PHD2 help - stable for a few minutes then goes crazy

[SiD the Turtle]

Hey all,

Looking for some help diagnosing this issue. Basically, my PHD2 guiding seems to be fine for a few minutes, then the guiding goes nuts in both axes and tries to do increasingly larger corrections. If I stop and restart guiding, again everything will continue fine for a few minutes before it happens again. The effect in my imaging is I get a few minutes of pin-sharp stars then a spiral around them. Here's the graph:

Kit as follows:

• HEQ5-PRO + Rowan Belt Mod
• Skywatcher Evoguide 50ED guide scope
• ZWO ASI 120MC-S guide cam
• Polar alignment via PoleMaster
• Guiding using Astroberry (ASCOM/INDI/KStars)

This problem has been happening for some weeks now. Things I've considered:

• I don't think it's the belt mod as it was occurring before I installed it and I've been looking for an excuse to mod- the only impact is that my guiding before it goes nuts is much better than it used to be.
• I don't think it's cabling as I have almost everything connected so it moves with the OTA, minimising moving cables.
• I don't think it's polar alignment as I'm using the PoleMaster and if I capture without any guiding, it's fairly good with minimal drift (obviously not good enough for taking a photo though).
• It's balanced well (I think), and besides I have the same issue with both my William Optics ZS73 which needs to be almost hanging off the mount to balance, and my Celestron 127MAK which sits nice and central.
• It's also a problem for targets straight up, close to the horizon and anywhere in between.
• The star mass and SNR seems fairly constant (or at least doesn't go nuts in time with the mount).
• My focusing seems fine too.

Any thoughts?

Edited December 26, 2020 by SiD the Turtle

[alan potts]

I am sure others know better than me but in my experience this is because you guide scope has moved or been moved and it need re-calibation. I have had the exact same thing about 6 times all told. Even when the scope was moved only a small distance fro where it was and I thought it wouldn't matter this happened, re calibrate the scope using your instructions which you can find in the help section.

Alan

[wimvb]

51 minutes ago, SiD the Turtle said:

Any thoughts?

Start with using the guiding assistant and use the recommended settings. Also make sure that everything is bolted down firmly, ie no movement between guidedcope and mount at all, and no finder guider in your finder shoe on the scope.

[almcl]

When did you last carry out a calibration? 

The graph reminds me one of where I forgot to calibrate at the start of the session.

[michael8554]

Screen grabs are often helpful. For example it's noticeable that Dec and RA are closely mirroring their movements.

Posting your guidelog, including a Calibration and Guide Assistant run, will provide much more info.

As Alan mentioned your guidescope, that model is on a wobbly finderscope-type mounting, that may be the problem (we're talking microns of wobble)

Michael

[valleyman]

Been getting the same problem with my ASIair. I swap the guide scope between Telescopes for imaging. After doing a Calibration it goes away and works perfect.

I do it now everytime before imaging. takes a few minutes but better that than get started with a sequence then have to stop to Calibrate

[michael8554]

3 hours ago, valleyman said:

Been getting the same problem with my ASIair. I swap the guide scope between Telescopes for imaging. After doing a Calibration it goes away and works perfect.

I do it now everytime before imaging. takes a few minutes but better that than get started with a sequence then have to stop to Calibrate

Indeed, changing the guidecam's orientation to RA and Dec will mess up the Calibration and hence guiding bigtime.

Michael

[Seelive]

10 hours ago, SiD the Turtle said:

 

That's a beautiful example of positive feedback - all OK until the first correction is made and then all hell breaks loose. Definitely a need for recalibration. (And I suppose it's a testimony to your belt drive mod that it's now a nearly perfect sinewave!)

[SiD the Turtle]

Thanks all, I bet it's calibration- I'd completely forgotten about that and in the last month I did get a new scope (the William Optics) and haven't re-calibrated since, it's got to be that! Just got to wait for clear skies here again in SE England.

Flexure is also probably an issue with the crappy mount that the ED50 has. The William Optics does have a kind of handle with a long saddle mount in it, I wonder if you get a compatible dovetail to replace it? I see if I were to buy the ED50 today it comes with one.

[TerryJ]

18 hours ago, SiD the Turtle said:

Flexure is also probably an issue with the crappy mount that the ED50 has. The William Optics does have a kind of handle with a long saddle mount in it, I wonder if you get a compatible dovetail to replace it? I see if I were to buy the ED50 today it comes with one.

I got a dovetail and rings from SVBony for my ED50 on WO ZS73.

 

[Stu Wilson]

Id go for calibration, I get the same on my NEQ6PRO with SW200p and Orion Starshoot Autoguider if I don't recalibrate every time out. Its fine if I do though.

Just made a Bahtinov mask for guidescope too and that's made a huge difference when focussed good. 

 

Stu

[SiD the Turtle]

Hey all, just wanted to bump this and say thanks, it was a simple as the calibration needing to be reset. My guide graph is now a lot more healthy, with an overall RMS of 0.74' on both axes!

Thanks to the weather I've only managed to get 10 subs so far, but the stars are round and Andromeda is surprisingly clear for my crappy suburban skies. Here's 10 subs stacked, stretched and de-greened. Looking forward to some clear skies to get a whole bunch more!