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Message No. 21886, Started by Vladimir91 on 10/06/12

Hi everybody!

I need to calculate scissor lift for my course project and I found this stuff

http://www.engineersedge.com/mechanics_machines/scissor-lift.htm

I want to specify one point? from people who have alredy deal with this problem.

I need to calculate Force Required for Equilibrium at Load Rx, for cacilating bending moment, then to select beam cross-section.
 For example, if we have, for example a W=payload waight= 4000 N; Wf=frame weight=4000 N; L=length of the scissor arm=1,8 m; Theta=angle between the scissor arm and the horizontal=5 degree(for fully retracted position); so:
Force Required for Equilibrium at Load Rx= (W+Wf/2)/Tan theta = 4+2/0,087 = 69 kN (!!!)
Bending moment = Rx*(L/2)/4 = 69*0,9/4 = 15,5 kN*m
 Now this moment require rectangular tube about 140x120x6 mm. This is too much (((
 may be mistake somewhere? I thint I mistake in selecting arm of a force?

 

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