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My DEC is running away from me


Obi Wan Ken00bi
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On 19/08/2018 at 10:52, Davey-T said:

Looks like the dec pulses aren't getting through or they can't override the backlash.

Did you try giving it a helping hand to override any backlash ?

Dave

Hi Dave and Louise,

Arghh... the problem keeps persisting. Only in West direction it seems. No meridian flip involved but straight after 2 star alignment on west stars, to a western  target (Vega, last alignment Star). Again the dec is having a mind of its own. I now tried your tip of helping it with my finger and that actually works. Whenever I gently lift the mirror so pushing tube into flat position (it wants to go upright on dec). What does this mean? A lot of dec backlash? The eq6 mount is brand new....

it just seems the dec guide pulses don’t come through properly somehow... 

Edited by Obi Wan Ken00bi
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Sorry very tired but I am sure its a balance issue in DEC. I could be wrong but try re-checking you DEC balance. I found the easiest way is to RA horizontal and DEC horizontal then release the DEC clutch then by putting a small weight on each side of your scope to check.

Due to me having the belt mod I need to be fairly neutral on balance. If you do not have the belt mod then I am sure you need to be heavy on one side and this will need to move to the opposite side after the flip.

 

Edited by spillage
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1 minute ago, spillage said:

Sorry very tired but I am sure its a balance issue in DEC. I could be wrong but try re-checking you DEC balance. I found the easiest way is to RA horizontal and DEC horizontal then release the DEC clutch then by putting a small weight on each side of your scope to check.

Haha no worries for apologies! I’m super happy you are helping out. I’ll rebalance the scope now as you said. I’ll report back 

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1 hour ago, spillage said:

Sorry very tired but I am sure its a balance issue in DEC. I could be wrong but try re-checking you DEC balance. I found the easiest way is to RA horizontal and DEC horizontal then release the DEC clutch then by putting a small weight on each side of your scope to check.

Haha no worries for apologies! I’m super happy you are helping out. I’ll rebalance the scope now as you said. I’ll report back 

 

Update 1: well I have rebalanced the scope and made it more front heavy on dec (it was balanced) and the problem is STILL here. Really unsure what this is. It can’t be backlash can it? 

CDC5182B-4352-4DF4-A4B3-01C1F4FB41B9.thumb.jpeg.617f688cd02751b24caba11eee062459.jpeg

Update 2:

a target further north and lower on the horizon (so more horizontal scope) gives normal guiding now.....

update 3:

problem keeps when guiding southward and looking towards zenith. I’m packing in for the night. I will tweak the mount backlash tomorrow and see if that helps. 

723562F3-CDE8-4706-AAF2-ACAB695107C5.thumb.jpeg.daaebf3997e2fb4a577d10ceb404d176.jpeg

Edited by Obi Wan Ken00bi
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Hi

You may need to a) trim out the motor backlash as much as possible (without causing the gears to bind) and b) also adjust the worm gear.

When you're pointing West - have you recalibrated and re-checked PA? Also, with a Newt you can get dynamic balance issues and pointing at the Zenith could be problematic but I've no experience...

Louise 

ps I see your exposures are only 0.2s - that's much too short. You want around 2s with good snr value

Edited by Thalestris24
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Is the system balanced in all positions and on both sides of the Meridian?  You can sometimes think you're balanced when the tube/camera assembly is parallel to the floor, but when you start moving the scope on the other axis you will see that it may not be in balance.  The fact you're guiding is not right after the flip suggests a balance issue somehow. I had a similar problem but in reverse - the guiding was bad with scope pointing East but was fine after the flip when pointing West.  

Move the scope about on all axis and it must always be in balance.

No tugging cables on the other side?  None?  People say "no, none" but *any* differential movement of the cable, maybe hanging off the guideport can cause slight movements of the CCD sensor inside the guide camera.  *Really* check for this.  It only has to move almost microscopically to effect the guiding.

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3 hours ago, kirkster501 said:

Is the system balanced in all positions and on both sides of the Meridian?  You can sometimes think you're balanced when the tube/camera assembly is parallel to the floor, but when you start moving the scope on the other axis you will see that it may not be in balance.  The fact you're guiding is not right after the flip suggests a balance issue somehow. I had a similar problem but in reverse - the guiding was bad with scope pointing East but was fine after the flip when pointing West.  

Move the scope about on all axis and it must always be in balance.

