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Graham

Question for larger dob owners.

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Graham

Larger dob owners refers to the scope not your waist size 😂

 

My Question.

I need to know the distance from the pivot point to the base of the scope on some of the larger dobs. 14, 16, 18 inch ect.

Estimates are more than welcome.

I need this info so I can finalise the drawings and get my horseshoe / split ring / yoke mount made.

Thanks

Graham

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Tweedledee

There are ways to calculate the exact  pivot position if you know all the component weights and their relative positions along the OTA. I can help you further with this if you can provide some more details.

 

I'm not sure how the following will help you, but my 14 dob pivots at 425mm from the bottom of the OTA and the OTA is 1580mm long. Each design will have a different pivot point dependent on its individual components and other 14" dobs will have different components and therefore different pivot points.

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Graham

Thanks. 

I don't need to work out the pivot point as such. What I am trying to do is get a rough idea of the variants so I can decide how long to make the yoke arms to give me full movement of the scope inside the mount. 

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BAZ

I am I guessing right that you don't as yet have the scope to mount in it? I think that making the mount first without the scope could cause you more problems than it solves. 

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Doc

How about designing extendable yoke arms locked via a large rachet handle. 

 

 

 

 

Edited by Doc

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Graham
4 hours ago, Doc said:

How about designing extendable yoke arms locked via a large rachet handle. 

 

 

 

 

 

Interesting idea. 

Unfortunately my design is an open lattice work which saves on weight without sacrificing rigidity. 

 

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Smithysteve

Hi Graham, have you designed the optical system yet?

i can send you my measurements for my 16” Lightbridge if you want them.

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Tweedledee

If you are planning to have the OTA well balanced in the yoke arms, then it would be ideal to calculate the OTAs pivot position. Then you will have precise measurements to work to and can then use this information to calculate the exact swing through positions and allow a suitable gap over and above that position.

 

Just taking a rough average from mine and other peoples dobs as you are suggesting, may or may not bear any resemblance to the actual balance position of your custom built OTA.

This may not be a problem if you are happy to add extra balance weights to either end of the OTA to force it to balance wherever you have fitted it in the mount, but we normally want to keep weight to a minimum.

 

The more accurate the initial information, the more accurately this can be calculated in advance to get all things near perfect.


This is easier to do than you may think. 😊

Edited by Tweedledee

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Graham

Thanks Pete. 

I do not have a custom built ota at the moment.  that will be awhile yet.

Unfortunately the mirror build got put on hold when I did my arm in.

I am just interested in getting some facts  and figures about dobs that are already out there. 

9 hours ago, BAZ said:

I am I guessing right that you don't as yet have the scope to mount in it? I think that making the mount first without the scope could cause you more problems than it solves. 

 

You guess correctly. Which is why I asked the question. 

 

Edited by Graham

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BAZ

I am just wondering that if you build the forks before you have the scope, they may end up longer than you need and get unwanted vibrations rather than having as short as possible. Mind you , if I know your engineering you could probably hang a tank in it. Just a thought. 😊

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Smithysteve

It might pay to consider upgrades to bigger optical tubes in the future, you might get aperture fever!

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Tweedledee
2 hours ago, BAZ said:

I am just wondering that if you build the forks before you have the scope, they may end up longer than you need and get unwanted vibrations rather than having as short as possible. Mind you , if I know your engineering you could probably hang a tank in it. Just a thought. 😊

 

2 hours ago, Smithysteve said:

It might pay to consider upgrades to bigger optical tubes in the future, you might get aperture fever!

After starting fabrication of parts for his horseshoe mount, Graham is not worried about vibrations, but still has concerns about whether he's left enough clearance for the OTA to swing through OK...😮

1horseshoe.jpg?raw=1

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Graham

There ----- I told them not to release any pictures until after it was painted. 😁

Edited by Graham

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Bino-viewer

Forgive the question (i'm not really in the know)

Why don't you just put whatever size  Dob you are planning on a tracking platform ?

 

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Graham
6 hours ago, Bino-viewer said:

Forgive the question (i'm not really in the know)

Why don't you just put whatever size  Dob you are planning on a tracking platform ?

 

 

This is for imaging. 

Tracking platforms are ok for visual but not so good for imaging. 

Edited by Graham

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