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DHB001
sage


Reged: 07/07/09

Loc: The Netherlands
Another CG5-GT "spikes during guiding"-thread...
      #3746083 - 04/15/10 07:23 AM Attachment (100 downloads)

Last night, I was trying out my radial guider on M51, hoping that my flexure would be a thing of the past. Well, I set up my equipment at around nine pm, went to bed around 4.30 am, and all this time in between only yielded 2 hours worth of usable data. That’s absurdly inefficient, and was caused by 2 things, 1) sudden jumps during guiding (see accompanying screenshot), and 2) difficulty finding a suitable guide star through my OAG (lost quite some time realigning after the meridian flip).

I want to find a solution for the first issue, because it has been bugging me ever since I got my current equipment about a year ago. I’ve already read a lot of threads about these jumps, and I think I’ve done as much as I could possibly do to minimize these jumps. Besides having relubed my mount, and in the process eliminating as much backlash/slack as possible, I have taken the following precautions:

1) Polar alignment procedure via my mount. This is accurate enough not to cause significant field rotation, but is sufficiently inaccurate to ensure a little drift in the DEC, so I can guide the DEC north only or south only, which keeps constant traction on the gears.

2) Make the RA axis a little east heavy, and the DEC axis back heavy (i.e., just a bit more weight on the camera side than on the corrector plate side). Again, this should ensure constant traction between the gears on both axes.

Now, I’m only using a C6, a Rebel XS / EOS 1000D DSLR and an Orion SSAG autoguider, the combined weight of which should be well within the operational limits of the CG5 mount. Yet, I still manage to get these jumps during guiding. What’s causing this? Does the fact that M51, when passing through the meridian, for me is almost right above me in the zenith, have anything to do with these spikes? Have I inadvertently made the imbalance on my axes too big? I only move the scope and the counterweight about 1cm (or just under half an inch) away from what I perceive to be the point of balance. Those of you who use this mount as well, do you preload your axes, and if so, by how much?

For those who want to see my guide logs, please see the links below. The first run was to determine whether to guide north or south on the DEC, and the last 3 to 5 runs I experimented a little with some settings, like dec algorithm, and aggressiveness and hysteresis combinations. But everything in between is ordinary guiding with the same settings used throughout (except after the meridian flip, when of course I switched between north only and south only dec guiding).

I really hope someone can help me combating this issue. Thanks to anyone who can offer any advice.

Guide log 1: http://www.mediafire.com/?jjeujy22mmy

Guide log 2: http://www.mediafire.com/?yjny3yii2wz

Bear in mind that guiding was done at 950-1000mm, which, with my setup, equates to a resolution of approximately 1.0 arcsec/pixel for the SSAG.


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rmollise
Postmaster
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Reged: 07/06/07

Re: Another CG5-GT "spikes during guiding"-thread... new [Re: DHB001]
      #3746091 - 04/15/10 07:33 AM

If the spikes were not periodic in nature, the obvious culprit could be wind or other vibration.

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DHB001
sage


Reged: 07/07/09

Loc: The Netherlands
Re: Another CG5-GT "spikes during guiding"-thread... new [Re: rmollise]
      #3746148 - 04/15/10 08:32 AM

Hi Rod,

Thanks for your response. The spikes were not periodic. According to the guide log, the first spike only happened after a little under a thousand corrections, but later during the night, they began to happen more frequently. Oddly enough, while most spikes were from the DEC axis, a couple of spikes were from the RA axis...

It was a clear night with no wind, so although otherwise a plausible cause, in this case it certainly could not have been wind. I cannot think of anything that could have caused vibrations. My setup stands in the middle of my backyard, on a terrace of street tiles. These tiles don't sag or wobble, and are really solid. Once I'm done focusing and framing, I use USB extension cables for my guide and imaging cameras, so that I don't have to get anywhere near my scope once it's busy imaging.


