DDM100 : What is the minimum weight on the OTA side?

[JeremyBrookfield]

I have a new DDM100 that I am trying (and failing) to balance in RA.

The Autoslew>Servo-Setup>Balance routine works correctly in DEC but fails in RA. The graphical display shows the upper, vertical, red line and, briefly, the yellow bar. The vertical line then moves back to the left. There are no error messages, the RA motor is then switched off and I am forced to restart Autoslew in order to try again.

Is it possible that the total load on the system is too small? My scope (an RH200) is light and audibly "chattered" before I added 25kg of additional weight on the OTA side. Now the system is quiet and vibrates gently. The single counterweight is 12cm from the top of the shaft - so quite close to the DDM100. It feels balanced. I have tried moving the counterweight incrementally to various positions that are then clearly out of balance. Nothing seems to help.

I can't find any logs that help in diagnosing balance issues.

What is the minimum OTA-side load for a DDM100? Or do I have some other issue, not forgetting that am I new to the ASA world and might be doing something stupid?

 

All ideas gratefully received.

 

Jeremy

 

 

[astrosirius]

1 hour ago, JeremyBrookfield said:

I have a new DDM100 that I am trying (and failing) to balance in RA.

The Autoslew>Servo-Setup>Balance routine works correctly in DEC but fails in RA. The graphical display shows the upper, vertical, red line and, briefly, the yellow bar. The vertical line then moves back to the left. There are no error messages, the RA motor is then switched off and I am forced to restart Autoslew in order to try again.

Is it possible that the total load on the system is too small? My scope (an RH200) is light and audibly "chattered" before I added 25kg of additional weight on the OTA side. Now the system is quiet and vibrates gently. The single counterweight is 12cm from the top of the shaft - so quite close to the DDM100. It feels balanced. I have tried moving the counterweight incrementally to various positions that are then clearly out of balance. Nothing seems to help.

I can't find any logs that help in diagnosing balance issues.

What is the minimum OTA-side load for a DDM100? Or do I have some other issue, not forgetting that am I new to the ASA world and might be doing something stupid?

 

All ideas gratefully received.

 

Jeremy

 

 

Hello Jeremy,

Nice pleased to meet you in this forum...

I have an DDM85 with incremental encoders (6 years old) and my experience after few telescopes, is that the mount feel more confortable with more medium and high payload than light load, this is true, at least my experience.

The theory payload without instrument of the DDM85 is 65 Kg and currently my setup is around 47 kg (RC16" plus equipments) and I have to say that I don`t have problems with the balance and vibrations, obviously after spent a little time to make a good setup playing with the PID in both axis. You will have to make an automatic balance to find out where the mount feels more confortable, but to start with you should try to reduce the parameters in case your setup is so light. 

About you answer, I really don`t know the minimum payload, but I have to say that my first setupr with a telescope with a 25 Kg weight wasn't posible to balance properly, I had to put another telescope and more weight to reach the correct balance.

Well, this is my experience
I hope it helps to you

Luis Romero Ventura
www.astrosirius.org
www.astrotolva.com

[robertp]

Hello Jeremy,

have you tried to do an auto tune of the servos before trying to optimize the balance? You mentioned that with the additional weights the mount vibrates gently. I can imagine that as soon as the balance routine tries to move your RA axis, the maximum error of the axis will be reached and therefore the motor shuts off. So I would recommend that you either do an auto tune or if that fails do a manual tune making sure that you get no vibrations (neither in tracking mode nor when doing fast slews) and then try to balance the mount perfectly.

Have you checked the servo-log whether it contains some hint what the problem might be?

Hope you get your problem resolved,

clear skies,

Robert

[JeremyBrookfield]

Hi Luis,

 

Thank you for your response. The total weight on the OTA side after adding 25kg of steel is approximately 38 kg. (25kg steel + 8kg telescope+ 5 kg focuser/camera/PC). 

That is 38% of the theoretical maximum payload. Surely that is within an acceptable range?

For a test, I added a further 5kg to the plate on the top of the scope. The system was in rough balance with the counterweight now at 25 cm from the top of the shaft. 

I still had the same problem.

It would be difficult to add more weight without exchanging the telescope or adding a second one. That is not something I wish to do in the hope that it fixes the Autoslew - Servosetup- Balance issue. 

Is there a way to log what the Balance software is doing and why it is complaining?

 

[JeremyBrookfield]

Hi Robert, 

Thank you for the interesting suggestion. It's raining tonight in the observatory but will try an autotune tomorrow. Are the relevant logs in C:\ProgramData\ASA\Autoslew\ClServoLogs?

 

Jeremy

[robertp]

Hi Jeremy,

that's correct, these are the relevant logs. Within the log from one of the sessions where you experienced the problem there might be an error message that could help track down your problem.

Best regards,

Robert

[robertp]

Hi Jeremy,

any progress with your problem?

Best regards,

Robert