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Thread: Meade 16" Light bridge Truss Mod

  1. #1
    Member sanath's Avatar
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    Meade 16" Light bridge Truss Mod

    Hi all,
    I recently started a project to modify an existing Meade 16" Lightbridge to a portable version so that it can be transported in a small vehicle or for air cargo, i used design ideas mainly from http://www.reinervogel.net and also from http://www.roelblog.nl/2012/11/bouwv...-truss-dobson/ and would like to thank Reiner Vogel and Roel Weijenberg for sharing their ideas.


    Design Constraints and some rules i followed
    1) mod must be performed with nondestructive methods of the lightbridge parts.
    2) parts from the older design can be used in the new one without altering it
    3) reusability to reduce the project cost
    4) portability should be achieved so the telescope can be transported for atleast domestic air travel

    Workflow :
    Day1-4: i used this time to plan out how and what alli must reuse from the older design and hence what new i will have to design from ground up.

    Day 4-7: Aquiring raw materials like aluminium shafts , hollow pipes and a slab of alumium

    Day7-15: Machining of aluminium mirror cell and truss pole ends and buying plywood sheets ,veneer sheet.

    Day16-18: Wood working for mirror box

    Day18-25: Assembling the OTA and checking for focus

    Day25-30: Making of rocker,ground board and Alt bearings

    Expenses: ( INR is indian rupees)
    Metal Milling /Lathe work: 6800INR= 106USD
    Plywood=18534INR= 289USD
    Carpenter=3000INR= 47USD
    Aluminium and casting=5150INR= 80USD
    CNC wood work=2100INR= 33USD
    Hardware, tools and misc: 5084INR= 79USD

    total = 634USD


    About the mod:

    i redesigned the mirror cell partially and used the mirror cell assembly from the lightbridge, i also reused the upper and lower truss holding rings and clamps,secondary cage and az bearings (lazy susan).

    i then had to redesign the new truss tubes based on some simple calculations and the rest of the calculations were from Reiner Vogels website, i had to modify some for my requirements.

    finally here are the pics :
    https://drive.google.com/drive/folde...zQ?usp=sharing
    http://imgur.com/a/pvjiU


    Problems yet to be solved:
    Friction in alt bearings, as i dont have access to ebony star or similar material in small quantity.


    comments and advice welcome.
    Last edited by sanath; August 25th, 2017 at 08:47 PM.
    Bangalore Astronomical Society

    8" GSO dob

  2. #2
    Member Don Pensack's Avatar
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    Try strips of FRP, the material often used to refinish shower stalls. It's bumpy and works great on large diameter trunnions.
    It's available at nearly every local hardware supply place, like Home Depot, OSH, or Loewe's.
    The bearings will still remain teflon.
    Lots of commercial scopes now use that material.
    Ebony Star is long out of production.
    Last edited by Don Pensack; August 19th, 2017 at 03:39 AM.
    Don Pensack
    www.EyepiecesEtc.com
    Los Angeles

  3. #3
    Member sanath's Avatar
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    [QUOTE=Don Pensack;5996]Try strips of FRP, the material often used to refinish shower stalls. It's bumpy and works great on large diameter trunnions.
    Hi Don,
    thanks for the info, i shall try this option, and what about teflon, can i use it on the entire surface or just small calculated pieces at 35º from centre at 4 points only ?
    Bangalore Astronomical Society

    8" GSO dob

  4. #4
    Member Don Pensack's Avatar
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    Teflon is 4 small pieces, as you note.
    The size of the 4 teflon pads calculated to keep pressure on each pad to around 15psi (around 1kg/cm²).
    Don Pensack
    www.EyepiecesEtc.com
    Los Angeles

  5. #5
    Member sanath's Avatar
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    Hi Don,
    thank you i shall try doing that, mine comes to 22mm X 41mm and four of these.
    Bangalore Astronomical Society

    8" GSO dob

  6. #6
    Member Don Pensack's Avatar
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    That's about 9cm² each, which would translate to a 36kg OTA.
    Pads can always be moved apart to increase friction or moved closer to decrease it.
    Don Pensack
    www.EyepiecesEtc.com
    Los Angeles

  7. #7
    Member sanath's Avatar
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    Hi,
    yes, the OTA is 36kg , and thanks for the tip, i didnt know about the distance/angle and friction relation
    Quote Originally Posted by Don Pensack View Post
    That's about 9cm² each, which would translate to a 36kg OTA.
    Pads can always be moved apart to increase friction or moved closer to decrease it.
    Bangalore Astronomical Society

    8" GSO dob

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