AVX Guiding Performance

[Freddie]

If it moves back south immediately it's obviously not backlash then. As PHD will send the same calibration step commands for south as it did for north you do have something very odd going on there though. 

[libraryman]

As Freddie said, 1st thoughts would be backlash, however there is the possible cause as PA...if pa is out then your star would be moving North...then when calibration asks it to move South; it is unable to fully overcome the drift North and will therefore be slower!

Backlash is an odd thing to deal with, it can appear that very little movement is detectable but....it can still be evident in calibration and guiding!

The best way to measure it is to use the guiding assistant at Dec zero just East of the meridian where you would calibrate.

However a front or rear heavy scope can confuse it a little as it will absorb some backlash!

Ray

[Rob63]

My PA is pretty good - I do 2star alignment + 2 calib stars followed by aspa, then I go to home pos, switch off and repeat.

After this I do a drift align with PHD2 and get my dec trendlines pretty flat.

I am thinking balance could be the issue as an ED80 with a reducer and DSLR is pretty camera end heavy!  With the medium length dovetail it cannot move forward enough in the saddle to be well balanced. I guess I could try and add some weight to the other end or try calibration with no camera or reducer in place.

I will give the guiding assistant a try and see if I can get anywhere by increasing my calibration steps.

Rob.

[Rob63]

Ok, I think I have got to the bottom of this. I took the cover off the Dec drive but had the scope loaded up as normal so I could watch the gears during operation.

I used PHD2 manual guide to send pulses and kept a close eye on what was happening.

There was no issue with backlash at all, when I pressed north it responded immediately after a few “norths” I pressed South, again, the response was immediate. All very confusing.

I then slewed the mount at a higher speed to have the scope facing 180 degrees to my first tests then I adjusted north a bit then south….. nothing happened on the south slew!

The Dec lock needed a bit more tightening than I had given it and once done it slewed ok.

I had always tightened the locks (I don’t believe they are true clutches on this class of mount) to the point where I would feel resistance and then give it a little bit more, never wanting to over-tighten. It seems this is not enough for my AVX.

I managed a quick test through the window (finally getting a small gap among all the clouds and rain last night) with my tighter setting on the Dec lock and surprise, surprise the south run worked as expected.

Needs a proper field test of course which, looking at the weather forecast, isn’t going to happen any time soon. However I am pretty confident that this is the solution.

A bit of a pain for something so trivial but at least I have a better understanding of how the mount works and I also know I have very little backlash.

Rob.