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  • Suspension position for suspension pedestal

    Discussion in 'Calculations' started by Bart van Driessche, Jan 17, 2019.

    1. Bart van Driessche

      Bart van Driessche New Member

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      For my thesis at the department of Industrial Design Engineering, I am developing a suspension pedestal. These kind of products are used regularly in boats (link) or truck seats and make use of two diagonal beams and a shock absorber. The vertical excitation can originates from waves or road undulations. A simple FBD can be found below.

      I was wondering if the location of the shock absorber, relative to the rear pivot points (A), affects the functioning/effectiveness of the system? If I am correct, placing the shock absorber more forward or backwards only puts more or less stress on the rear pivot points. Yet, by using proper bushings this may not affect the functioning/effectiveness of the system. Assuming the construction is stiff enough to withstand the weight (Fw).

      Or, is it better to decrease the distance between the center of gravity (C), in relation to the rear pivot points (A)? E.g. placing the center of gravity at location C'.

      Or, e.g., placing the shock absorber more forward at location B', so that the center of gravity (C) is located between point A and B'?

      seat pedestal.PNG
       
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    3. MSHOfficial

      MSHOfficial Well-Known Member EngineeringClicks Expert

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      I think you should place your shock absorber in a way so that you center of gravity falls somewhere around the middle of the top plate. That would make the joints and the connection rods a little lighter in terms of stress taken and the stresses in both joints would be similar. So, if you make your con rods and joints without any taper, your con rods can be utilized very well. However, if this is not an option I would prefer going with CG at point Cā€™. that would give lower moment on the right side than on the left side of the structure. And you could make your lower plate stronger (in terms of plate thickness ā€“ thicker) and the joint would also need to be made so that it holds higher reaction moments and make the con rod as a tapered design (not necessarily, only if you want to save on some weight or material).

      But still the best option from my side would be having the center of gravity somewhere around the center for best usage of the con rod and the joints.
       

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