Hi

I’ve just been trying out the simulator to see how the different focus routines work with regards to backlash (and my sct mirror lifting).

I set a backlash of 500 so it would be noticeable, however only linear 1 seemed to use it. Linear seemed to have its own idea and used 100 while iterative and polynomial didn’t seem to do any backlash compensation.

Is this just the simulator or do they work (or not as the case maybe)m like this in real life?

Regards

Nigel

ok will answer my own question.
The manual says iterative and polynomial are for focusers with ‘well controlled backlash’ . I assume that means they expect no backlash and therefore need compensation.
For linear it says it manages backlash. Only for linear 1 does it mention use of the backlash setting.

Seems there’s little point in putting a value for backlash unless you are using linear 1 and have a bigger backlash than 5 times the initial step size.

Oh well.

So there are a couple of things at play:
1. Does your focuser have its own method, outside of Ekos, of dealing with backlash?
2. Does the focuser driver deal with backlash? Some do and some don't - depends on whether the author of the driver implemented it or not. If it does deal with backlash where does it get the backlash value from? One place would be the indi backlash field / backlash field on the focus tab (which are linked BTW).
3. What does the focus algorithm itself do:
- Iterative and Polynomial do not use backlash.
- Linear uses 5 x Initial Step Size
- Linear 1 Pass uses value in the Backlash field if this is > 0, or 5 x Initial Step Size if the value in the Backlash field is zero.

So you need to have backlash controlled in 1 and only 1 place.

Hi John

1. I’ve got a Celestron focus motor. I use the indi driver which gets the backlash settings from ekos. There’s no other backlash compensation function such as setting dip switches.

2. I’ve looked at the indi driver code and it goes on about backlash but I’m not entirely sure how the code works. I will try setting the backlash to something that will make an obvious movement and try it out.

3. Seems a bit of a mess. Surely they should all implement backlash at the appropriate points in their algorithm or they should leave it to the driver. If you don’t set it in ekos then linear and linear 1 do their own thing, if you do then it gets used by linear and linear 1 and gets set in the indi driver. I cannot remember seeing an enable backlash compensation in ekos so no way of turning it off there, there is a flag in the indi driver but that seems to get set by ekos…

My hope is that the indi driver implement’s backlash compensation and is able to identify when linear and linear 1 do there’s and not do it again. Otherwise I’m stuck with only using linear and linear 1.

ok just had a quick twiddle. Pressing the inwards button in ekos results in the backlash compensation being used taking it further clockwise than needed followed by it moving counter clockwise ie outwards to the correct position. Selecting the outwards button just results in it moving counter clockwise.

This looks to be what I was hoping for, now I just need to wait for a clear night to try out the autofocus.