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seeker372011
scholastic sledgehammer


Reged: 03/05/04

Loc: Sydney , Australia
Re: Another CG5-GT "spikes during guiding"-thread... new [Re: DHB001]
      #3748034 - 04/16/10 03:27 AM

Wierd. I too would have said wind in fact i am Impressed it even brought it back after such huge spikes

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DHB001
sage


Reged: 07/07/09

Loc: The Netherlands
Re: Another CG5-GT "spikes during guiding"-thread... new [Re: seeker372011]
      #3748075 - 04/16/10 05:09 AM

And what's even worse, I know my mount is able to pull off precise guiding for extended periods of time. The link below is to a guide log of last September, when I was imaging the Elephant Trunk nebula for 5 hours straight. I was also using a separate guide scope in side-by-side configuration at the time, so a more heavy and balance wise complex configuration than a single tube plus OAG. Can't think of anything I did that night that was different from other nights I have been imaging. It was the only one time everything went 100% according to plan. So I'm really puzzled by the recurrence of this spike issue...

Log of everything going perfectly with sbs config: http://www.mediafire.com/?ong2zzimduy


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bardo
scholastic sledgehammer
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Reged: 09/13/09

Loc: US
Re: Another CG5-GT "spikes during guiding"-thread... new [Re: DHB001]
      #3748099 - 04/16/10 05:42 AM

mirror flop? play in the OAG somewhere? backlash compensation on?

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DHB001
sage


Reged: 07/07/09

Loc: The Netherlands
Re: Another CG5-GT "spikes during guiding"-thread... new [Re: bardo]
      #3748216 - 04/16/10 08:31 AM

Mirror flop? --> I was already having these spikes when I was using a guide scope (a refractor), so that seems unlikely.

Play in the OAG? --> extremely unlikely. The SSAG sits all the way down in the guider tube (no play possible), screwed tight with two screws. The screw which allows the guide tube to rotate I also screw really tight once I'm done rotating. Believe me when I say everything on the OAG is screwed down tightly.

Backlash comp? --> never ever used. Always on zero, both Dec and RA.

At first I thought perhaps my polar alignment was still too "correct" to induce sufficient drift in the Dec guiding, so that stiction might have caused the spikes, but on a few occasions, it was the RA that began to spike, so those spikes were definitely not caused by stiction...


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Eddgie
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Reged: 02/01/06

Re: Another CG5-GT "spikes during guiding"-thread... new [Re: DHB001]
      #3748348 - 04/16/10 10:12 AM

I am going to venture a guess. It is ONLY a guess. I do not image, but I have had this problem with visual observing.

As the load moment on the mount shifts over the course of a session, what happens is that the loading of the worm gear against the face of the worm wheel can change. The result is that the worm wheel can "Bounce" off of the face of the worm gear and then "Catch up."

The culprit is usually too much space between the worm and the worm wheel faces.

The easiest experient to see if this is the case is to always positivly load the faces. When imaging on the eastern hemisphere, slide the counterweight down a bit so that the worm is always pushing "Hard" against the wheel.

When working on the west, raise the counterweigt so that the weight of the telescope is pullling back against the movment of the mount.

I have seen these mounts bounce many, many times even visually. As the loading moment shifts due to tracking, the pressure (especially if the scope is CAREFULLLY balanced) can change causing slight jumps.

Just a thought, but I know it happens visually. One of my mounts (my LXD-750) required a lot of fussy adjustment to get the worm tight enough but not so tight is would stall. The telescope has a VERY long weight and balance moment, and changing from a light eyepiece to something like a 31mm Nagler would cause it to start bounching if the balance changed in some attitudes.

This can also happen in both axises of course.

These mounts tend to be sloppy mechanically. I don't mean that in a negative way saing that they don't have good table manners. I mean that they are not assembled to particularly close tolerances.

Try loading both axises more positivly and see if the condiition improves.

Regards.


