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Balancing Newton on DDM60pro


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#1 Adamo

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Posted 26 March 2015 - 02:54 PM

Hello

 

My name is Adam i bought DDM60pro.

I have a problem with the balance of newton 8".

When OTA pointing south (in RA axis) the balance perfectly !

When OTA pointing west or east the balancing is lost!.

Similarly in the axis DEC.

if the telescope is horizontally the balance is perfectly !

In another position, it is only worse.

Have any of you had this problem?
How to solve it?

how it is possible to keep balance in every position with Newton OTA?

 

Best regards Adam Kisielewicz



#2 RamaSpaceShip

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Posted 26 March 2015 - 08:00 PM

Hi Adam,

 

A solution is to first compensate for the weight of the focuser and all stuff on it, by adding an appropriate counterweight on the oppositite side of the OTA.

 

Don't also forget the influence of the cables! If they are not linked to the OTA, they have a variable position depending on the position of the OTA, and as such they can ruin the expected balance.

 

Good luck.

 

Bernard



#3 GeorgeCarey

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Posted 27 March 2015 - 02:45 PM

Is this what people really do? I can understand if the focuser and camera are 'off centre' then it might be necessary to add a weight to the side of the camera.

If that is done does it really need another weight on the opposite side of the scope tube?


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


#4 lukepower

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Posted 27 March 2015 - 07:38 PM

Hi George,

 

in my case (my OTA just went through a transformation from Cassegrain to Newton) I had to add two 2-Euro coins as counterweight on the opposite side of the OTA to the camera, otherwise I had position errors all the way...

Of course, this can happen with a tube with 60cm in diameter, I suppose...


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


#5 RamaSpaceShip

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Posted 28 March 2015 - 12:26 AM

Hi George,

 

 

Is this what people really do?

I don't know (I own a Dall Kirkham)  but they should to ensure a good balance for all tube positions. The idea is to have the OTA equivalent to a thin bar so that moving it along its axis can provide perfect balance.

To ensure that, each section of the OTA must be balanced wrt the tube axis.

It is easy to get this for OTAs having the focuser on the axis (like the Cassegrain) but harder for Newtons and the like.

 

If you don't do that, you risk to get the behaviour Adam is observing. The motors can compensate for the unperfect balance, but not in all cases.

 

Best regards.

 

Bernard



#6 Waldemar

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Posted 28 March 2015 - 12:49 PM

Is this what people really do? I can understand if the focuser and camera are 'off centre' then it might be necessary to add a weight to the side of the camera.

If that is done does it really need another weight on the opposite side of the scope tube?

I had to compensate for the focus motor (direct wormdrive, weighs about 450 gramms) on my TEC 140... so yes, that is what you have to do to get perfect balance in all positions. The bigger the diameter, the larger the problem, of course.

In order to find the right compensation weight and position, I rolled the tube over a flat surface and fiddled around until it laid still in all positions. Sounds weird, but it worked!

 

Regards, 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.  

#7 GeorgeCarey

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Posted 28 March 2015 - 01:17 PM

I have a Newtonian telescope. I can see that the lateral balance of the focuser and camera system needs to be in line with the central axis of the telescope.

But I am still finding it hard to accept that a similar weight needs to be on the opposite side of the scope for perfect balance.

This diagram may help to show what I mean:

 

balance.jpg

 

 

The small red dot shows where the Centre of Mass of the OTA will be in a Newtonian. The fact that it is not in the centre of the tube (green dot) should not matter. Provided it is along the dotted line it should be perfectly balanced in all positions.


Edited by GeorgeCarey, 28 March 2015 - 01:18 PM.

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


#8 GeorgeCarey

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Posted 28 March 2015 - 01:21 PM

Before you shout at me, I realise I put the focuser on the wrong side.    :wacko:   But the principle is the same.


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


#9 Waldemar

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Posted 28 March 2015 - 03:03 PM

hahaha, don't worry George. I think there's a slight misunderstanding here.

I am talking about radial equilibrium about the tube axis.  So called three axes balancing:  http://www.brayebroo...equatorial.html

 

Regards, 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.  

#10 GeorgeCarey

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Posted 28 March 2015 - 03:39 PM

Thanks Waldemar,

The first two posts resulted in a statement that there needed to be a counterweight equal and opposite to the focuser and camera for a Newtonian on the opposite side of the tube. This is what I am querying.


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


#11 RamaSpaceShip

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Posted 28 March 2015 - 05:29 PM

Hi George,

 

Your solution works perfectly, providing that the OTA is turned at the exact position where  its centre of mass is in the plane formed by its axis and the dec axis.

As I wrote, the solution I proposed works for all OTA positions.

 

I agree that yours may be much simpler.

