Moonlite Nightcrawler: "Zero" won't function


When I attempt to return my Moonlite Nightcrawler focuser to the home position, it does not move. The control panel tells me that the focuser is idle. Also of note, the rotator portion works fine when I hit the Zero button on it’s control panel. Here is the log:


Looks like this is a bug in backlash compensation. Also it seems odd that you would need a backlash compensation direction of OUT on this focuser. Not saying this doesn’t need to be fixed…just that the backlash direction on this particular focuser should probably be IN (and honestly probably not needed).



Any ideas on solutions?


Are you talking about home on the rotator?


What seems to be happening is that the user is clicking on the move to Zero button in SGP. SGP is applying the backlash and is sending a move command with an invalid value -200. The driver is correctly rejecting this because it is outside the allowed move range of 0 to MaxSteps…

The simplest way to avoid this is for the user not to try to move to the zero focuser position from within SGP. It won’t affect movement around the focus position.

Otherwise SGP needs to monitor the positions it sends to the focuser and ensure that they are in the allowed range, even for backlash moves. SGP could also check the error and ignore InvalidValue exceptions on the backlash move.


What I am not sure of is why one would want to move a Nitecrawler to zero focus position (which is why I thought they meant the rotator). I have two of them (great equipment, BTW) and one normally sets up the draw tube extensions so one is close to the middle of the 1 inch travel. That would be maybe around 35-40 thousand counts. Jared is also correct that the backlash direction on almost any focuser should be IN when using SGP and that there would be few if any situations where one would want the focuser to be moving out for it’s final move to focus. He is also correct that this focuser has close to zero backlash.


You can disable backlash compensation or park at 200 rather than zero until the big is fixed.



I don’t have a permanent setup. So I have to break down and put the scope in it’s case when I’m done for the session. The only way that it’ll fit in the case is with the focuser at “home”.


This is my first time sending logs into the forum. So as not to assume, what you’re saying is that I have a bug in my SGP that, once worked out, will have an update that rectifies it?


Yes, there is an issue with backlash compensation that is not allowing it to go to zero.

Regardless of this it seems odd that you need backlash compensation with this focuser and even stranger that you have it going in the OUT direction. So while there is an issue with SGP, you may want to reconsider those settings as well, unless you have a reason for them?



That’s great! No, I have no reason for those settings that I can think of. I will make the changes and report back!


Unchecking the backlash box did the trick. Thanks, all for your assistance!