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A truly flawless, successful night!? First in a while...

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#1 Jon Rista

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Posted 17 July 2017 - 01:10 PM

It's been quite a while since I could say I had a flawless night of imaging...but, I can say it again: Last night was flawless! I have been having some odd balance issues with my setup for a while. I used to use a counterweight on a string wrapped around the mount to the east side. That worked great for a while...then stopped working at all. Never understood why, but since losing the ability to do that, I've had to deal with balance issues. It seemed as though the right balance point was always changing, so I had to fiddle around with my counterweights on each side of the meridian each night until things stabilized and I stopped losing subs to jumps and drags. That's been the case for, well, most of this year. A bit last year as well. 

 

I tried adding the additional weight-on-a-string again a couple of nights ago. I really like that particular solution, as it keeps the mount east-biased without me actually having to fiddle with the counterweights. It would also make automated meridian flips possible...something I really want to work, so I can sleep at night while my sequences run (at the moment, every time I flip, I have to go out and readjust the counterweights to get back to east bias again, otherwise I lost the majority of my subs to stars that either jump around or drag across the frame). At first the additional weight did not seem to work at all...so I added some weight (each on is only 2.5 pounds, started with just one), and it seemed to be far too heavy. I tried different kinds of strings...nylon and other polymer strings stretch and bounce, so I was trying twine and other non-stretchy materials. I think the strings were snagging or binding along the mount, so it just wasn't working. My payload isn't all that heavy...from what I can tell, it's 13-14 pounds (down from nearly 20 pounds back when I was using the Orion ST80 for my guide scope), and the mount capacity is 45 pounds. The payload is a bit "oddly shaped" though...it's got a long arm and a motor on the end for the focuser, then a shorter arm with the USB hub on the other side. It doesn't exactly balance well in DEC, but it seems to balance fine in RA. Anyway...still no luck with the weight on a string. 

 

Last night started out...disappointing. It LOOKED like I was going to have problems...my dec axis would deviate out about 2" from the mean periodically...about once per sub. I was about ready to take a sledgehammer to the whole mount and just pound it to pieces, but I noticed that my subs did not seem to be picking up the deviations...the stars looked fine. My RMS was 1.05". Far from the worst I've had, but not my historic norm of ~0.6". There were light gusts last night, and it may have been that those gusts were affecting the mount, given the direction I was pointed in early in the evening. I decided to let it go....and....somehow, maybe the wind died off, it worked itself out. The deviations stopped. My guide graph flattened out, dropped to an RMS of 0.65" after about an hour. I did not lose one single sub last night...and managed to acquire 100 of them, 20 on one object, 80 on another, three minutes each. That's almost six hours of subs (factoring in time for the periodic dither and hourly autofocus), strait from twilight to twilight (well, after twilight in the AM, I may actually lose a sub or two to dawn! :p) I can't say that I've had a night that just...ran, on it's own (barring the meridian flip and manual counterweight rejiggering), from dusk till dawn, in a very long time.

 

I suspect the balance and tracking issues will return, it's been my bane this year with AP. I'll probably have to tear the mount apart and rebuild it again at some point...or maybe I'll finally break down and drop seven grand or so on a high end mount. For now, though, I'm hoping my newfound smooth tracking persists, and allows me to get subs reliably throughout the next few clear nights (we are supposed to have a couple over the next week). 


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#2 bmhjr

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Posted 17 July 2017 - 01:36 PM

Sounds good for a change.  I have a few days off at the end of the week and I have my fingers crossed for some clear skies in the mountains.  At least one night!  



#3 Ricky

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Posted 17 July 2017 - 01:37 PM

Nice report Jon. Ive been dealing with eggy stars despite very good rms numbers in both ra and dec...less than .90" in ra and less than .50" in dec. I do properly imbalance both axes according to which part of the sky im imaging in but am wondering if the amount of imbalance is important. My scatter data shows a very similar eggy form...

#4 rockstarbill

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Posted 17 July 2017 - 02:27 PM

Great to hear! I have had 3 days of nearly flawless imaging myself which has been great as I can actually get sleep and get data without trading one off for the other. 



