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Balancing Newton on DDM60pro


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#21 GeorgeCarey

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Posted 15 September 2015 - 03:36 PM

And this one?

http://forum.astrosy...cing-the-ddm60/

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


#22 w0mbat

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Posted 16 September 2015 - 01:19 AM

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


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


#23 Waldemar

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Posted 16 September 2015 - 08:43 AM

"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
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.  

#24 w0mbat

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Posted 16 September 2015 - 08:57 AM

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


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


#25 MarkS

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Posted 16 September 2015 - 09:00 AM

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



#26 GeorgeCarey

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Posted 16 September 2015 - 09:25 AM

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.


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


#27 GeorgeCarey

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Posted 16 September 2015 - 09:27 AM

If you take a photograph of your system, from the front of the tube looking down towards the mirror, it might make it easier to describe what you need to do.

Talk of axes, planes etc is confusing.


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


#28 RamaSpaceShip

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Posted 16 September 2015 - 10:49 AM

Hi Ian,

 

 

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?????

 

I will try to be simple. You need to reason it terms of centre of gravity. The important thing here is that just the centre of gravity of the OTA matters. (This is static balancing, dynamic balancing is only needed when using high rotation speeds, and would be more complex).

 

The goal of balancing the Dec axis is to put the centre of gravity of the whole OTA exactly on the RA axis. Nothing else is needed.

 

To be able to reach that goal, you can, as a first step, put the centre of gravity of the OTA in the plane formed by the RA and Dec axes,

so that sliding the OTA along its axis will allow to move its centre of gravity on the RA axis and thus realise the balancing.

 

George's method replaces the RA axis by a thread for convenience, so that it becomes easy to show when the centre of gravity of the OTA is in the plane formed by the thread and the OTA axis.

 

So yes, radial balance is sufficient.

 

Hope you understand better.

 

Bernard



#29 w0mbat

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Posted 16 September 2015 - 02:06 PM

Thanks so much to you all for your help.

It seems to me that the source of my confusion is, as is often the case I find, terminology and what a word means to different people.

There are an infinite number of radii in a circle so, to me, radial balance means balanced across all radial directions such that a round object could be placed in any position on a level surface and not roll.  It seems clear to me now that this is not the meaning being used in most of these discussions.

I think Mark has used the correct term to describe what it seems is necessary.......lateral balance.

So after digesting all that has been written the understanding I have reached is as Mark says:-

 

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.

 

 

Thanks again to you all. I just wish ASA would get it's act together and publish manuals that properly explain important issues such as this to all it's customers.

Regards

Ian


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


#30 Waldemar

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Posted 16 September 2015 - 08:38 PM

For me the radial balancing using rolling on two up-side-down aluminum T profiles worked great.

No more problems. The scope should not roll in any position. Simple and effective.

 

Well anyway, just my 2cts

 

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.  

#31 w0mbat

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Posted 17 September 2015 - 02:32 AM

Hi Waldemar,

I agree that your solution is the ideal way to achieve "perfect" radial balance. However in the case of larger Newtonian apertures the weight necessary to achieve  this becomes very large and therefore the moments of inertia may become a concern especially on a DDM60.

As I have said I have already constructed and tested a counterweight system mounted on top of the tube rings. With this I can achieve radial balance in all OTA positions when rolling on level rails. However this adds around three kilograms spaced about 100mm above the top of the tube rings. This then will of course mean adding a similar weight to the counterweight bar. It was at this point I became concerned about the added inertia this involved and started asking questions in this thread.

I could try this system back on the mount but my inexperience makes me nervous about this.

I would appreciate any comments as to whether my concerns are justified.

As you have seen other users say full radial balance is not necessary as long as the focuser is exactly aligned with the counterweight bar and then any lateral imbalance is corrected with small weights to make the focuser assembly weight symmetrical around the Dec axis plane.

The steep learning curve continues!

Regards and thanks

Ian


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


#32 GeorgeCarey

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Posted 17 September 2015 - 12:12 PM

Full radial balance IS necessary, and can be achieved by a single weight, somewhere near the focuser/camera.

This shows radial balance:

 

001.jpg

 

 

'Lateral' balance is illustrated looking sidelong at the telescope:

 

002.jpg

 

The red circle shows a possible position for the counterweight.


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


#33 MarkS

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Posted 18 September 2015 - 12:46 AM

Hi all,

 

I think we have had some definition problems on this thread.

