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Equipment Discussions >> Mounts

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contraf15
member


Reged: 10/24/09

Re: Is this performance typical of G11? new [Re: neilson]
      #5680753 - 02/15/13 07:04 AM

Hi Neilson,

As I mentioned on the Gemini 2 forum, I am seeing the same gremlins with slow RA tracking unguided. Last night I re-flashed the firmware and was able to get a good guiding calibration, but I'm not ready to declare the issue solved. It did this before and then started tracking at about half normal sidereal rate, that's an issue I haven't even mentioned in this thread yet. Maybe a Mach 1 would have been the better answer from the start. I know my wife hasn't appreciated all this time spent troubleshooting....

Jeremy


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neilson
professor emeritus


Reged: 08/22/10

Re: Is this performance typical of G11? new [Re: contraf15]
      #5680909 - 02/15/13 09:05 AM

Hi Jeremy,
I'm not happy about all the time I have wasted on this myself. Last night I was able to get it to track correctly for a short time unguided. Then the gremlins came back and messed it up again.
A Mach I would be nice, but I have to settle for a G-11. I never thought I would end up using the phrase "settle for" when refering to my new G-11.

The best I had been able to get the new worm Scott sent me to track was 15 arc.sec. Then I switched out the gear box and I got a few runs of 9.5 arc sec of PE total. But these runs weren't as smooth as the 15 arc sec. runs.

I have been getting a high spike in the frequency spectrum (using PecPrep) every run at 31.9 Worm Spur Gear. I am guessing that indicates I need to try a different gearbox. Does that sound right?

neilson


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gdd
Pooh-Bah


Reged: 11/23/05

Loc: N Seattle suburb, WA
Re: Is this performance typical of G11? new [Re: neilson]
      #5681583 - 02/15/13 01:59 PM

Hi Neilson,
Yes, the 31.9 sec spike is caused by the worm spur gear. Replacing the gearbox can fix that. Another way is to use PEC by defining a custom mount and with an 8 minute period (180 tooth worm) and doubling the number of encoder positions.

Gale


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neilson
professor emeritus


Reged: 08/22/10

Re: Is this performance typical of G11? new [Re: gdd]
      #5681702 - 02/15/13 02:46 PM

Hi Gale,
Thank you for verifying the worm spike gear is the gear box on the G-11 mount.

I didnt understand exactly what you meant by defining a custom mount or the 8 minute worm. The G11 has a 4 minute worm though.

Could you explain further

Thank you
neilson


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gdd
Pooh-Bah


Reged: 11/23/05

Loc: N Seattle suburb, WA
Re: Is this performance typical of G11? new [Re: neilson]
      #5681771 - 02/15/13 03:22 PM

The 32 second spur gear period repeats 7.5 times every 4 minute worm gear period. This is not an integral number of times so standard PEC using a 4 minute worm period cannot remove it. However, Gemini allows a custom mount to be defined for the worm/gearbox combined system which has a 8 minute period where the 32 second harmonic repeats times. Defining a custom mount with a 180 worm wheel tricks Gemini into creating a PEC curve that repeats every 8 minutes. Since the motor must turn twice as many revolutions in 8 minutes to retain the same rotational rate, the number of encoder steps entered into Gemini must be doubled. This only needs to be done for the RA.

Gale


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neilson
professor emeritus


Reged: 08/22/10

Re: Is this performance typical of G11? new [Re: gdd]
      #5682126 - 02/15/13 06:37 PM

Hi Gale,
Wow, That is a really neat trick. I thank you for giving me this information. I will definately try this when I record my PEC curve. It should help me a lot.Thank you.

neilson


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contraf15
member


Reged: 10/24/09

Re: Is this performance typical of G11? new [Re: neilson]
      #5686049 - 02/17/13 09:52 PM

Nothing but clouds here tonight so I spent some time on my gearboxes. I have some interesting observations.

I have three gearboxes (one spare) so I decided to disassemble the spare and replace the plastic tabs that hold it together with some precision flat head screws. I took it completely apart, which wasn't hard since there are only four pieces. I cleaned out all of the old grease (which is really new grease since the mount is brand new), then I painstakingly cleaned every tooth on each cog. I regreased everything with Super Lube (that is now the only kind of grease anywhere on the mount) and put it back together with the screws.