#5 JPSTAR

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Posted 17 July 2017 - 03:39 PM

Jon,

Does the string run over a pulley?  If so, It shouldn't catch or bind.

 

I use 30 lb test copolymer fishing leader which seems to be a bit heavier than normal monofilament line, and 1 to 1.5 lbs of hanging weight.  The line wraps around the faceplate on the RA axis on my G-11 which is ~ 2.5 inches in radius.  To estimate the eight I needed I used a cheap spring balance hooked around the bottom of the counterweight shaft when the shaft was horizontal to measure my typical East-heavy imbalance. By taking ratios of the CW shaft length and the RA face radius I found that I needed 1lb to 1.5lbs to duplicate the prior imbalance that I was using.  Other G-11 users have reported that 1 to 2 lbs works well for the string-weight system.

 

Now I'm trying to do something similar for DEC.

 

Best,  Joe  


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#6 Jon Rista

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Posted 17 July 2017 - 03:51 PM

Well, apparently I lied. I thought I had good subs for the whole night, but on closer inspection with blink zoomed in more, I have now found that a very large range of subs actually had enough star trailing to cause registration not to work. I guess I hadn't had it zoomed in to 100% the first time through, and I couldn't see them, but StarAlignment didn't like the subs. So I lost about a third to half of the data last night. 

 

Ah well, guess a perfect night isn't possible anymore. shrug.gif



#7 Jon Rista

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Posted 17 July 2017 - 03:56 PM

Yeah, lost over a third of the subs. Shortly after the tracking issue, seems some thin high clouds moved through that affected the focus. Again, guess I wasn't zoomed in all teh way last time, and couldn't see the difference in blink. At 100% size, a large group of subs are clearly blurred more than the others, enough that I wouldn't want to use the subs. The tail end of the night and the beginning of the night, with a small patch inbetween, seem fine...but over a third of the subs were lost. I've got around 45 left out of the 80 acquired. 

 

I don't know what the deal is with my mount, but I guess it's time to rip it down to it's parts and pieces again... I hate doing that, such a huge time-consuming job...


Edited by Jon Rista, 17 July 2017 - 03:57 PM.


#8 Jon Rista

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Posted 17 July 2017 - 04:17 PM

Jon,

Does the string run over a pulley?  If so, It shouldn't catch or bind.

 

I use 30 lb test copolymer fishing leader which seems to be a bit heavier than normal monofilament line, and 1 to 1.5 lbs of hanging weight.  The line wraps around the faceplate on the RA axis on my G-11 which is ~ 2.5 inches in radius.  To estimate the eight I needed I used a cheap spring balance hooked around the bottom of the counterweight shaft when the shaft was horizontal to measure my typical East-heavy imbalance. By taking ratios of the CW shaft length and the RA face radius I found that I needed 1lb to 1.5lbs to duplicate the prior imbalance that I was using.  Other G-11 users have reported that 1 to 2 lbs works well for the string-weight system.

 

Now I'm trying to do something similar for DEC.

 

Best,  Joe  

No pulleys..no real good way to get any mounted (I tried in the past), not at lest without drilling the crap out of the mount body. Even if I did get some pulleys in place, I am pretty sure I'd have a tough time keeping the string running over them throughout the night, the angles are just not very conducive to this kind of thing. 

 

So no issues with that fishing leader stretching or anything like that? The weights don't "bounce" on the string? I may give that a try...the various kinds of strings I have used so far are probably far more prone to catching than a fishing line. 

 

My Atlas has a lot of angles and corners, locking screws, grooves, etc. where the string can catch. I'm starting to wonder if maybe drilling a hole through the RA housing, so I could put a small eyelet on the eastern side, so I could just drop the weight and string directly off the east side. That would eliminate the need to have the string wrapping around the mount...and it might actually work...

 

I've thought about doing the same thing with the DEC axis. Haven't come up with a good solution that would work for all orientations. What are you considering doing there?


Edited by Jon Rista, 17 July 2017 - 04:18 PM.


#9 Peter in Reno

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Posted 17 July 2017 - 04:47 PM

Or you could get a really nice used A-P Mach1 mount for a very good price. It will work very well with TEC 140 scope. Not worthwhile tinkering with the mount too many times.