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NewAstronomer
Post Laureate
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Reged: 09/03/04

Loc: Northeast, PA U.S.A
Re: Another CG5-GT "spikes during guiding"-thread... new [Re: Eddgie]
      #3748396 - 04/16/10 10:34 AM

Power supply? Or weight shift. I dragged out my SVP recently for quick planetary views with my new refractor and I'm using 4 D batteries , except 1 of the 4 is really a rechargable AA in a shell. Things seem to be fine for awhile them blamo, the mount shifts rsdically on the RA, then a little latter tracking and DEC movement stops working but the green light stays on...I throw in another AA and it seems fine...but keeps happening.

I'm going to buy 4 new D's before next session to see if that is in fact the problem. What do you use for power?

Edited by NewAstronomer (04/16/10 10:35 AM)


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DHB001
sage


Reged: 07/07/09

Loc: The Netherlands
Re: Another CG5-GT "spikes during guiding"-thread... new [Re: NewAstronomer]
      #3748668 - 04/16/10 12:52 PM

Eddgie,

Thanks for your suggestion and explanation. I know exactly what you're referring to. I did preload both axes last week, and I thought I had imbalanced them enough, but now I'm not entirely sure anymore.

By the way, how much preload is enough, and when is it too much? What will happen then? Will it not constantly overshoot if the mount is too much out of balance?

At this point, I too believe a balance issue is the most likely cause of all this.

NewAstronomer,

I use a celestron powertank. I bought all my current equipment about a year ago, and although scope and mount are secondhand, the powertank is brand new. I'm pretty sure that it's working fine. I haven't had any trouble in the power department to date. Slewing, tracking etc. all goes just fine, never a glitch or anything, so although theoretically it is possible that it's not working 100%, I have no real suspicions at the moment that that is in fact the case.


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DaemonGPF
Redonkulous
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Reged: 03/22/08

Loc: Aurora Colorado
Re: Another CG5-GT "spikes during guiding"-thread... new [Re: DHB001]
      #3748768 - 04/16/10 01:34 PM

1+ for load shift/balance. My CG5 was very picky about balance.

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Eddgie
Postmaster
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Reged: 02/01/06

Re: Another CG5-GT "spikes during guiding"-thread... new [Re: DHB001]
      #3748949 - 04/16/10 03:22 PM

I would think just enough to ensure that the worm faces stay in contact.

The fact is that the gearing in these mounts provides a HUGE amount of torque magnification. These mounts will drive in even severely out of balance conditions. Now, I don't recommend using more pre-load than you need, but just having the mount SLIGHLY out of balance is sometimes not enough.

As the telescope's angle changes, and this is ESPECIALLY true with refractors, them load moment often changes. This is because the load is often very assymetric.

Many people balance with the OTA level to the ground and the polar shaft level to the ground. What you MIGHT find is that the mount is ONLY fully balanced in this ONE position.

As you change orientations, the moments of leverage get all twisted around.

The suggestion I would make is to balance in the orientation similar to where the mount will be when it is actually in use.

How much? I would expect that for imaging, a little more pre-load is a bit better than a not. Again, the motor torque is hugely magnified and you are NOT going to hurt anything.

This may cause the current drain on your power supply to go up a hundred milliamps or so, but you aren't going to hurt anything.

I could be wrong, but if it is irregular, then I think that this is one of the most likely issues.

Of course you may have some other slop somewhere. The spur gears between the motor gearbox shaft and the RA shaft should be checked for mesh along with the worm, but again, if you pre-load, it should not matter.

Try preloading with enough load that the mount is CLEARLY out of balance and let us know if it solves the problem.

If it does, and later you decide you want to attack the issue of the slop, let me know and I will walk you though how to check and what to do.

Regards.


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Eddgie
Postmaster
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Reged: 02/01/06

Re: Another CG5-GT "spikes during guiding"-thread... new [Re: Eddgie]
      #3748958 - 04/16/10 03:25 PM

Oh, and of course it would be unfair to not to mention this. You COULD have binding becuase of too much pre-load already, but this is unlikely unless your gears are dry. If the worm gears DO get dry, the teeth can chatter against one another. Unlikely, but not out of the question. If the mount is very old and has never been greased, it could be an issue.

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DHB001
sage


Reged: 07/07/09

Loc: The Netherlands
Re: Another CG5-GT "spikes during guiding"-thread... new [Re: Eddgie]
      #3749288 - 04/16/10 06:38 PM

Thanks DaemonGPF and especially Eddgie for your input.

Eddgie,

As far as gear slop and potentially dry worm gear teeth are concerned, one of the first things I did after buying my equipment last year, was re-lubing the mount (with Super Lube, which I've read so many good things about here on CN) and ensuring that backlash/slack between the gears (both worm and spur) was minimized. I did this by following the instructions of Tim Doucette (see here), which is based on the well known instructions of Astronomy Boy, but for the newer CG5-GT.

By the way, what exactly do you mean by binding, Eddgie? I know what stiction (static friction) is, but I'm not sure I understand what you mean by binding. Don't think it's the same, or is it?

I will definitely test pre-loading my mount "excessively" asap, and as soon as I've got results, I will let you all know. The weather forecast is very favorable for the weekend, so unless this Icelandic volcanic ash is seriously blocking the sky (which I think it won't), I should be able to report back very soon.

Thanks again to all you guys who came up with ideas the last couple of days. I've got a good feeling we'll soon have this issue sorted out.


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Eddgie
Postmaster
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Reged: 02/01/06

Re: Another CG5-GT "spikes during guiding"-thread... new [Re: DHB001]
      #3749468 - 04/16/10 08:22 PM

Well, the "Binding"would simply be tiny momentary chattering of the worm wheel/worm gear teeth or if the mesh is not correct on the spur gears, you can have a tiny amount of hitching of the gears as the successive teeth come into contact.

Anyway, look forward to the results.


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DHB001
sage


Reged: 07/07/09

Loc: The Netherlands
Re: Another CG5-GT "spikes during guiding"-thread... new [Re: Eddgie]
      #3751129 - 04/17/10 08:51 PM

Well, it's now 2.50 am here, and I just finished what turned out to be a very disappointing test session. It seems the spikes at best were just as bad as earlier this week, but it was mostly worse. Tomorrow I'll post the guide logs of last night, plus the notes I made of the things I tried and at what time I tried them, so that you can see the effects (or lack thereof) they had on the guide graph.

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Eddgie
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Reged: 02/01/06

Re: Another CG5-GT "spikes during guiding"-thread... new [Re: DHB001]
      #3751189 - 04/17/10 09:39 PM

Well, I am sorry that my suggestions were not helpful.

Don't know if it is elelctrical or mechanical now. Wish I had another idea.

Hopefully someone else will have some ideas.


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DHB001
sage


Reged: 07/07/09

Loc: The Netherlands
Re: Another CG5-GT "spikes during guiding"-thread... new [Re: Eddgie]
      #3751645 - 04/18/10 06:22 AM

I've processed the guide log in Excel, and also provided it with comments about what I did, for those interested.

The guide log in Excel, with comments: link

I think one or more of the issues below could be causing my problems.

1) the DEC is too stiff, causing stiction.

I already regreased my mount once before, before I got hold of Super Lube, and it doesn't matter what lubricant I use, the Dec axis won't spin as easy as the RA does. I think it has a lot to do with the fact that the Dec has no bearings whatsoever, unlike the RA.

2) as a consequence of 1), the net result of scope preload and deliberate polar misalignment to induce permanent drift in the dec was insufficient to prevent stiction to occur, creating spikes during guiding.

3) preloading works, but not when imaging in zenith.

M51 is very high above the horizon for me, so I'm always imaging this object very near zenith. With the scope pointing nearly straight upward, there's almost no lever arm for the force, created by the preload, to exert torque on the dec gears.

4) preload in dec and deliberate drift from slight polar misalignment are in opposite direction.

