Hi Robin,
Would it be possible to have a feature that allows an entry for step offset within the focuser panel by the IN / OUT controls. This would be used to compensate backlash and effectively always end any out movement with an in movement which means the tooth / teeth on the rack and pinion would always be engaged in the same direction.
For example if I had a step offset of 50 and moved the focuser out 25 steps it would actually move out 75 steps and then in 50 steps so always ending on an inward motion. For inward movement the offset would not be used as therorectically the rack and pinion should always be in contact.
I know there is a backlash option in the Ascom driver for my Sesto Senso but have not been able to make this function, so I am not sure if Sharpcap uses it or whether it is an issue with the Ascom driver. Also to adjust it you have to close the focuser open the setup and then change the value and then reopen the focuser were as a directly accessible value in the focuser panel would make tweaking far easier.
Hope this makes some kind of sense.
Cheers
Nick
Focuser step offset to finish on an inward movement
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Re: Focuser step offset to finish on an inward movement
Hi Nick,
typically focuser mechanisms have backlash in both directions to approximately equal degrees regardless of the physical design of the mechanism of the focuser and focus motor. Pretty much any mechanism with gears or a rack and pinion will behave this way. As you've noted, most Ascom focuser drivers do have some sort of backlash setting configure that works in a similar way to the idea you're describing – basically it adds an extra amount of movement when you swap the movement direction of the focuser to try and take you through the backlash region to the position where the drive starts to engage and move the camera again.
It may be worth digging a little deeper into why the backlash option for your Ascom driver is failing to work correctly as I would have thought that would basically fix your issue if it was operational and adjusted correctly.
Cheers, Robin
typically focuser mechanisms have backlash in both directions to approximately equal degrees regardless of the physical design of the mechanism of the focuser and focus motor. Pretty much any mechanism with gears or a rack and pinion will behave this way. As you've noted, most Ascom focuser drivers do have some sort of backlash setting configure that works in a similar way to the idea you're describing – basically it adds an extra amount of movement when you swap the movement direction of the focuser to try and take you through the backlash region to the position where the drive starts to engage and move the camera again.
It may be worth digging a little deeper into why the backlash option for your Ascom driver is failing to work correctly as I would have thought that would basically fix your issue if it was operational and adjusted correctly.
Cheers, Robin
Re: Focuser step offset to finish on an inward movement
Hi Robin,
Will play with it a bit more to see if I can work out what is going on with the focuser / driver as I did play with the backlash setting and could not get consistent results between inwards and outwards travel as when I get the one right the other appears to get worse. So I have it set to 0 at present and when focusing manually add an additional number of steps if I need to do an out focus if I have overshot whilst focusing inwards then come back up to the correct point using inwards focus only.
The other reason for always inward focusing is that the focus tube is then locked on to the pinion and rack teeth so cannot slip outwards which it can potentially do if the backlash clearance is between the rack and pinion teeth on the inward side of the focuser which it is if you end on an outfocus movement and the backlash setting in the Ascom driver will not help with this hope that makes sense.
So I think I may carry on with the current method as I then know the focus motor is locking any further movement after the last inwards focus as it then goes into holding mode and locks the spindle.
Cheers
Nick
Will play with it a bit more to see if I can work out what is going on with the focuser / driver as I did play with the backlash setting and could not get consistent results between inwards and outwards travel as when I get the one right the other appears to get worse. So I have it set to 0 at present and when focusing manually add an additional number of steps if I need to do an out focus if I have overshot whilst focusing inwards then come back up to the correct point using inwards focus only.
The other reason for always inward focusing is that the focus tube is then locked on to the pinion and rack teeth so cannot slip outwards which it can potentially do if the backlash clearance is between the rack and pinion teeth on the inward side of the focuser which it is if you end on an outfocus movement and the backlash setting in the Ascom driver will not help with this hope that makes sense.
So I think I may carry on with the current method as I then know the focus motor is locking any further movement after the last inwards focus as it then goes into holding mode and locks the spindle.
Cheers
Nick