Tracking issues

[rubecula]

I feel that I've done something stupid so please don't laugh

The other night I was imaging at about 45 degrees above the horizon using PHD2 to control the tracking and dithering.  The scope seemed to be swinging backwards and forwards (see guide log PHD2_GuideLog_2016-11-29_182654.txt starting at 22.06.40).  I had understood that this was a backlash issue when imaging overhead so was surprised to see it when quite a way from the zenith. The mount was definitely east side heavy.

Under another subject I had been advised that shock cord could be used to put some tension between the axes so that there was no need to re-position the counterweights during a meridian flip. I assumed that this would help prevent this sloshing around.  I attached some bungy cord thinking that I had followed the instructions given, but now I'm not so sure.

Have I got the cord in the correct place?

I tried imaging with this set up the following night and it trundled along with some slight side to side movement and then the guide star suddenly shot off across the screen. (see log PHD2_GuideLog_2016-11-30_183317.txt starting at 19.01.12)

The guide star was quite feint, could this be the issue or is it because I've put the cord in the wrong position?

Thanks

 

[cjdawson]

I'm no expect when it comes to this. so I could very well be wrong...

looking at that picture, my first thought is - is there enough play in the bungie to allow the RA axis to move freely over the whole session?

I get that the idea is to provide a little pull, but if that bungee rungs out of spring, it'll be rock solid.  This will bind everything up, and might even cause the gears to be stripped.

[SonnyE]

I'm always interested in PHD2 and guiding posts, it furthers my understanding of the program and process.

While I use a refractor myself, I use PHD2 and a guide scope and camera. The other night while dabbling about with the time in PHD2 I noticed that if I set the time at 3 seconds, I got wider RA swings in the target window. Last night I upped the time from my 1 second setting to 1.5 seconds and noticed a widening of my RA again, though not as wide as 3 seconds. (Seemed natural, linear) So if you might be running a wide time frame, possibly it is confusing the issue.

I use a naturally tail heavy balancing, and a slight East heavy (I believe, or West) balancing. Those off-sets from "Perfect Balance" gives my gearing a preload under most conditions, simply by gravity. No bungies to befoul the nights pleasures.

My goal has been to be able to do remote operation. So my wiring and cabling are loomed and adjusted to run with my equipment, and to stay out of the way of binding or fouling.

So try and have gravity work with you, and for you.

 

 

 

[rubecula]

CJ - you're correct that is completely wrong, but I'm not sure what the right way is using a bungy cord.  I've found another idea on a different website that involves hanging a weight on a string over the east side of the scope.  This also provides a constant pressure to keep the RA gear constantly engaged and so prevent backlash issues.

SonnyE - the idea in tensioning the RA gears this way is to avoid having to re-position the counterweights after doing a meridia flip.

[SonnyE]

On 12/4/2016 at 03:31, rubecula said:

CJ - you're correct that is completely wrong, but I'm not sure what the right way is using a bungy cord.  I've found another idea on a different website that involves hanging a weight on a string over the east side of the scope.  This also provides a constant pressure to keep the RA gear constantly engaged and so prevent backlash issues.

SonnyE - the idea in tensioning the RA gears this way is to avoid having to re-position the counterweights after doing a meridia flip.

I have yet to need to readjust my counterweights at all. Pre-Meridain or Post-Meridian flips.

In fact, the only requirement I've had was to close PHD2, and open the program new and start it up per usual.

As soon as PHD2 has done it's run through Post-Meridian, everything continues just like before. Except now my Image is 180 degrees from the Pre-Meridian.

If the telescope is in balance before Meridian, it will also be the same Post-Meridian.