A question about PEC

[barx1963]

I am using an Orion Atlas AZEQ G mount (same as the SW AZEQ6) with guiding via an Atik OAG and Atik GP guide camera, software is SGP for image acquisition, PHD2 for guiding and CDC/EQMOD for mount control.
I have been happy with my guiding generally but have noticed a distinct periodicity in the guide graph with an obvious cycle in RA. So I decided to try PEC last night. Just ran the auto PEC routine in EQMOD as a starting point and the improvement was obvious. For the first couple of hours, my guiding was running at between 0.5" and 0.6" RMS (previously it was usually around 1.3") and that was with a few lurches caused by the dither routine.
I did notice that as my target approached the meridian, the performance dropped until it was no better than I had been achieving without PEC activated. I had set up my mount so it was slightly unbalanced (scope pointing east so moved a counterweight down)
Any thoughts?

Malcolm

[glend]

The effect of " east side heavy unbalance" on worm and ring meshing diminishes as you approach the Meridian tipping point and thus worm and ring gear slop is more likely to show up in your graph. I had the same issue with my NEQ6 (belt mod) mount, the graph would deteriourate near or just on/after Meridian. Other than tuning out worm end bearing play, and careful mesh clearance setup without binding can help, not much more can be done about it in those mount designs. Perhaps a total belt drive mount like an Avalon Linear may avoid it, but any retained gear facing system has the possibility of slop ( although spring loading the worm (like in the new CGX), are innovations designed to eliminate it). I will let you know what i find when i get my CGX setup.

[peter_4059]

You could try making it a bit more east heavy so it is still east heavy as it approaches the meridian.

[Camelopardalis]

But how much east heavy is heavy enough :help:

[barx1963]

Thanks guys. I suspected it was the case, which was why I mentioned the unbalancing. I had worked out that I could run a fair way past the meridian, but looks like I am going to have to work out how to do painless meridian flips next!!

Cheers

Malcolm

[Camelopardalis]

I usually balance mine so that's it's balanced...guiding generally in the region of ~0.4-0.5 px rms. Next time I'll have to try it east heavy a bit and see how it runs...

[peter_4059]

I normally set mine so the counterweights overcome stiction in the RA bearings (clutch released) in all orientations of the CW shaft - ie horizontal to near vertical.

[Camelopardalis]

Thanks Peter...next time the clouds part I'll give it a go :thumbsup: