RoboFocus re play in motor shaft

[strongmanmike (Michael)]

I have RoboFocus fitted to my NGF XTn focuser via the brass extension sleave.

Anyone using RoboFocus out there who can confirm it is normal that the motor shaft should have a bit of rotational play even when connected to the focuser and powered on?

If it is normal, why doesn't this affect positional accuracy and focus stability?

Cheers
Mike

[rogerg (Roger)]

Hmm..

I don't remember mine having any play in the shaft at all. It might have had a tiny bit, but I don't remember it.

The software that comes with RoboFocus (or mine at least) does have backlash compensation to cater for the kind of situation you talk about. I'd suggest using it otherwise I would expect the focus to be slightly out due to the backlash.

Roger.

[jase (Jason)]

Doesn't sound normal Mike. In the two RF units I've owned, the focusers have had no rotational movement. There should be no push/pull movement of the draw tube with the RF engaged. The stepper should hold the draw tube firm in place. Might be something specific on the XTn. Had not problems with the NGFC. As Roger mentions you can use the RF control panel or FocusMax to address this, but it would be better to resolve the issue instead of compensating for it.

[strongmanmike (Michael)]

Thanks Roger and Jase

I asked Jerry at Technical inovations and he said it was normal but his email reply confused me slightly and didn't answer my questions well enough (IMO) so I thought I'd ask the wider imaging comunity.

All three replies from guys on the SBIG group all say backlash (play) in the motor shaft is normal and that I can either remove it with the backlash compensation in the RF/focus software or when using it manually, as I am, just approach focus from the loaded direction.

Must admit, I would have thought precision repeatable "Robo" focus would have needed rock solid positioning not an approximation..?

Cheers guys

Mike

[rogerg (Roger)]

Well, in your situation, it will be repeatable once you program out the backlash. I think it's reasonable to accept a little backlash in any gearing, but I'm no expert.

I find my robofocus certainly is repeatable, it's so precise I have never noticed any error in its movements, and I don't use any backlash correction. But I suspect that observation is influenced by many factors in the setup (for example focal length affecting how much focus movement is made before focus change is observed).