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DDM RA axis going bad?


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#1 maxmirot

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Posted 19 September 2016 - 06:07 PM

I am getting bad errors in RA and this has increased .


https://www.dropbox....rrors7.pox?dl=0


Have a look at the autopoint file and tell me what you think.

Thanks


Max

#2 lukepower

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Posted 19 September 2016 - 06:31 PM

Max,

I didn't look at your file, however there is a remote possibility that the axis is not tracking well due to mechanical reasons, like a defective bearing, a strong hit during operations or transport, and the likes...

This is something you should discuss with ASA support...


Lukas Demetz
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www.skygemsobservatories.com
Astro Dolomites Observatory, Skygems Network
Santa Cristina Valgardena, Italy
20" Cassegrain-Newton on ASA DDM85XL


#3 maxmirot

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Posted 19 September 2016 - 08:24 PM

Max,

I didn't look at your file, however there is a remote possibility that the axis is not tracking well due to mechanical reasons, like a defective bearing, a strong hit during operations or transport, and the likes...

This is something you should discuss with ASA support...

 

RA is bad, this what it looks like to me.  Btw. there has been no transport since I got the mount.

RA errors was always a little worst than DEC but this got worse.

 

I am able to get balance perfect in DEC in all positions using CWs in including radial adjustment. RA is never perfect in all positive.

Please load the the file and tell me what you think.

 

Max



#4 MarkS

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Posted 20 September 2016 - 12:19 AM

Hi Max,

 

I've looked at your file, and compared the figures to a 21 star pox file from my DDM60. I see no significant differences. What is showing you that the RA pointing is off?

 

Mark



#5 maxmirot

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Posted 20 September 2016 - 04:08 AM

The errors are spread out along the RA in a non random manor.    RA error is about 8-10x greater.  Also this over 100+ stars.

 

This suggests to me something wrong.



#6 lukepower

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Posted 20 September 2016 - 07:38 AM

Max,

hm, what about polar alignemnt and radial balancing? What kind of OTA do you have on your mount?


Lukas Demetz
------------
www.skygemsobservatories.com
Astro Dolomites Observatory, Skygems Network
Santa Cristina Valgardena, Italy
20" Cassegrain-Newton on ASA DDM85XL


#7 maxmirot

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Posted 20 September 2016 - 01:56 PM

Polar alignment is less than 3 min. (The models that are coming out now vary so much it hard to show that).

 

I have a radial balance. I null balance using a CW along the tube and a radial CW. When I am done DEC is in balance in all positions.

I can't get RA to balance in all positions. The residual pointing errors show up in RA.

 

The OTA is an Astrophysics Riccardi Honders 305mm with Optec Gemini focuser-rotator which supports up to 25 lbs.

 

I checked the scope for loose components. The back of OTA opens for cooling so I was able checked the mirror and rear corrector. It is all rock solid.

The AP OTA is not user adjustable.  I am sure they set all optics as firmly possible without pinching them.

 

Max



#8 tbaehnck

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Posted 20 September 2016 - 02:54 PM

Hi Max,

 

could you quote a picture of your setup. I didn't understand why RA  should be not balanced in all positions. Normally it much easy then DE because you have no off axis weight.

Thomas



#9 maxmirot

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Posted 20 September 2016 - 03:02 PM

Exactly! It should be much easier to do than DEC. It is giving problems and that shows it the pointing data along the RA axis.

 

Max



#10 maxmirot

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Posted 20 September 2016 - 03:11 PM

Have a look at the errors. That tells me there something wrong.

Attached Files



#11 maxmirot

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Posted 20 September 2016 - 03:23 PM

Or how about this one. Note the polar aliment and collimation were not adjusted. One this one is over 40 stars the last one over 110 star.

 

Result should be constant unless the OTA or mount has loose components. Everything is rock solid from the ground up.

 

Would a loose optical component favor one axis???

 

I make remove the AP RH OTA and put my TEC a refractor  as a experiment.

 

However, the errors might be only present with a heavier weight OTA.

 

Max

Attached Files



#12 RamaSpaceShip

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Posted 20 September 2016 - 05:28 PM

Hi Max,

 

Did you check your cables?

If you have a cable that does not go through the mount, it may influence the balance and create some errors. Such a cable must be attached in a way where it does not create any extra effort to the motors.

 

Best regards.

 

Bernard



#13 maxmirot

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Posted 20 September 2016 - 05:53 PM

Yes,

 

I have very great cabling.

Power and USB all comes through the mount. Nothing to drag on the mount or it's bearings.

 

Max



#14 lukepower

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Posted 20 September 2016 - 06:35 PM

Hm interesting..

What about motor tuning? Maybe the tuning on RA is too aggressive? Or the slew settle time is too short?


Lukas Demetz
------------
www.skygemsobservatories.com
Astro Dolomites Observatory, Skygems Network
Santa Cristina Valgardena, Italy
20" Cassegrain-Newton on ASA DDM85XL


#15 Waldemar

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Posted 20 September 2016 - 06:41 PM

How about vibrations of the pier or tripod?

I experienced some problems with vibrations caused by a 'rat-cage' on my pier.

 

Waldemar


Waldemar
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Mount: DDM85 Standard 12V ; Telescopes: TEC140 + 140FF + Quad TCC ; Celestron RASA; TMB 92SS + 27TVPH Cameras: ZWO ASI 174MM cool; SBIG STF8300M; ATIK4120EX; TRIUS SX-36
Filters: Astronomik and Baader NB + RGB; Lunt double stack 75 mm unobstructed signature series + BF 3400; Dutch weather and light polluted skies.  

#16 MarkS

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Posted 20 September 2016 - 11:22 PM

Hi again Max,

 

I suggest you shoot some images, say, 5 or 10 min subs, preferably with MLPT, to see how much of a problem you have.

 

Mark



#17 pesa

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Posted 03 October 2016 - 12:42 PM

Max,

Since I have the same problem and support suggested to me that hysteresis might be the "villain" in my scenario you might check too what they suggested:

Make a new model with random points so that dec isn't always is constant across meridian. Then compare with old model.

Or to the same effect (as I see it): make a model on only one side so you dont ever pass meridian when building the model.

Then experiment with slews and tracking on that side.

Perhaps ricardo-honders have a fixed main mirror but hysteresis could easily come from focuser also.

If tube is a bit loose dont tighten too hard or something will break when motor tries to move tube. I did that and now I cant do anything untill ASA sends it back. DAMN!

When I get the focuser back I will do this but also keep model area smaller than one whole side. Not only meridian shifts can make focuser change position...

 

pelle



#18 maxmirot

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Posted 03 October 2016 - 02:31 PM

I can not see how this the focuser. 

I am using the Optec Gemini it supports 10kg and is very made very well. 

Perhaps I am can detect movement in the focuser using a dial indicator.

 

What version of autoslew are you using?



#19 pesa

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Posted 03 October 2016 - 10:24 PM

I'm using 5.2.2.8

 

pelle



#20 maxmirot

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Posted 06 October 2016 - 04:37 AM

Let us know what happens. I am going back to guiding

Max






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