This is something I just thought of.

Could it be that if the drift caused by polar misalignment is south in the dec, but the scope preload on the dec axis is to the north, that guiding the dec becomes hard to do for PHD (or any guiding software for that matter), because corrections tend to overshoot?

Maybe I should do only one of two things: either balance the scope in Dec and do a rough polar alignment so that there's a slight unidirectional drift in Dec, or do an accurate polar alignment and preload the Dec axis....


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bardo
scholastic sledgehammer
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Reged: 09/13/09

Loc: US
Re: Another CG5-GT "spikes during guiding"-thread... new [Re: DHB001]
      #3751718 - 04/18/10 08:21 AM

just put the motors on a vixen and be done with it

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Richard Scott
scholastic sledgehammer


Reged: 07/25/06

Loc: Tampa FL
Re: Another CG5-GT "spikes during guiding"-thread... new [Re: bardo]
      #3751764 - 04/18/10 09:00 AM

I worked for years with a CG-5 and I got a few spikes but nothing like you are experiencing.

Two thoughts,
#1 Try lapping the gears by dry running both the RA and DEC without any OTA the 10 or 20 full 360-degree rotations. If there is a bit of crud or two on one or more of the gear faces, that may rub it off.

#2 Try a AC/DC power converter. I found that my CG-5 ran a lot happier at 14/15 volts than it did at 11/12 volts. The extension cord is something of a pain, but after I went the converter route I never went back.

Good luck
Richard


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groz
Carpal Tunnel
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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
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Reged: 11/19/06

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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
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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
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Reged: 09/13/09

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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


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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


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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
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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
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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
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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

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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
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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
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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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sdh
member


Reged: 10/13/06

Re: Another CG5-GT "spikes during guiding"-thread... new [Re: Gregk]
      #3764708 - 04/23/10 10:38 PM

I have the same mount and have seen this problem and a wide variety of other issues. My tracking / autoguiding success has been hit and miss.

I have a few inputs for you. First, recognize that this mount has no ball bearings in the DEC axis like it does in the RA axis. Second, one of the parameters you can look at in the PHD log is how large the pulse is that is being sent to the mount. I suspect that this number is growing, and growing, and eventually when the mount is 'ready' to move it jerks in that direction. You can determine if this theory is true by looking at the PHD logs for the DEC corrections being sent. So, my theory is, the mount is sticking (consistent with your observation of stiff DEC axis), PHD corrections are growing, and growing until they hit a large number and then it jumps too far. In my case, I limited my PHD DEC corrections to 1000 and rebuilt the DEC axis. I believe limiting the PHD corrections fixed this particular problem.

Also, I cannot tell you that I have perfected my ASGT tracking / autoguiding. I still struggle with this mount and have very inconsistent results. Sometimes perfect, sometimes a mess. Good luck.


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Gregk
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Re: Another CG5-GT "spikes during guiding"-thread... new [Re: sdh]
      #3764892 - 04/24/10 01:04 AM

"I have a few inputs for you. First, recognize that this mount has no ball bearings in the DEC axis like it does in the RA axis."

Mine does! I just had it apart They are small but see link.

My mount seems to stick more when it is cold and lower in latitude.

One thing I noticed is that the end play nut on my RA worm bearing had no grease where it made contact with the outer edge of the bearing surface and created allot of drag Now it is much smoother after adding some synthetic grease

Bearings here for DEC and RA

Edited by Gregk (04/24/10 01:10 AM)


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sdh
member


Reged: 10/13/06

Re: Another CG5-GT "spikes during guiding"-thread... new [Re: Gregk]
      #3764924 - 04/24/10 01:53 AM

Actually, that is not the ball bearings I was referring to. The ones shown in the link are the ones on the worm, yes there are ball bearings there. What I meant was that there are no ball bearings on the DEC axis shaft like there are on RA. Since the shaft is just the shaft dragging on collars that it is inserted in, it is a prime candidate for stiction. When I last had mine apart I used very fine sand paper to try and smooth out these interfaces, but they were pretty rough originally. I should have been more clear about what I meant originally. Thanks for helping me clarify this.

