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losing level after relocating countries... calibration specific to a region?
  • chapman
    Hi all,

    I've got a gimbal which has been working really well for about a year, but when I recently moved from Canada to Australia is has begun to act a little strange. It starts off level and reacts well to begin with but after a period of time it starts to lose the horizon and float around in a very lazy way until it eventually loses control and just flops around.

    If I switch profiles it snaps out of it and back to level again.

    Two questions:
    1) is there anything location/region specific about the Alexmos boards and their calibration?
    2) Is there some sort of re-levelling that happens when you switch profiles? I have noticed this previously, that if my horizon is off a little I can often fix it by flicking to another profile and back very quickly. Does this give a clue about something not quite right with my setup? It obviously knows where level is, as it finds it instantly when I switch modes, so why isn't it staying there?

    Any help appreciated. This gimbal has been working really well and I'd hate to have to go back to square 1 and recalibrating the IMUs and tuning again.

    Cheers,
    Andrew
  • Garug
    You should calibrate the IMUs now and then anyway, it is no big deal, normally complete IMU calibration can be performed just rotating the camera. You can save the old values by saving EEPROM (32 bit boards feature).

    Are you skipping Gyro calibration at startup? If yes, you should calibrate the gyro first. that is quite possible enough and requires just putting the gimbal to steady floor and pressing calibrate gyro.

    Earth rotation affect the gyros (x,y,z) much differently at different latitudes. Accelerations are not affected much by latitude, but temperature affects both gyros and accelerometers.

    It could be also that something has sifted during transport etc. verify IMU attachment and maybe performing follow offset calibration.

    If you store Profiles and EEPROM, you should be able to go back as it was if something goes wrong.
  • chapman
    Thanks Garug -- I tend to always take the IMUs off the gimbal and calibrate on a flat surface. You think leaving them on and only having it approximately level on each axis is sufficient?

    I've read so much about the need to get the accel calibration *absolutely* perfect with the Alexmos boards.

    But I didn't realize saving EEPROM would bring along the calibration values, so I guess it's pretty safe to try regardless.

    Though any thoughts on the fact that changing profile instantly fixes it? To me that shows it seems to have a good idea of what level is, but for some reason it needs reminding sometimes ;)
  • chapman
    More clues on this one, after recalibrating both IMUs failed to fix it.

    If I hold the gimbal hand-held, tilt the frame up and roll to the side, then the camera loses the horizon. If I rotate the frame to the right the camera leans right, and vice versa. With bluetooth connected I can see in the GUI that it is sensing both the frame and camera angle correctly, but not keeping the camera level. For some reason it can see that the camera is off on an angle, but isn't trying to bring it level again.

    If I disable the frame IMU, then it behaves properly again.

    Also, with the Frame IMU on, if I turn the motors off and on a few times, it works its way level again.

    Weird!

  • Garug
    I would just calibrate the IMUs on gimbal. Even if you do 1 point calibration only, you should not have the problems you describe. It is something else than calibration related, or the calibration is performed really badly.

    Are the frame IMU directions and locations correct, where is it installed?

    Also make sure this is not RC related. Disable all RC and see if the problem remains.

    Note: for gyro calibration the Gimbal must be absolutely still, on a steady floor etc. It does not need to be leveled. Disable gyro calibration at startup and perform it carefully when needed.
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