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Replace GM-8 Gemini I w/ Atlas?

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#1 Ranger Tim

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Posted 07 March 2013 - 04:16 PM

I have had my GM-8 for a couple years and have never really gotten it dialed in so that PHD can use my SSAG to track well. Perhaps I am too picky, but my tracking always has some stupid fault that results in a high failure rate. I am shooting with a Canon on an AT6RC, 50mm guide finder (SSAG). I am not a beginner and am sure there are some issues with flexure that I need to address, but I have reached a point where the Losmandy is just not giving me the results I had anticipated. I do not have the money for a G-11 and would rather just sell to reinvest in an Atlas. I could then also pick up a NexSX board for my Sphinx. Any advice from the braintrust? It has gotten to the point where I haven't got the patience to get out there and image because of the frustration. Will I encounter the same amount of grief by switching mount platforms? I believe the Atlas will carry the load better and will give me a fresh start.

My GM-8 is in great shape and has a fine record of excellent go to accuracy with the Gemini, it just refuses to behave well when guiding with PHD. I don't intend to go back down the rabbit hole diagnosing the guiding issues but want to hear some push-back from Losmandy zealots and some urgings from Atlas enthusiasts. Here is an example of my last shot for a reference of what the GM-8 accomplishes. It is agony to get two full hours of data with no footballs.

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#2 JoseBorrero

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Posted 07 March 2013 - 05:23 PM

I use a G11 and have a variety of scope including the AT6RC, I also lately have been guiding with a 50mm miniguide scope and the SSAG with very impressive RMS on PHD. I dont know if PHD settings can work similar on others mount scopes but If you like to try my numbers here they're:
RA agressiveness:97,
RA hysteresis:28,
MaxRA:391ms,
MaxDec:391,
MinMo:0.05,
Calibration step: 1000ms.

I went to a G11 because I knew I would try a variety of scopes, lately a C11, Meade 8 and ED80, I think is a good experience to be below the minimum overload range, would say by 40%, this mount 60lb payload if I have 35 lbs with C11 miniguide scope and camera,FW, that will be alright. Now, I have seen users using the AT6RC and the Atlas and the 50mm guiderscope, user like Rigel123, he's the best sample of the setup you trying to describe. And looks that work very well.

#3 orlyandico

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Posted 07 March 2013 - 08:12 PM

Tim, I think it's simply a case of your guide scope being too short.

I have been fighting declination guiding in my AP600 for years without much success (that's why I bit the bullet and got a Mach1) but what I noticed with the 600 is that my keeper rate was much higher when I used an OAG. Even when imaging at 720mm!

So if you could take a barlow to your 50mm guider.. try that and see..

#4 SMigol

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Posted 08 March 2013 - 12:11 AM

I used a GM8 for a long time, gradually peeling the layers of the onion with astrophotos. I really pushed that mount as far as I could. Got the Gemini 2 kit, One piece worm and block, HD tripod, and spent a lot of time tearing it down and cleaning it out.

Went with the G11 when I could get a good deal on a used one and migrated the G2 kit from the GM8 to the G11. Since you are already used to the Gemini 1, you could get a decent price on a G11 without goto and do the swap.

What drove me from one to the other was:
1. Weight. I was already at 18 lbs and knew that I was pushing the capabilities of the mount.
2. Flexure. While a lot of the problems with this issue were more with the rings and dovetails and camera sag and thus were not with the mount, I still feel that the burden of making things stiffer was better served by the G11.
3. Upgradeability. There are more aftermarket kits and parts and experience available with the G11 vs the GM8.

I still have my GM8. I've not decided if I want to keep it as a grab and go just yet or if I want to use it as a dedicated wide field platform.

I've learned a lot more with the G11 that the GM8 prepared me to understand. I think that when I go back to the GM8 to use as an additional platform, I'll be much more productive.

Regarding the Atlas, I've heard great things about them from people that use them. There's still gnashing of teeth - as far as I can see it's not much different than the Losmandy camp. There is a wealth of knowledge from people all over the place that have figured out their own setups.

