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Heavy Payload on ASA85DDM


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#1 Botschafter.Sarek

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Posted 09 August 2015 - 10:37 PM

Hi - after now getting all my componenst together today was first time I put my "final" scope onto the DDM85 (Standart) 

 

My first tests using a 6 inch Refractor run's very well and smooth... 

 

Now having much more payload (40kg) on the mount, I did not expect that every thing is easy... 

 

I'm absolutely aware that I'm will be maybe not able to do fast move with such a payload..... but I guess from nominal data it should work. 

 

What currently could observe is: 

 

-RA run's slowly but okay.

-DK moves just about 5 degree (of slow movement) and after that I'll receive an errormessage and can''t move further... 

 The telescope is more or less in balance in DK - so I guess it should work.... 

 

I'm not look for fast move - knowing that the payload is high... - but I like to slow moves without big trouble... 

 

I hope/guess I can improve by somehow "training the drvies" - any guess about how to come to stable setup

Maybe lowering the maximum slew speed? 

 

(and please don't answer simply - "get an bigger mount..")

 

Thank You. 

 

Georg.



#2 TimC

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Posted 10 August 2015 - 01:10 AM

Hi Georg,

 

You will need to very precisely balance the scope and accessories in all axes to have success.

All the best,

Tim



#3 lukepower

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Posted 10 August 2015 - 07:28 AM

+1 to Tim,

 

I have (in the meantime) about 120kgs of equipment on my DDM85XL; and of course the corresponding counterweights. It's all about balance: Especially the radial balance on the outer parts of the tube are critical, and little things like a small O-ring may be needed to get good balance.

 

"More or less in balance" is definitively not an option, trust me. You will have to check balance in every position you can think of: Turn off the motors, move the scope by hand to the new position, turn on the motors and let the balance tool run. Fix the balancing, and go on to the next position.

You might need to iterate through this several times as you might find things that cause trouble (like a hanging cable, or a focusing motor on one side of the tube, etc).

Well worth the efforts :)


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


#4 Botschafter.Sarek

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Posted 10 August 2015 - 02:17 PM

Hi - thank you for your first answers ....

only one comment ... maybe I was not precise enough... Writing in balance more or less means the scope does not move itself having drives off. So it was somehow in balance - but your answers indicates that this level is not enough - I've to reach the next level - to get to the O-ring level needs definitive some time..

I guess, I've to make myself familar with the Balance Tool - I hope the description in the pdf files is sufficient
In addition I will buy a spring scale to measure the fources needed to move the scope...

So more come...

Thank you - so far..

Georg.

#5 Botschafter.Sarek

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Posted 30 August 2015 - 02:12 PM

Hello - 

 

meanwhile I worked on the balance of the tube. (20 Inch Newton on a DDM85 standard - weight ~42 kg) 

 

I checked it with the inbuild balance tool of autoslew.

 

Telescope pointing to the south and I worked on the RA-axis to bring it into balance - balance tool shows bars close together at less than 1 A current. So I assume it's ok. 

 

Now I focus in the DK-axis. My latitude is about 50 degree, so if I look on the DK coordinate - it runs from zenit to the horizon from +50 (zenit) to -40.

 

I started a zenit first bring the telescope into the balance putting some weights north / south on the extend tube at the level of the DK axis. - So this weight positions should have no impact the balance in horizontal position. Balance Tool indicates bars close together @ 1.0 A current level. 

 

I moved the telesope down do DK = -30 degree (check limits is disabled) and turn the telescope in the balance here also. Balance Tool shows same balance level.. 

 

After that I move step by step and check out balance at several DK's. 

 

Essentially I found out, that there are small areas where the movement in DK works and other in between there it does not (position error in DK). For what ever reason the range of possible movement is close to 6 degree and the inbetween regions with position error is 10 degree..

