iPhone and iPod measurement of brake pause

Discussion in 'Gen 3 Prius Main Forum' started by bwilson4web, Feb 9, 2010.

  1. bwilson4web

    bwilson4web i3 and Prime

    Joined:
    Nov 25, 2005
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    Location:
    Huntsville AL with 2014 BMW i3-REx
    Vehicle:
    2017 Prius Prime
    Model:
    Prime Plus


    Recently "Austingreen" made a brilliant suggestion to get acceleration recording software for an iPhone or iPod Touch. This software can record the X, Y, and Z axis acceleration and if running at 50-100 samples per second, measure the duration of the brake pause. Now I don't have any ready recommendations of which software to use. I'm testing "Accel Data" with my iPod Touch. However, last week I started using dedicated accelerometers to document the brake pause:
    [​IMG]
    This $80-110 part is dedicated to recording acceleration whereas my iPod is how I listen to interesting content like "What Drives Us" and other quality podcasts.

    If you have an iPhone or iPod Touch, acceleration recording software can also measure maximum acceleration, G-force in a tight turn (tires,) or even a pulse and glide profile. One simply 'integrates' the acceleration plus a constant to reconstruct velocity. Integrating the velocity plus a constant gives distance but without recording direction too, not really a useful map. Still, it is a good tool to study Prius (or any other) vehicle performance.

    To integrate the acceleration data, take the time difference between two samples and multiply it times the average acceleration. It is best to calculate a new time that is the average of the two values. Then add the result to the previous data point. The first data point is a constant, the initial speed in the appropriate units (either SAE or metric.) You'll also need to use the Z-axis scale (vertical) to check the calibration for 1 G. We can go over specific examples once you have some data. Note, it is important that the iPhone or iPod Touch not slide around but be fixed relative to the vehicle.

    There are other ways to integrate the data and some ways to reduce noise. Regardless, without recorded data, it is difficult to accurately quantify any effect.

    BTW, some of the 'car' applications for iPhone and iPod may also provide a more user friendly data presentation. I tend to work with engineering units and data but don't be afraid to 'expand the envelope.' I would like to hear about other iPod or iPhone applications.

    Bob Wilson
     
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