-35rs of in the field service. It weighs 50# but it is bulletproof, stable, & rack mountable.

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#88 Hilmi

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Posted 31 January 2013 - 01:01 PM

OK, this is after my third rebuild of the mount. What did I do different? Well I swapped the RA & Dec gearboxes out, I lubricated the gearboxes with spray lubricant, I spent 10 minutes cleaning the tube where the axis shaft fits. No to see if this can be sustained.

Edit: This guided performance

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#89 JoseBorrero

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Posted 31 January 2013 - 01:11 PM

That graph is about right with maxim dl, PHD is another matter also have better settings.

#90 Startraffic

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Posted 31 January 2013 - 01:25 PM

Hilmi,
Maybe a little bit of grit down in the threads or gearbox, slight mis-alignment of the bearings, better grip of the couplers, better penetration of the lube, a bad reversible hydro-dynamic-magito-blogowitz generator (:question:)? I hated those kind of problems when I was a electronics tech, no discernible reason for the fix.

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#91 Hilmi

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Posted 31 January 2013 - 01:31 PM

I spoke too soon!

As soon as the guide star was lost the stars went all over the place. Could be a balance issue? Software bug? Looks to me like the tracking problem is solved, but another problem has been introduced

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#92 EFT

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Posted 31 January 2013 - 01:36 PM

OK, this is after my third rebuild of the mount. What did I do different? Well I swapped the RA & Dec gearboxes out, I lubricated the gearboxes with spray lubricant, I spent 10 minutes cleaning the tube where the axis shaft fits. No to see if this can be sustained.

Edit: This guided performance


Looks good so far. :)

#93 Hilmi

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Posted 31 January 2013 - 01:42 PM

OK, here is a 10 minute exposure guided, slightly oval but good enough for me. This is unbinned on my STT-8300, 0.69 arcsecond per pixel.

Now I need to find the cause for the run away Axis. I will start by flashing the firmware on the mount to get a clean start.

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#94 Hilmi

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Posted 31 January 2013 - 03:18 PM

After diagnosing the problem I suspect the clutch is slipping. I must have contaminated it with grease while working on the mount

#95 korborh

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Posted 31 January 2013 - 10:10 PM

Hilmi, that guiding graph is spectacular. Similar to my AP1200. Are the MaximDL settings correct for your scope/FL/CCD ? Your graph shows guiding at <1/3" RMS, which is pretty darn good.

#96 orlyandico

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Posted 31 January 2013 - 11:31 PM

ditto. was out with the Mach1 against last night. am usually only getting 0.6" rms with Maxim.

#97 Hilmi

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Posted 01 February 2013 - 01:10 AM

Hilmi, that guiding graph is spectacular. Similar to my AP1200. Are the MaximDL settings correct for your scope/FL/CCD ? Your graph shows guiding at <1/3" RMS, which is pretty darn good.


Can't be sure about accuracy of numbers as my OAG has a built in reducer which basically changes the focal length compared to the numbers I entered in the settings. By the time the clouds rolled in last night and I gave up on testing I had managed to consistently take 10 minute exposures. I am getting my pier today as I have finally found some people crazy enough to lift it from my parents house and bring it to my house. Thats maybe 100 kg down 3 floors then up 3 floors again. I suspect guiding performance will improve some more with a stable platform. The pier will also allow me to better route the cables thus reducing cable drag

#98 Startraffic

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Posted 01 February 2013 - 02:37 PM

Hilmi,
That looks great to me. It doesn't take much grease on the pads to make them slip. DAMHIKT
How is the STT-8300 work for you? I've been drooling for months but maybe by this summer I can afford it. I just got the HGM & depleted my Astro budget until then unless I can get my G11 sold. THAT would help a bunch.

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#99 contraf15

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Posted 02 February 2013 - 12:09 AM

Hilmi congrats on the improvement! I tried my setup tonight with a completely different computer running all of the software. That allowed me to guide throug ASCOM instead of the ST-4 port (no idea why that won't work on my other computer). My graph is below. For reference, this is the STi guiding through SBIG OAG. Scope focal length is 952mm. With the 0.7x reduction of the OAG, the scale is 2.29"/pixel. The graph shows deviation in pixels, so I'm still seeing these crazy >10" jumps. I have now eliminated the computer, guide port, and software as possible causes.

How did you clean the RA axis? I'd appreciate any specifics you can provide.

Jeremy

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#100 Hilmi

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Posted 02 February 2013 - 01:09 AM

Startraffic,

So far the STT is working out really well for me, but I need to be careful with cable management. The camera has the following connections:
1) Power
2) USB
3) Filter wheel cable (could have been made shorter, I don't know why it's a mile long)
4) HDMI cable to control OAG camera (again, could have been shorter with low profile)
5) ST4 guide cable (optional, but unless your mount doesn't guide well through pulse guide, I don't see the point)

Now imagine how many possible points of snagging that provides you with!

Jeremy,

After stripping the whole mount. I sprayed tons CRC contact cleaner into the hole where the axis shaft fits. then I bunched up some tissue paper and shoved it in there with a rod. When it got to the bearings I would twist it around to clear the bearings. I did this around 5 times for each axis. Then I regreased all bearings with some fresh grease. Check there are no bits of tissue paper left behind when done.

I used the mount successfully to image last night but near the end of the session I started to hear some screeching sounds from RA axis. I think that the gear meshing was too tight and these new high torque motors just wont stall! So I am going to strip the RA worm gear again next weekend to check for damage and clean out any excessive muck that might have been formed from the brass getting ground due to forced rotation. I'll also check, maybe the grease I put was not enough. Either way, my mount has never worked this well since I purchased it.

I am finding the declination axis is misbehaving now, which I did not have before. It is bouncing back and forth in a sinusoidal fashion and the problem is more prominent when pointed at certain parts of the sky. I suspect this is a combination of backlash setting and a balance issue.






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