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groz
Carpal Tunnel
*****

Reged: 03/14/07

Loc: Campbell River, BC
Re: Another CG5-GT "spikes during guiding"-thread... new [Re: Richard Scott]
      #3751973 - 04/18/10 11:17 AM

When you are set up for imaging, where are all the cables located. Every time I've seen jumps start happening, then go out and look at the scope, a cable from the camera was caught up somwhere and dragging. As the scope moves around, the cables can really end up in some odd locations if they are not all tied in place.

After learning that lesson, cables now always end up tied off in locations such that they wont have this problem. All the cables from the cameras and filter wheel go to a common point which is attached to the mount head, then a loop of slack before the bundle attaches again to the base, and from there off to where they need to go.


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vdb
sage


Reged: 12/08/09

Re: Another CG5-GT "spikes during guiding"-thread... new [Re: Richard Scott]
      #3752135 - 04/18/10 12:35 PM

The last couple of days I've been imaging M51 as well with the same mount, I have a 70mm refractor as guider, parallel mounted to a Mak-Newt 150mm ...
Guiding is reasonable well, but when approaching zenith it goes from "ok" to bad ... I don't have the spikes as you do though, it just drifts away. I also try to preload, but that doesn't seem to work. My polar alignment is rough, so guiding stays in one direction for dec ...


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DHB001
sage


Reged: 07/07/09

Loc: The Netherlands
Re: Another CG5-GT "spikes during guiding"-thread... new [Re: vdb]
      #3752382 - 04/18/10 02:53 PM

I've checked everything on the dec axis again today. Gear mesh, backlash, the works. Couldn't find a thing wrong here. Moving the axis manually via the spur gear goes very smoothly for the entire 360 degrees. I did however notice that the worm gear cover of the dec axis, where you attach the scope or side by side plate to the mount, was making contact with the rest of the mount, i.e., there was no gap between it and the dec axis housing. So I dug up two small washers, so that the cover now has about 1 millimeter of clearance from the dec axis housing. I have no idea if the drag from the direct contact between the two metal parts could possibly have caused jumpy shocks when guiding, but I figured the washers could only make the mount perform better.

I also followed your advice, Richard, and I've turned the dec axis via the handcontroller around for 10 or so full rotations, so that any crud should likely have been washed away by now.

Groz, thanks for thinking along. I did in fact at one point suspect cables being stuck as a possible cause, but unfortunately the cables had ample room for manoeuvre at the time I was having these jumps, so they're probably not the cause of this problem.

I still think this is a mechanical problem, most likely related to balance. My next step will be to try balancing my scope the best as I can, and let the dec drift only be caused by a slightly inaccurate polar alignment. At least then I'll be sure that I have only one source of dec drift, not two, which should make further troubleshooting easier.

I'll keep you guys posted.


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DHB001
sage


Reged: 07/07/09

Loc: The Netherlands
New symptom new [Re: DHB001]
      #3752816 - 04/18/10 06:38 PM

Okay, so I just did some more testing, this time with a carefully balanced dec axis, so that the only source of dec drift was going to be a slight inaccurate polar alignment, and the results are the same as yesterday and earlier this week. Still frequent spikes. I did try to change some parameters in PHD, like aggressiveness and hysteresis, and although you can see some minor changes in the guide graph, changing these parameters does nothing to eradicate the spikes.

I had to stop testing because it was becoming cloudy, and while disassembling my rig, a new and very interesting symptom presented itself. I wanted to set the mount to its two index positions, so that removing the scope etc. would be a bit easier. So I loosened the RA and Dec knobs to move the axes, and I swear to God, when I wanted to move the Dec axis back to the index position, it was unusually stiff.

After moving the dec axis from left to right a couple of times, moving it was as "smooth" as usual again (i.e. still much stiffer than the RA). But that first turn, it definitely was much stiffer than normal.

What does this symptom indicate? I have greased my mount with Super Lube, which is supposed to be such a good lubricant. Does it mean I have used to much, or perhaps to little grease? Does it indicate another problem? It's only like 10 degrees C, or around 50 degrees F, here outside. That's well within the operating limits of Super Lube, so it should have been lubricating just fine.

