G force and rate of deceleration

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    Deceleration Force Rate
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Discussion Overview

The discussion revolves around the relationship between an accelerometer's output during the braking of a motor vehicle and the rate of deceleration. Participants explore whether this output is directly proportional to deceleration and the implications for plotting deceleration rates using derivative functions.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions if the negative output of an accelerometer during braking is directly proportional to the rate of deceleration and whether this can be predicted using a derivative function.
  • Another participant asserts that once the accelerometer output is converted to engineering units of g's, it should be directly related to the rate of deceleration.
  • A different viewpoint suggests that the relationship is not exactly proportional, noting that higher quality accelerometers yield outputs closer to the ideal, and recommends checking the specifications for the specific model used.
  • Another participant emphasizes that not all accelerometers are designed to measure negative acceleration effectively, indicating that the suitability of the device is crucial.
  • One participant raises the importance of ensuring the accelerometer is properly mounted on the car body, as incorrect placement could affect measurements.
  • Additionally, it is mentioned that an accelerometer mounted on the wheels could calculate linear acceleration/deceleration, but only under conditions where the wheels are not skidding.

Areas of Agreement / Disagreement

Participants express differing views on the proportionality of accelerometer output to deceleration, with some suggesting a direct relationship while others highlight limitations based on the accelerometer's design and mounting conditions. The discussion remains unresolved regarding the exact nature of this relationship.

Contextual Notes

Limitations include potential variations in accelerometer specifications, the impact of mounting location on measurement accuracy, and the conditions under which the vehicle is operating (e.g., skidding). These factors may influence the relationship between accelerometer output and deceleration.

lawrence fickett
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gee i am not worthy of being here with you guys but i must know is an accelerometer's negative output due to the braking of a motor vehicle directly proportional to the the rate of deceleration of the motor vehicle and can this be predicted using a derivative function? And if I were to plot the negative g's how would the deceleration rate plot compare.

Sorry to bother you'se with such a trivial question, but I've been researching this and can't seem to get a definitive answer. I am preparing a patent using the above and don't want to make a claim that can't be proven.

Many Thanks
 
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Assuming that you have already converted the accelerometer output signal to engineering units of g's, it should be directly related to the rate of deceleration. 1g = 9.80665 m/s2.
 
lawrence fickett said:
is an accelerometer's negative output due to the braking of a motor vehicle directly proportional to the the rate of deceleration of the motor vehicle
Not exactly proportional, but the better (and usually more expensive) the accelerometer is, the closer to that ideal it will be. There will be a data sheet or other specification for the particular model that you're working with. It will include the details for that particular model, including (most likely) a plot of the output signal as a function of the actual negative acceleration.

If you haven't already, you might try googling for "accelerometer specifications".
 
lawrence fickett said:
is an accelerometer's negative output due to the braking of a motor vehicle directly proportional to the the rate of deceleration of the motor vehicle

You would hope so.

As Nugatory said, not all accelerometers are perfect. Not all are designed to measure negative acceleration (eg deceleration) as well as positive. You would hope the designer picked one that was suitable.
 
I suppose we should also check that the accelerometer is mounted on the car body and not something loose inside the car like a box of tissues or a passenger.

Likewise an accelerometer mounted on the wheels (measuring angular acceleration) could be used to calculate the linear acceleration/deceleration but only if the wheels aren't skidding.
 

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