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Thread: I'm planning building an EQ platform

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    Default I'm planning building an EQ platform



    Hi

    I have a 8" dobsonian telescope (203 / 1200) and i would like to motorise it for astrophotography,
    I searched here and there for informations which explain me I had to calculate my telescope's center of mass, which I did,
    so here's a plan : https://image.noelshack.com/fichiers...221-163023.jpg
    (not to scale) G is 3cm offset with the center of the scope.
    I've seen platforms with eliptical parts and wheels, but the distance between the center of the scope and base of the earth axis is only 25.5cm long, I dunno how to calculate the eliptic part dimensions but I think it will be tiny if I make one on the south part. I don't really know.
    If someone could explain me what kind of platform I need and how to calculate the dimensions I would appreciate it !

    There can be some mistakes in my sentences, Je suis français
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    Default Re: I'm planning building an EQ platform

    Very nice to meet you Aero787! You may want to introduce yourself to everyone else.

    http://www.astronomyforum.net/forum-...introductions/

    You also might want to check out the Yahoo group that specializes in equatorial platforms.

    https://beta.groups.yahoo.com/neo/gr...errer=pack1209

    I attempted an equatorial platform myself once -- actually more a barn-door platform since I'm on the equator. Not very successful. It worked for visual but not for astrophotography. (Just warning you ahead of time.) And also keep in mind that you may have trouble getting your camera to focus using a Dobsonian.

    Anyway, the one thing I know about the dimensions is that there are highly dependent on latitude. Your back and front circular cutouts for the top of the platform are different sizes and the difference depends on latitude. The YAHOO group has some files that tell you how to calculate the sizes of the two circular cutouts.

    Clears,
    Joe
    In lumine tuo videbimus lumen

    SCOPES: DIY f/4.5 17.5” Dob -- Meade f/9 102mm APO
    MOUNT: Celestron AVX
    CAMERA: Canon 450D / Orion-SSAG / Fujifilm X-A1 (mirrorless)
    EPs: TV Nagler 13mm / PARKS Gold Series--5 pieces / Zhumell 3mm

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    Default Re: I'm planning building an EQ platform

    Well, thanks

    Why didn't your platform work ?

    Don't worry about the focus, I lifted the primary miror a bit, works fine as you can see : https://www.flickr.com/photos/136051461@N08/

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    Default Re: I'm planning building an EQ platform

    Quote Originally Posted by Aero787 View Post
    Well, thanks

    Why didn't your platform work ?

    Don't worry about the focus, I lifted the primary miror a bit, works fine as you can see : https://www.flickr.com/photos/136051461@N08/
    Nice pictures!

    In my case, the problem was my Dob and getting good polar alignment. The longer the focal length, the more accurate your PA has to be.

    For my 17.5" Dob, FL = 2000mm. Without accurate PA, even a good GEM mount (assuming it could handle the enormous weight) would have trouble with FL = 2000mm for long exposures. The images would show star-trails (as you have in one or two of your M42 images).

    I'm not saying you will fail. On the contrary, your Dob is probably more manageable than mine. And many have been able to build a good Eq Platform and make it work for AP. But the greater your FL, the more accurate you have to be -- more accurate with your cutouts, more accurate with your motor speed and more accurate with your PA.

    I got very good accuracy with my motor speed (I was using a stepper motor powered by an Arduino). PA was difficult with such a big Dobsonian (~60 kg).

    Clears,
    Joe
    In lumine tuo videbimus lumen

    SCOPES: DIY f/4.5 17.5” Dob -- Meade f/9 102mm APO
    MOUNT: Celestron AVX
    CAMERA: Canon 450D / Orion-SSAG / Fujifilm X-A1 (mirrorless)
    EPs: TV Nagler 13mm / PARKS Gold Series--5 pieces / Zhumell 3mm

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    Default Re: I'm planning building an EQ platform

    you might want to try to make a barn door platform like the one i'm building:

    Equatorial Base For Dobs Build Log

    it's easier to build and there is more room for error

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    Default Re: I'm planning building an EQ platform

    Looks great !
    But why do you want me to build one if there's more room for error ?
    I will be using a 1200mm telescope, I need to be very precise !

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    Default Re: I'm planning building an EQ platform

    i hope you mean 1200mm focal length, not aperture lol. what i meant by that was if it's your first time building an eq platform, you're likely to make a small error which will translate into a larger problem that's hard to correct. with a barn door platform it's easier to build and correct your small errors. However, it is a lot bulkier.

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    Default Re: I'm planning building an EQ platform

    I found this great spreadsheet to calculate every part of a platform. The original site seems to be gone - so I don't know who made it originally. (I've put it in my Dropbox temporarily for you - I'll keep looking for the original file.)

    https://dl.dropboxusercontent.com/u/...calc2012-2.xls

    This is a good page to start with: Don Peckham

    And this thread walks you through an elegant design: Making an equatorial platform - ATM, Optics and DIY Forum - Cloudy Nights

    Mine is pretty cheap and dirty. Here are a few pictures...

    members/moffjarjar-albums-my-diy-dob-eq-platform-picture149274-ta-da-i-plan-adding-some-adjustable-feet-needs-some-trimming-varnish-i-might-lighten-up-top-base-some-cut-outs.jpg members/moffjarjar-albums-my-diy-dob-eq-platform-picture149272-bottom-base-i-wanted-lightweight-cheap-i-commandeered-wheels-old-pair-skates.jpg members/moffjarjar-albums-my-diy-dob-eq-platform-picture149271-top-angled-runners-set-34-1-degree-latitude.jpg members/moffjarjar-albums-my-diy-dob-eq-platform-picture149273-clever-bit-drive-shaft-repurposed-bike-inner-tube-connection-set-into-metal-housing-we-found-fits-perfect-screw-serves-inner-axle-holds-all-place.jpg members/moffjarjar-albums-my-diy-dob-eq-platform-picture149270-notice-setting-circle-i-added-previously-love.jpg
    Looking up! ~Jeff // Skywatcher 8" collapsible Dob. Love it. // Celestron Powerseeker 114 EQ. Not so much. Camp scope? // A DIY Dob EQ platform. It works, but needs tweaking! // DIY imaging camera made from a used webcam, not working well yet. // I'm attempting DSLR photos with the Dob - hoping!

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    Default Re: I'm planning building an EQ platform

    and if you want more info on the barn door tracker here's the pdf from CamelHat, or Henk, where he explains how it all works:

    http://www.astronomyforum.net/attach...oortracker.pdf
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    Default Re: I'm planning building an EQ platform

    Well thanks guys !
    I think before building the platform i will try making a small one (barn door) for my canon 1200d, i'll see what mistakes i can make and i will later try to not do them on the telescope's platform
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