The gearbox seemed to turn much smoother than before, so I did the same thing to the other two. Then I installed the modified gearboxes on the mount.

When I turned on the mount to slew through the range of motion on each axis, I initially thought I had done something wrong. The slews were SIGNIFICANTLY quieter than they had been before I did this. I mean it didn't even sound like the same mount. I'll have to check the PE and tracking next time I get a clear sky, but I suspect that if the gearboxes were producing that much audible noise they were also introducing a fair amount of mechanical noise. I wish I had recorded before and after audio clips of this thing, it was that much of a change. Stunning.

Jeremy


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Hilmi
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Reged: 03/07/10

Loc: Muscat, Sultanate of Oman
Re: Is this performance typical of G11? new [Re: contraf15]
      #5686327 - 02/18/13 01:12 AM

Jeremy,

Do you mind posting a picture of how you pried apart the gearbox? I tried to open mine but I felt like I was going to break something!


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contraf15
member


Reged: 10/24/09

Re: Is this performance typical of G11? new [Re: Hilmi]
      #5686629 - 02/18/13 09:06 AM

Hi Hilmi,

I followed the instructions (with pictures) here:

http://gemini-2.com/Gearbox_mod.php

The only difference is that I drilled all three holes and pulled it apart before I installed any screws. In the instructions he recommends completely installing one screw at a time, but if your objective is to clean it out that wouldn't work. It comes apart immediately after you drill the holes. The hardest part for me was finding screws small enough for this job. I had to order them.

Jeremy


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neilson
professor emeritus


Reged: 08/22/10

Re: Is this performance typical of G11? new [Re: contraf15]
      #5686831 - 02/18/13 11:32 AM

Hi Jeremy,
My new worm is giving me a spike at 31.9 in the frequency spectrum of Prcprep. Its the worm spur gear. I have a spare gear box that I grabbed the motor buy mistake and it poped the gearbox apart. So yesterday I decided to clean all the grease out and put super lube. I cleaned the gears teeth with a toothbrush and alcohol. I thought of drilling holes and putting screws but instead I took the easy way and used J-B weld epoxy. And of corse the weather went bad so I couldn't test it last night.
Before I put the motor on I had sprayed some silicone spray in the hole in gear box. I think I washed the grease off the gears. After reading your post I wish I would have used screws. I am glad you wrote that you drilled the holes with the cover on. I think I will take it apart again and regrease it. I'm going to drill holes and use screws like you did. Thats great advice. Currently I have long plastic cable ties wrapped over the motor and gear box so the gear box doesn't get popped apart by accident again. But if the gearbox is screwed together it wont pop apart. cool.

neilson


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neilson
professor emeritus


Reged: 08/22/10

Re: Is this performance typical of G11? new [Re: neilson]
      #5687270 - 02/18/13 04:31 PM

Hi Jeremy,
I couldnt get my RA gear box apart I had J-B welded together. I used a bent piece of wire to put grease in the gearbox gears. Now the RA is very quiet, I like that.

I decided to try and put some grease on the DEC gearbox. When I would turn the shaft it was hard then easy alternating. I sprayed silicone but nothing worked. I decided to put the gearbox I had removed from the RA before onto the DEC.

Then I was unplugging the wire from the RA without holding the motor and the gearbox came apart. So I cleaned it up and greased the gears. I drilled 3 holes and screwed it together. Now I dont need the cable ties because the motor is solid. very solid, and very quiet.

The clouds have cleared so I plan to test it tonight.
Thanks for the advice on the gearbox Jeremy. Otherwise I would have never found the bad gearbox on my DEC drive. I am experiencing problems with my DEC and I'm hoping this resolves them.

Neilson


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neilson
professor emeritus


Reged: 08/22/10

Re: Is this performance typical of G11? new [Re: neilson]
      #5688219 - 02/19/13 02:14 AM

Hi Everyone,
I was able to test my mounts gearbox overhaul for 6 hours tonight. I did many PE tests. I noticed a number of frequency spikes in Pecpreps frequency spectrum that weren't there before. The 31.9 worm spur gear spike is still there. All the new spikes are different worm harmonics (what ever that is).

