Yes I've got an Argo navis on my 12" GSO dob (as per my tagline below) and yes it is a winner!
I have had some probs occasional with various grub screws, locknuts, etc, slowly working lose so that in the middle of a nights observing such that I'll suddenly find alt or az tracking "skipping" but I've sowly been gwtting all of these undder control as they occurr. I want to add that none of these issues are probs with the Argo Navis itself but rather poor maintenance (by me) of things that need to be kept "tight".
(I bought this as a 2nd hand package with the AN pre-installed, I didn't install it as such so I'm still coming to grips with these things. I've said this before but I think I have it all by the agates now.
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I'm at work at present, but will post some images when I can. I have the AN unit itself mounted up near the focusser using nothing more elaborate than good old velcro.
I've also found that the azimuth encoder cable which runs down past the eyepiece rack can get itself tangled up and caught tight under the edge of the rack - by running it literally through the fabric loop on the end of the tensioner spring and then over the right hand end of the ep rack it remains in place and does not foul up at all even when moving the scope through the entire altitude range repeatedly.
