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Stuck mount and PEC

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#1 ManojK

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Posted 31 July 2013 - 03:52 AM

Hi all, I have an Atlas EQ-G on which I have been using PEC with good success (PHD Logging and PECPrep used to make the PEC data).

Unfortunately tonight when I was parking the mount, a cable snagged and I heard this gut wrenching noise. I stopped the mount and untangled the cable. Just so I would not lose the align data and the park position, I loosened the clutches and made EQMOD park again to my custom park position. Scope didn't move since the clutches were loosened and when EQMOD said the mount was parked, I then repositioned the mount by hand and tightened the clutches. A subsequent unpark and goto seemed just fine (indicating that the align data was still accurate and my hand repositioning was correct).

The question is, does this mess up the RA worm position as it relates to PEC (note that at no point did I use some other method to engage the RA worm). Or, even when the mount was stuck on the snagged cable, did the worm continue to turn and hence EQMOD always knew the worm position? If EQMOD lost the worm position at any point I would have to redo PEC isnt it?

Misery loves company, so would love to hear from others who have been in this situation and what you know about PEC. No equipment was damaged so that's some good consolation.

#2 mayidunk

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Posted 31 July 2013 - 06:26 AM

Last night I came very close to crashing my mount while it was slewing to an object. Thankfully, I saw it about to happen, and hit the buttons just in the nick of time, aborting the slew just as the scope touched the pillar! No harm, no foul, just a clean pair of pants were needed!

As for your PEC, I have no experience, but am sure someone with experience will be chiming in real soon! In the meantime, I would imagine that you probably would have been able to tell right away if something was wrong. I believe these mounts' clutches may be adjusted to allow them to finally slip, before any real damage occurs. However, that's just an educated guess on my part.

As for the PEC, if the output shaft to the worm gear slipped, then you may need to redo the PEC training, as the computer probably determines the rotational position of the worm gear based on positional data from either the motor itself, or an attached sensor. However, I would imagine that it's probably pinned to the shaft to prevent that form happening, even under normal use. You might just try playing your PEC back, and see if it's still giving you good results. You might also want to double check for backlash, as the stress may have loosened up the gear train, which I imagine you would see when you play back your recorded PEC. If the playback isn't as good as you think it should be, I would look at the backlash, first. But, again, I don't have experience in this as regards telescope mounts, so someone with this mount will hopefully provide clearer insight for you.

I kinda felt your pain last night... good luck!

#3 shawnhar

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Posted 31 July 2013 - 07:47 AM

I don't think the PEC or EQMOD care if the motors are moving the mount or not, just the worm gear, and there ain't no clutch on that.

#4 ManojK

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Posted 31 July 2013 - 10:23 AM

so what happens when the mount is stalled and the motor is trying to drive the RA? Does the worm gear just crunch? If it keeps moving something else has to slip, right?

#5 Stew57

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Posted 31 July 2013 - 11:53 AM

With a stepper the motor tries to keep stepping but can't. The motor should not be powerful enough to damage the gears or electronics.

With a servo the motor will keep getting more current until something breaks or burns out.

#6 EFT

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Posted 01 August 2013 - 09:52 AM

In this circumstance the stepper skips and makes a terrible noise but does no damage. However, the mount contains no position sensors so the computer thinks that the motor continued stepping as told so that it now thinks the axis is on a different part of the worm for PEC purposes. It will be necessary to redo your PEC because the computer no longer has any idea of the true position of the worm in relation to the axis.

#7 mayidunk

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Posted 05 August 2013 - 06:23 AM

How did this end up? :question:

#8 ManojK

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Posted 01 September 2013 - 12:16 AM

Hey all, sorry I went silent on it. Looks like no damage done to the mount. Also the PEC seems to be still valid (surprisingly). I may redo the PEC pretty soon though since I don't think I had enough cycles when I did it initially.






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