No reaction to inputs in RA / position tracking error / slewing the wrong direction

[MichaeL]

Dear commununity,

first, I'd like to say it's lovely this community exists and we ASA users can keep in touch 🙂

I'm using one of the first DDM60s with old encoders and Elmos electronics. Recently I had to set up my software completely new after my old PC crashed.

Recently I experience the following:

- In the RA-axis the mount didn't react to any inputs (neither autoslew buttons nor joystick). DE-axis was fine.

- Several times the RA-axis stopped tracking and "Servo Error" was shown in red in autoslew. The log window showed "position tracking error". After clearing the servor error and powering RA again the same happened: RA didn't quite react to move inputs -> Servor error -> Position tracking error

- Meanwhile a GoTo went crazily wrong: The mount slewed to the ground and ran against the tripod (ignoring all limits). The position was shown correctly in Cartes du Ciel (!), but the  slewing command to the motors was totally wrong. 

 

Between these issues I was closing / starting autoslew and plugging the usb-adapter in and out.
After compunter restart and switching the mount on/off. The error disappeared and I was using Sequece successfully for hours. 

But still, these are quite mysterious problem for me and I have no clou where to look for an answer ? Could the motorparameters improve the unwillingness to react ? It is possible autoslew had multiple and contradicting position information ?

Best Regards and clear skies,

Michael

 

 

[MarkS]

Recently I had to go through commissioning a new laptop. I thought I knew what I was doing as I had been using two ASA systems for years. It turned out that I had forgotten about some critical but simple steps, and after the mount heading off for the wrong hemisphere and refusing do what it was told, I gave up and called Wolfgang at ASA for a Teamviewer session. He sorted it in about 2 minutes - much to my shame!

The basic problem was, that in spite of having all the software and program data properly installed, it is critical that you 'Set new Homeposition' after having done the Homefind and then pointing the scope at the zenith or some star.

This may or may not be your problem, but the erratic behaviour points something of this sort.

Others may have better ideas, but in any case it won't hurt go through the manual and check that the fundamental first set-up steps have been followed.

Only then should you start looking for subtlties🙂

Mark

 

[MichaeL]

Thanks for your thouhts Mark. I did a homefind indeed, but eventually something went wrong (or I`m out of training). I'm postive this could help avoidig the erratic slewing !

On the other hand I'm more and more convinced the motor problem "position tracking error" and the fact the mount doesent react to the joystic in RA result from another reason.

I shoud've mentioned my Telescope is quite heavy and bulky (22Kg 12" Newton, needs the extra long bar and 7 counterweights) and the problem mostly occurs close to the horizon !

It kinds of remindes my of the problems described in the "DDM85 position crash" thread and the problem described in http://geoastro.co.uk/asa.htm.

Maybe I should try to optimize the motorparameters for heavy load and improve the balancing ?

How could this look like, maybe increasing the I-faktor ?

Best regards,

Michael

[MarkS]

With a heavy load, balance is very critical on both axes, particularly RA. The total load (OTA plus camera etc) should not exceed 28 kg for the DDM60. Overloading these mounts must be avoided!!!

Read the recent discussion on balancing - I think it's the 'DDM85 position crash'. It is definitely a case of near enough is NOT good enough! Balance is critical.

Tuning the motor parameters is well covered in the manuals. Always worth a read, even if one knows what one is doing, but I suggest you don't try to push the PID numbers too hard - the system will tell you that you have gone too far by going into oscillation. I'm not sure, but I suspect that very high PID settings may exacerbate motor current increases over time. Relaxation slews at intervals during a run is good practice.

I'm not sure what you mean when you say that the problem mostly occurs close to the horizon. Why would you image there? If you try to send the mount too close the lowest altitude limit, it will get into trouble. In any case, for good imaging it is best to limit altitude to above 40 degrees or so. I set the limit in Autoslew to 25 degrees, but never image below 40 degrees.

Hope this helps.

Mark

[MichaeL]

Mark, after I read the "weird behavior" thread I'm almost certainly sure your approach to the erratic slewing problem is correct ! It's the Homefind.

 

Sorry, I wasn't clear when I said "close to the horizon". I meant more like 30-35°. Somehow low Alt values seem to trigger the problem.

I will definitly spend more effort on the absolut perfect balance !

But the scope with everything on it is below 23Kg. My "D" value ist really low to avoid oscillations, P and I are moderate and on comparable levels.