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DHB001
sage


Reged: 07/07/09

Loc: The Netherlands
Re: Another CG5-GT "spikes during guiding"-thread... new [Re: sdh]
      #3765312 - 04/24/10 10:55 AM

Well, unfortunately, I won't be doing any updates any time soon. It appears that the motherboard of my laptop has died on me yesterday. No laptop, no autoguiding. I was going to have dinner, so I closed the lid of my laptop so that it would go into hibernation, and when I wanted to resume, it never came back on again. Every bit of info I've found on the internet seems to indicate my mobo is toast.

As for the CG5 / teflon situation, I did some testing with a relative of mine, who is a retired mechanic, and I might not even buy any teflon. If you take out the plastic washers that surround the aluminum worm gear, the movement is much smoother than with washers. All of the metal surfaces that come into contact with the aluminum worm gear are really smooth. On top of that, the surface areas of the dec shaft and dec housing that come into contact with the aluminum worm gear are much smaller than the surfaces created by the introduction of the plastic washers, creating far less friction than the washers. If I move the dec axis without the plastic washers and use an ever so small amount of Super Lube on the top and bottom of the aluminum worm gear, there seems to be hardly any static friction, unlike when I use the two big plastic washers.

Unfortunately, because of the laptop situation, I cannot test anything yet, so I'm postponing the purchase of teflon for now, because it may well be unnecessary.

Will keep you guys posted.


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vlad10
member


Reged: 04/20/06

Loc: Alicante (Spain)
Re: Another CG5-GT "spikes during guiding"-thread... new [Re: DHB001]
      #3767532 - 04/25/10 02:57 PM Attachment (63 downloads)

I too, should join the "spikers" club with this mount. Really, you would think that with so many of us around, somebody in Celestron would take note and do something about it? As it stands, I would really consider not buying another mount from them - ever.
My graph is so similar to yours DHB001. Does this attachment look similar to you?

I currently have no solution for this and just about feel like pulling my hair out. Or throwing the mount off the terrace. Whichever comes handier at the moment.I cannot believe that 600$ later and autoguiding with this mount is a matter of luck!
For the record I use the 8" reflector, guiding with a converted finderscope and qhy5, imaging with dsi ii. Weight is to a minimum possible, still under 10kg

Edited by vlad10 (04/25/10 02:57 PM)


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DHB001
sage


Reged: 07/07/09

Loc: The Netherlands
Re: Another CG5-GT "spikes during guiding"-thread... new [Re: vlad10]
      #3767681 - 04/25/10 04:16 PM Attachment (61 downloads)

Yes Vlad, unfortunately, that graph looks awfully familiar.

As I mentioned before, unfortunately my laptop is now dead, and I cannot proceed to do any more testing at the moment, but I feel really optimistic about leaving the plastic washers that surround the aluminum worm gear out altogether. I've got a pretty strong feeling that they're responsible for the spikes, which imho is static friction.

Provided that the load bearing surfaces in the dec housing and dec axis (see the pictures below and in the following post) are sufficiently smooth, I think that when you use a little bit of grease, chances are the spikes will subside, if not completely disappear.

As you can see, I've got my dec axis fully disassembled at the moment, and while testing by hand, I could really feel a difference between using washers or not. With a washer between the dec axis and the aluminum worm gear, if you move the axis tiny amounts by hand to replicate guide corrections (while applying firm downward pressure on the axis in order to replicate scope load), the motion is jerky. Doesn't matter if I use grease or not (as a matter of fact, grease makes it worse, because the washer will stick to the aluminum worm gear).

On the other hand, if you don't use a washer, and you apply the tiniest amount of grease on the top of the aluminum worm gear, the motion seems to be much, much smoother. Now, I only felt this by hand and cannot yet confirm this through actual guiding performance, but I'm pretty optimistic.

