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Troubleshooting a wayward guider


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I've had a chronic issue with my guiding setup that I haven't heard others bring up, but ... am wondering if someone has encountered this kind of behavior and how they addressed it.

I've have a pretty middle-of-the-road AP set up (see sig for specs). For the most part, I have no trouble guiding: that is, when the guiding is working, it works well enough. Reasonably tight round stars, etc.

However, every 90-120 minutes or so (on average), the mount will suddenly plunge off along the DEC axis: usually moving north, I think. It's moving so fast that I can see the stars moving between exposures in PhD2 (every 3 seconds). It'll keep moving until I unplug the cable between the laptop and the guider. Just stopping guiding in PhD2 or disconnecting (in PhD2) the guider and mount has no effect: I have to physically pull the cable out of the laptop. PhD2 knows there is a problem: before it loses the guide star it is desperately trying to push the mount back, to no avail. After 10 minutes of swearing and getting things in frame again, I can continue taking exposures, but I've lost 20 minutes of precious time. Worse, at this point, it's preventing me from just letting things run for a few hours on their own so I can take a nap and be more functional in the morning, with more photons collected as well.

I've tried replacing both the cable from the laptop to the guide camera and the camera to the mount (an ST-4). This winter I thought it was the cold, and the problem did seem to subside this spring, but it's come back with a vengeance recently. Most recently, I've noticed that it seems more likely to happen after a big RA dither, but last winter I wasn't dithering at all and still having issues.

Has anyone seen behavior like this before? Short of starting to replace expensive things (laptop, guider, mount), any other ideas what to try?

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Hi

Not sure if I can help - something going wrong after such a long period of ok running could be tricky to diagnose! First thought is a power interruption - are you powering from a battery or via mains? One thing you could try is running your setup unguided just to monitor it's behaviour without phd. Are you running the latest version of phd2? What does the log show when it goes wrong? Do you have mount limits set? How are cables run - any chance of snagging? I guess it's going to be a bit of trial and error...

Louise

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Thanks for the ideas. I'm 99% certain it's not the meridian: in the clear stretch we had at the end of June I was imaging the Veil which is well east of the meridian and having issues. I'm fairly certain it's not cable drag or the scope colliding with the mount ... but have wondered if the cables are wiggling slightly on the laptop side, where it's a loser fit.

I run on mains ... hadn't really thought of that potentially being a problem but maybe I should. One thought I've had is to get an uninterruptable power supply (like the kind you might get for your home or work computer) and run things off that. If I understand UPS's correctly, they deliver a smooth power by powering things directly off a battery (whether the main supply is live or not), which should eliminate fluctuations in current.

I'll look into PhD2 and the logs as well, though I'm less suspicious of it because it seems to be aware that things are going off track. It seems like somehow the mount is getting a continuous signal to move north, overriding whatever PhD is telling it.

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It still sounds like a connection issue to me, and there are 4 parts to each cable (plug & socket on each end) where the problem may lie. A little squirt of some anti-corrosive agent might help. The other possibility is internal to the mount - connections between controler and motors..

ChrisH

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49 minutes ago, Joel Shepherd said:

Thanks for the ideas. I'm 99% certain it's not the meridian: in the clear stretch we had at the end of June I was imaging the Veil which is well east of the meridian and having issues. I'm fairly certain it's not cable drag or the scope colliding with the mount ... but have wondered if the cables are wiggling slightly on the laptop side, where it's a loser fit.

I run on mains ... hadn't really thought of that potentially being a problem but maybe I should. One thought I've had is to get an uninterruptable power supply (like the kind you might get for your home or work computer) and run things off that. If I understand UPS's correctly, they deliver a smooth power by powering things directly off a battery (whether the main supply is live or not), which should eliminate fluctuations in current.

I'll look into PhD2 and the logs as well, though I'm less suspicious of it because it seems to be aware that things are going off track. It seems like somehow the mount is getting a continuous signal to move north, overriding whatever PhD is telling it.

Hiya

Yeah, you've reminded me now - I've actually had similar problems (but had forgotten!) with my laptop usb connection. In the end I tightened things with the aid of a small folded piece of card to wedge the connector fairly tightly, and also used a short flying lead with a female connector so that I didn't have to mess with the dodgy connection at the laptop end :)

Louise

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  • 2 weeks later...

We finally got a reasonably clear night tonight (with more on the way in a couple of days), so @Thalestris24 I took your suggestion and wedged the troublesome cable's end into the laptop with a narrow piece of folded card stock. That may have done the trick: I was able to take dithered lights continuously for two hours, with only one hiccup (a camera disconnect, which is infinitely better than the mount launching off in some unexpected direction). Much better than the last few attempts, and gives me hope that I might be able to catnap at some point without risk of losing hours of clear-sky time.

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I'm glad you seem to have (hopefully) found the source of the problem.  After many hours of swearing and hitting things, I've come to the conclusion that the biggest single source of issues surrounding astrophotography is USB.  Cables, sockets, drivers, chipsets, hot unplugging - it's all a nightmare.

One solution to your problem may be to run all your USB connections through a single high quality powered USB hub, connecting the hub to a USB socket on your laptop that isn't giving you problems .

Just to make sure, could you knock up a little jig that holds the USB cable in a fixed position relative to the laptop?

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Yeah, at work I'm always the guy in the back muttering "VGA. VGA. VGA." while people struggle with their HDMI or teensy-whosey-whatsit connector that sometimes connects and sometimes doesn't. VGA had those nice little thumbscrews on the side, so you could tighten the connector down and be sure it didn't budge no matter how much you shoved the desktop or laptop around. Solid. Dependable. Not USB.

Anyway ... Would you (or anyone) have a recommendation for a good quality powered USB hub? One for which there is some evidence that it'll function smartly at sub-freezing temperatures with high relative humidity? :-)  I'll whine a bit about having to run more power out to my site in the garden, but significantly less than about the mount lunging off on its own.

With regards to a jig, regrettably my fabricating skills aren't great. The bit of folding card stock gave reasonable results, and I can live with that for a little while until some better hardware is available. Until then ... what is that better hardware?

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5 hours ago, Joel Shepherd said:

Thanks @sloz1664: do you use that with an external power supply or do you power it off your laptop's USB? Also, do folks have particular cable brands they'd recommend?

Hi Joel,

 

It is a 12v powered hub, which I use from an external power supply in my obsy, but can be powered from a 12v source out in the field. I have had issues in the past where hubs have had insufficient power to drive all my equipment. This hub has not let me down.

Steve

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