 

Peter


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#10 rockstarbill

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Posted 17 July 2017 - 05:25 PM

There is also that new Losmandy mount with 50lbs of AP capacity.

 

http://www.losmandy.com/gm811g.html

 

Waiting list though... :( 



#11 jhayes_tucson

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Posted 17 July 2017 - 06:52 PM

Jon,

You aren't the only one with these issues.   I run 20 minute exposures all night and it's rare that I get a full run of flawless data.  Wind gusts or other little gremlins often sneak up to mess with things.  Sometimes the problem is obvious but a lot of times I can't tell what happened.  I work really hard to avoid meridian flips.  My AP mount always knows where the back of the scope is relative to the pier so it has the ability to start CW up if a pier crash can't happen.  That feature is really nice and I try to use it whenever possible.  There are only a few areas of the sky where a meridian flip is absolutely required.  Recently, I was having trouble and added weight (8 lbs) to the front lower lip of the OTA and it made an amazing difference.  I've tested my mount and the backlash was so low that I couldn't even measure it so I'm not completely sure why this trick with the weight worked.  But it was easy to see in the guide error plot.

 

Anyway, thanks for sharing your experience.  It's nice to know that I'm not the only one experiencing this kind of stuff.

 

John



#12 Jon Rista

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Posted 17 July 2017 - 06:59 PM

Jon,

You aren't the only one with these issues.   I run 20 minute exposures all night and it's rare that I get a full run of flawless data.  Wind gusts or other little gremlins often sneak up to mess with things.  Sometimes the problem is obvious but a lot of times I can't tell what happened.  I work really hard to avoid meridian flips.  My AP mount always knows where the back of the scope is relative to the pier so it has the ability to start CW up if a pier crash can't happen.  That feature is really nice and I try to use it whenever possible.  There are only a few areas of the sky where a meridian flip is absolutely required.  Recently, I was having trouble and added weight (8 lbs) to the front lower lip of the OTA and it made an amazing difference.  I've tested my mount and the backlash was so low that I couldn't even measure it so I'm not completely sure why this trick with the weight worked.  But it was easy to see in the guide error plot.

 

Anyway, thanks for sharing your experience.  It's nice to know that I'm not the only one experiencing this kind of stuff.

 

John

Yeah, there always seems to be something. Granted, I've got an Atlas rather than an AP. :p I guess issues are to be expected. But lately, I think there is really something wrong, and I think it's going to take pulling the mount apart to see what's what. I belt modded it a couple years ago, and that really helped with DEC axis responsiveness, but I did have a problem where the grub screws that hold the pulleys to the motor axes came loose, even with some threadloc. I am wondering if I may not have a balance issue, but instead have a pulley slip issue. I thought I heard something that might be that the other night, but it stopped before I could verify. Anyway, if it ends up being cloudy tonight, I think I'll just disassemble it and hypertune it again. 



#13 Jon Rista

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Posted 17 July 2017 - 07:01 PM

Or you could get a really nice used A-P Mach1 mount for a very good price. It will work very well with TEC 140 scope. Not worthwhile tinkering with the mount too many times.

 

Peter

Well, that may very well become the top item on my list ahead of the TEC140. I thought the rigrunner rework some months back fixed these issues. They seemed to be fixed, then they returned. I've been very careful about adjusting my counterweights to recover proper balance after a flip (flips are necessary at the moment to get enough time on target since the targets are directly overhead, and my FW will hit the mount too early in the evening if I don't flip), but there still always seems to be one kind of issue or another. If the next hypertune doesn't fix it, then yeah...probably time to check out CNC and AMart. 



#14 Jon Rista

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Posted 17 July 2017 - 07:03 PM

There is also that new Losmandy mount with 50lbs of AP capacity.

 

http://www.losmandy.com/gm811g.html

 

Waiting list though... frown.gif

I heard about that a while back... Does anyone know if this mount uses belts? I couldn't see in any of the photos whether the worm was belt driven or if there were transfer gears. 