As long as the load bearing surfaces are smooth, and you use a little lubrication, no extraordinary wear should occur, especially since the dec axis really doesn't move that much, apart from alignment and the occasional slewing.


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DHB001
sage


Reged: 07/07/09

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Re: Another CG5-GT "spikes during guiding"-thread... new [Re: DHB001]
      #3767682 - 04/25/10 04:17 PM Attachment (65 downloads)

...

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vlad10
member


Reged: 04/20/06

Loc: Alicante (Spain)
Re: Another CG5-GT "spikes during guiding"-thread... new [Re: DHB001]
      #3767970 - 04/25/10 06:08 PM

You are a braver man than I am. I have yet to stick my hands inside it
fortunately mine is still under guarantee, it will go back to the dealers here in Spain soon, although I am not very optimistic about it...
Thanks for the pics, I can't quite tell which are the plastic washers? If the mount is also used for visual work then chances are they will erode very quickly if you leave them out - I have read the worm gears are made of aluminium!!


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DHB001
sage


Reged: 07/07/09

Loc: The Netherlands
Re: Another CG5-GT "spikes during guiding"-thread... new [Re: vlad10]
      #3768115 - 04/25/10 06:52 PM

If you find it hard to identify the plastic washers, it's probably because they aren't in any of the pictures.

I hardly ever do any visual observing. It's mostly photography (or at least that's what I've been trying to do for the last year, lol). So other than alignment and meridian flips, my dec axis doesn't really move that much. And even during aligning or meridian flipping, the movement of the dec axis is never more than a fraction of a circle. Again, as long as the metal load bearing surfaces are smooth and you take care to ensure these parts stay lubed, I don't think the worm gear will wear that quickly. I'm not saying that it won't wear at all, but I just don't think it's going to happen that quickly.

However, if your mount is still under warranty, you're right not to take it apart. Let the dealer sort it out. Though I would be surprised if they would find a solution for this spiking issue.


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Bootlegger
sage


Reged: 01/15/10

Loc: Iceland
Re: Another CG5-GT "spikes during guiding"-thread. new [Re: DHB001]
      #3768863 - 04/26/10 02:42 AM

Hi all.

These graphs you are diplaying are very familiar to me.

My solution was taking the mount appart, relubing and polishing, the mount became better than new and FWHM of stars a lot smaller in images.

Nonni.


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bardo
scholastic sledgehammer
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Reged: 09/13/09

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Re: Another CG5-GT "spikes during guiding"-thread. new [Re: Bootlegger]
      #3768879 - 04/26/10 03:18 AM

the lxd75's have 2 bearing assemblies for the dec axis and they dont do any better.

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vlad10
member


Reged: 04/20/06

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Re: Another CG5-GT "spikes during guiding"-thread. new [Re: Bootlegger]
      #3768909 - 04/26/10 04:13 AM

Hi Nonni,
Which parts required polishing?
And does it work for you now?

Cheers


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vlad10
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Re: Another CG5-GT "spikes during guiding"-thread. new [Re: vlad10]
      #3770918 - 04/27/10 04:37 AM

Just an update.
I have spend some time last night guiding both east and west, and this time I watched carefully the messages in PHD. My graph would alternate between smooth, spikes and DEC drifting away until disappearing all together, and it is all consistent with the same problem.
Doug is completely right, and this is in fact an identified problem , its called "stiction" and is detailed on the PHD forum. Basically at some point and for mechanical reasons, the DEC axis gets "stuck". If you read the log messages, PHD tries to correct the drift by gradually increasing the length of the pulse. I had my max set to 350 and this was not enough - as a result, the DEC graph would slowly drift away from the graph (how slowly depends on your polar alignment), with PHD desperately logging "S= dur 350ms" and unable to do anything about it. I then increased the max to 1000ms. As a result, when it reaches about 700-800ms it finally manages to "unstuck" the dec axis and wham! - it throws it to other side of the line, usually this is because the inertia of the unblocking axis who's been accumulating momentum. Sometimes its stuck less bad, and it manages to release it once it reaches about 400-500ms.
Solution: NONE with the software. In my case is still under warranty, so back it goes, but I imagine its what Nonni said, relubing, polishing, and also possibly changing any bits inside that might have deformed (anything plastic sound like a candidate for me )
I hope this helps.