No tugging cables on the other side?  None?  People say "no, none" but *any* differential movement of the cable, maybe hanging off the guideport can cause slight movements of the CCD sensor inside the guide camera.  *Really* check for this.  It only has to move almost microscopically to effect the guiding.

Thanks for this advice. Guiding did improve when I rebalanced, so I’m getting closer to the problem I think. I have the cables out of the camera going into some cable shoes/ cable fasteners, so that should not be the problem, but I will check. I didn’t know it always needs to be in balance (thought mainly when things are horizontal). I’ll rebalance further and better!

To Louise; I’ll get rid of the Dec backlash tomorrow by tuning the scope. That should also help.  For now it’s ????

Getting closer....

 

edit: I really wouldn’t know what I would have done without the help of SGL/ all of you. ?

Edited by Obi Wan Ken00bi
Added compliment to SGL :-)
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Hi guys and gals,

Unfortunately the problem is still there! I'm getting hopeless really. ?  I've tried all your tips.:

- It's not meridian flip related, this is the second night I only looked west, calibrated west and 'guided' west.

- I've got rid of the wobble in Dec by adjusting the tiny screws on the mount, but this didnt resolve the problem.

- It's not a dec balance issue: I've tried balancing Dec multiple times, a bit forward heavy, balanced, balanced when vertical, a bit rear heavy. It does not make a difference

- I have reset all PHD2 settings, increased and decreased the aggresiveness, Mx Dec, Hysteris.

Here is the same graph I get every time:

IMG_8536.thumb.jpg.b1c1fd47f922cb32fe309df1d41aa25a.jpg

 

The point where it goes back to 0 is where I stop guiding for a sec and restart:

IMG_8552.thumb.jpg.5b8d230fca7af568badcd4054d7c9044.jpg

 

- It's only pointing west that is the problem. Pointing east guiding works, although I got this message:

IMG_8537.thumb.jpg.b000ecd511243f2240a7d05430120ae1.jpg

But after, the guiding works ok (the seeing is horrible, but at least no dec running away).

IMG_8538.thumb.jpg.6318e7fe648f995febf0361e4222b215.jpg

 

I've run out of options. 

The last thing I will try is connecting the mount to eqmod and pulse guiding through ascom, although I dont see why it should make a difference and have never tried this before.

?

Here are some images of my setup, maybe you can see a mayor flaw? 

48C972D5-B8F0-4652-AEF4-BF2BB8FD921A.thumb.jpeg.9eb80c9754fb7f001478d2b6e6057492.jpeg

6E57F5D2-0F1E-4A12-BC27-90C8B6EF7EDC.thumb.jpeg.d7ba5030899eb32dd0fb6818dff1f09a.jpeg

25BC7921-1E4D-42F3-A691-90E801A27571.thumb.jpeg.55df1e6f4224e2cf31f6ff606d3df6f3.jpeg

9B56C7FA-9316-4BE2-AF2B-CA658E10552A.thumb.jpeg.0d79202c041e4ec80bfc4ebf4b7d771d.jpeg

C9CD3E1D-098D-4E15-9620-1815B308B0BB.thumb.jpeg.8c5eec1bae92a8129f32fd5b2ea1c990.jpeg

 

Edited by Obi Wan Ken00bi
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1) try the star cross test in PHD2.

2) the only PA figures I've seen in your post was 12 arcmins, which isn't  brilliant. But I would try misaligning your PA so that the dec trend is below the x axis, which is the opposite to the trend in your posts, and then set dec guiding in one direction only to counteract this trend.

3) Are you moving the mount North for several seconds to take up the backlash before each Calibration?

4) Are you using the settings suggested by running the Guiding Assistant for several minutes? Untick the measure backlash box to save time, you already know it's too big to measure !

Michael 

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Hi

Oh you have an eq6-R...… That is a belt-driven mount so no backlash! However, if it's anything like my heq5 with belt drive then you have to have the scope perfectly balanced. No east heavy. In all three axes - RA, DEC and vertically. Newtonians are notorious for dynamic balance issues. I don't know if there are any belt tension adjustments with your mount but cos I had to install my belt drive, I had to fiddle about to get it just right. Also, you're guide cam in the diagonal doesn't look good....

Louise

edit:

ps your calibration doesn't look right - probably because your scope's out of balance. Also, do display your star profile so you can assess the guide star quality - you want the highest snr you can get without clipping the peak.