#5 Startraffic

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Posted 08 March 2013 - 12:34 PM

Tim,
I've never had a G8. I started with a used G11, DDS, PS & HD tripod. I added the encoders, OPW, & finally G2. I loved that mount but with a 10"f4SNT, 90mmf3 GS & cameras I felt it was pushing it's limits @ #40. I bought another Older HGM-200 with G1. It is what the G11 is to the G8 & still performs like a champ. I migrated the G1 from the HGM & the G2 to the HGM. Both are great mounts. I contacted Losmandy about the HGM & they still had parts. I needed a set of Bearings & Clutch pads & wanted a Polar scope. I got the bearings & pads but no Polar Scope was made for the HGM. The mount is pre-1995, & they still had parts in stock! That alone says a lot about the company that builds mounts as a side job.
You already have & know Gemini. I can tell you for a fact the parts will swap over & perfectly. You'll need to tell Gemini it's now on a G11 instead of a G8. The single biggest problem IMO with the G8,& G11 are the original worm blocks. Not a great design, too many points of possible misalignment. The MFWB, Ovision, & OPW are an answer. Proof of that is the new GM's come with them. The option is the worm itself, Steel or Brass upgrade for $65. No brainer Brass. I put one on the RA on the G11 & the mount was transformed. My BP dropped, & PEC went from the mid to upper 20's to lower 30's to 3-4". After running the PEC it came down even further to 0.5", completely acceptable (for me YMMV). If the worm starts to lag, Loosen one bolt, give the thumb screw a 1/8 turn, let the mount pick back up & tighten the bolt back up, done.
I've seen a number of G11's come up recently on CN & AM for >$1500 running the DDS. Add in a Brass OPW & you're still ahead of the cash flow.

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#6 gdd

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Posted 08 March 2013 - 01:56 PM

The option is the worm itself, Steel or Brass upgrade for $65. No brainer Brass.


If you don't specify brass vs steel with the OPW, which do you get these days?

Gale

#7 frolinmod

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Posted 08 March 2013 - 05:33 PM

At this time I would no longer buy a new Orion Atlas EQ-G (aka Sky-Watcher EQ6 SynScan).

The new Orion Atlas Pro AZ/EQ-G (aka Sky-Watcher AZ-EQ6 GT SynScan) appears to fix just about everything that people have ever complained about with the older mount. I'd get that one instead.

#8 Startraffic

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Posted 08 March 2013 - 06:57 PM

Gdd,
The G8;G11 options are "OPW without worm $295, with High precision worm $355" http://www.losmandy.com/access.html.
So, you can reuse your existing worm, steel or brass, or buy a new brass one. The price between the G8 & G11 is the same. I did notice that they don't sell the stainless worms anymore. The Titan already has the OPW but only stainless worms.

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#9 andysea

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Posted 08 March 2013 - 08:04 PM

Why don't you try to use an OAG before giving up on the mount?

#10 Raginar

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Posted 08 March 2013 - 08:44 PM

RT, I think it's tunable. Perhaps it requires a new worm (depends on the age), perhaps it just needs to be regreased. Have you tried the losmandy Yahoo! Group yet? I think they might be able to give you ideas on what you need to do. What is your periodic error right now? How do you balance? How's your declination balance with the 6RC?

The mount 'should' be perfect for the size scope you're using. I think we can probably figure it out for you :).

But, an Atlas with a AT6RC would be good too. How much you want for your GM8? :D

#11 gdd

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Posted 08 March 2013 - 08:46 PM

I don't intend to go back down the rabbit hole diagnosing the guiding issues


But if you are having guiding issues that are not related to the mount, switching to an Atlas will not solve anything.

Gale

#12 neilson

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Posted 09 March 2013 - 12:38 AM

Hi Tim,
I have owned Meade, Skywatcher, and Celestron mounts. I think my CGEM DX mount is the best mount I ever owned. It did great imaging right out of the box. I have been reading alot of good stuff about the new Atlas mounts. I almost bought one. But instead

Last December I bought a new G-11 Gemini 2. It had 28 arc sec. of PE. I got an OPW with brass worm and got 31 arc.sec. of PE. And thats after alot of tweaking. Guided it still had football stars. After some complaining Scott made me a new worm with 9 arc sec of PE. This worm is much smoother too but I still cannot get consistantly round stars.
I never had so much trouble trying to image with any of my other mounts.

Neilson

#13 orlyandico

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Posted 09 March 2013 - 03:19 AM

:tonofbricks:

for every happy G11 story there is a Neilson story. Or maybe the happy folks never pipe up so we hear all the sad stories.

