Guiding Dec is going Mad

[johnb]

Hi

Using kit in sig and my guiding which is normally fine is really odd, RA is perfect but Dec keeps wandering off the screen, head downwards, ive checked cables etc and there is nothing catching - any ideas, its a perfect night and I hate to lose time

John B

[Sparrow]

I had this problem on a reguilar basis and in the end found that I just wasn't geting my polar alignment close enough. By tweaking the declination to increase it slightly, it solved the problem. It would appear that PHD can only cope with a small misalignment before it begins to struggle and fail to correct DEC.

Regards

John

[rocketandroll]

Mine was doing that... turned out I had a dead pin (pin 6) in the ST4 port on the mount. Not sure that helps if it was working before... or the following morning... but might be worth a look if the problem persists?

Ben

[johnb]

Thanks. Will look at that. John b

[JohnC64]

Hows the balance of your mount?. Since following the advice to balance the scope in both horizontal and vertical directions my PHD Guiding has improved no end.

John

[Shibby]

I hope you don't deem this a hijack John, but I was about to post a new thread about a similar issue, then I saw your thread.

My guiding is going funny also in the Dec direction, resulting in several raw subs such as the attached.

PHD just doesn't seem able to correct the error, which I can only assume is some kind of backlash as it's always a sudden movement creating 2 seperate star images.

I don't know about you John, but for me the guiding is perfect for about 20 minutes at a time then the error occurs. (/goes to watch the balancing video)

What are people's opinions on guiding in RA only? Worth a try?

[JohnC64]

Hi Lewis,

I have had a similar problem with the mount jumping but only on *very* cold nights when my mount is cooling down. Its almost as if the cold is causing something in the mount to contract and then there is a sudden jump (bit like the pipes creaking in the central heating when you turn it off). can only think its the ascension bolts jumping against the tab

It has only happened twice and both sub zero nights. and it stops happening after 40 mins. PHD corrects though but i end up with a sub with the stars in two positions and a faint line in-between

Cheers John

[Starflyer]

I've been struggling with this recently too, PHD just doesn't seem to be sending long enough pulses and DEC ends up drifting. I was out on Saturday and experienced the same problem, max DEC was set at 400ms but it was sending 15 - 25ms North pulses and it was still drifting. I was quite well polar aligned but there was a slow drift with the guiding off. I tried calibrating three times at different calibration step settings, but it was still the same each time.

I found a workaround that worked for me, maybe worth a shot if you have DEC drift. I use an EQ6 pro, EQMOD, PHD and use pulse guiding by the way.

Set the guide rate in EQMOD to 90% in RA and 30% in DEC, calibrate and start guiding as normal, the calibration in DEC will take longer so make sure your calibration step is high enough for it to complete, but not so high that you don't get enough steps in RA.

I started guiding again and it was drifting as described above, I then increased the DEC guide rate to 50%. This gave less drift - my thinking being that the actual DEC guide rate was now higher than the calibration data thought it was, another tweak to 70% and the DEC guiding was spot on.

This worked throughout the night for me, but I know in this game you haven't found a fix until you can repeat it for a few nights

Cheers,

Ian

[Starflyer]

PHD just doesn't seem able to correct the error, which I can only assume is some kind of backlash as it's always a sudden movement creating 2 seperate star images.

A sudden movement is usually backlash, wind or a cable snag. To help combat DEC backlash slightly unbalance in DEC and guide DEC in one direction only. ie. choose North or South from the DEC guiding options depending on which way your DEC graph is drifting.

[Shibby]

Thanks very much for the tips John and Ian, that's all very interesting and useful info. Next time, I'm going to take the time to work on improving the balance and experiment more with the PHD settings.