It's been quite a while since I could say I had a flawless night of imaging...but, I can say it again: Last night was flawless! I have been having some odd balance issues with my setup for a while. I used to use a counterweight on a string wrapped around the mount to the east side. That worked great for a while...then stopped working at all. Never understood why, but since losing the ability to do that, I've had to deal with balance issues. It seemed as though the right balance point was always changing, so I had to fiddle around with my counterweights on each side of the meridian each night until things stabilized and I stopped losing subs to jumps and drags. That's been the case for, well, most of this year. A bit last year as well.
I tried adding the additional weight-on-a-string again a couple of nights ago. I really like that particular solution, as it keeps the mount east-biased without me actually having to fiddle with the counterweights. It would also make automated meridian flips possible...something I really want to work, so I can sleep at night while my sequences run (at the moment, every time I flip, I have to go out and readjust the counterweights to get back to east bias again, otherwise I lost the majority of my subs to stars that either jump around or drag across the frame). At first the additional weight did not seem to work at all...so I added some weight (each on is only 2.5 pounds, started with just one), and it seemed to be far too heavy. I tried different kinds of strings...nylon and other polymer strings stretch and bounce, so I was trying twine and other non-stretchy materials. I think the strings were snagging or binding along the mount, so it just wasn't working. My payload isn't all that heavy...from what I can tell, it's 13-14 pounds (down from nearly 20 pounds back when I was using the Orion ST80 for my guide scope), and the mount capacity is 45 pounds. The payload is a bit "oddly shaped" though...it's got a long arm and a motor on the end for the focuser, then a shorter arm with the USB hub on the other side. It doesn't exactly balance well in DEC, but it seems to balance fine in RA. Anyway...still no luck with the weight on a string.
Last night started out...disappointing. It LOOKED like I was going to have problems...my dec axis would deviate out about 2" from the mean periodically...about once per sub. I was about ready to take a sledgehammer to the whole mount and just pound it to pieces, but I noticed that my subs did not seem to be picking up the deviations...the stars looked fine. My RMS was 1.05". Far from the worst I've had, but not my historic norm of ~0.6". There were light gusts last night, and it may have been that those gusts were affecting the mount, given the direction I was pointed in early in the evening. I decided to let it go....and....somehow, maybe the wind died off, it worked itself out. The deviations stopped. My guide graph flattened out, dropped to an RMS of 0.65" after about an hour. I did not lose one single sub last night...and managed to acquire 100 of them, 20 on one object, 80 on another, three minutes each. That's almost six hours of subs (factoring in time for the periodic dither and hourly autofocus), strait from twilight to twilight (well, after twilight in the AM, I may actually lose a sub or two to dawn! ) I can't say that I've had a night that just...ran, on it's own (barring the meridian flip and manual counterweight rejiggering), from dusk till dawn, in a very long time.
I suspect the balance and tracking issues will return, it's been my bane this year with AP. I'll probably have to tear the mount apart and rebuild it again at some point...or maybe I'll finally break down and drop seven grand or so on a high end mount. For now, though, I'm hoping my newfound smooth tracking persists, and allows me to get subs reliably throughout the next few clear nights (we are supposed to have a couple over the next week).