Thanks in advance for those who can help me with deciphering this new clue.


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Gregk
Carpal Tunnel
*****

Reged: 11/19/06

Loc: San Tan Valley, Az,
Re: New symptom new [Re: DHB001]
      #3753283 - 04/18/10 10:34 PM

My Cg-5 was acting up a while ago and to cure it Dec drifting not so much spiking I had to use a 1 sec guide camera exposure in PHD time If I use a bright star I reduce the gain of the DSI. You could have a build up of grease but you would have seen that

Greg


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DHB001
sage


Reged: 07/07/09

Loc: The Netherlands
Re: Another CG5-GT "spikes during guiding"-thread new [Re: Gregk]
      #3753623 - 04/19/10 04:27 AM Attachment (69 downloads)

I don't know if it'll help someone to recognize what's going on with my mount, but I've made an analysis of what happens during guiding, based on one of PHD's guide logs. The pattern shown here repeats itself constantly.

The top graph represents the RA distance (blue) and Dec distance (brown), the bottom graph displays RA duration (blue) and Dec duration (brown). The dec guide mode at the time was south only, i.e., when the dec deviates above the center line, PHD gives guide pulses to bring the dec down again. When it's below the center line, PHD does nothing.


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bardo
scholastic sledgehammer
*****

Reged: 09/13/09

Loc: US
Re: Another CG5-GT "spikes during guiding"-thread new [Re: DHB001]
      #3753677 - 04/19/10 06:18 AM

okay throwing out some ideas..

usually this happens when its loading the worm and then when it finally does WHAM! it over corrects. but since you're doing south only this cant be the case. unless you're balanced in the wrong direction...

so you know its nothing obvious mechanically i.e. no bent worm or clearly binding parts. so i think its a PHD setting issue. with my lxd75 i see this fairly often. and it takes some playing to get it right.

if i see something like this happening i first try shorter guide exposures, or maybe longer. just experiment.
sometimes i get a good result with dec on auto and tuning the backlash comp so that it reacts quickly to guide commands.

judging by your OP it looks like the PA is way off considering how fast it moves back on its own. maybe with it being so out of alignment its working too hard? ever been able to test how long of exposures you can get before field rotation sets in with it that far off?


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DHB001
sage


Reged: 07/07/09

Loc: The Netherlands
Re: Another CG5-GT "spikes during guiding"-thread new [Re: bardo]
      #3753696 - 04/19/10 06:57 AM

Hi Bardo,

Thanks for thinking along.

Maybe my mind isn't fully up to speed yet, but I don't understand how you arrive at the conclusion that it's not something mechanical. If the guide pulses don't seem to work immediately, and after the mount does begin to respond, it continues moving without input from the guiding software, how is that indicative of something software related instead of mechanical?

What I did for polar alignment was the 2-star + 4 alignment, and then the polar alignment routine from the hand controller. I've checked the accuracy of this method a while back by doing a drift alignment with EQalign after the HC PA routine, and I can say that using the HC method to get PA is pretty accurate (better than I expected actually).

When you're referring to my OP, I take it you're referring to the screenshot in the first post of this topic? Let's see. The star moved about 7 pixels down in approximately 40 steps @ 2.5 seconds. The resolution of the guider was approximately 1.0 arscec/pixel, so that's 7 arcsec of drift in 40 * 2.5 seconds. That's a speed of 4.2 arcsec/minute, or a drift of 252 arcseconds/hour, or just over 6 arcminutes/hour of drift. Is that a lot? I don't know.

Edit: I found a polar alignment error calculator (http://celestialwonders.com/tools/polarErrorCalc.html), and if I input the data calculated above, plus the declination of M51 (47 degrees), it says my PA is off by 23.5 arcminutes to the west.

Don't know much about PA accuracy, but is that too much for an autoguider to handle?


Edit 2: I've been doing some calculations on some of the other spikes in my guide log, and first of all, they don't all move at the same speed, but mostly the speed with which they drift back seems to indicate a polar misalignment of approximately 10 arcminutes. Now to me, that should be manageable by PHD...

