Scissor Lift calculation

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

 

http://www.engineersedge.com/mechanics_ ... r-lift.htm

 

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.

 

hmck57, could you please upload your analysis on some other site, I can't access the facebook page.

 

I reposted the analysis to twitter: http://twitpic.com/3tmecf.

 

guy, have you been able to review the analysis at http://twitpic.com/3tmecf?

 

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.