Interpretation of Accelerometer Measurements

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Discussion Overview

The discussion revolves around the interpretation of accelerometer measurements taken during impact tests on football shin guards. Participants explore how to analyze the data collected from a 4.3 kg striking mass dropped from various heights, particularly focusing on understanding the readings and their implications for assessing the performance of the shin guards.

Discussion Character

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

Main Points Raised

  • One participant expresses confusion about the accelerometer data, noting that the graph appears messy due to the weight bouncing off the shin guard multiple times.
  • Another participant points out that the accelerometer's readings drop linearly instead of instantly to zero at the start of free fall, which raises concerns about the data's reliability.
  • There is a suggestion that a wider range accelerometer might be necessary, as the current one has a limit of 2g, which may not capture the maximum acceleration during impact.
  • Participants discuss estimating maximum acceleration based on the deepest indent made by the striking mass, with one proposing to calculate the acceleration needed to bring the falling speed to zero over the distance of the indent.
  • Questions arise regarding which falling speed to consider when estimating impact force, as well as the method for calculating maximum deflection and impact force from the accelerometer data.
  • One participant expresses urgency in clarifying these points due to an upcoming presentation related to their honors project.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the interpretation of the accelerometer data or the appropriate methods for analysis. Multiple competing views and uncertainties remain regarding the readings and their implications for assessing shin guard performance.

Contextual Notes

Limitations include the accelerometer's range, the assumptions about the relationship between acceleration and impact force, and the uncertainty regarding the interpretation of the graph data.

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I have performed an impact test on different football shin guards to assess their performance. I am however confused with the readings measured by the accelerometer I have used. The sensor was attached to a striking mass of 4.3 kg which was dropped at different heights.
The graph I have attached shows the data collected by the accelerometer (y-axis) versus the time (x-axis) for an impact test at drop height of 20 cm.
Can anyone help me understand how to read this data? (i assume the graph looks messy because they weight 'bounced off' the shin guard a few times).
How can I use this data to assess guards performance?
 

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The data will be difficult to use. Starting at time=0, you would expect it to instantly drop to zero as free fall begins. It slopes down linearly over a 10'th of a second. That is hard to explain. Then, when it first hits, the measurements are limited at about 32000. That is a serious problem. It makes it impossible to know how high it really went. I think you need an accelerometer with a wider range.
 
The accelerometer I used had a range of 2g. So you suggest 3g?
The physical impact begins when the acceleration hits the x-axis right? Does the pick of the graph represent the maximum indentation of the striking mass on the shin guard?
 
It's hard to guess how high the acceleration might get. 3g might not be enough either. I think it is safe to assume that the deepest indent came from the impact with the maximum acceleration. You might get an estimate of the maximum acceleration by calculating how much acceleration would go from the falling speed to 0.0 in the distance of the deepest indent.
 
What falling speed? The one from the peak or the initial one?

So, the physical impact between the two bodies occurs between time 154 to 198 yea? Say i consider the data recorded from 154 to the peak, if i integrate it once I would get the velocity vs time graph, and if i integrate that again I would get the deflection vs time graph right? So from there I'd be able to estimate the maximum deflection of the striking mass?

How can I estimate the impact force? Initially I thought of finding the g-force and then converting it into Newtons, but I am not sure if that is the impact force on the sin guard..

Sorry for so many questions, I have my viva presentation of my honorous project in a couple of days and I've been trying to figure out my results for ages without success
 

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