Weird PHD graph and ruined pictures.

[Datalord]

Tonight I had a bit of frustration happen with a weird symptom I have never seen before. I polar aligned my mount, did a new pointing model with Celestron PWI and everything seemed normal. Then I started shooting.

first this happened:

Then I did a new pointing model and started over:

Same odd spike. I've watched and it doesn't come at fixed interval, so it is seemingly random, happening from anywhere between 20s to 2 minutes apart.

The shape looks so alike in all these pictures I can't help feel that this is some known issue, maybe a feedback loop gone haywire?

[kens]

Most likely a mechanical problem. Cable drag would be something to look at first. A picture of your setup might offer some clues

[Datalord]

Drag sounds odd. As you see from ra, the lines drastically jumps from middle, to one side humours all the way to the other and then slowly settles. With drag it would just be a constant, no? 

[drjolo]

I would also say it is some mechanical problem. Could you describe / picture your setup? Does this first jump always start in the same direction?

[Adreneline]

Morning!

I had exactly the same type of graph a couple of weeks back following a rebuild/belt-mod of my NEQ6 mount.

One of two things fixed it - it was either me adjusting the backlash on the DEC drive or it was tightening the DEC drive shaft, where in an attempt to not overtighten the bearing I had not tightened it enough and it developed axial play. Either way it was a mechanical problem which gave rise to a plot exactly like yours.

HTH and good luck trying to sort it out.

Adrian

[Datalord]

16 minutes ago, Adreneline said:

Morning!

I had exactly the same type of graph a couple of weeks back following a rebuild/belt-mod of my NEQ6 mount.

One of two things fixed it - it was either me adjusting the backlash on the DEC drive or it was tightening the DEC drive shaft, where in an attempt to not overtighten the bearing I had not tightened it enough and it developed axial play. Either way it was a mechanical problem which gave rise to a plot exactly like yours.

HTH and good luck trying to sort it out.

Adrian

Good grief, I really hoped this would not be the case. It's a year old CGX and this started happening just last night.

1 hour ago, drjolo said:

I would also say it is some mechanical problem. Could you describe / picture your setup? Does this first jump always start in the same direction?

 I'll take a picture today and post it. Yes, always exact same way.

[Stub Mandrel]

It starts with a big deviation in RA, not DEC so it isn't DEC backlash.

IT looks like sticky RA, particularly as the correction overshoots so much.

This could be a catching, rather than dragging, cable. It could also be the guidescope moving.

[Datalord]

1 hour ago, Stub Mandrel said:

It starts with a big deviation in RA, not DEC so it isn't DEC backlash.

IT looks like sticky RA, particularly as the correction overshoots so much.

This could be a catching, rather than dragging, cable. It could also be the guidescope moving.

I went out to look at the scope to take a picture and in the daylight saw a cable caught in the mount. DOH!

I really hope this is the problem and not something internal to the mount. I'll follow up when I shoot tonight.

[Stub Mandrel]

1 hour ago, Datalord said:

I went out to look at the scope to take a picture and in the daylight saw a cable caught in the mount. DOH!

I really hope this is the problem and not something internal to the mount. I'll follow up when I shoot tonight.

Bet it is!

If you use sigma clipping in DSS (and not all subs are affected) it will do a good job of hiding the defects, especially if you can add some more unaffected subs.

[Datalord]

Sadly, no, that didn't solve the problem. Still seeing this. I have tested a few other things without resolving the issue. Definitely no cables caught anywhere tonight. I started the night with a new PA and point model, just because why not.

The two main differences between last night and the one before where everything worked (on the same target):

1. I changed my cameras power supply from a separate to use my Pegasus Ultimate Powerbox. I changed it back tonight. No difference.

2. I changed my guidecamera position to improve focus on it. I re-checked all screws and everything is tight. 

Other things I tried was:

Gently hold onto to the counterweight for a second. Produces this exact graph.

Pressing slightly on the guidescope, produces this graph.

Changing PHD from 2 seconds to 1 second. Drastically reduces the frequency of this happening, but doesn't eliminate it.  <---This one has me baffled.

I'm out of ideas of what to try and pretty desperate. I don't want to open the mount to do anything in there, so I'm looking to anything I can try to eliminate or rule out the possibility of the mounts internals having a problem. Any ideas out there?

 

 

 

[michael8554]

You can see in both your graphs that RA shoots off due to a mechanical or power problem, because PHD2 corrects after the event, it isn't PHD2 initiating the event.

Could be the hot weather tightening up your clearances ?

What was your PHD2 Calibration like ?

Picture of your setup?

Michael

[Stub Mandrel]

Silly thought - the tripod isn't on grass or some other surface such that standing by a tripod lg causes that problem?