 

I would like to suggest three definitions related to DE balance for future use, as I'm sure balance issues will come up again:

 

1. Full radial balance means that the CG of the OTA/camera/finder etc lies on the OTA axis.

 

2. Lateral balance refers to the position of the CG of the OTA system relative to the DE axis when viewed from the front or back of the OTA.

 

3. Longitudinal balance refers to the position of the CG of the OTA system along the length of the OTA relative to the DE axis.

 

Just a suggestion: it doesn't really matter what the definitions are as long as we are all using the same ones.

 

Regards,

Mark



#34 GeorgeCarey

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Posted 18 September 2015 - 09:54 AM

Good idea Mark.

In that case, my posts have been based on the theory that lateral balance is needed, but full radial balance is not necessary.

Obviously longitudinal balance is also required.


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


#35 w0mbat

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Posted 19 September 2015 - 12:49 AM

Thanks George and Mark. We now have a consistent basis from which to discuss this issue.

Ian


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


#36 MikePaling

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Posted 06 October 2015 - 01:57 PM

Hi everybody ... I am new to this forum.

 

After having a good look at the DDM60pro mount at the recent IAS show at Stoneleigh Park here in the UK I am seriously considering buying one .... this is the reason for me joining the forum.

 

After reading this thread about balancing a scope on the mount I am becoming a little bit discouraged ....

 

My question is .... whatever scope is fitted to the DDM60 ... is it absolutely vital that the scope is 100% balanced in every possible way before the mount will work as well as it should?

Looking at what has been written in this thread it seems that all sorts of small counter weights are needed in all sorts of places  ... and the sizes of these weight are only relatively small (often only a few grams) in comparison to the weights of various equipment added to the main scope.

Also I have seen all sorts of jigs and contraptions being used to help fine tune the balancing of the scope with any additional equipment.

Will the "direct drive system" used on the ASA mounts cope with set-ups which are even slightly out of balance ... compared to mounts that use more mechanical engagement using gears???

 

Just how critical is this "balancing problem" ??? I am worried :-(

 

Mike



#37 GeorgeCarey

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Posted 06 October 2015 - 03:45 PM

Hi Mike,

Did they have the mount running at the show? I went early on Friday and they were still setting it up.

Do not be too discouraged about the balancing issue. I am the lunatic who used the 'hang it from a wire' technique, mostly because I can't resist tinkering with things beyond the point that normal people would have stopped. As far as I know, nobody else has gone to such lengths.

Having said that, the DDM mounts are much fussier than the normal gears and worm type mount. As you will have seen at the show, the only thing that holds the scope in place and tracks the stars is a very strong magnetic field. If the scope is unbalanced then the currents rise and the software can get into a frazzle.

 

I have had my mount for five years and balance has not been a major issue. I did have a few mechanical problems but ASA paid for the mount to be shipped back to Austria and repairs were not charged for.

 

George


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


#38 robertp

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Posted 06 October 2015 - 06:14 PM

Hi Mike,

 

even though the DDMs require more care in balancing the scope, from my experience there is no need to get it even close to perfect. I use the mount alot for solar imaging and I put whatever scope I use on the mount, balance it roughly just by moving the axis in both directions until they feel similar (I hardly ever use the balancing tool within autoslew). During my imaging sessions, I often take my doublestack filter off the scope, replace the eyepiece by a ccd and never bother to rebalance.

In a permanent setup, trying to achieve a close to perfect balance is certainly worthwhile, especially when you completely rely on a bigger pointing file. When using MLPT, I guess that a slight off-balance does not matter.

 

But like George, I sometimes feel a need to try to get something perfect. However, before you spend hours balancing your scope in a test rig, make sure that e.g. the saddle plate does not put your perfectly balanced scope off-center.

 

Best regards,

 

Robert



#39 MikePaling

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Posted 07 October 2015 - 09:55 AM

Hi George and Robert ....

 

Many thanks for taking time to reply to my question .... I feel a lot happier now :-)

 

I have been trolling through all other references to the "balancing problem" and can now see that it doesn't have to be 100% perfect although very desirable to get things as close as it can be.

 

I didn't realise that there was a "Balance sensor" routine available in the software which sounds very useful indeed .... I hope that this is easy to use when I eventually get my DDM60!

 

Regards Mike



#40 GeorgeCarey

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Posted 07 October 2015 - 11:23 AM

Where are you in the UK, Mike?

I am happy to give advice when you get it. The learning curve can be a bit steep.


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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