Edited by DHB001 (04/19/10 07:19 AM)


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bardo
scholastic sledgehammer
*****

Reged: 09/13/09

Loc: US
Re: Another CG5-GT "spikes during guiding"-thread new [Re: DHB001]
      #3753771 - 04/19/10 08:24 AM

you said you have went over the mount and cant find anything. as well its a rather common issue. so thats why i think its probablly not mechanical. or not anything mechanically out of the ordinary anyway.

its over-correcting, i think, because PHD is calculating what length of pulse to give and when nothing repsonds it will give higher and higher pulses. then suddenly it over-shoots. thats how i read the data anyway. from the last graph it seems like it did the over-shoot in one quick pulse. instead of multiple pulses in the wrong direction. so its not "continuing moving without input" its one giant over-reaction, the guiding stops as the drift-misalginment brings it back north and the process starts over. the rest of the south drift is minor and im thinking should be looked at as an anomoly. its small enough to be from seeing or something by the looks of it.

all i can say is i see it with my lxd75 and im sure nothing is mechanically wrong.
so i think your pulse duration shows that its giving hypothetically 200ms pulse and notes the star continues a north drift. but that 200ms pulse went to loading the gears a little further. but PHD doesnt know that, all it knows is that it didnt move enough so it needs give an even longer pulse next time. so then it tries say a 400ms pulse. and that loaded the gears lets say 99%, but still didnt move the star. so PHD sends a 700ms pulse and that one caused it too go way too far now that the gears were loaded.
you can see on the bottom line that the duration is climbing every iteration as the north drift continues.

make sure all the worm block screws are very snug as ive had them losen on me and the whole shaft had play even when clutches were engaged. also i tighten my dec worm much tighter than the RA. the motors have torque enough even when its tough to turn by hand. ive yet to bend a worm by doing this and it does give much better reactions when guiding.

as for polar alignment as long as you can get exposures that dont have field rotation for any given amount of time that you want to shoot subs at then you're okay. if you can go 5 minutes and not see any then it should be good enough for the autoguider. i was just saying it as a possibility.

ya know have you tried to get feedback from the PHD yahoo group?


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DHB001
sage


Reged: 07/07/09

Loc: The Netherlands
Re: Another CG5-GT "spikes during guiding"-thread new [Re: bardo]
      #3754057 - 04/19/10 11:12 AM

Bardo,

I fully understand what you're saying with respect to the loading of the gear and the star initially still drifting further away. But shouldn't this sequence of events happen only once, namely at the beginning of the guiding session?

I mean, the dec drift is constant and in one direction, so as soon as the mount has "settled" and the dec gears are properly loaded, any guide pulse given from that moment onward should theoretically result in an immediate move by the mount. But what you can see in my guide logs, is that this process of what seems to be loading and then overshooting happens time after time.

But what if the gears were in fact loaded the whole time during guiding, apart from the very first couple of minutes (the so-called settlement time)? In that case, the initial lack of movement, followed by the violent overshoot to me looks like there was an initial source of friction that was holding the dec axis in place, and after sufficient guide pulses, the resistance finally broke. In other words, stiction. The stiffness I witnessed yesterday, when I was manually resetting the mount to its two index positions after it was becoming cloudy and I had to stop testing, seems to support excessive friction as a likely source of the overshooting. Now, if this is true, is it caused by too much grease, too little grease, or something else?

By the way, I did check the four screws that hold the worm in place. They were still very snug. Thanks for the suggestion.


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Chris Rowland
professor emeritus


Reged: 02/28/05

Re: Another CG5-GT "spikes during guiding"-thread new [Re: DHB001]
      #3754141 - 04/19/10 11:45 AM

Try a different guiding program, Guide Dog for example.

Or try a different way to send the guide commands if that's possible.

Are the guide commands sent by a PC? I suppose they must be because PHD is being used. Maybe some other activity on the PC is causing a stop guiding command to be delayed.

I've found that collecting email at the same time as guiding not to be a Good Idea.