#15 Jon Rista

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Posted 17 July 2017 - 07:38 PM

So, I've been fiddling with the mount. I don't think the belts are popping, but does anyone know what a slight squelching/screeching sound from the motors might indicate? The belts don't feel too tight (maybe even a bit too loose, actually). It is not persistent...it might happen for a short while then it seems to stop on it's own. At the moment I have no idea if there is a corresponding impact to tracking or not.



#16 schmeah

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Posted 17 July 2017 - 08:01 PM

Yikes Jon! That's a lot of work and a very complex balancing act in trying to deal with the dreaded flip. And John notes how hard he works to avoid the meridian flip.  You mentioned dropping 7 grand for for a high end mount. You can get an M Uno for just under 6K and...flip  bedamned! 

 

 

Derek



#17 JPSTAR

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Posted 17 July 2017 - 08:18 PM

Jon,
The string-weight system to provide bias on the DEC is a bit challenging to design. I recently came across this mechanical retractable reel that could simplify matters for a DEC bias system (and it could also be used for RA):
http://almarkenterpr...ngth-42-inches/

From the graphs in the link, it looks like this device could provide a reasonably constant force to the DEC as the fairly long string is extended or retracted (unlike a rubber band or bungee.)   I plan to give it a shot.

And no, I have not had any issues with that fishing leader stretching. I was a bit worried that it might start swinging around in the wind, but so far no problem.  I guess that if it gets that windy, it’s time to quit anyway.  I suppose the weight could always be put inside a larger plastic tube if that gets to be a problem.

To answer your question, the new Losmandy mounts with tucked in motors use spur gears.  See the attached discussion with a comment by Scott Losmandy on that:
https://www.cloudyni...-gm8/?p=7669345

Best,
Joe



#18 rockstarbill

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Posted 17 July 2017 - 08:25 PM

 

There is also that new Losmandy mount with 50lbs of AP capacity.

 

http://www.losmandy.com/gm811g.html

 

Waiting list though... frown.gif

I heard about that a while back... Does anyone know if this mount uses belts? I couldn't see in any of the photos whether the worm was belt driven or if there were transfer gears. 

 

No belts. 



#19 Peter in Reno

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Posted 17 July 2017 - 08:27 PM

I do not understand some people's fear of Meridian Flipping. If you use SGP, it's pretty easy to do, at least for A-P mounts. With SGP, Meridian Flipping is fully automatic and no user's intervention.

 

Can the longish TEC 140 scope work with M-Uno mounts? I assume M-Uno mounts work best with shortish OTAs.

 

Peter



#20 Jon Rista

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Posted 17 July 2017 - 11:20 PM

I do not understand some people's fear of Meridian Flipping. If you use SGP, it's pretty easy to do, at least for A-P mounts. With SGP, Meridian Flipping is fully automatic and no user's intervention.

 

Can the longish TEC 140 scope work with M-Uno mounts? I assume M-Uno mounts work best with shortish OTAs.

 

Peter

It's not as easy to do with some mounts as with others. I imagine it's pretty easy with an AP1100. It's a bit of a PITA with the Atlas, since you really cannot operate that mount without it being east-biased enough. I have to go outside, readjust the counterweights, then go in and recenter the object, redo PHD calibration, etc. all to make sure things function properly after a flip. It's not a matter of fear, it's just annoying. :p Plus, they kind of **** over if you want to do multiple targets a night, multiple flips...nah. So you end up doing what you can to avoid flips, track past the meridian as long as you can, so you never flip, which makes it easier to deal with the whole thing, image multiple targets a night without readjusting counterweights, etc. 



#21 Jon Rista

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Posted 17 July 2017 - 11:22 PM

I may have found a temporary solution to my string weight problem. I loosed one of the DEC housing bolts, tied a small string around it (fishing line to come later), then tightened the screw again. This basically drops the weight right off the east side of the mount, without the need for it to wrap entirely around the mount. Hoping that will resolve the issues I've had with the string catching or whatever the issue is... 



#22 David_Ritter

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Posted 17 July 2017 - 11:27 PM

So, I've been fiddling with the mount. I don't think the belts are popping, but does anyone know what a slight squelching/screeching sound from the motors might indicate? The belts don't feel too tight (maybe even a bit too loose, actually). It is not persistent...it might happen for a short while then it seems to stop on it's own. At the moment I have no idea if there is a corresponding impact to tracking or not.