 

Edited by Thalestris24
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Hmmm. I’ll see what I can do to balance it even better then ? 

1. What is wrong with the guide cam in th star diagonal?

2. With balacing vertically, do you mean around the green axis in image below? So rotating the Newton inside the rings basically.... Like this:

axis.thumb.jpg.db58545df70eca7456c020730ec3ec19.jpg

I hope I don’t need to open up the mount to mess with the belt drives, it’s brand new. I’d rather send it back to the supplier. 

My plan for tonight:

1. Only put the st80 guidescope on the mount, leave the Newton off, just to make sure it's not a mount / guide signal related problem

2. Once I can guide in all directions, I'll set up the newton, balance it in 3 axis, and I'll try to guide with my small 50mm guidescope instead of the 80mm

3. I’ll try using the suggested settings after guiding assistant

4. Run star cross and open star profile.

Edited by Obi Wan Ken00bi
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4 hours ago, Obi Wan Ken00bi said:

Hmmm. I’ll see what I can do to balance it even better then ? 

1. What is wrong with the guide cam in th star diagonal?

2. With balacing vertically, do you mean around the green axis in image below? So rotating the Newton inside the rings basically.... Like this:

axis.thumb.jpg.db58545df70eca7456c020730ec3ec19.jpg

I hope I don’t need to open up the mount to mess with the belt drives, it’s brand new. I’d rather send it back to the supplier. 

My plan for tonight:

1. Only put the st80 guidescope on the mount, leave the Newton off, just to make sure it's not a mount / guide signal related problem

2. Once I can guide in all directions, I'll set up the newton, balance it in 3 axis, and I'll try to guide with my small 50mm guidescope instead of the 80mm

3. I’ll try using the suggested settings after guiding assistant

4. Run star cross and open star profile.

Hi

It's not normal to use a diagonal for a guide cam. It will invert the image and may also reduce guide star brightness. I'm not sure if an inverted guide cam will affect how everything works. It could add flexure. Yes, you need to balance vertically with the counterweight  bar horizontal. As you say, that will likely involve rotating the scope in it's tube rings. Be careful it doesn't slip down! I think the eq6-r is quite new? Might be worth posting separately to see if anyone else has had any issues.

Louise

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5 hours ago, Obi Wan Ken00bi said:

Hmmm. I’ll see what I can do to balance it even better then ? 

1. What is wrong with the guide cam in th star diagonal?

2. With balacing vertically, do you mean around the green axis in image below? So rotating the Newton inside the rings basically.... Like this:

axis.thumb.jpg.db58545df70eca7456c020730ec3ec19.jpg

I hope I don’t need to open up the mount to mess with the belt drives, it’s brand new. I’d rather send it back to the supplier. 

My plan for tonight:

1. Only put the st80 guidescope on the mount, leave the Newton off, just to make sure it's not a mount / guide signal related problem

2. Once I can guide in all directions, I'll set up the newton, balance it in 3 axis, and I'll try to guide with my small 50mm guidescope instead of the 80mm

3. I’ll try using the suggested settings after guiding assistant

4. Run star cross and open star profile.

Good video on balancing. its a newt too 

 

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Hi all,

Thanks to Louise, I think I have found the problem. By removing the star diagonal, the problem seems fixed! The seeing is quite bad as it's hazy, but guiding, with the balanced Newtonian and st80 works fine now in western direction. My PA also is a lot better I guess. This hobby is tough eh? But I'm glad I know it's not a problem in the mount or software, just my own incompetence. hihi.

And with all your tips and help, I've never seen such a nice flat guide curve before! SGL rocks and I will do my best to return the favor by helping others on this forum :)

Just look at that bullseye!

bullesye.thumb.jpg.d8c8be71c7404ceccffcc18e85fbe7f9.jpg

Guiding assistant says PA is pretty good!

pabetter.thumb.jpg.d2a404beda97f279a4f6b8903baa095e.jpg

 

 

 

 

Edited by Obi Wan Ken00bi
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  • 1 month later...
10 minutes ago, Obi Wan Ken00bi said:

I believe to have finally solved the issue. A broken st4 guide cable!! Got a new 6 pound cable and all seems fine (last night at least). Let’s hope that was the issue!!

 

so sorry for all your trouble, but I did learn a lot again and now have a very nicely balanced setup!

a good reason to ditch the st4 cable , one less cable to worry about

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