But dispite those readings the PE graph is alot smoother and my PE even went down a little. All that plus its quieter and sturdier. I think your ideal is a winner Jeremy. Thanks.

I had swapped out the DEC gearbox but this one is noisy and not as smooth in my PE graph. I am going to grease it up tomorrow. At times the Dec would stop slewing and the RA is so quiet I didn't realize it was still moving.


Neilson


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contraf15
member


Reged: 10/24/09

Re: Is this performance typical of G11? new [Re: neilson]
      #5709739 - 03/02/13 11:24 PM Attachment (24 downloads)

Just an update - With the new worm, the overhauled gearboxes, the addition of a 3rd needle bearing on the RA axis, a puck to extend the DEC axis an additional 2 inches for motor clearance, a 12" pier extension, and cleaning and regreasing every part of the mount I am finally getting the kind of tracking I thought I would with this mount. It wasn't easy and it took a ridiculous investment of time and frustration over the last two months, but as the picture shows I am now consistently getting sub arc-second RMS tracking with it. If I had it to do over I would get a Mach 1. I have spent almost as much money, but if you add what I have spent in time there is no comparison. The only good thing about all of this is what I have learned about mounts...it's been a good education, and I now literally know every screw, bearing, and component of this thing plus what each does to performance.

I still haven't measured PE, I'll try to get that done soon but I don't intend to take unguided shots so I'm not overly concerned.

One last story to finish out this saga. I had the entire setup assembled in the backyard earlier this week under a Tele Gizmos 365 cover (mount, OTA, camera, filters, etc). All told there was around $13,000 of equipment back there. I had no idea we were forecast to get a massive windstorm in Texas...

The scope cover acted like a giant sail as wide as the length of my 127mm OTA (about 4 feet), which just happened to be oriented perpendicular to the prevailing wind direction. 50 knots of wind took the entire setup over while I was at work and laid it flat on its side. The DEC gearbox was crushed, the posts that hold the DEC motor and gearbox asembly to the mount bent about 30 degrees, and the camera detached from the OTA by popping the threads on the field flattener. Fortunately I had a spare gearbox that I had already overhauled. I bent the posts back, put on the new gearbox, fixed the field flattener, and everything is as good as new (the picture below is from tonight). Morals of the story: 1) knowing the mount can be very useful, 2) don't leave expensive equipment set up outside (or at least check the forecast better than I did), and 3) personal property insurance is probably a good idea once you get above a certain threshold with this stuff!

Jeremy


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Hilmi
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Reged: 03/07/10

Loc: Muscat, Sultanate of Oman
Re: Is this performance typical of G11? new [Re: contraf15]
      #5709785 - 03/03/13 12:15 AM

Is that RMS reading set up in pixels or arc seconds?

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contraf15
member


Reged: 10/24/09

Re: Is this performance typical of G11? new [Re: Hilmi]
      #5709960 - 03/03/13 05:20 AM

It is pixels in the picture. In arcsec, it was .28 to .45 last night.

Jeremy


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Hilmi
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Reged: 03/07/10

Loc: Muscat, Sultanate of Oman
Re: Is this performance typical of G11? new [Re: contraf15]
      #5709964 - 03/03/13 05:25 AM

That's around what I am getting out of mine now. If only I could get the DEC backlash resolved then it would be pretty much perfect (not taking into account the effort expended).

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contraf15
member


Reged: 10/24/09

Re: Is this performance typical of G11? [Re: Hilmi]
      #5709967 - 03/03/13 05:33 AM

I'm sure you've already tried this, but I found that nearly all of my dec backlash was due to the spacing of the blocks holding the dec worm and not the mesh of the worm with the wheel. When I tightened the blocks, I did so while squeezing them together to eliminate any possibility of the worm moving laterally between the bearings. The dec backlash is negligible now (with the worm/wheel spacing backed off just slightly from as close as I can get it).

Jeremy


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