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Difficulty balancing with Netwotian + large saddle

Beginner Celestron Equipment Mount Reflector
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#1 daltomagne

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Posted 22 June 2021 - 06:38 PM

Anyone own the Explore Scientific n208CF astrograph or similar Newtonian? I recently upgraded to a CGX-L and am having a really hard time keeping balance. I can balance RA just fine, but DEC is only balancing in the horizontal position. I lose balance pretty quickly once in a more vertical position, you know like where the sky is...  The imbalance is more pronounced when OTA is pointing East.

I do rotate the OTA so the camera and guide scope are inward, toward the center of mass. However, because of the saddle's size, I can only move the dovetail or the OTA in the rings so far before the focuser or guide camera/scope bump against the saddle or saddle knobs.

 

A couple solutions I am going to try;
1. get a longer dovetail. Moving from ~8" V to 14" Losmandy dovetail. Should hopefully give more flexibility in OTA placement.

 

2. move the guide scope and camera to the top of the OTA, away from the center of mass but free from the saddle/knob obstruction. There is a handle on the OTA with a 1/4-20 screw slot, so I could try to find a guide scope mounting shoe that fits over the handle, but no luck yet at least from Amazon. I guess I could also replace the handle with a mounting plate, and sacrifice a little ergonomics.

 

Am I on the right path to correcting balance? If anyone else has any ideas I'm all ears.   

 

Thanks and clear skies,

Dalton

 

*I can take pictures when I get setup later this evening. 


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#2 Avgvstvs

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Posted 22 June 2021 - 06:56 PM

The dovetail looks pretty short.

Reclamping and rotating the OT may work (imaging system above or below when the mount is in its neutral position). But a longer dovetail is always a good choice

I don't have a F3.9 but and F5 and it balances well but I have a 12" on it

It shouldn't be hard to fix


Edited by Avgvstvs, 22 June 2021 - 06:58 PM.

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#3 RalphMeisterTigerMan

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Posted 22 June 2021 - 11:29 PM

I'm afraid I really can't help you but I'm dying to know what a "Netwotian" telescope is. LOL!

 

Obviously is must be a TIPO, or TWIPO or perhaps even a TYPWAD...just kidding. Sometimes we type so fast that what we intend to type and what comes out are two different things. 

 

Unfortunately, telescope OTA balancing can be something dynamic, especially if the load changes. Only those Amateurs who are fortunate enough to have a permanently mounted scope in a dome or roll-off-roof observatory with a heavy-duty mount with a massive multi-ton concrete "anchor" pier do not have that dreaded "balance" problem.

 

The only thing I could suggest is sliding counter-weights on a rod, the kind that you could find on the old C11's and C14"s.

 

Clear skies and keep looking up!

RalphMeisterTigerMan


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#4 spereira

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Posted 23 June 2021 - 06:55 AM

Moving to Reflectors.

 

smp


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#5 MitchAlsup

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Posted 23 June 2021 - 10:56 AM

The key to balance at all positions is that the CoG of the scope must pass through the axes of the GEM.

 

This means where the focuser stands out on one side, there needs to be an opposite weight down low on the other side.

 

This means where the finder is attached, one needs a weight on the other side counterbalancing it.

 

I reiterate: the CoG of the scope must be positioned where the DEC and POLAR axes cross. The balance weight of the GEM is to reposition the moving mass of scope plus moving parts of mount onto the polar axis from the CoG of the scope. It is not to balance the (unbalanced) scope on the GEM.


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#6 belliott4488

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Posted 23 June 2021 - 11:26 AM

Anyone own the Explore Scientific n208CF astrograph or similar Newtonian? I recently upgraded to a CGX-L and am having a really hard time keeping balance. I can balance RA just fine, but DEC is only balancing in the horizontal position. I lose balance pretty quickly once in a more vertical position, you know like where the sky is...  The imbalance is more pronounced when OTA is pointing East.

I do rotate the OTA so the camera and guide scope are inward, toward the center of mass. However, because of the saddle's size, I can only move the dovetail or the OTA in the rings so far before the focuser or guide camera/scope bump against the saddle or saddle knobs.

 

A couple solutions I am going to try;
1. get a longer dovetail. Moving from ~8" V to 14" Losmandy dovetail. Should hopefully give more flexibility in OTA placement.

 

2. move the guide scope and camera to the top of the OTA, away from the center of mass but free from the saddle/knob obstruction. There is a handle on the OTA with a 1/4-20 screw slot, so I could try to find a guide scope mounting shoe that fits over the handle, but no luck yet at least from Amazon. I guess I could also replace the handle with a mounting plate, and sacrifice a little ergonomics.

 

Am I on the right path to correcting balance? If anyone else has any ideas I'm all ears.   

 

Thanks and clear skies,

Dalton

 

*I can take pictures when I get setup later this evening. 

I also have the E. S. N208CF and have encountered similar difficulties.

 

In my case, it's because I'm on an iOptron CEM40 mount, which has their "Z-shaped" configuration, that is, the DEC axis is offset to the opposite side of the mount from the counterweight shaft. What that means is that the OTA is shifted rearward, so that I risk the focuser and camera bashing into the mount head as the DEC crosses the zenith.

 

In my case I solve this with your Solution #2: I keep the focuser and camera on the far side of the OTA from the mount. This has the obvious disadvantage of moving the combined center of mass of the OTA and camera farther from the RA axis, so I have to move the counterweights farther or add more weight to compensate. That's not a huge deal, since I'm still well under the payload capacity for my mount, but the greater moment of inertia isn't ideal.

 

So far I haven't delved into guiding, but when I do I anticipate attaching a dovetail plate to the OTA handle and then mounting the guide scope to that. I'm pretty sure I've seen examples of that on other Exp. Sci. scopes.

