Does backlash change as the mount tracks across the sky?

[swag72]

This may be a silly question - I don't know!

I was having a real play last night with guiding and Maxim settings and had it so that at +/- 0.5 pixels I was almost on a flat graph. The way that I did this was by altering a backlash setting on my Y axis to 0.2 (Sorry, on Maxim don't know if Y is DEC or RA). So it was guiding lovely on NGC7635.

Than as it got higher in the sky, the graph on the Y axis began to change and gave a kind if zig zag (one point up, then one down, one up, one down) pattern. So I put the backlash setting back to 0 and off it went, nice and straight again.

Can someone explain this and why it happened? I don't for one minute think I have a problem ( ... for a change!!), but just thought someone could explain it to me.

[Psychobilly]

How have you got the setup balanced - is it slightly heavy camera end? It helps to keep constant mesh in the gear train and stop wallowing in the gear train backlash.

[swag72]

Setup is well balanced!! I will change it to heavy camera end. Is that the reson I got that result with the graph then? As the mount got higher and the camer end dipped lower, it effectively cancelled out any backlash?

Probably wrong!!

[Psychobilly]

You also want to be a slighlty out of balance in RA... again to ensure positive contact...

Were not talking massively out of balance just an ickle bit...

Peter...

[themos]

The way that I did this was by altering a backlash setting on my Y axis to 0.2 (Sorry, on Maxim don't know if Y is DEC or RA). So it was guiding lovely on NGC7635.

backlash should only be an issue for DEC, as it's very unlikely you'd have to correct so much in RA that you'd end up going eastwards!

When you say you altered it, what setting did you start with?

I guess the higher the backlash value, the more it will spin the gear trying to find contact with the other side of the tooth. So if you give a backlash value that is too high, it will end up over correcting and you get a zig zag. That's just a guess, though.

[swag72]

I changed the backlash amount next to the calibration steps in the 'settings' menu. Only changed it on the Y axis (Is that the DEC axis in maxim?).

Perhaps just better if I change the balance!!

[ollypenrice]

I started a thread on backlash in DEC near the zenith. It's in the imaging discussion section.

You can expect to change values during a long run but why is never always dead clear!

Olly

[swag72]

Cheers Olly, I did see the thread regarding adding weights - Seems like most things in guiding are unexplainable!!

[themos]

They are explainable, we just don't gather enough data.

[ollypenrice]

...which means they are inexplicable!!

It ain't called the dark art for nothing.

Olly