• Welcome to engineeringclicks.com
  • Scissor Lift calculation

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

    1. nabilishes

      nabilishes New Member

      Joined:
      Jan 2011
      Posts:
      1
      Likes Received:
      0
      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
       
    2.  
    3. guy

      guy Member

      Joined:
      Jan 2011
      Posts:
      12
      Likes Received:
      0
    4. hmck57

      hmck57 Member

      Joined:
      Feb 2010
      Posts:
      21
      Likes Received:
      0
    5. guy

      guy Member

      Joined:
      Jan 2011
      Posts:
      12
      Likes Received:
      0
    6. hmck57

      hmck57 Member

      Joined:
      Feb 2010
      Posts:
      21
      Likes Received:
      0
    7. hmck57

      hmck57 Member

      Joined:
      Feb 2010
      Posts:
      21
      Likes Received:
      0
    8. GarethW

      GarethW Chief Clicker Staff Member

      Joined:
      Jul 2009
      Posts:
      1,429
      Likes Received:
      5
      Hi hmck: for your info you can display images in posts:

      Here you go:

      [​IMG]
       
    9. hmck57

      hmck57 Member

      Joined:
      Feb 2010
      Posts:
      21
      Likes Received:
      0
      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

      Joined:
      Mar 2010
      Posts:
      15
      Likes Received:
      0
      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

      Joined:
      Feb 2010
      Posts:
      21
      Likes Received:
      0
      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.
       

    Share This Page

    By using this website you agree to our Cookies usage. We and our partners operate globally and use cookies, including for analytics, personalisation, ads and Newsletters