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Thanks guys! I suppose I could have looked this up but I was lazy.? This makes a lot of sense and 8x guiding rate for the adjustment is not quite instantaneous, but probably good enough. I hope folks don't too envious of me having ?5x more integers to work with, a tick in favor of smaller step sizes. ? So the long and short of it is my TVC value is equivalent to 20 in regular parlance.?

Peter

Brian,

As a representative of the manufacturer I appreciate that you responded to my two posts, but I would ask that you please read them carefully as you are in part providing your customers with I feel incorrect/imprecise information.? The backlash was measured via the Allen key method outline previously and did not involve PHD2.

If gravity plays a role then it in likely due to the needle bearing problem I outlined in earlier postings. I.e. Shifting of the Dec Axis due to a slop in the needle bearings sure to the weight and position of the scope. The shaft is out of spec for these bearings. These bearings where designed to be pressed into place. When done correctly the bearing ID is reduced slightly. The bearings are a light press (Scott himself has said as much). I pressed them in with my fingers! The shaft needs to be exactly 1.25". Mine is 0.004 to 0.006 under size this makes a big difference.?

Did you read read my explanation for how PHD2 works? Yes it does issue a single large pulse when reversing compensation, but it takes that amount of time to take effect. It does not matter if it dynamically adjusts through the night or session to session. It's irrelevant. If the backlash reversal pulse is longer than the guide imaging rate you have a big problem. This will undoubtably lead to instability within PHD2.

Lastly, you absolutely do not want to use a conservative value for TVC, you want to use the correct value. What do I mean by that? For those who use auto focus there is a curve where the minimum point on the parabola is the point of focus. This is true of TVC. Too small a value and backlash remains. Too large and backlash increases but in a negative way, which no doubt leads to the instability you noted. I think it's your job to study this in a precise meaningfull way. Replace my Allen key with a timing circuit. This way you can precisely measure TVC as a function of backlash. I see no reason why thus is not a fixed function. I take your point about being conservative as you do not want to be on the wrong side of the parabola. But setting an arbitrary, often too small a value, makes no sense in my opinion.

Look the backlash problem in my setup was due the excessive pressure put on the thrust bearings. This resulted in too much force needed to move the ring gear. This in turn forced considerable pressure to build in the gearbox and coupler resulting an uncorrectable large backlash. This was resolved with new thrust bearings and determining the correct value for TVC. Until I built my open worm assembly, where I had access to the various elements, I struggled to understand what was really going on, and certainly did not appreciate how important TVC was to eliminating backlash.

Peter