+Graham Posted April 25, 2018 Share Posted April 25, 2018 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 Link to comment Share on other sites More sharing options...
Tweedledee Posted April 25, 2018 Share Posted April 25, 2018 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. +Graham 1 Link to comment Share on other sites More sharing options...
+Graham Posted April 25, 2018 Author Share Posted April 25, 2018 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. Link to comment Share on other sites More sharing options...
BAZ Posted April 26, 2018 Share Posted April 26, 2018 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. +Graham 1 Link to comment Share on other sites More sharing options...
Doc Posted April 26, 2018 Share Posted April 26, 2018 (edited) How about designing extendable yoke arms locked via a large rachet handle. Edited April 26, 2018 by Doc +Graham 1 Link to comment Share on other sites More sharing options...
+Graham Posted April 26, 2018 Author Share Posted April 26, 2018 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. Link to comment Share on other sites More sharing options...
Smithysteve Posted April 26, 2018 Share Posted April 26, 2018 Hi Graham, have you designed the optical system yet? i can send you my measurements for my 16” Lightbridge if you want them. +Graham 1 Link to comment Share on other sites More sharing options...
Tweedledee Posted April 26, 2018 Share Posted April 26, 2018 (edited) 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 April 26, 2018 by Tweedledee +Graham 1 Link to comment Share on other sites More sharing options...
+Graham Posted April 26, 2018 Author Share Posted April 26, 2018 (edited) 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 April 26, 2018 by Graham Link to comment Share on other sites More sharing options...
BAZ Posted April 26, 2018 Share Posted April 26, 2018 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. ? +Graham 1 Link to comment Share on other sites More sharing options...
Smithysteve Posted April 26, 2018 Share Posted April 26, 2018 It might pay to consider upgrades to bigger optical tubes in the future, you might get aperture fever! +Graham 1 Link to comment Share on other sites More sharing options...
Tweedledee Posted April 26, 2018 Share Posted April 26, 2018 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...? Smithysteve, +Graham, tuckstar and 2 others 4 1 Link to comment Share on other sites More sharing options...
BAZ Posted April 26, 2018 Share Posted April 26, 2018 Sort of what I imagined to be honest. ? Tweedledee 1 Link to comment Share on other sites More sharing options...
+Graham Posted April 26, 2018 Author Share Posted April 26, 2018 (edited) There ----- I told them not to release any pictures until after it was painted. ? Edited April 26, 2018 by Graham Tweedledee and Smithysteve 1 1 Link to comment Share on other sites More sharing options...
+Bino-viewer Posted April 26, 2018 Share Posted April 26, 2018 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 ? Link to comment Share on other sites More sharing options...
Brantuk Posted April 26, 2018 Share Posted April 26, 2018 Here's all the measurements for the LB 16" - hope it helps ? http://www.derekscope.co.uk/wp-content/uploads/2010/03/Size-of-Meade-Lightbridge-16-inch.pdf +Graham 1 Link to comment Share on other sites More sharing options...
+Graham Posted April 27, 2018 Author Share Posted April 27, 2018 (edited) 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 April 27, 2018 by Graham +Bino-viewer 1 Link to comment Share on other sites More sharing options...
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