Shock absorber problem

  • Thread starter geewhiz
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Main Question or Discussion Point

I am trying to design a bicycle cargo rack that uses shock absorbers to protect sensitive equipment (i.e. a laptop computer). I have data for the maximum height from which laptops can fall without damage as well as the maximum acceleration to which they may safely be subjected. I am planning to do an experiment that measures the change in acceleration of a bicycle riding over a bump at ordinary travel speeds. I would like to use this data to select appropriate shock absorbers for my purpose. My problem is that I am unsure how to identify the appropriate quantities (i.e., force, energy), and relate them to the appropriate parameters of a shock absorber(damping coefficient etc.).

My specific questions are:
1) (Assuming force is the appropriate qty) How can I relate the fall height of a computer to the force it sustains on impact?

2) If I can measure the change in acceleration of the bicycle, how can I relate this to the force applied specifically to the cargo load (as opposed to the cargo load, bicycle and rider)?

3) Once I determine the force to which the load is subjected, how do I relate this to the appropriate parameters of the shock absorber?

Any insight you may be able to provide is greatly appreciated! Sorry for the long post.
 

Answers and Replies

  • #2
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Just because a computer can fall from height X and still work does not mean it should be subjected to continuously repeated forces equivalent to falling from 1/2 X. I think your design objective needs to be to carry it with as little shock as possible.

That being said, the term "shock absorber" is a misnomer. Shock absorbers do not absorb shock, springs do that. Shock absorbers prevent harmonic oscillations of the springs by converting kinetic energy into heat.
 
  • #3
256bits
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That being said, the term "shock absorber" is a misnomer.
That gave me a laugh as you are the frist person I have ever heard say such a truthful profound statement. colloqual english is very bad at times.

To the OP - in analysis it is called a damper.
 
  • #4
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Thank you for your replies.

Re: "Shock absorbers do not absorb shock, springs do that," I guess my conception of a shock absorber includes both a spring and a damper. It seems that they are usually both included in the same unit. Ideally I would be able to find the optimal spring stiffness as well as damping coefficient, but I don't know how to calculate either without determining the force exerted on the cargo load.
 
  • #5
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Hello,
I am narrowing down my question in hopes of generating more of a response. Could anyone help me understand how to determine: 1)the energy that would be transferred to an item stored on a cargo rack from a rider going over a bump at a certain speed and 2) the acceleration that the cargo would experience. I know this is an extremely complex problem, but any information you might be able to provide to simplify it would be greatly appreciated.
 

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