Hey Roger,
Yeah, it's truly frustrating!
I finally enabled focus convergence in FocusMax the other day, with 2 steps and 10 samples. That is working even better than the usual standard focus run. It takes a bit longer, but, I'm constantly hitting HFDs of 1.4-1.7 on 4th-5th magnitude stars. That's with a RoboFocus step size of 2, as well. I suspect if I decrease that to 1, it might get even better. Now with the Moon nearing full phase, I might spend a night recalibrating with a step size of 1.
The thing that annoys me, as I mentioned in your thread, is that this has been a staple setup for FSQ/STL owners for ten years. I read nothing but positive things about it and just can't work out why I'm having these dramas. Rally emailed me with suggestions about slippage due to gravity which makes perfect sense. His suggestion of buying a bigger focuser also makes sense. Just need to wait until the funds allow such big purchases.
All I can do is tighten down the system even more than it already is. I initially noticed that when the focuser was sitting in the supplied bracket, when turning the focus knob, the whole assembly would oscillate up and down. This was likely because the bracket was sitting at an angle. I loosened everything and manually turned the knob and let the RoboFocus motor and the bracket find a happy spot where there was no more oscillation. I slowly began tightening the bracket to the base of the focuser and kept turning the focuser knob to make sure there wasn't any oscillation after each turn. This has helped a lot -- making me get down to losing 5 position units per focus run, as opposed to hundreds.
I'm now thinking that I might get a local sheet metal fabricator to make me a new bracket out of 3/16" aluminium which will get bolted down on to the finder scope bracket. The bracket base is at a 45 degree angle and it should be quite easily to manufacture and mill a bracket. This might help solve my oscillation problem, too. The supplied bracket from TI was not 90 degrees square. It's slightly acute. I emailed TI asking to buy another bracket but haven't received a reply. Will just design my own and get the local place to fabricate it for me.
H