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Mechanical Engineering
Alex Hearn

Basic engineering help with force / lever calcs

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Hi, can someone help me calc this?  Way beyond my math skills ;)

Right-angle lever pushing against a spring, I think this is a 3rd order lever but don't know how the right-angle changes things.  I need to determine where to place the pivot for the spring on the lever to balance - weekend project welding up a ghetto rocking chair.

2017-08-20-12.05.40.jpg

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From Free Body Diagram:

(180 lbs)  (12 in) = (650 lbs/in) (delta) (X) sin(theta)

X is the horizontal distance shown in picture

theta is the angle (shown as 20 degrees)

delta is the travel (maximum 3 inches)

From that, you could get Y (shown in pic) as 

Y = X tan(theta)

Y cannot be more than 15 inches, of course.

Lever.jpg

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Also it is how precises you require control over the movement of free end of the angle. it required less spring force you can fix spring pivot away from the angle pivot. YOu can choose that pivot based on limit of spring tensions and free end movement requirements.

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