That doesn't sound good. My EQ6 is belt modded too and it sings while it slews and very quietly whistles while it works. (wow.. getting literary here...)

 

Anyway, squelching or screeching is almost always trouble in a stepper motor system. When a stepper binds though it usually makes a sort of grinding sound and from your description I don't think that's what's happening. You've probably heard that if you've ever set the mesh so tight it binds. So squelching/screeching might indicate an electrical problem in the motor control board or maybe low power.

 

It could also indicate something like the mesh being too tight or maybe a pulley rubbing on the opening in the housing between the main part and the worm gear assembly. Or a belt rubbing against the pulley? Hard to tell though, particularly on the Atlas with everything hidden from view.

 

As for the tracking issues, I've noticed that thin high cloud often makes my mounts track poorly too. I don't know enough to exactly explain why but I think the light from the guide star flickers a bit when poking through the cloud. Same thing seems to happen when the aurora kicks in up here.

 

Whatever the problem turns out to be, I hope you get to the bottom of it. And if you do go to a higher end mount I do think you will be pretty happy regardless of what you get. I've done some upgrades and so far the better mounts are working well for my purposes. I recently went to a very nice mount and it does track very well. But what makes me the happiest is that it just works every time and no fiddling required (so far anyway!)


Edited by David_Ritter, 17 July 2017 - 11:28 PM.


#23 Jon Rista

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Posted 17 July 2017 - 11:38 PM

David, thanks for the comments. You are dead on about what it sounds like. It isn't quite like grinding, but pretty close, with a faint bit of screech in it. And the real problem with the Atlas is just that, everything is on the back side of the motor housing, pointed against the rear wall...so getting eyes on the problem is basically impossible. I have seriously considered cutting out the back of the motor housing and fitting in some plexiglass or something, just to make it easier to troubleshoot those darn motors. 

 

I've measured my electrical system, which I updated to a RigRunner back near the beginning of the year. I get 12V solid all the way through. I'm running power from a pretty reliable 12V 10A AC/DC supply, which I've also measured with my oscilloscope, and the power is pretty clean. 

 

It's probably a problem with the motors or pulleys. That's probably going to mean opening the mount up...or at least the motor housing, and pulling the motors out. 

 

If the high end mount you got is the GM1000 in your signature, I assume that means the 10Micron GM1000 HPS? Heh, of all the high end mounts out there, from what I understand, those are some of the most flawless. I'd LOVE one of those...the absolute encoding would be so nice against the constant light wind we have around here. 


Edited by Jon Rista, 17 July 2017 - 11:40 PM.


#24 David_Ritter

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Posted 18 July 2017 - 12:02 AM

I figured your power would be good but its always worth mentioning just in case. So, yes, mechanical or maybe problems in the motor control board then.

 

When I used to repair stepper controlled printers sometimes the output power stage would start to fail and the motors would sound funny and slight screeching or whining would be how we described the sound. We didn't usually fix boards, even back then, so we usually just swapped out whatever board the power stage was on. 8 or 9 times out of 10 that fixed it if the mechanical's checked out ok first. I know, probably not realistic in your case but if someone local has an Atlas maybe ask to borrow their motor board to test with if they are ok with the risk.

 

But even though the motor drivers could be the issue, most often it was something mechanical before something electrical. Belts would wear out or stretch (not as good as the ones we use now though and they ran a lot faster), bearings could fail or lubed parts would dry out. And sometimes foreign material would end up in the moving parts as well. So, you are probably right to open it up and have another go at the mechanical side before looking at the board.

 

And yes you are right, the new mount is a 10Micron GM1000. And indeed it is wonderful. Still though, for dealing with wind I plan to take my open-top tent when I go out of town. The 10Micron does recover wonderfully from bumps, wind and the like but it does cause the RMS to jump and since I already have the tent I may as well use it.


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#25 Jon Rista

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Posted 18 July 2017 - 12:28 AM

Well, I guess that's the plan then. But, some other day. It seems the cloud demons are preoccupied somewhere else tonight, so I just hooked everything up to get more OIII data while the moon is away.


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