It is still disappointing for a $3600 mount, and a cautionary tale for anyone deciding to upgrade from an Atlas or EQ6. Or even CGEM - although the CGEM has the notorious 8/3 harmonic, the G11 has the equally notorious 31.7 second harmonic...

All the tales that I've read here seem to inevitably point to one conclusion: if you're at Atlas/CGEM level and want a significant improvement, the G11 ain't it. Not to say the Atlas/CGEM are superior - I think they're not, but they're also less than half the price.

I still do not think an Atlas/EQ6 is a meaningful improvement over a GM-8 - at best it would be equal, albeit with more payload - but you can meaningfully improve an Atlas by adding the Aeroquest worm, which is only $100.

If you really don't want the GM-8, I'd say go for the Atlas. If you get one with a huge PE, the $100 Aeroquest worm will immediately bring you down to 15" p-p or less. This is also assuming you can get decent $$$ for the GM-8. I would not buy the new AZ-EQ6 though; untested, not sure if you can get Aeroquest worms for it, etc. etc.

#14 RogerRZ

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Posted 09 March 2013 - 05:37 AM

There seems to be a big hole between the CGEM/Atlas and the next meaningful performance step, isn't there? I've been tearing myself apart with this very question, and I think I'm near a conclusion. I hope it's the right one... ;)

#15 Raginar

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Posted 09 March 2013 - 11:10 AM

Roger,

I dunno, I picked up a used Mi-250 for just a tad more than a G-11 would've cost. I think the big thing is to aggressively test your rig with PEMPRO and be willing to send it back if it doesn't meet expectations. Most the stories I read about are,"I bought a new G11 and it isn't performing..." and the individual spends months troubleshooting it... if they'd sent it back and got a new one, maybe it was a bad batch? Instead they elect to fight through it, learn a bit about the mechanics of the mount, and end up getting a phenomenal mount.

I think a G11 is usable. Orly last time I checked you can get around the 31.7 by doubling your worm gear time in PEMPRO and the fixing a curve to it. Mind you, I don't have one, that's just what I've read.

My guess is there are lots of happy G11 owners out there. Otherwise Scott wouldn't be in business. We just tend to generalize quite a bit (CGEM/G11/only buy AP) :D

#16 Ranger Tim

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Posted 09 March 2013 - 11:12 AM

Interesting comments. Thanks to all who took the time to respond. More folks from the Losmandy camp, but that was expected. And thanks for the numbers Jose, I'll give them a shot.

Yes, the grass is always greener on the other side. I constantly question myself whether I made the right move going to the GM-8 instead of the Atlas. It seems there are many examples of people getting great results with the Orion mount and I would like to move to an eight inch imaging reflector at some point. I also have some homemade glass that will end up around 20 lbs. net when finished that I would like to mount, and the GM-8 will be struggling to handle it.

I'm going to put the Losmandy on a post in the yard and try to resolve any flexure issues once more before I cash it in for another, heavier mount. I still have my Sphinx for portable visual set-ups and really love it except for the declination bounce. The temptation to upgrade to a G-11 is also present because the Gemini I will transfer easily.

I have torn my GM-8 apart multiple times and it is Superlubed and tuned to a high degree - I cannot see any improvement in the mechanicals unless I am overlooking something. When I received it second-hand it was in less than ideal shape (to be charitable) and I learned a great deal about how to field strip it and solve problems. The worms are still original - several were supplied, along with a one piece block that has bad bearings. All original worms are stainless and none causes any better P.E. than any other. I guess $60 is not much to lose in an attempt to try and better the P.E.

I think the main problem I have is the interface between the Gemini and PHD. It seems to bounce back and forth, involving worm backlash and I can't get a handle on it regardless of balance issues. Each time I set up it is a different animal so I am looking forward to a permanent pier in order to remove some variables. Are you tired of burning through 3 hours of dark time just to get in the ball park? ME TOO! "Can you say observatory? Sure, I knew you could."

If folks want to continue to respond I would love to read what they have to say, but I guess I was just lapsing into a pre-season venting before I get carried away with galaxy season efforts. This is my favorite time of the night sky calendar. I think I would still like to hear more from Atlas owners about whether they are really happy or whether they are enviously looking across the fence from the other side. Perhaps the key may be found in a G-11 upgrade. I have friends that tried it and are still happy they made the switch. My mileage may vary! There is no point in trying to upsell me into a more expensive mount (>$1500) because that is totally out of my budget. Please look at my signature line...

