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  • mechanical system for segment (bar) translation and rotation

    Discussion in 'The main mechanical design forum' started by Tiha, Nov 17, 2012.

    1. Tiha

      Tiha New Member

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      Hello,

      I have a mechanical design problem I have been working on for a week without a proper result.

      I am trying to conceive a mechanical system, possibly a 4-bar linkage, which can displace a 150 mm long bar which is at 15 degrees angle from the vertical (position A on the image below) into the following position: up by 200 mm and to the right horizontally by 750 mm (position B). The final position of the 150 mm bar is vertical. Hope this is understandable. I attached an image to make it clearer:
      http://navigo.ro/download/mechanical_system_problem_formulation.jpg

      Real life formulation of the problem: this should be the support system of the left (and mirrored the right) back wheel of a trike, and the purpose of this mechanism is to retract the wheel to the center of the trike (and straighten it by 15 degrees and lift by 200 mm). The arm should bear considerable load when extended (1500 mm wheelbase, approx. 100 kg total weight with driver), but doesn’t need to support the trike and triker when retracted.
      The 150 mm bar can be vertical in both end positions, if that makes the problem far easier to solve.

      I made up a mechanical system to solve this problem partly. This moves a vertical 150 mm bar along the horizontal axis. It is far from perfect as it is only a partial solution, but I still attached it to make the problem more easy to understand.
      This is a link to the mechanical system I made up:
      http://navigo.ro/download/mechanical_system_incomplete_solution.jpg

      Thank you for your time in reading this. Any help is appreciated on what and how to do about this problem. If you refer to articles/books, please refer to ones publicly available on the web, as I don't have much access to mechanical design textbooks.

      Best, Tiha
       
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    3. s.weinberg

      s.weinberg Well-Known Member

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      Excuse me for being brief. On my phone.

      If you don't care about path, one solution seems fairly easy. Take 2 points on bar. Find start and end location for each.
      Then find a point for each that is same distance from start and end. Those are pivots. Pin connect and rotate from start to end.
       
    4. Rafael_Amen

      Rafael_Amen New Member

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      4-bar linkage solution:
      Let your moving bar be bar 1.
      Draw a straight line between the start position of the upper end of bar 1 and its final position. You can choose any point on the midpoint perpendicular to this line to be the ground point for bar 2. The other end is the moving upper end of bar 1.
      Do the same thing for the lower end of bar 1 and you have bar 3.
      "Bar 4" is the imaginary one connecting the two ground points you chose.
      Which ground points you choose depend on linkage strength, available space for movement, etc. Anyone of them will perform the movement you want.
       
    5. Tiha

      Tiha New Member

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      Thank you for the replies. 4 bar linkage works fine geometrically, but structurally needs some tweaks to be solid enough.
      Finally built a 1:1 scale model and exploring geometry variations.
      Thanks again.
       

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