 

+54.0 to +47.5 degree     movement ok - in balance with less when 1.0 Ampere (shown in the Balance Tool)

+47.5 to +38.0                  does not work -> position error
+38.0 to +31.4                  movement ok - in balance with less when 1.0 Ampere (shown in the Balance Tool)
+31.4 to +21.4                  does not work -> position error
+21.4 to +15.5                  movement ok - in balance with less when 1.0 Ampere (shown in the Balance Tool)
+15.5 to +05.0                  does not move -> position error
+05.0 to -00.7                  movement ok - in balance about 1.0 Ampere (shown in the Balance Tool)
-00.7 to -10.8                   does not move -> position error
-10.8 to -16.8                   movement ok - in balance about 1.0 Ampere (shown in the Balance Tool)
-16.8 to -27.3                   does not move -> position error
-27.3 to -33.1                   movement ok - in balance about 1.0 Ampere (shown in the Balance Tool) 

 

I understand that balance is a important topic - but I don't understand why the telescope is in balance at DK = 50 and ~25 degree not but at 2 degree again without changing any weight. 

 

On top: if I move manually the telescope in a region of position error and rerun the Autostart Testing for the DK axis, it work for a few degree.. - very strange

 

In addition: if I move the telescope by RA, I see small changing of DK((!) even in case I do not push the DK button..(~1 arc sec / sec) - for me unexpected.

 

Any Idea / comment ? 

 

Georg



#6 RamaSpaceShip

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Posted 30 August 2015 - 10:17 PM

Hi Georg,

 

You should read this thread, it will help you to find the perfect balance in Dec and RA. For Newton telescopes it is not really easy.

 

But once this is done, you will be able to run at full speed on each axis. I have also an OTA of about 40kg on my DDM85 standard, and I have no problem to get a speed of 15 degrees per second.

 

Bernard



#7 Botschafter.Sarek

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Posted 31 August 2015 - 08:50 PM

Bernard,

 

Thank you for your comment which makes me a little more hoping my issue can be resolved.. I see your scope has roughly the same weight as my does, but I guess it's not a Newton and theirfore have not such a long tube as my does.

 

I've read the thread you mentioned - the idea to do so is very interesting. To do so for my tube needs a lot of preparation - so it well take some time...

 

What I do not understand is why a potential inbalance is able to create such a strange behaviour move through Deklination having Region there it works and inbetween there are regions where it does not work...  And by running the autostart procedure in a "dead" region is changing the situation.

 

As well I do not understand, why pushing O/W Buttons creates a change in Deklination..

 

Georg.



#8 RamaSpaceShip

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Posted 01 September 2015 - 10:01 AM

Hi Georg,

 

 

I guess it's not a Newton and theirfore have not such a long tube as my does.

It's a Dall Kirham, but the long tube, well balanced, will only have a lower acceleration, not a lower speed.

The fact is that the balance error has much more impact on a long tube weighted far from the Dec axis, than on a DK weighted much closer from the Dec axis.

 

 

What I do not understand is why a potential inbalance is able to create such a strange behaviour move through Deklination having Region there it works and inbetween there are regions where it does not work...  And by running the autostart procedure in a "dead" region is changing the situation.

 

As well I do not understand, why pushing O/W Buttons creates a change in Deklination..

The issue is that the weight at the end of a Newton tube creates a variable torque (unless it is well balanced like George did in the indicated thread), and this torque depends on the relative position of the tube. It is possible to model it, and the result is certainly very "chaotic", which can explain your strange behaviour.

 

So, even if it appears painful, George's recipe is a reliable solution.

 

Bernard



#9 GeorgeCarey

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Posted 01 September 2015 - 01:40 PM

Have you turned on data logging? This is a good way to see what the currents are doing  when you get errors.

 

George


ASA DDM60Pro, homemade 8" and 10" reflectors, QSI 683 camera, Astrodon 5nm filters, Pulsar dome observatory. Website: http://www.geoastro.co.uk


#10 Botschafter.Sarek

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Posted 28 January 2016 - 11:14 PM

 

 

 

Hi @ all ....

 

I just want to inform the community about the status of my issue

 

After some checks performed by Phillip Keller through a Teamviewer Session, it has been stated that the Mount has a defect in DK-Axsis.

So the mount have been turned back and I choosen the opportunities to upgrade to the next level.

 

After getting the mount back it looks good - even in case of a "medium" balanced scope, it moves as it should. The only open issue is that I could not choose high speed movements because my Setup is still a "pilot setup" and not rebust enough against oszillations. This would be the next improvement.

 

So now the more interessting times Begins, because I can start working on my projects.

 

Georg.






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