When I'm doing planetary imaging it's scary how far you can deflect the image by standing near a tripod leg.

[Datalord]

2 hours ago, Stub Mandrel said:

Silly thought - the tripod isn't on grass or some other surface such that standing by a tripod lg causes that problem?

When I'm doing planetary imaging it's scary how far you can deflect the image by standing near a tripod leg.

It's a fair question. The tripod is standing on tiles and is quite stable, so I don't think that is the issue.

14 hours ago, michael8554 said:

You can see in both your graphs that RA shoots off due to a mechanical or power problem, because PHD2 corrects after the event, it isn't PHD2 initiating the event.

Could be the hot weather tightening up your clearances ?

What was your PHD2 Calibration like ?

Picture of your setup?

Michael

Sigh, yeah, I'm pretty convinced it's something internal by now. I guess it could be the heat, the summer has been hot and my shed is not exactly equipped with AC. One thing I haven't tried is plugging the mount into its own powersupply. I'll try that tomorrow to rule out power funk.

Now, a picture of my setup. Don't lose your mind, this is supposed to be a temporary setup until I get my 12" RC, so there is clutter. The green stuff is a weight to balance off the camera. I have checked over and over that the cables are loose and things are free to move.

If this turns out to be something I can't just fix, is this something for the warranty? It's 11 months old.

[kens]

Looks like flexure central. The adjustable rings on the guide scope are notorious. See if you can replace them with solid rings. And cables hanging off the end of the OTA have a lot of leverage. Lets say the movement was 10". That is equivalent to 50 microns at 1 metre so over 300mm or so it needs only 17 microns movement. Try routing the cables along the axes

[michael8554]

Intermittent power loss is a possibility.

I would make a short loop  of the power cable from the power socket and tie that off so that the plug can't move as the mount tracks.

I agree with Kens, a 50mm guide scope and a ZWO 120MM doesn't  need adjustable guide rings. Pretty much my setup, I've a!ways got plenty of guide stars wherever the main scope is pointed.

But going back to your original post, investigate what you've changed since your run of successful guiding ended.

Michael 

[Stub Mandrel]

34 minutes ago, michael8554 said:

I agree with Kens, a 50mm guide scope and a ZWO 120MM doesn't  need adjustable guide rings. Pretty much my setup, I've a!ways got plenty of guide stars wherever the main scope is pointed.

+1 on one setup I have very rigid rings (actually a tube) but on my other guidescope is permanently aligned in a clamshell.

[Datalord]

Hmm, 17 microns is indeed quite small. I just can't for the life of me understand why it would happen like this. The guidescope is tightened and very stable.

I'll try the power and change the cable routes tonight.

[Datalord]

Ok, "tonight" turned out to be almost a week later due to the fabulous British skies (including blocking the bloody lunar eclipse ?).

Anyways, in one hour I haven't seen the issue yet. I have changed the cable routing, didn't change the power cable.

But one thing I also did was to change the weights. It was perfectly balanced before, so I moved the counterweight a little bit, so it was a tiny bit leaning into the gears at all times while shooting the Veil. However, this is not a long term solution, as I want this to be capable of 100% remote capability, so I'll have to test this out again sometime soon.

 

EDIT: While I wrote this post, it happened twice. Unbelievable...

[Dragon_Astro]

Strangely my heq5 has started to do something similar with PhD too, but only in RA.

Its never done it before and my cable set up is always the same, but now it's started suddenly shooting off the graph in RA and setting back down again. The last time I was out imaging it happened twice within the 10min sub I was doing at the time.

My heq5 is quite a few years old now, I'm wondering if it's in need of a regrease? Or a belt mod hehe

[Datalord]

Well, I contacted the seller to lament my trouble. In turn I got some pointers to check from the UK Celestron technician, which I fumbled around with. Firmware updates, power supplies etc, neither of which fixed the issue.

Yesterday evening I went out to try some more and the mount was dead. Stone cold dead. Bricked. Nothing worked at all. So I guess these problems were an indicator of something worse to come. I am now officially unable to do anything... ?

[Stub Mandrel]

You say 'bricked' - does the power light come on? Your issues could well be caused by a poor connection somewhere in the power lines.

That said, if it's an issue inside the mount, definitely a warranty job!

[Datalord]

5 hours ago, Stub Mandrel said:

You say 'bricked' - does the power light come on? Your issues could well be caused by a poor connection somewhere in the power lines.

That said, if it's an issue inside the mount, definitely a warranty job!

My other equipment on the same main power line is working fine, computer, camera etc. And I tried multiple sources, so yes, warranty it is. I can only dread the mess I have to go through to ship 50kg...  ?