Dec spikes, what does this mean?

[Euan]

I've just started some subs on the Jellyfish nebula on an EQ6, and I'm getting huge spikes in Dec. The calibration was a bit strange, it was really struggling to move south and I had to put on the Dec pulse width override in EQMOD to bring it back into line, and then the spikes.

It seems to only happen at this altitude, further north or south and it's not there.

Anyone seen something like this before? The balance is fine so the only thing I can think of doing is re-doing the worm adjustment

[adamsp123]

Yes I have seen it, and in my case I had flexture due to bad cable mangement, ensure all is tight and all cables are strain relieved, after that try a different guidestar.

Hope that helps.

[davew]

Hi Euan,

You may well have sorted this by now but....

I'm going to take a wild stab at this. So treat it that way. I'm no expert.

Looking at the RA line it seems to see saw even when traveling up or down on the graph. The DEC is wild. I've been trying to think what would give such a recuring patern. All that springs to mind is that you may have had two or more stars that the guider is picking up. Maybe in a line N / S.

Does this always happen when pointing around these coordinates ?

Perhaps try realigning the guide scope to pick up one good star and try again.

Dave.

[Euan]

I gave up imaging last night and just started trying guiding in a few different positions to see what would happen.

No matter where I went in the sky this started happening, I reckon it first started at the end of my last imaging run at the start of the month.

There's nothing obvious in terms of cables, obstructions, etc so I'm going to take the motors out and re-do the worms, hopefully it's not something serious!!

[davew]

That blows my theory out then

Good luck with the worms. Perhaps it's end float. { my non expert thoughts again }

Dave.

[Starflyer]

The Dec error looks quite regular and symmetrical, If I'd ruled out poor balance / something snagging then I'd suspect a mechanical problem in the Dec axis.

If you had the logging turned on in PHD then ask those knowledgeable people at the EQ6 Yahoo group to look at your log file. They have a huge amount of combined experience in interpreting PHD logs and suggesting possible causes and fixes.

Let us know how you get on,

Ian

[ollypenrice]

You say the balance is fine. By this, do you mean the scope is in near perfect balance? I would try making it camera end heavy to see if that helped. I'm just thinking it could be Dec backlash.

Olly

[FraserClarke]

In an effort to help you rule of "d'oh" moments -- have you check PhD is still trying to guide in dec? Not been turned off in software by the gremlins??

Good luck tracking it down

[adamsp123]

Have you checked the balance with the scope/CW horizontal and the scope sitting at the vertical? Does the scope try and move in DEC?

[SteveP]

Euan

That's a very regular pattern on Dec. What's the time scale? In particular, what's the duration from peak to peak?

Steve

[Euan]

BACK IN BUSINESS!!!

It is definitely one of those Doh! moments, when I upgraded the mount I forgot to tighten the hex screws holding the worm position on Dec. It's a miracle that I've had good guiding for months...

It had managed to tighten up a bit, hence why Dec was really struggling.

Thanks for all the input and ideas

[Starflyer]

That's a lovely looking graph, glad to hear you got it sorted