Tracking problem

[apolkowski]

Hello,

I have been using my ASA DDM60 for over a year without issues. Unfortunately after last session in April the mount started to behave strange. It finds the home position, then I sync it to a star, then the tracking starts, but when I make a photo, the stars are lines, not points. When I stop tracking and make continuous 1 second exposures, I see stars moving as the the sky moves. When I start tracking the stars are moving in the oposite directions which means that the tracking speed is higher than it should be. At the same time the position of the telescope shown in Autoslew does not change as the mount would be pointing perfectly to the star. 

Location of the scope is taken from the GPS and is correct. Local time is OK too.

Servos tuning completes without errors and manual tuning shows that the mount behaves as it did before. Balance is OK.

The mount is set on a permanent pier and i did not change its position.

I did the factory reset, new Autoslew installation, clean installation with deleting data files, and I tried to use another PC. This did not help.

Do you have any idea what else I should try to fix it?

Regards,

Andrzej

[robertp]

Hello Andrzej,

very strange behaviour! I once had a problem with tracking speed being noticably off and tested everything I could think of. In the end, the problem was a parameter in the Cl-servo.ini file that obviously got corrupted. I only found it after comparing all entries in the ini-file against those of an older version, that I still had. The paramater was "Encoder Resolution per Revolution (or mm)" of the RA-axis. Somehow, the value was wrong which lead to the axis moving too slow or too fast. I had no clue, how this could happen but as in your case everything was fine and the next day the problem occured.

When you did a new installation of autoslew, did you also delete all ini-files or did you just deinstall autoslew and then installed it agains? In the latter case, autoslew takes over the old ini-files. Maybe you can deinstall autoslew again, delete all files in ProgramData/ASA/Autoslew (or better rename the directory) and then do a clean install. Or if you still have an older version of the Cl-servo.ini compare the entries.

Other than that, I can't think of why your mount should behave so weird.

Hope you find a fix for your problem,

Robert

 

[robertp]

Hello again,

sorry, I just saw that you already did a clean installation (even on a different PC), so a corrupt ini-file can not be your problem.

Robert

[apolkowski]

Thanks @robertp. I wonder if ASA has any "residual" memory in the mount that can influence the behaviour of servo drives.

[RoWal]

Hi I am part of a small team and we have a DDM60 in a remote observatory, occationally we have seen unstable tracking, and also had tha RA or DEC motor turn off due to high currents... You sat you had your mount for over a year, is it permanently mounted in an obseratory?

Our specific issue has probably a range of root causes...

1. When starting a night sessions motor currents are OK, but increases over and hour or two until reching the levels when you start getting positino errors in the servo log, eventually motor(s) are turned off due to to high currents (+3.0 A) - this will of cource create lines in stead of round start

1.1 One potential reason for motor currents to increse over a time is internal stiction due to... clumping of grease in the bearings.. an issue I have been researching and discussing with bearing experts.. and that is not discussed much enough in the astro photograpy community, it takes a few yeas for this issue to arise as the mount has to be exposed to moisty condition - as i will be in a permanently mounted observatory (.. if the observatoruy is not in a geographically dry location ;).
We believe this is our major problem... the best solution is to replace standard bearing grease with high grade white lithuim grease that is very resiliant against aiging (clumping du to absorbing moist over time).. the short term practcal solution is .. release slews - ensure the mounts svings around a number of times befor a night session, manually och via somkind of script (we have a script solution). 

2. Communication issues. We have found out that the USB cable between the computer and th  mount must be high quality, Autoslew has intens communication going on with the mount and is VERY sensitive to interferece or poor connectivity... This is an issue we are having right now. Of cource moist condition play an importat role here as well... it affects the connectors. We now has to order regulas cleaning and apply contact spray to the connectors - the reduces the issue fom some time, but the isse appears to gradually increase over time so we will probaly have to do som serious maintenece before end of 2024...

3. Alignment and or pointing model issues.. we have found it is very beneficial to take time to get an as accurate polar adjustment as possible, we have use the QHY polemaster to set the polar adjustment, we run it 3-4 times to make it as good as possible. The we have set up sequence and make a pointing model we redo the model 2-3 times a year.. 

4. Configuration issues, balancing and performing tuning of the motor currents (PID setttings) make big difference, This can be really tricky due to the fact we operate remotely.. so balancing require we call in local service staff..  but most of the tuning we can do remote (not the parts requiring tapping the scope to manuellay se PID parameters though),,

So.. as you can se we have a range of issues that all come inte play, and we have to deal with them remotely...

So if you have not solved you issues i wuls suggest

-Check cables, clean and apply som contact spray to reduce potential communication issues

-Find your way to make "release" slews to remedy potiential grease clumping in the bearings in your mount (If you want I can describe this issue in more detail..)

-Be VERY thorough when balancing your mount, watching the balancing graph is not accurate enounh, open a command window an tail the servo log as the currents are displayed in the log and that gives much higher accuracy...

 

Finally - When everyting works, this is a fantastic mount, we easily have 10 minutes unguided subs, we tried 15 min, it works but is impractical nowadays due to all the satellites etc that reduces sub quality  with good precision

And, hope some of what I described here may come in use for you