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
I didn't get the same results as engineersedge.com - see my post here for the free body and analysis: http://www.facebook.com/photo.php?fbid=10150359515860231&set=a.118314440230.207323.577220230&ref=nf guy - have you checked the analysis at http://www.engineersedge.com/mechanics_machines/scissor-lift.htm? If you think I'm incorrect please explain.
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.
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.
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.