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  • Scissor Lift calculation

    Discussion in 'Calculations' started by nabilishes, Jan 23, 2011.

    1. nabilishes

      nabilishes New Member

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      For a project i need to calculate the forces in the arms of scissors lift. I attached the calculation i made. It would be nice if anyone could check the calculation out whether i made errors or i missed out something.

      I devided the scissors arm to their single parts (1) and (2) for the calculation

      Thankssss....http://twitpic.com/3spjw8
       
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    3. guy

      guy Member

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    4. hmck57

      hmck57 Member

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    5. guy

      guy Member

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    6. hmck57

      hmck57 Member

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    7. hmck57

      hmck57 Member

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    8. GarethW

      GarethW Chief Clicker Staff Member

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      Hi hmck: for your info you can display images in posts:

      Here you go:

      [​IMG]
       
    9. hmck57

      hmck57 Member

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      Well, I stand by my free body - I believe it is correct. This analysis takes into account the weight of the arms - I don't believe your analysis did. If the weight is significant you may want to make this change. See http://twitpic.com/3tmecf for the FBD.
       
    10. Valmiki

      Valmiki Member

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      Without checking the calculations, some discrepancies are clear:-

      First, Guy's suggestion DOES take into account the weight of the scissor arms.

      Second, "apples and oranges" comes to mind, because Guy's suggestion shows the horizontal force, and HMCK's suggestion shows a force aligned with the inclination of the scissor arms.

      I think that the whole debate exists due to lack of clear communication.

      Somebody's having a conversation without the listening part.

      I'm sure both calculations can be reconciled, and there is no disagreement.
       
    11. hmck57

      hmck57 Member

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      Look again...

      First, the original analysis is here: http://twitpic.com/3spjw8. This is the free body I said didn't take into account the weight. Look at the free body - there is no weight component.

      Second, apples and apples - both the calculation at the engineer's edge site and my free body calculate the (horizontal) actuator force (F), but they aren't equivalent:
      Engineer's Edge - F = {W+Wa/2}/Tan(phi) (see http://www.engineersedge.com/mechanics_machines/scissor-lift.htm)
      HMcK57 free body - F = {W+Wa}/[2*Tan(phi)] (see http://twitpic.com/3tmecf)

      These two equations aren't reconcilable - assume a weight of Wa=200lb, a load of W=1000lb, at an angle of phi=60deg:
      Engineer's Edge says F = 635lb
      HMcK57 says F = 346lb

      If I'm missing something, please show me.
       

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