Chris


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Javier1978
scholastic sledgehammer


Reged: 02/12/09

Re: Another CG5-GT "spikes during guiding"-thread... new [Re: Richard Scott]
      #3754204 - 04/19/10 12:22 PM

Hi, I guide with guidemaster and sometimes have the same issue with my eq3 mount.

My guess is that itīs a DEC balance issue (at least in my mount), if not, it would always be a problem and itīs not.

When I move by hand the DEC axis, itīs quite smooth in some positions, but when I change to others I can fell some little jumps in one direction. Iīm sure that movement create those jumps when guiding.

Maybe Iīm wrong, but I donīt think the program would give such an aggressive correction to create that spike. So double check your dec balance and, maybe, when guiding in one direction only, try to lightly overload one side if things are going wrong, if still got spikes, try to overload the other side.

Just I thought.

Anyway, good luck!


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DHB001
sage


Reged: 07/07/09

Loc: The Netherlands
Re: Another CG5-GT "spikes during guiding"-thread... new [Re: Javier1978]
      #3754275 - 04/19/10 12:48 PM

Chris, Javier,

Thanks for coming up with new ideas and suggestions.

I'll definitely look into another guide program. It's an easy thing to check, but since I have in the past had way better results than I'm having lately with the same hard- and software configuration throughout, I have some reservations about the odds that it could be the source of my current troubles.

I also suspect that it's something with the dec axis itself. As I mentioned yesterday, I noticed it was unusually stiff after testing, and after a few times moving it back and forth it got smoother again (but still stiff compared to the RA). I'm pretty sure that if I could somehow get my dec axis to rotate as smoothly as the RA, there probably wouldn't be a problem with guiding. But the RA has ball bearings, and the dec has nothing. I'm still wondering what could have caused the temporary stiffness I noticed yesterday, and whether it somehow affected my guiding performance...


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Javier1978
scholastic sledgehammer


Reged: 02/12/09

Re: Another CG5-GT "spikes during guiding"-thread... new [Re: DHB001]
      #3754419 - 04/19/10 01:48 PM

I donīt think switching to another guiding soft will solve your problems. I think itīs a mechanical issue of the DEC axis. Maybe your DEC axis is to tigh and itīs affecting the movements in some areas and you canīt get a really accurate balance in DEC. Same thing happens to me but I did not disamble my mount yet. I too used to have better results with same set up that now.

I understand you, itīs annoying. I would let you know if I find out something.

Edited by Javier1978 (04/19/10 04:00 PM)


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bardo
scholastic sledgehammer
*****

Reged: 09/13/09

Loc: US
Re: Another CG5-GT "spikes during guiding"-thread... new [Re: Javier1978]
      #3754699 - 04/19/10 03:56 PM

yep should only be once until its loaded. it doesnt make sense. but it seems like if it were stiction its wouldnt be behaving similiar to backlash issues. in that it takes multiple pulses before reaction. its would have to be full on binding while the motors give all their torque and still can turn. stiction would only be from the grease being too thick. i would think you would still be getting some reaction if that were the case. too much grease would probablly just end up making the inside of the mount messy with the excess that gets pushed out from between the ring gear and the dec shaft.
you can double check the whole dec assembly and mkes sure there are no unusual spurs or metal deformaties. then before you put the worm back on lock the ring gear with the clutch and turn the dec shaft by hand to see if you're getting unusual stiction or binding anywhere.

heres what i say you do next time out if you havent laready.

-experiment with exposure times
-experiment with dec on auto and backlash comp to the point that it reacts fast to pulses but doesnt over shoot. mine usually sets somewhere between 70-90% for this.
-experiment with the dec balance as both front and rear heavy and neutral.
- try just a calibration with auto then go back to south only.

if it continues after that some issues can be checked off the list. i approach it from the mindset of whatever it takes to get it to work right, not necessarily what is logical in the end.

p.s. not sure if you have mentioned it ealier but check the gears on the motor and worm shaft and make sure the encoders are good. just to eliminate any possible issue.


