absoluteIMU TILT readings greater that 128 (179-180)
 NXT and EV3   Started by Kevin Clague   2017-03-19 14:01:47 -04:00   Comments: 2    Viewed: 77

  1. Kevin Clague
    Kevin Clague Member
    I am using absoluteIMU using ev3dev plugged into sensor port 1.  The Users guide says that the TILT readings for any axis should be in the range from -127 to 128, and that zero should represent no tilt for an axis that is hoizontal.  

    Using ev3dev-c library to access the sensor in C and a little program to read tilt axis readings over and over.  When the X axis is pointing straight down, I get a reading of 0 for tilt-X, this seems to conflict with the description in the User Guide.  When the Y axis is pointing straight down, I get a reading of 0 for the tilt-Y.  When the Z axis is pointing straight down (the red face of the sensor is facing down and parallel to the floor, I get a reading of 177.   When I red face is point up (parallel with the ceiling), I also get readings of 177.  Given the range is supposed to be -127 to 128, and the value 177 is out of range, is this some sort of error condition?

    Bypassing the libev3dev-c stuff, the direct file system access to the device provides similar results with the sensor stationary and leveled in the horizontal plane:

    robot@ev3dev:~/imu$ cat /sys/class/lego-sensor/sensor0/value0

    108

    robot@ev3dev:~/imu$ cat /sys/class/lego-sensor/sensor0/value1

    83

    robot@ev3dev:~/imu$ cat /sys/class/lego-sensor/sensor0/value2

    178

    User guide says the tilt readings should be zero in this case, yet none of them are zero.  Given the behavior of X and Y, I would expect Z to be zero in this case.

    I see out of range values for X and Y axis when I'm trying to hold the device in my hand.  I assume the tilt is computed based on accellerometer readings.  Does this out of range value mean we cannot trust the readings from the sensor for this sample?

    Feedback?
    Kevin Clague, 2017-03-19 14:01:47 -04:00
  2. setht
    setht Member Staff Member
    Good morning! Could you please send a copy of the little program you ran, and any setup commands to configure the sensor in this state?
    setht, 2017-03-20 10:48:50 -04:00
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