 

So you need to add another (and first) step to the balancing work: turn the tube to put its centre of mass in the plane formed by its axis and the dec axis (and preferably below the tube axis to minimise the effects of a position error). This roughly means to align the focuser axis with the dec axis below the tube.

 

You can use Waldemar's method to find the precise correct position:

- put the OTA fully equiped on two horizontal bars

- wait until it is stable

- the line joining the 2 points of contact with the bars must cross the dec axis.

 

 

Best regards.

 

Bernard



#12 Adamo

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Posted 30 March 2015 - 12:49 PM

Thank you for all the answers.
My camera is directed to the center.
I'll do the photo and I put in the forum.
George, I understand your figure but how to do it in practice?
:rolleyes:

How to balance the DEC axis?

perhaps like this:

 

Best regards Adam

Attached Files



#13 RamaSpaceShip

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Posted 30 March 2015 - 07:39 PM

Hi Adam,

 

George's idea is to avoid the addition of weight.

 

To balance the dec axis, you either move the OTA in its rings, and/or move the dovetail plate on its support until you reach the perfect balance.

 

If it is too hard to get the exact balance by this way, you can do the best you can and then add a very small weight to improve the balance.

 

I personnaly chose to add a threaded bar on the dovetail plate to do an effortless precise adjustment of the dec balance (see this post: http://forum.astrosy...e-adjustment/).

 

Best regards.

 

Bernard



#14 Adamo

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Posted 30 March 2015 - 09:31 PM

Hello

I did like the photo and it is much better :)
I have yet to finalize and will be fine
Thank you for your help :)

 

Best regards Adam

Attached Files



#15 GeorgeCarey

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Posted 31 March 2015 - 09:31 AM

The way I see it is that any counterweights need to be placed according to this diagram:

 

 

balance2.jpg

 

 

M3 in red is the counterweight.

Looking along the axis of the OTA, you need to consider any weight that is not symmetrical. In this case I have looked at the asymmetry of the camera, and the weights of the tube ring knobs. Weights on the left side of the central line should balance those on the right.

Exactly where M3 goes is not important as long as it agrees with the balancing equation.


Edited by GeorgeCarey, 31 March 2015 - 09:33 AM.

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


#16 MarkS

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Posted 31 March 2015 - 12:00 PM

George,

 

You are right. I have done a detailed calculation which agrees with your statement.

 

Because my set-up is mobile, and I cannot guarantee to get the camera oriented exactly each time, I use one or two 45gm counterweights (3 x 50c AUS) to fine tune the DE balance as per your diagram. (I just attach with electrical tape in the best position as indicated by a digital ammeter :) )

 

Regards,

Mark



#17 Waldemar

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Posted 31 March 2015 - 01:31 PM

I totally agree with you, George.

I have been stressing this principle a couple of times already, but you made it nicely visible.

It is the only way to get a nice balance in every position.

 

Regards,

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.  

#18 Adamo

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Posted 01 April 2015 - 08:56 AM

George, this diagram is very good!

Thank You :)

Everything apply in practice and should be fine.

What the longest exposures snapshots?

 

Best regards Adamo



#19 w0mbat

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Posted 15 September 2015 - 03:02 PM

Hi,

As I have a permanent setup my objective is to achieve good balance in all positions. I have my OTA (ASA N10) off the mount (DDM60 Pro)  to investigate the radial balance of the OTA.

There is a HUGE radial imbalance of several kilograms (Ok3 plus corrector plus camera).

I have read this thread over and over and I am still not convinced that I really understand.

Are we saying that I do not have to fully balance the OTA radially as long as the remaining imbalance is centred and symmetrical about the plane of the Dec axis?

In other words, if I were to place the OTA on horizontal bars with the focuser pointing down and add small weights to correct the asymmetries until the focuser is perfectly vertical  and then ensure the focuser centre line is on the plane of the Dec axis then that is all I need to do?

I have already constructed a counterweight system to fully radially balance the OTA (which is working) but I am concerned about the weight it adds and even more about how far that extra weight is from the mount. And then I would have to add even more to the RA weights. So it is starting to seem like a bad idea to radially balance the OTA in all positions when the imbalance is so large.

So could someone please confirm that fully radially balancing the OTA is actually unnecessary as long as there is no imbalance about the plane of the Dec axis and that the large remaining imbalance in the Dec axis plane will not matter when trying to achieve good mount balance in all sky positions?

Thank you,

Ian


ASA DDM60Pro, ASA N10 Astrograph, Orion ED102T CF Refractor, Canon 60Da DSLR, Sirius 2.3 Metre Observatory, WIN10 Pro 64bit.


#20 GeorgeCarey

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Posted 15 September 2015 - 03:31 PM

Hi Ian, have you seen this thread?

http://forum.astrosy...cope-balancing/

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





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