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Gregk
Carpal Tunnel
*****

Reged: 11/19/06

Loc: San Tan Valley, Az,
Re: Another CG5-GT "spikes during guiding"-thread... new [Re: DHB001]
      #3755665 - 04/19/10 11:33 PM

HI Again

Maybe this thread might help you I had this problem with dec after installing a linger 700mm guide scope. Before installing the 700mm scope I had been using a 388mm scope

Having the extra length added more to imbalance away from the center of the mount even thought RA dec were in balance
I presume this added to any Worm gear anomolies.

How well is you Dec Calibration Does it come back to the central axis,,,

Also try a shorter exposure on the guide camera

Check this thread

Greg


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DHB001
sage


Reged: 07/07/09

Loc: The Netherlands
Re: Another CG5-GT "spikes during guiding"-thread... new [Re: Gregk]
      #3755937 - 04/20/10 04:43 AM

Hi Greg,

Thanks for referring me to that thread. The spikes you were having look an awfully lot like mine, only yours were less pronounced.

I can hardly imagine that a skewed center of gravity could be the source of the spikes. Because of its size, the C6 has no capacity to carry a guide scope in piggy back configuration, so either I have to guide via a guide scope in side by side configuration, or I have to use an off axis guider. I've already tried bottom heavyness, top heavyness, and precise balance on the dec axis, and none of them seemed to help eliminate, or even reduce the spikiness.

The spike issues I'm currently having are while using an off axis guider, so my imaging train is as follows: C6, reducer, OAG, DSLR and SSAG. That's both compact and light, and should be no problem for the CG5. I posted a guide log of sep 25 earlier in this thread, and that night I imaged the Elephant Trunk nebula for 5 hours straight, and I had no spikes during the entire night. Guess what? It was in side-by-side configuration, so more complex weight distribution and heavier as well.

Come to think of it, maybe the SBS configuration helps to keep preload on the declination axis when imaging near or in zenith (which is basically what I was doing while imaging M51 last week), because you have two axes which you can balance: 1) front <-> back heavy and 2) main scope <-> guide scope heavy (left-right, if you will).

As far as the dec returning to the center, that's something that doesn't happen (assuming you're referring to PHD calibration). It's also something that doesn't need to happen, as long as the gears of the declination axis are loaded when doing north calibration. That's something I always take care of. When (trying to do) imaging, I always do a precise goto, so that I can focus on a bright star near my imaging object, and to center the object of course. When focus and framing are satisfactory, I push the enter button, and the mount slews to the imaging target. As you know, the mount always makes sure the gears of the declination axis are north loaded (as if you were to do a manual slew by pressing the up and right buttons, if you know what I mean).

I'm currently thinking about trying to get hold of some teflon sheet, to do what AlanT did (see the thread you referred to). He made teflon rings to smoothen his declination axis. Might be worth a shot...


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Gregk
Carpal Tunnel
*****

Reged: 11/19/06

Loc: San Tan Valley, Az,
Re: Another CG5-GT "spikes during guiding"-thread... new [Re: DHB001]
      #3758022 - 04/21/10 12:48 AM



Maybe Here to get Teflon Spacers


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DHB001
sage


Reged: 07/07/09

Loc: The Netherlands
Re: Another CG5-GT "spikes during guiding"-thread... new [Re: Gregk]
      #3759344 - 04/21/10 04:49 PM

Hi Greg,

Thanks for the suggestion. I found another source for teflon over here. I would still need to cut the teflon into the right shape of course, but that shouldn't be difficult. As these guys are located in Germany, for me, it's both faster and more economical to order my teflon over there.

I'll keep you guys posted. Could take a few weeks though, since I first need to disassemble my dec axis to check the dimensions of the rings (the thickness in particular), need to order the teflon, need to re-assemble the dec axis, and then wait for clear skies to do some more testing of course...


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Gregk
Carpal Tunnel
*****

Reged: 11/19/06

Loc: San Tan Valley, Az,
Re: Another CG5-GT "spikes during guiding"-thread... new [Re: DHB001]
      #3760281 - 04/21/10 11:40 PM

Here they areSteve told me to look here THey have them for LXD-75 Atlas CG-5 etc

Spacers Sold here in the US


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