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CALIBRATION.md

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Calibration

When the calibration_mode is set to 1 in the fximu_params.yaml file, the unit outputs raw sensor values at /imu/raw topic.

The complementary filter is not initialized, and the hard iron and soft iron corrections are not processed, but device is configured according to sensor_read_rate, output_rate_divider, gfsr, and afsron the yaml file.

Procedure

Notice: sudo apt install socat

  1. Set calibration_mode to 1, and select sensor_read_rate 100hz and output_rate_divider to 2 setting output rate to 50hz, in the fximu_params.yaml file.

  2. Run roslaunch fximu fx.launch to launch rosserial.

  3. Run rostopic echo /imu/raw to verify raw data is being published, and device is in calibration mode.

  4. Run socat.sh provided in scripts directory. This will create /dev/ttyCAL0 and /dev/ttyCAL1 virtual ports.

  5. Run perms.sh provided in the scripts directory. This will fix the permissions of newly created devices.

  6. Run cal_bridge.py program provided in the scripts directory. This python program will read data from /imu/raw topic, and then send those values to /dev/ttyCAL0, which will be forwarded to /dev/ttyCAL1 by socat, as plaintext raw values.

  7. Verify that the calibration system is running: screen /dev/ttyCAL1 115200 you should see values running as:

Raw:-73,2054,120,22,-17,51,232,631,277

To quit screen press CTRL-A and \ keys.

Raw sensor data is output as an array of 9, as explained below:

data[0] = accelRD.x;
data[1] = accelRD.y;
data[2] = accelRD.z;
data[3] = gyroRD.x;
data[4] = gyroRD.y;
data[5] = gyroRD.z;
data[6] = magRD.x;
data[7] = magRD.y;
data[8] = magRD.z;

If you are making the calibration on robot, Steps 1, 2, 3 should be done in the robot, while the 4,5,6,7 should pe performed on the host.

MotionCal

To Perform the actual calibration: Download and compile https://github.com/altineller/MotionCal. This is a slightly modified version of the https://github.com/PaulStoffregen/MotionCal. The portslist.cpp file has been modified so it can see our pseudo terminal /dev/ttyCAL1 port.

The prerequisites for compiling the program under ubuntu 20.04 are explained at https://github.com/altineller/MotionCal/blob/master/README.md

Compile the program by issuing make. If you have problems building MotionCal program, see: https://forum.pjrc.com/threads/57378-Cannot-make-MotionCal-for-Linux

You should turn the sensor until you see see red dots arranged as a sphere like in the picture below:

MotionCal

Rotate the sensor in all directions until gaps are less than 1% and variance less than 2%. At this state you can get a screenshot of calibration screen, and put those values in the hard and soft iron correction matrices defined in fximu_params.yaml file.

Licenses

tr000003 license