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Member #93510

Member Since: December 1, 2009

Country: United States

  • Part of the issue is that the wrong sensor was used. The issue with the accel is that the gravity vector dominates in all cases and even though a one can guess at the zero motion cal state the resulting accel values in anything other than the z vector (gravity) are going to limited by the delta v of the bag and the length of the sensor from the pivot point of the mounting.

    This is generating the V^2 / R (distance between mount point and sensor) values of acceleration. By inspection it's obvious that gravity is always dominate that the motion of the bag is pretty much planar although I haven't really computed the x-y rotation vectors yet.

    We don't want to measure linear acceleration, we want to measure angular velocity and angular acceleration

    Had a 3 axis gyro been used the hits hits would have been extremely evident since the slopes of angular velocity ( angular accel) would clearly show an external impact force opposed to the angular accel in free fall which is essentially gravity trying to rotate the bag down to the zero momentum state

    If a 6 axis DOF sensor is used with something with a bit more computation horsepower (SAMD21 board) the 6 axis fusion would be able to count hits and the energy impacted on the bag given the mass of the bag and the pivot length. Gaming controller sensor fusion is usually 125 Hz so 500 Hz may be problematic just because of the I2C transfer times. I need to do some math and see if a Bosch or Invensense IMU can sample @ 4g / / 500 Hz

    my 2 cents

    cheers bob m (Wizard of Make / Atmel)

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