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Tapio
Pooh-Bah


Reged: 09/24/06

Loc: Tampere, Finland
Re: Another CG5-GT "spikes during guiding"-thread. new [Re: vlad10]
      #3770944 - 04/27/10 05:44 AM

Let me tell my experience, although with different mount.
I have a HEQ5 Pro and I wasn't too happy with DEC autoguiding.
It seemed random too, sometimes worked okay but more often it was useless no matter what I did.
So my solution now is to do as accurate polar alignment as possible (with the help of WCS and webcam).
This takes about 10 minutes before I star imaging and now I can skip dec autoguiding altogether and still have managed 4-5 min subexposures which is pretty much what I need in my moderately light polluted skies.


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DHB001
sage


Reged: 07/07/09

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Re: Another CG5-GT "spikes during guiding"-thread. new [Re: Tapio]
      #3816762 - 05/20/10 03:03 AM

*UPDATE*

It's been a while, but my laptop has been fixed and last night the weather was finally decent enough to do some testing. I apologize for the delay. As mentioned earlier, I wanted to see how guiding performance would be without the plastic washers that surround the aluminum worm gear.

My first bit of testing was on M51 , which is the object that caused me so much trouble with spikes a few weeks ago. M51 for me has now passed the meridian, but is still practically right above my head in zenith. The dreaded spikes in the dec guiding turned out to be still present, albeit nowhere near as frequent as a few weeks ago. So maybe removing the plastic washers has helped somewhat. Maybe not. I need to do some more testing to be sure. Although the frequency of the spikes has been lower, it was still not good enough for imaging, unfortunately.

However, when I later aimed my scope at M13, an object that is high in my night sky, but not as close to my local zenith as M51, guiding became extremely smooth. No spikes during the 30 minutes I tested (before I called it a night). Dec and RA guide graphs smoothed to +/- 1 pixel in PHD, which approximately corresponds to an equal amount of arcseconds (according to CCDcalc).

Hopefully, I can put in a little more testing in the coming nights. But the initial conclusion of last night was that omitting the plastic washers seemed to have made guiding less spikey in zenith, but still too unreliable for decent imaging. On the other hand, guiding in an area a bit further removed from zenith appeared to be trouble free (though admittedly, 30 minutes is too short for any definite conclusions).

To be continued...


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philming
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Re: Another CG5-GT "spikes during guiding"-thread. new [Re: DHB001]
      #4528470 - 04/19/11 08:39 AM

Hi there !
Very interesting post and test i may say.
Just a question. Did you have those spikes before removing the washers when shooting M13 ?
I'm in the process of regreasing my CG5 too, and was wondering about geting the Teflon washers.
What I have noticed when reassembling the mount was as follow : The two large washers you are refering too seem to hurt the rotation of the axis indeed. When puting it all back together, i did as i felt right : put one washer on top and at the bottom of the teethed crown. And it seemed like they wouldnt actually fit on top (ref. to your second picture). When reassembling the shaft in the housing, the washer would simply get crushed, it had been just to big.
I thought i had it wrong and was supposed to put both of them, on top of one other at the bottom of the shaft. Seemed right so far, but removing them alltogether might be a better idea.
That leads to another question : I have a very hard time reassembling this part. Seems like if I dont slide the axis very smoothly and very upright into the housing, it's going to get stuck, no matter how much grease I put on it. It's mostly the crowned gear that gets stuck, and is a real pain to remove. Did you notice that as well ?

Regards,

PS. Sorry off topic question. How can I get notified when a response is posted on topics I post in ? Haven't found the option so far...


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