How is "Vibe" measured? (Not just for copter!)

ArduCopter
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I am curious. What is the difference between acceleration and vibe? We know that vibe < 15m/s/s is good, acceleration is in [-3m/s/s 3m/s/s] for X and Y, [-15m/s/s -5m/s/s] is okay for Z.
How is the “vibe” computed? My theory is summing of rotational acceleration (gyro) and translational acceleration (pure acceleration), but we need a vector (a radius) for this computing. If yes, where this point is in the chassis?

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If not, could someone show me the theory?
Thanks in advance.

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If you just Google search “Arducopter vibration”, the 1st link will take you there.

  • Capture the raw x, y and z accelerometer values from the primary IMU
  • High-pass filter the raw values at 5hz to remove the vehicle’s movement and create a “accel_vibe_floor” for x,y and z axis.
  • Calculate the difference between the latest accel values and the accel_vibe_floor.
  • Square the above differences, filter at 2hz and then calculate the square root (for x, y and z). These final three values are what appear in the VIBE msg’s VibeX, Y and Z fields.
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