Derek,
I think you misunderstood what I said. Using the Allen key method, I measured the backlash at around 2sec by counting. I then found the appropriate TVC value to completely eliminate the backlash per what I could see. The Allen key method is very precise. Even a fraction of rotational movement is detectable visually. There is no involvement of PHD2. For the record, The 2.5s measured backlash in PHD2 was from last week before I changed out the thrust bearings and devised the Allen method to make measurements during the day and figured out the correct TVC value.
I'm think this argument that PHD2 cannot measure the backlash on the SLW is highly dubious. Backlash is backlash after all.??I would suggest to Losmandy they create a TVC compensation curve that precisely relates the measured backlash value to the correct software compensation value. This way folks can measure their backlash in PHD2 and set the optimal TVC value.
Why it's important and why you should worry about it.?
I could be wrong on this, but If your backlash is say 2.5s and TVC = 0, PHD2 sends out a large 2.5 backlash pulse + guide pulse. It takes the mount 2.5s to respond and take up the backlash. If your guide interval is say 1s, PHD2 will see no movement in Dec and send out another guide pulse. It will then send out a third guide pulse before it registers any movement. It has now sent out a guide pulse 3 time the amplitude of what was intended, and it will then look to compensate for this over correction in the opposite direction. I think this is why the Dec plot can often look so erratic. If say the backlash is under 1s, then it should register the guide pulse and not send out any further unnecessary pulses.?
If the TVC value is set to the correct value, there entire 2.5s backlash will be compensated for almost instantly (I assume because Gemini moves the Dec motor at a faster than guiding rate). However, I have often seen suggested a TVC setting of 10 or 20. Thus is too small a value for this backlash value. It more likely has to be set to between 120 and 150. Really, this has the be properly studied and should be the responsibility of the manufacturer.?
If you are happy with what works for you that great. I'm more focused on getting to the route cause of some of these problems. I do this so you don't have to?
Peter
