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    BNO 055 calibrate using horizontal plane rotations only? And having to recalibrate too often.

    RobAtLab
    Member

    BNO 055 calibrate using horizontal plane rotations only? And having to recalibrate too often.

    Excuse me, I've bought some of your BNO 055 compass sensors for use in letting a robot navigate, is there any way to calibrate these (atleast calibrating the compass and accelerometer elements if not the gyro which I'm not using) by only rotating on a single plane?

    I've mounted the boards on a robot and therefore it can spin on the spot with it's wheels, and it can because of it's design manage a deliberate and controlled 10 degrees of back-forth pitch, but it can't by itself do anything to rotate the compass board in ALL 3 axes. All it can do is a fast spin clockwise or anticlockwise about the vertical axis (normal to the PCB on which the BNO 055 chip sits), or slowly do a 0 to 20 degree pitch range about the axis pointing parallel to the longer length side of the BNO 055 chip.

    I don't need accuracy on all three axes, just in the horizontal plane (my board is arranged on the robot such that the componentless side of the board has a normal pointing to the sky, and the other face of the board, where the chips are SMD soldered on to, has a normal pointing to the ground). As I don't need compass data in the other dimensions is there any way to calibrate well enough for use in the horizontal plane by using only movements in the horizontal plane?

    I have been using the adafruit bno055 library on an atmega328p, similar to an arduino uno but fitted with other components on a custom board, to interface over I2C to this sensor. I can work on modifying the library to add any extra features your BNO 055 datasheet describes which the library doesn't implement.

    I'm working in a situation where my robot must be able to find a globally determined heading relative to "north" for where-ever it currently is, it is NOT a problem in my application if where this north is changes with position, so long as it does so more slowly than 5 degrees of difference per metre of travel along the floor. So when travelling in a "straight line" it is ok if this straight line deviates by 5 degrees per metre, but  the robot would still need to have the same perception of where "north" is at a given location if it later returns to that same location.

    I think the device is operating in the NDOF fusion mode, with the faster, not needing full figure of 8, type of calibration enabled. I wonder if shifting to a non-fusion compass mode could help, or if this would leave the sensor useless for navigation. 

    In running test code to get the value from code doesn't print anything higher than a 1/3 for the magnetometer confidence until rotations on >=2 axes are made, it can get to 2/3 with some rotation about the vertical axis (that is to say staying on the horizontal plane) and a little bit of gentle tipping on one other axis, it refuses to reach 3/3 without the robot being hefted up and waved around in all directions. I wondered if there were any features on the BNO 055 which let you put it in to a horizontal plane mode, without having to get deeply involved with complex sensor fusion algorithms.

    Also, as my robot drives around, probably due to passing through different magnetic fields in the environment such as from steel structures under the floors, confidence sooner or later drops down again, and usually within a few metres and a very few minutes. The confidenc level does not manage to persist at the level it reaches after calibration for as long, even though I had thought that calibration remained from power-on of the sensor until power-off. I could well understand, and handle the resulting robot situation, if the presence of such altered field regions just caused local navigation confusion, but having to recalibrate is very bothersome.

    P.S. the board is in a robot, but I've been careful in the design and kept it well away from the robot's motors (which are small and low current anyway) and from any metal structural pieces, most of the robot is made from plastic, or high current wires. From checking around the robot using other tools I am confident that my motors should NOT in any way be interfering with the BNO 055. The BNO 055 is on a separate small daughter board from the other circuitry of the robot. The only metal, except header pins, anywhere near the BNO 055 is the end of an M2.5 screw 23mm away, and the side of another about 20mm away, this latter one could be removed if necssary.

    Thank you

    11 REPLIES 11
    FAE_CA1
    Community Moderator

    Re: BNO 055 calibrate using horizontal plane rotations only? And having to recalibrate too often.

    Hi,

    Thanks for your inquiry.

    Even though you design your robot carefully to minimize the magnetic interference to BNO055, it is still difficult for BNO055 to output accurate absolute heading angle with respect to earth magnetic north. This is because when the robot is moving in the room, the surrounding magnetic field is not always constant. Only if the robot is working outdoor in a clean area, the BNO055 heading can be accurate and robust.

    So you should use BNO055 IMU (6DoF) mode without using the magnetometer inside. However, after a few turns the robot may get lost which means that it doesn't remember the heading at the beginning of its motion because of the gyro bias drift. BNO055 yaw angle output in IMU 6DoF mode is not the absolute heading. So you may need to figure out a way to calibrate the yaw angle output from BNO055.

    Thanks.

    RobAtLab
    Member

    Re: BNO 055 calibrate using horizontal plane rotations only? And having to recalibrate too often.

    Are there some sort of requirements on how fast or smoothly the sensor must be rotated so as to get good confidence? because I'm finding that whilst lifting the robot up by hand and turning it around egst calibration to 3 very fast having the robot spin, even with tilting effects too, never gets calibration higher than 1. This is driving me crazy, surely there must be a way to accept adequate-ish global compass headings without having to do all this calibration. Its like the calibration routine was specifically designed to be impossible for a robot's actuators ever to produce, yet trivial for humans. I'm trying to make this robot more autonomous. All I need from this compass is for it to act roughly like a normal hand compass, not great inside and terrible around certain anomalies, but a hand compass manages to give good enough directions most of the time, is there no way to get this devce to act in some sort of calobration free compass mode. Thanks

    RobAtLab
    Member

    Re: BNO 055 calibrate using horizontal plane rotations only? And having to recalibrate too often.

    P.S. I have been using the magnetic confidence value in my code which controls my attempts to have the robot execute a clibration manoeuvre, would I be betetr off using the overall confidence value?

    FAE_CA1
    Community Moderator

    Re: BNO 055 calibrate using horizontal plane rotations only? And having to recalibrate too often.

    Hi,

    If you attach a hand compass on top of the robot and look at the needle of the compass, you will see the needle moving left and right when the robot is moving. So you may consider using BNO055 IMU mode without magnetometer.

    Thanks.

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