1. ## Scissor lift strength

I want to specify one point.
When I calculate Force Required for Equilibrium at Load Rx, and it's value is 70000 N. And as shown here http://www.engineersedge.com/mechani...issor-lift.htm on "Free Body Diagrams:" length of one scissor member 1,8 meter. For calculating longitudinal moment of inertia (Wx) of my beam cross section I need to use formula bending moment= (Rx*length of one scissor member)/4
then Stress=bending moment/Wx and finally
Wx=bending moment/Stress
am I right?

2. So, nobody knows?
I think this is too much. 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; 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 This is too much (((
may be mistake somewhere?

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