I don't get to look at this forum much, so sorry for the lag in response time, but I'll be back. Thanks again!

#17 Raginar

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Posted 09 March 2013 - 11:26 AM

RT, going permanent will make you very happy. Skipping setup/tear down really made the difference for me. I found I didn't mind doing alignments... but being able to skip polar aligning AND setup/tear down??? Totally worth it.


Good luck!

#18 orlyandico

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Posted 09 March 2013 - 11:30 AM

Also... a really good polar alignment will make guiding much less hassle - you can use longer guide exposures (which smooth out atmospheric seeing and rapid gear noise) and there will be less corrections necessary.

#19 Startraffic

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Posted 14 March 2013 - 08:45 AM

Orlando,
You're right. It's very confusing & frustrating for the ones who get the "Monday morning" mounts. I've heard on the Yahoo site that they got a batch of bad worms last summer & those were installed & shipped. I think Hilmi over in Oman got one of those which caused him a ton of problems. Scott did send him a new set, but it took several months of troubleshooting on Hilmi's part to figure it out. Shipping it back was simply not an option for him. I got lucky when I upgraded to the OPW. My brass worms were awesome right out of the bubble wrap. I put one in the original worm block setup & worked my way through that refit. A 4" 'C' clamp became my best friend. I think Neilson may have also been a part of that batch which may explain some of his problems. I'm not sure who is doing the QC at HGM, but the G11's seem to be having problems that the new G8's & Titan's aren't having.
I can say that of the 6 mounts I've had a DS114, ETX90, Vixen GP, LXD-55, G11, & the HGM-200. The G11 & 200 have given me the least problems, but none of them have been trouble free. Most of the problems I had were due to poor maintenance. The G11 had a broken gearbox & hadn't been lubed so it was having serious motor lag issues. The HGM had a frozen bearing, & the other 3 were so gummed up I just replaced them. All of which Scott had in stock.

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#20 neilson

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Posted 14 March 2013 - 07:23 PM

Hi,
My third worm installed in my mount got 9 arc sec total PE. I polished it and now I consistantly get 3 arc. sec. total PE. I think my G-11 mount is terrific now. But my Gemini 2 is not. I had been testing my mounts goto's using alignment stars, they are good. But now after about 24 stars in the East/West models and a drift alignment I find that unless the DSO is close to an alignment star it will be close to the edge of my T1i's big imaging chip or hanging off the edge of it. I'm using a 9.25 Edge ota. I have been testing this for several days now. I have redone models several times each night and tried many different DSO's but if they arn't really close to an alignment star they are never close to the middle of my chip. Aparently even after a good east west model you must sync to a star near each DSO you want to image if you want it near the center. They wont improve the goto's to modern mount standards.

I have also found that the PEC is erased each time you turn the mount off. And you must retrain it.
I use the ethernet and PHd guiding and 3 out of every 5 days I get a lock up and have to restart my computer. 2 out of 5 days the mount locks up and I have to restart it. I was expecting these issues to be over after the last update, but they were not. The only thing I noticed was the stop sign and the removal of the IC and NGC catalogues. A substitute NGC catalogue was added but now were told getting an IC catalogue is not looking good.

At the $3,200 price point. I expected better. My Meade mounts goto's are centered or close to centered . My Celestron gets perfectly centered goto's. I'm told if I want goto's on my Gemini 2 to be centered or close to it I have to use my computer and other software or switch to a 400mm ota. No thanks.

This is not acceptable to me, I will probably be getting rid of this mount. I gave it every chance and fixed some of the problems but goto's are too important. I didn't want to, but I'm not going to spend half of each night modeling, then looking at a star map to find stars names that are real close to each DSO I want to image that night so I can make models around them.
I am willing to go through the overly long initial modeling(alignment) but I expect it to be accurate. Not to have to do additional modeling for each DSO goto.

neilson

#21 gdd

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Posted 14 March 2013 - 08:27 PM

My third worm installed in my mount got 9 arc sec total PE. I polished it and now I consistantly get 3 arc. sec. total PE.



I Neilson,

Going from 9 to 3 arcsec error by polishing the worm is quite an improvement! What did you use and how?


