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Balancing Newton on DDM60pro


Adamo

Question

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

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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

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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...

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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

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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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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
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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

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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

post-4398-0-18822200-1427716088_thumb.jpg

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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.astrosysteme.com/index.php?/topic/245-dec-balance-precise-adjustment/).

 

Best regards.

 

Bernard

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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
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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

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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

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Hi George,

Yes I have seen those threads. In fact reading the various posts about balancing and the various methods used is probably the source of my uncertainty.

For instance, in following your thread about suspending the OTA on a wire I was initially puzzled as it seemed to me that your method would be completely insensitive to any radial imbalance in the vertical direction. That is why I am asking. Are you saying that as long as any radial imbalance in the OTA is symmetrical about the Dec axis plane that it does not matter and will have no negative effect on the mount operation?????

 

If that is so then all is well and I will not have to add a lot of weight.

If that is not so then I would have to add several kilograms spaced around 100mm from the top of the tube rings to achieve full 360 degree radial balance. The ASA OK3 focuser with Wynne corrector inside and a camera attached is very heavy.

I have spent a lot of time fiddling with balance. Similarly to others I have never been able to achieve good results with the Autoslew balance tool in all positions. I have assumed that it was OTA radial imbalance that was the source of this problem. I am trying to correct that.

So to eliminate the possibility that I am misreading/misinterpreting other people's language or diagrams I am after a simple direct statement.

Do I have to achieve full 360 degree radial balance of the OTA such that it would sit balanced in any position on a level plane?

Or is it enough to place the focuser centrally in the Dec axis plane and then correct for any remaining asymmetries about the Dec axis plane with small weights?

Sorry if I am slow but there are so many seemingly contradictory statements made about balance that I would like to be certain.

Of course, if there were comprehensive manuals for ASA products I would not need to be asking these questions!

Regards

Ian

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"Of course, if there were comprehensive manuals for ASA products I would not need to be asking these questions"

 

there you go! That is pinpointing the problem...

Even with my TEC 40 I had the same problems when I attached a heavy focus motor.

i.m.h.o. radial balancing is very important to get things working correctly.

 

BR

Waldemar

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Thanks Waldemar. But I am still left with the questions I asked above.

What is meant by radial balancing?

Do you think that we should be using your rolling method to achieve radial balance in all positions?

Or is George's method sufficient which (as far as I understand it) places the imbalance in the Dec plane and just corrects for asymmetries of weight around the Dec axis plane?

I will do whatever is necessary. I just can't get a direct answer as to which method will work best for all position good balance in a permanent setup.

Ian

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Hi Ian,

 

If you align the corrector/camera assembly exactly co-axial with the counterweight bar (looking from the front), and you have 'perfect' longitudinal balance about the DEC axis, all you need to worry about is any lateral imbalance.

 

The main contributors are the camera/filterwheel assembly, a finderscope if you have one, and the focuser motor on the OK3. If these off-centre weights cause any residual moment about the DEC axis, they must be balanced out. 

 

I do a final lateral trim each time I set up (mobile), using small weights stuck to the OTA in the right places with electrical tape.....

 

Regards,

Mark

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The hanging on a wire method shows radial balance - that is why I came up with the idea.

It also shows lateral balance.

If you look along the length of the telescope tube then the wire should be exactly perpendicular to the telescope mounting plate if the radial balance is good.

If the wire is perpendicular to the plate no matter what direction you look, then balance is good in all planes.

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