G11 drift problem

[astroboy]

Hi All
Thought i would check with other users of G11s ( non Gemini ) how long they are able to take unguided shots for , the limit on my setup ( 900mm FL ) seems to be 45 secs ( the scope is well polar aligned ).
This seems to be a drift problem rather than a PEC issue , the mount just dosn't track at the correct rate .
ATS tells me that no other owners have had this problem ( although I found one one the web ).
Ive cleaned out the grease and replaced it with a better oil .
The mount works well with autoguiding its just unguided stuff thats a bit limited .
any ideas

Thanks
Zane

[Robby]

Initially I'd suspect polar alignement. You say it's well aligned though. How did you do the polar alignment?
What direction is the drift? Is it definately only RA drift, or is there some DEC drift... Also near the horizon the tracking is sometimes not so good. Try using the "King" rate in this case.
If you can quantify how bad the errors are I maybe able to help more. Use the graph-log fuction in K3CCDTools and then you should be able to quantify exactly what is going on.
Cheers

[[1ponders] (Paul)]

Hi Zane.

How long have you had the mount and has it always had this problem? I've successfully imaged for 3 min unguided at times. If you drift is in DEC then I don't see how it can be anything other than polar alignment. There is no PE in the DEC axis as the motor doesn't operate unless a correction is applied during guiding. Its a passive axis.

How do you polar align your scope? Drift or polar scope? Have you tried K3CCDTools to help drift align.?

Is you scope well balanced fore and aft on the Dec axis? If not how tight is your dec clutch. could it be slipping unddr off balance weight?

There is one other thing I can think of, and the only way I know of how to check it is to use an Argonavis with the latest TPAS upgrade. If you have always had the problem you may have a non-orthagonality problem with your Dec axis and mount head. I had this problem with my GM8 and didn't know it until Gary and I were trying to get my Argo to work and we couldn't get good accuracy. We tested with the new firmware (beta then) and found a non-collimation issue (nothing to do with mirrors) that wouldn't allow me to get an accurate polar alignment or drift alignment, even if it looked like it in K3. That's about the only other thing I can think of.

[astroboy]

Thanks Paul and Robby
I've had the mount for about eight years and has never tracked very well .
I did a drift alignment so that should be ok and the drift is in RA only . I'm carefull with the balance issue.
I use an argo navis with it and usualy gets things on the ST2000 chip.
Next full moon I may check everything again but it just seems to be made for a planet that revolves a couple of min's faster than ours ( I may have to move there )
Also I tried training PEC with the ST2000's auto guider to see what that would do but seemed to make things worse.
I appreciate your help with this .

Zane

[[1ponders] (Paul)]

Have you downloaded the latest AN firmware with TPAS? That would help to check the mount itself.

If it's only in RA have you thought about getting the newer precision worm and gears?

I'd give you some electronics advice but Robby would only laugh at me He's the man for that side of things.

[Robby]

Also check the motor couplings. The little grub screw that secures the shaft could be slipping. Also does the motor sound nice and smooth with an even soft ticking sound? If not you could have a "2-phasing" problem where the motor will appear to run normally, but will often drop a pole switch & slow down. Is the mount running too fast or too slow? Too slow could indicate gear slipping or a motor problem. Another thing to try would be to swap the RA & DEC motors and see if that helps.
If you know anyone with another control box, try that. Process of elimination should eventually get you there!
Good luck...

[astroboy]

Thanks guys
I have a precision worm , but come to think of it the motor often dosn't sound so smooth I'll check tonight.
I wonder if I stuffed up the electronics when I first used an auto guider off the same power supply , not a good thing to do apparently not that the Sbig book tells you otherwise.


Thanks
Zane

[bird (Anthony Wesley)]

Zane, I had RA drift problems for a while... turned out that I had the latitude set to 33S instead of the correct 35S for my location - the website I used for this gave me the wrong number and I (stupidly) didn't double check it.

So after a drift alignment to stop any DEC movement I was left with residual RA drift, and it had me wondering was going on.

Now that I've fixed it there is no drift anymore :-)

Bird

[astroboy]

Thanks Bird but i don't think its a polar alignment issue . But I think Robby maybe onto something with the 2 phasing idea .
I could hear that the RA motor wasn't making an even ticking sound but now and then ( as you say ) dropping out or slowing down.
Should I do a motor swap ( I think I've tried that in the past though ) or do I need a new motor.

Thanks again everyone
Zane

[Robby]

Hi Zane,
Try the motor swap first, but it is possibly an electronics box problem. Is there anyone you know close by with a G-11 (or GM-8) that you could borrow to compare.
If it is an electronics box problem then they are faily cheap to replace from astromart. Folk are always upgrading to Gemini systems & off-loading there standard controllers & motors cheaply (seen them around the US$150 mark).
Good luck.
Cheers

[astroboy]

Thanks Robby
I'll give it a go

Zane