#1  
Old 25-01-2009, 09:17 AM
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PHD Calibrating NOT

Hello There,

Need some help. I think Leo had the same problem some time back but I can't find anything about it.

PHD is telling me it can't calibrate itself in RA as there is not enough movement of the star.

Is there a way to adjust anyhting in PHD ???

After spending many hours drift aligning my permanent mounted EQ6 I don't feel inclined to missalign it again.

Carrying a 250mm F6 Newtonian plus 80 - 100 mm guidescope alignment and balance is very critical. The less adjustment PHD has to make the more chance I have of getting round star images.

Alexander
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  #2  
Old 25-01-2009, 09:56 AM
Dennis
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Has the system worked correctly previously and now no longer works,or…
Is this the first time you have tried using PHD to auto guide?

From my personal experience, if the system has previously worked successfully:
  • Either I have forgotten to plug in the auto guider cable to my mount so no motor movement/calibration signals are getting to the mount,…or…
  • I have inadvertently unchecked the checkboxes to make the mount move in X and Y.
Cheers

Dennis
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Old 25-01-2009, 10:27 AM
thunderchildobs
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Click on the "Brain" Icon.
You will then see different options.

Change the RA Agressiveness. Then experiment with the values.

Also check if the scope is balanced in RA.

Brendan
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Old 25-01-2009, 11:58 AM
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Thanks Dennis and Brendan

Yes, it has worked previously and is still working near the celestial equator. It only starts to play up the further south I go.

It will not calibrate. After 50 or so steps trying to calibrate in RA it will stop and tell me that there is not enough movement in the star to calibrate in RA.

The scope is balanced as close to perfect as can be. A 30gram sinker will start it moving in RA.

A good 10 minutes exposure without any Dec. guiding can be taken with the Canon 400D.

I normally have guiding in Dec. turned of.

RA is a different story.

Have increased/decreased agressiveness without any luck. Have also increased the time interval from 2.5sec to 10sec between checken for drift whilst PHD is guiding.

Alexander

PS: I meant Leon from Ballarat, noyt Leo, who, if I remember rightly ahd that problem a while back
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Old 25-01-2009, 12:21 PM
Dennis
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Hi Alexander

Hmm, your symptoms may sound like backlash in RA?

Near the equator, objects move in larger arcs for a fixed time period compared to when nearer to the SCP, so maybe PHD “runs out of time” in just taking up the slack in the gears, before the gears “bite” again to produce a real movement?

Cheers

Dennis
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Old 25-01-2009, 12:25 PM
Dennis
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Hi Alexander

Also, whilst I think of it, some mounts benefit from being slightly imbalanced; that is, with the OTA on the E of the mount, if you undo the clutches the E side should be (slightly) heavier. This should ensure that the drive train gears are meshed and so they push the mount up hill as it were.

Cheers

Dennis
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Old 25-01-2009, 02:22 PM
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Hello Dennis

Got me b.......... too. Bl.... Frustrating. Have been imaging for the last few month without any problem. Then this happens out of the blue.
Seperated all wires, power/data so there shouldn't be any interference.

Checked all connections etc. etc.

Adjusted the backlash in RA after it happened the first time.

Have a clamp, around 250 grams, which I attach to throw the scope slightly out of balance to allow for any backlash creeping in. Easier then moving the counterweights.

Maybe may shoestringastronomy autoguide box is playing up.... I was hoping for an easy solution.

Alexander
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Old 25-01-2009, 02:43 PM
Dennis
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I can appreciate your frustration and feel for you!

The only other time I had what might be a similar experience, although only in GoTo slews rather than auto guiding, was when on my Vixen GPDX mount, one of the tiny grub screws that locks the brass gear on the worm shaft loosened and so was slipping, but not every time.

All I can suggest is to go through the mechanical drive train and check that something similar hasn’t occurred? Also, just make sure that all the locking clamps, clutches, etc. on the mount are clamped firmly.

Good luck!

Cheers

Dennis
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Old 25-01-2009, 03:09 PM
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Hi Dennis,

Have a look at the attached Test Image of m42 - 10min ISO400 - original untouched JPG image -taken autoguided with PHD in RA only, half an hour after the problem started further south.

No Problems calibrating, took approx. 20 steps for west and east.

Alexander
Attached Thumbnails
Click for full-size image (m42_10x11x400_20090124_199 (Large).JPG)
42.6 KB32 views
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Old 25-01-2009, 03:30 PM
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I've never got calibration working in PHD with my Q-Guider. Tried several times. I have never worked out what's wrong, it just doesn't move the mount for some reason. Works fine in CCDSoft so I've stuck with using CCDSoft and can't use PHD, only because of the problem with calibration.
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Old 25-01-2009, 05:26 PM
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PHD works fine for me - are you seeing the LED on the GPUSB change colour indicating it is receiving guide signals from the computer - could switch off DEC guiding and see if it is still changing colour. Also can you hear the mount responding to the guide signals when it is trying to calibrate. You should also see the star (and the PHD box I think) moving around the cross hairs when it is trying to calibrate. If it isn't moving and the first two checksare ok then perhaps the clutches are slipping?

Peter
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Old 26-01-2009, 10:14 AM
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Thank you all for your various bits of advice.

Problem sorted, but not fixed.

My memory still works and it was Leon who had the same problem.

PM'ed Leon and after following his advice sorted the problem.

Leon's and my own mount are aligned as close as possible to the SP, discounting diffraction and atmospheric turbulence. So the drift of stars near the SP is very very small.

PHD, to calibrate itself, needs some movement of the selected guide star. As there is no drift or so small that PHD can't detect it it will not be able to calibrate itself.

Leons fix, which he found after trail and error, was to select different guide stars in the field until PHD calibrated. Worked for me last night whilst imaging around the LMC.

Also found out that near or around the SP, PHD will calibrate easier on a bright star. Although it will take many more steps in calibrating then when moving further away from the southpolar region.

Alexander
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