Thanks,
Gale

#22 neilson

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Posted 14 March 2013 - 09:58 PM

Hi Gale,
I was impressed by the results myself. I have a bench grinder and I install a buffing wheel made for bench grinders. I have a polishing compound thats a solid stick form. I press the compound into the wheel every so often and it grinds some off. into the cloth wheel. Then I very carefully press the worm into the wheel. I hold both ends. It will try to fly out of your hands. If it does it could damage the worm. I slowly turn the worm. It must get warm to polish the metal and smooth it. I only press it in about 15 to 25 seconds at a time. You will notice it get smooth and shiney quickly. after about 2 to 5 minutes its done. You have to clean the excess compound off the worm. You only have to polish the middle since thats the only place the gear contacts the worm. I don't advise doing this because it's easy for the wheel to pull the worm out of your hands and send it flying. You can also get seriouse injuries. I have read of others using one of those dremel tools with a little buffing wheel and polishing compound. It would be safer. I already had the bench grinder and wheel for 20 years so I dont know where to get one now.

I install my worm with very little backlash. My power supply has an amp meter and when I slew it draws about 0.40 amps, or less than half an amp. Then I slew from one end to the other in RA about a dozen times, pausing after each slew for 20 seconds although the motor stays cool. When I was done it was only drawing 0.29 amps when I slew. I feel only a tiny bit of backlash when I wiggle the counterweight bar. Almost none.

neilson

#23 orlyandico

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Posted 14 March 2013 - 11:17 PM

If such improvements are doable with a bench grinder and polishing wheel,

1) why doesn't Losmandy do this (they could charge more for it)

2) why doesn't Ed Thomas do this?


Neilson, regarding the GoTo accuracy -

I think I am having better GoTo accuracy with my Mach1, but it's still not perfect, because with these 1-star-align mounts, GoTo accuracy is determined by both how good your polar alignment is, and how orthogonal your OTA is to the mount.

Even if your PA is perfect, if your OTA is not perfectly orthogonal, you'll still have some pointing errors. Situation is the same - need to sync on a bright star near the DSO (near meaning within about 10-20 degrees) to get a good GoTo.

In my opinion the most accurate GoTo's are had with the Celestron Nexstar.

I actually had this idea... if you could combine a Nexstar with an AP mount, you'd have a mind-boggling combination. The AP mounts all have their motors separate and external, with a normal mil-spec connector. So if somebody built a motor board that is compatible with Nexstar but set up for the gear ratios of the AP.... then this would be possible.

I know that the NexSXD folks already have done this for the Vixen mounts.

#24 neilson

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Posted 15 March 2013 - 02:08 AM

Hi'
I do a drift Polar alignment. I have checked the ota's orthoganal several times. My goto's to the alignment stars are dead center now just not to DSO's, unless they are pretty close to an alignment star. After 24 stars in a model you would think everything would be dead on. But with Gemini 2 you are expected to build additional modeling where you plan to image. The Gemini 2 alone costs $1,600. That's more than most mounts cost.

I am still having lock ups in PHd from the ethernet bugs that require me to restart my computer and handbox lockups that require me to restart my mount and start over.

After most of my DSO goto's are on the edge of my imaging chip again tonight. And two were completely off the chip. Jupiter, and a nebula were centered. The handbox locked up. PHd locked up and several times I had runaway in RA. All this tonight. And most nights.

Because of all of this I will be getting rid of my new G-11 Gemini 2 tomorrow. Mostly because of the requirement for extensive alignment modeling that give poor goto's at best. Everything should get fixed eventually with future firmware updates but they are not going to fix the poor goto problem. I will be buying another new CGEM DX with its very accurate goto's. And an aeroquest worm probably.

I don't know why polishing my worm lowered my goto's but I have tested it a dozen times over several days. Maybe I just got lucky. Polishing the worm this way is difficult and dangerouse if it gets away from you. With PEC I get 1.7 but it must be retrained each time the mount is turned on. I was really happy I got the PE so low but it makes letting the mount go very hard.

neilson

#25 orlyandico

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Posted 15 March 2013 - 02:46 AM

PEC training disappears every time you power off? :tonofbricks:

what kind of thing is that Gemini 2?!?!?! that sort of non-permanent PEC is what you expect from early 1990s Celestrons or the CG-5. Not a pricey piece of electronics like the Gemini 2.

Having a CGEM, I would respectfully suggest that you don't downgrade to one from a G11... maybe try to get the Gemini 2 unit changed. or buy a Gemini 1.... PEC works on those things :o






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