Design Bicycle Cargo Rack w/ Shock Absorbers for Laptop

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Discussion Overview

The discussion revolves around the design of a bicycle cargo rack that incorporates shock absorbers to protect sensitive equipment, specifically a laptop. Participants explore the theoretical and practical aspects of measuring forces and accelerations experienced by the cargo during bicycle travel, particularly over bumps, and how these relate to the selection of appropriate shock absorber parameters.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • The original poster (OP) seeks to relate the fall height of a laptop to the force it experiences upon impact, questioning how to calculate this relationship.
  • The OP also inquires about measuring the change in acceleration of the bicycle and how to isolate the force applied to the cargo load from the total system (bicycle and rider included).
  • There is a discussion about the terminology of "shock absorbers," with some participants arguing that the term is misleading and that the function of a damper is to convert kinetic energy into heat, rather than absorb shock.
  • One participant humorously acknowledges the misnomer and emphasizes the importance of distinguishing between springs and dampers in the context of the OP's design.
  • The OP expresses a desire to find optimal parameters for both spring stiffness and damping coefficient but feels uncertain about how to calculate these without first determining the forces involved.
  • A later post seeks clarification on how to determine the energy transferred to an item on the cargo rack when riding over bumps and the resulting acceleration experienced by the cargo.

Areas of Agreement / Disagreement

Participants generally agree on the need for a nuanced understanding of shock absorbers and their components, but there is no consensus on the specific calculations or methods to determine the forces and parameters relevant to the OP's design challenge. Multiple competing views and uncertainties remain regarding the best approach to the problem.

Contextual Notes

The discussion highlights the complexity of relating physical quantities such as force, energy, and acceleration in the context of bicycle dynamics and cargo protection. There are unresolved mathematical steps and assumptions that participants have not fully addressed.

Who May Find This Useful

This discussion may be of interest to individuals involved in mechanical design, particularly those focused on transportation solutions, as well as hobbyists and engineers looking to understand the dynamics of shock absorption in practical applications.

geewhiz
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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.
 
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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.
 
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.
 
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.
 
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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