 

EDIT: I forgot to respond to your report that your OTA is balanced only when it's horizontal. That sounds like the combined center of mass of your OTA, focuser/optics, and finder is either directly above or directly below the DEC axis when the OTA is horizontal. If you move the OTA away from horizontal and it continues moving away - especially if it does this in either direction - then the C-O-M is above the axis. If it tends to move back toward horizontal, then the C-O-M is below the axis.

 

In either case, the solution is to rotate the OTA in its rings to bring the C-O-M closer to the DEC axis. This usually (for me, anyway) means rotating it so that the focuser is slightly to one side and finder is on the other side. They're the only parts that contribute to the C-O-M being off the axis of the OTA, so getting them balanced is the trick.


Edited by belliott4488, 23 June 2021 - 11:36 AM.

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#7 kathyastro

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Posted 23 June 2021 - 12:25 PM

I balanced my Newt by removing the guide scope from the finder shoe and mounting it on a second dovetail mounted on the top of the rings.  That way, it is always in balance laterally.

 

I balance the scope laterally by rotating the OTA so that the camera is on the centreline.  There are two positions where this will work: focuser up and focuser down.  Focuser up will work for all mounts, but it requires more counterweight moment.  I slid my scope forward slightly so that I could mount the OTA with the focuser down and still have the camera clear the counterweight hub on my CEM-60.

 

Since that position put the longitudinal balance too far forward, I slid my guide scope back on its dovetail to compensate.


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#8 daltomagne

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Posted 24 June 2021 - 02:00 AM

I'm afraid I really can't help you but I'm dying to know what a "Netwotian" telescope is. LOL! The only thing I could suggest is sliding counter-weights on a rod, the kind that you could find on the old C11's and C14"s.

Oof! I need to get more sleep... As for sliding counterweights, I could give that a try but if I can, I'd like to avoid more pieces to tinker with during setup/teardown.

 

The key to balance...means where the focuser stands out on one side, there needs to be an opposite weight down low on the other side.

I'm attempting this now, in both positions with focuser facing CoG and away from CoG. I currently have the guidescope/cam and focuser/DSLR/CC equidistance on either side of the of the Dec axis and they are similar in weight (around 1.5lb). I can more readily achieve this in some positions while the weight is on opposite side of OTA, away from CoG, but when rotating the optics facing CoG I run into the saddle obstruction. While I'm waiting on a longer dovetail I could spend some time practicing balancing OTA while away from CoG, but that isn't ideal for my cabling, which admittedly also needs work.

 

the greater moment of inertia isn't ideal. I anticipate attaching a dovetail plate to the OTA handle and then mounting the guide scope to that.

I hear you on the greater moment of inertia woes. The few nights I've been able to achieve good balance for my intended target, I've had some windy nights and every little gust shifts the OTA, guidecam, and ultimately the DSLR sensor undesirably. I think I will ultimately swap out the handle for a dovetail and sit the guidescope/cam on top the rings. I am hopeful that weight will help counter the camera/accessories, which combined with a longer dovetail will give me better placement of the OTA in general and avoid the saddle obstruction.

 

I balanced my Newt by removing the guide scope from the finder shoe and mounting it on a second dovetail mounted on the top of the rings...I slid my scope forward slightly so that I could mount the OTA with the focuser down and still have the camera clear the counterweight hub...I slid my guide scope back on its dovetail to compensate.

These are excellent suggestions Kathy! I love the idea of mounting the guide scope up top and having it adjustable in position on the dovetail. Along with offsetting the focuser/imaging train on RA, it gives some flexibility on the Dec axis balancing.

 

Thanks for the suggestions everyone. 



#9 belliott4488

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Posted 24 June 2021 - 07:49 AM

I balanced my Newt by removing the guide scope from the finder shoe and mounting it on a second dovetail mounted on the top of the rings.  That way, it is always in balance laterally.

 

I balance the scope laterally by rotating the OTA so that the camera is on the centreline.  There are two positions where this will work: focuser up and focuser down.  Focuser up will work for all mounts, but it requires more counterweight moment.  I slid my scope forward slightly so that I could mount the OTA with the focuser down and still have the camera clear the counterweight hub on my CEM-60.

 

Since that position put the longitudinal balance too far forward, I slid my guide scope back on its dovetail to compensate.

Yet another clear and concise explanation from kathyastro! laugh.gif

 

So far I haven't delved into auto-guiding, but now I have another incentive to do it sooner rather than later. 


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#10 daltomagne

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Posted 26 June 2021 - 01:48 AM

Thanks again everyone, for the suggestions. I am currently waiting on a 19" Losmandy dovetail and a V-style dovetail to replace the handle and add the guidescope up top. I'll update on improvements once everything gets in.   



#11 bokemon

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Posted 26 June 2021 - 08:00 AM

I also have this problem with a 8" newt where the balance point with the camera pointed down hits the saddle. One solution is to purposely add weight to the back of the scope.  This in turn will allow you to slide the scope further forwards in the clamp.



#12 KLWalsh

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Posted 27 June 2021 - 07:38 AM

A trick to help get a scope dynamically balanced - ie., balanced in Dec when the scope is horizontal *and* when the scope is vertical - is to clamp a ‘vice-grip’ pliers to the dovetail bar, or the saddle, or to the counterweight bar, depending on which location is most convenient. Of course, wrap the jaws with something soft to prevent marring the surface where the pliers are clamped.
You might have to re-balance the scope in RA, due to the slight weight of the pliers.
Once the scope is dynamically balanced, you should be able to aim it in any direction and have it stay where it’s put, even with the clutches/brakes off.
If you’re doing photography, you want to dynamically balance the scope first, then move a counterweight to make the scope slightly ’East-heavy’ to reduce worm gear backlash.


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