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Dann

Declination Guiding Problem

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(I know DEC PE doesn’t exist but it almost look like one).

DEC PE does exist in exactly the same way that RA PE exists. With a good polar alignment the DEC axis does very little and so DEC PE will not show. However, with a bad polar alignment the DEC axis will need to keep moving in one direction, albeit much slower than the RA axis, and PE will show up.

Cheers,

Chris

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You really shouldn't be changing the guide rate simply to achieve a certain "calibration" result.

Hi Chris,

I completely agree but just to clear this up I'm not looking for a certain number of calibration steps to get guiding working. They are just an indicator that the settings are OKish. The point of changing the guide rate is that the mount doesn't take enough notice of the guide commands when the values are set too low. I started, by mistake, with both RA & DEC set to x0.10 and for ages have struggled to get the mount to keep up with the guiding. Once I changed the rates (to x0.30) my guiding started working.

My approach is to get a guide rate that works well with a calibration step. If it's too low it doesn't.

Regards

Mark

Edited by mark7331
I think I was a bit rude. Sorry. :)

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so here is promised update... not good one, but let me start from beginning.

I have removed guide scope and attached guide cam directly to main scope in order to increase focal length and improve DEC axis balance (which was pretty good).

calibration in RA went smoothly but mount could not calibrate in DEC, so I have changed DEC rate to 0.9 and DEC backlash to maximum in EQMOD. After that calibration in DEC in north directions went quick in about 15 steps but when it went to South direction star has hardly moved back to original position. PHD however started to guide.

I had to decrease DEC rate to 0.2 and DEC backlash to 0 in order to make DEC graph smoother. I have also changed guide in DEC to north only as my PA was slightly off on purpose.

So for few minutes tracking in DEC was as it suppose to be, but then old problem again. Star has jumped large distance to North and as guiding was in North only, nothing has stopped this movement.

From pictures below you can see that this was not caused by huge pulse guide. So it must be mechanical issue. I have tried to tighten and then loosen DEC clutch, but same happened again and again...

now only thing what I can think off which can help is taking apart mount and try to put it together hoping that this will solve issues I have got, but to be honest I am not sure where to look (which part can cause this what is happening)

I think I have to take few days off and dont walk into conservatory where mount is storred :)

post-22553-133877669467_thumb.jpg

post-22553-133877669475_thumb.jpg

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Ouch. I hope it's not mechanical. :)

Just a thought Bamus but have you tried, once calibrated, reducing MxRA and MxDEC. Maybe PHD is over compensating? Try 500 ish?

Mark

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Ouch. I hope it's not mechanical. :)

Just a thought Bamus but have you tried, once calibrated, reducing MxRA and MxDEC. Maybe PHD is over compensating? Try 500 ish?

Mark

Hi Mark

I don’t think overcompensating is an issue in my case. As you can see from EQMOD pulse guide monitor, PHD was not sending any long pulses at the time when star has moved rapidly to South.

Anyway, I have took apart my mount on Sunday and degreased all moving parts. It moves now more easily than before (perhaps resistance in DEC axis didn’t allow star to move as much as it should be and some kind of internal pressure was building up and was released from time to tome – hence this big star shift to South) . I have also slightly adjusted DEC motor position so now teeth in-between gears are tight together (hope not to tight) and any movement in DEC motor is translated immediately in DEC worm movement.

Hope this will help, if not that I have got no other idea what can help. First clear night I will give it a go.

regards

Adam

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ok, have done some tests and it is slightly better. calibration first time for long time was correct in N-S direction and most of the time graph was acceptable, but from time to time I do get peaks. I think I have to accept cheap mount will behave like that although still dont understand where this problem comes from and how to solve it completely.

I have also run PecPerp and while RA graph was most of the time between +-2 arcsec, DEC graph was between +-3 and highest peaks went to up tp 11 arcsec

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post-22553-133877671719_thumb.jpg

post-22553-13387767174_thumb.jpg

post-22553-133877671748_thumb.jpg

Edited by bamus

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Adam, sorry you're still having trouble. How long are the gaps between the peaks in DEC activity? Do you get, for example, 5 minutes of smooth guiding then a blip?

Maybe you're right about the mount but I wonder is there a way to test it? Could you, for example, use an artificial star and see when (or if) the mount misbehaves?

If you can get 5 minutes of good guiding then maybe that's acceptable for the mount...

Mark

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HI All

I think I’ve got it sorted J I took my mount completely apart, cleaned and greased all moving parts. Corrected all slacks between motors and mount. Put it back together (I thought I have used to much or too thick grease as axis were not moving as freely as they used to), have done proper PHD drift polar alignment, and have changed Dec algorithm Lowpass filter. Not sure what main reason for improvement, but peaks from DEC graph are gone and I can do 10 minutes exposures without any sight of stars trails. I so glad that it works now.

Graph in PECperp is not within +-1.5 arc sec in both axis. Without guiding my old EQ5 has got PE within +-18 arc sec which is huge improvement from previous measurement of +-40 arc sec J

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Glad that you got to the bottom of it. Was it easy to do? Also, what grease do you use? Is there specific stuff to use for the mounts?

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actually it was easier than I thought it will be. I have used B&Q brand lithium grease.

  • Like 1

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For what is worth I had this issue a couple of months ago, it was backlash in DEC, I can see some peeps thinking that a 're grease' cured it, but in fact its probably because the dec lash was fixed on the re assembly. My penny worth... 

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As Merlin says and make sure as much backlash is adjusted out of your mount as possible. I find I have to change my Dec imbalance depending which side of the meridian I'm pointing which fits the targets you mention.

Sent from my iPhone using Tapatalk

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As has already been suggested, guiding in only the one necessary direction in Dec (experiment to find which that is) is an excellent cure for oscillation. Being slighty misaligned is a positive advantage in this situation, but not enough to give rotation.

Olly

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