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Old 06-06-2020, 09:40 AM
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g__day (Matthew)
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Backlash compensation questions...

Hi Folks,


My mounts Dec gears have a discernible amount of backlash as a result of the motor being a fraction of a mm too far from the worm gear. I have previously reset the motor position to move it as close as its mounting bracket holes allow, but to perfect it I would have to file the motor brackets to allow it to physically sit closer to the gear wheel.


PHD2 backlash assistant says there is some 1662 ms or ~ 10 arc seconds play in the gear (see attached shot).


The SkyX Professional Edition with a 360 star model shows a discernible North South running streak in my pointing result - making me wonder again if this is a clear sign of backlash at play (see attached picture).


So my question (if I don't want to physically re-machine my DEC motor's bracket - which I will do as a last resort) - can this discernible backlash be accounted for best by setting backlash compensation in my mounts hand controller - or do I try and do this in The SkyX and PHD2 and/or other programs?


The Skysensor2000-PC that controls my Vixen Atlux has a backlash compensation setting between 0 - 999 from memory. It is currently set to about 40. Is my best course of parameter changes to:

  1. Set the hand controllers DEC backlash compensation to zero and try to adjust for all the backlash in TSX and PHD2 and other programs?
  2. Raising the hand controller DEC backlash until PHD2 and TSX Tpoint shows improved pointing and guiding?
  3. Biting the bullet and re-drilling the motors brackets until the motor can be correctly position?
If it is initially try approach 1 - is there a preferred way to instruct TSX to allow for DEC backlash and the same for PHD2 (although its wizard seems to detect it - not sure if it account for this determined backlash)?


Many thanks all!
Attached Thumbnails
Click for full-size image (~~PHD2 Guiding Assistant v06.jpg)
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Click for full-size image (~~Tpoint model 360 stars.JPG)
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Click for full-size image (~~SS2K-PC Backlash.jpg)
183.1 KB10 views

Last edited by g__day; 06-06-2020 at 09:55 AM.
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Old 06-06-2020, 01:34 PM
rrussell1962
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I know zip about guiding but I had a quick look at my SS2K manual and it suggested setting the backlash compensation values for both axis to zero when using an auto guider. Although the paragraph did refer to the old Vixen auto guider, I have no idea if the suggestion has a more general application.
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Old 06-06-2020, 03:59 PM
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g__day (Matthew)
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Yes I recall that - but I am not sure what the backlash settings actually do - one would imagine engage the gears early when the motor direction changes.


Think I might give it a test tonight. Play with values from 0 to a few hundred (until over shoots occur) and see what PHD2 wizard thinks about it and see if a 16 star Tpoint re calibration looks better or worse RMS with differing values of Dec backlash set.

Last edited by g__day; 07-06-2020 at 11:50 AM.
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