Another CG5-GT "spikes during guiding"-thread...
Posted 26 April 2010 - 02:18 AM
Posted 26 April 2010 - 03:13 AM
Which parts required polishing?
And does it work for you now?
Posted 27 April 2010 - 03:37 AM
I have spend some time last night guiding both east and west, and this time I watched carefully the messages in PHD. My graph would alternate between smooth, spikes and DEC drifting away until disappearing all together, and it is all consistent with the same problem.
Doug is completely right, and this is in fact an identified problem , its called "stiction" and is detailed on the PHD forum. Basically at some point and for mechanical reasons, the DEC axis gets "stuck". If you read the log messages, PHD tries to correct the drift by gradually increasing the length of the pulse. I had my max set to 350 and this was not enough - as a result, the DEC graph would slowly drift away from the graph (how slowly depends on your polar alignment), with PHD desperately logging "S= dur 350ms" and unable to do anything about it. I then increased the max to 1000ms. As a result, when it reaches about 700-800ms it finally manages to "unstuck" the dec axis and wham! - it throws it to other side of the line, usually this is because the inertia of the unblocking axis who's been accumulating momentum. Sometimes its stuck less bad, and it manages to release it once it reaches about 400-500ms.
Solution: NONE with the software. In my case is still under warranty, so back it goes, but I imagine its what Nonni said, relubing, polishing, and also possibly changing any bits inside that might have deformed (anything plastic sound like a candidate for me )
I hope this helps.
Posted 27 April 2010 - 04:44 AM
I have a HEQ5 Pro and I wasn't too happy with DEC autoguiding.
It seemed random too, sometimes worked okay but more often it was useless no matter what I did.
So my solution now is to do as accurate polar alignment as possible (with the help of WCS and webcam).
This takes about 10 minutes before I star imaging and now I can skip dec autoguiding altogether and still have managed 4-5 min subexposures which is pretty much what I need in my moderately light polluted skies.
Posted 20 May 2010 - 02:03 AM
It's been a while, but my laptop has been fixed and last night the weather was finally decent enough to do some testing. I apologize for the delay. As mentioned earlier, I wanted to see how guiding performance would be without the plastic washers that surround the aluminum worm gear.
My first bit of testing was on M51 , which is the object that caused me so much trouble with spikes a few weeks ago. M51 for me has now passed the meridian, but is still practically right above my head in zenith. The dreaded spikes in the dec guiding turned out to be still present, albeit nowhere near as frequent as a few weeks ago. So maybe removing the plastic washers has helped somewhat. Maybe not. I need to do some more testing to be sure. Although the frequency of the spikes has been lower, it was still not good enough for imaging, unfortunately.
However, when I later aimed my scope at M13, an object that is high in my night sky, but not as close to my local zenith as M51, guiding became extremely smooth. No spikes during the 30 minutes I tested (before I called it a night). Dec and RA guide graphs smoothed to +/- 1 pixel in PHD, which approximately corresponds to an equal amount of arcseconds (according to CCDcalc).
Hopefully, I can put in a little more testing in the coming nights. But the initial conclusion of last night was that omitting the plastic washers seemed to have made guiding less spikey in zenith, but still too unreliable for decent imaging. On the other hand, guiding in an area a bit further removed from zenith appeared to be trouble free (though admittedly, 30 minutes is too short for any definite conclusions).
To be continued...
Posted 19 April 2011 - 07:39 AM
Very interesting post and test i may say.
Just a question. Did you have those spikes before removing the washers when shooting M13 ?
I'm in the process of regreasing my CG5 too, and was wondering about geting the Teflon washers.
What I have noticed when reassembling the mount was as follow : The two large washers you are refering too seem to hurt the rotation of the axis indeed. When puting it all back together, i did as i felt right : put one washer on top and at the bottom of the teethed crown. And it seemed like they wouldnt actually fit on top (ref. to your second picture). When reassembling the shaft in the housing, the washer would simply get crushed, it had been just to big.
I thought i had it wrong and was supposed to put both of them, on top of one other at the bottom of the shaft. Seemed right so far, but removing them alltogether might be a better idea.
That leads to another question : I have a very hard time reassembling this part. Seems like if I dont slide the axis very smoothly and very upright into the housing, it's going to get stuck, no matter how much grease I put on it. It's mostly the crowned gear that gets stuck, and is a real pain to remove. Did you notice that as well ?
PS. Sorry off topic question. How can I get notified when a response is posted on topics I post in ? Haven't found the option so far...