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No South PHD calibration movement on Orion Atlas

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#1 crosseyedcricket

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Posted 10 September 2013 - 09:45 AM

I've had some trouble develop with my Orion Atlas (EQ6) mount in autoguiding lately. During PHD calibration, East/West calibration is fine, North is fine, but when it starts calibrating back South, the star doesn't move.

The 'clearing DEC backlash' operation also seems to take longer than it used to.

I looked back at my PHD logs and saw that this happened once before right after I got the mount, then no problems over the last year. The last 4 sessions show two with this problem and two without. My hopeful suspicion is that there may be a spot or section of the DEC gear that doesn't align as well with the worm and that I just reach that section occasionally.

There is no play at all in the DEC axis when the clutch is engaged and the DEC axis rotates smoothly all the way around when the clutch is released.

My plan is to try rotating the DEC axis a bit with the motor, then release the clutch and reset it (to hopefully start using a different part of the gear).

Anyone else run into this?

Thanks!

-David

#2 orlyandico

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Posted 10 September 2013 - 11:48 AM

if there is no play in DEC with the clutch enabled, then your DEC worm mesh is too tight. this would explain your behavior. North works because PHD will keep pulsing the North signal until it sees movement. but then (due to stiction) it would take even longer South signals to move south. Which you don't see anymore because PHD will use the same number of South signals as it did North signals.

#3 crosseyedcricket

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Posted 10 September 2013 - 01:53 PM

That makes sense. I had only considered the possibility of loose mesh / backlash as being the culprit for PHD not moving the mount..not a 'too-tight' gear mesh.

I have not ever adjusted any gear mesh on this mount, but I did buy it used.

I still wonder why it would calibrate fine most of the time, but not on other occasions. Perhaps load balance and target declination might be factors to overcome the stiction in the instances where calibration worked correctly?

I do get N/S DEC corrections when guiding, but the performance is better when the calibration completes correctly.

I will look into backing the worm off just very slightly and see if that helps.

Thanks for your insight.

-David

#4 rmollise

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Posted 10 September 2013 - 02:34 PM

It's easy to determine the problem. Does the scope move normally when you push the south button? If so look for a cable or other electrical/electronic problem.

#5 crosseyedcricket

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Posted 11 September 2013 - 01:56 PM

Rod,

Thanks. It does move in DEC when pressing the buttons on either the hand control or on the PC (when connected through EQDIR). There is rattling noise when starting and stopping movement, but during DEC movement the motor sounds smooth.

I have access to another Atlas mount that I may try with my same guiding setup to see if I can further isolate the issue.

#6 David Pavlich

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Posted 11 September 2013 - 02:31 PM

You might also try the manual function of PHD to ensure that it's talking to your mount in all directions.

David

#7 rmollise

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Posted 11 September 2013 - 03:07 PM

"Rattling" is normal for an EQ-6.






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