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Serious calibration problems
  • Hi, I'm a newbie to all this so please be patient. I've just started an interest in RC and bought myself a quadcopter (DJI Phantom) and a gimbal for my GoPro Hero3. I've now tried to follow the instructions to perform an initial calibration of the gimbal sensors. But something must have gone terribly wrong, because when I now connect the gimbal to SimpleBGC GUI v2.2 b2 the following happens: the Pitch dial turns upside down and the arrow points to the left; when I perform a gimbal pitch, the Roll dial moves; when I do a gimbal Roll, the Pitch dial moves. And if I hold the sensor board upside down the Pitch dial correctly (?) points to the right. I've obviously managed to screw this thing up completely, but how can I correct it? I really need someone's help here. Thanks.
  • Solved, please ignore. I now better understand how things work.
  • Good job!
  • Sorry but I have to reactivate this thread. I thought I had solved the problem because I managed to turn the PITCH arrow in the right direction by using the vaalues -Z and X in the sensor setup. After that I had no time to look at this anymore until now when I find that the problem with the ROLL and PITCH dials still do not correspond to the movement of the gimbal. To recap: when I lean the camera forward the ROLL dial moves anti-clockwise; when I drop the camera to the right (seen from behind) the PITCH dial moves clockwise. I've tried to cure this by changing the Motor Outputs settings but nothing seems to be able to have effect on this behaviour. What am I doing wrong or what am I not doing that I should? Thanks in advance.
  • It sounds like you've mounted the IMU incorrectly if the dials in the application do not correctly correspond to the motion of the IMU. You can switch the "AXIS Top" and "AXIS Right" settings to correct this without the need to readjust the IMU's physical position provided that you have it square to the motors. Just change those two settings until it seems to make sense with the dials/realtime data. Don't worry about the motors at this point because they could need to be be inverted or not depending on setup and they'll just mess with you head if you have more than 1 thing incorrect. Once you have something making sense in the dials/graph turn your motors back on and see if they need to be inverted.
  • Thanks for your comments. To emphasise, the problem is that a gimbal PITCH movement affects the ROLL dial, not the PITCH dial, and the realtime data shows movement of GYRO-X, not GYRO-Z. I'm unable to change Axis-Top and Axis-Right so that the dials/graph displays make sense, and this doesn't make sense.
  • if you have your rig sitting flat in the correct orientation then in your realtime graph one of the 3 accelerometer AXIS should have an offset value which is coming from gravity. This your TOP axis so set that in the sensor box of the basic tab. As for the roll/pitch being inverted this is probably caused by the orientation of the IMU you can easily fix this by swapping the motors outputs. It'll obviously read incorrectly but if you switch the TOP and RIGHT sensor settings and then swap the motor outputs it should work. if you have the time though I'd suggest remounting the IMU so the the +x axis is pointing to the right and the +Z axis is pointing UP. This will alleviate the headache of switching things in software/hardware wiring.
  • What is odd here is that I can change the directions of the ROLL and PITCH dials in the Basic tab by using different values for Top and Right, but so far I've been unable to see any differences when playing around with different Motor Output values in the Advanced tab. The description of these pull-downs is quite clear but it simply doesn't take effect. Correct me if I'm wrong here: if I leave the settings in the Basic tab and only make changes to the Motor Outputs settings (ROLL -> Pitch out, PITCH -> Roll out), then I would expect to see different dial and realtime values. I don't see any changes. And just to test, I set all motor values to 'disabled', performed a WRITE + disconnect, repowered the gimbal, connect, but the dials and realtime data are still displaying what they always do. Isn't that odd?
  • I'd suggest leaving the motor outputs set at defaults; swapping them round will have no effect on the realtime dials (they're meant to show you input, not output), and it'll get confusing in the long run. No need to move the IMU, either, as long as it's mounted square and solid.

    However you've mounted your IMU (12 possibilities), there will be a combination of Axis top and Axis right settings that'll work.

    If your Pitch and Roll are the wrong way round, it suggests your IMU is flat (parallel to the ground) but sideways compared to the camera view - that is, the pins are facing to the left or right. That's fine - but the Axis right setting will be either +Y or -Y instead of X.

    Make sure you hit Write after changing the setting.

    Pitch and roll should now be on the correct dials on screen. They could be inverted, arrow nosing down when you tilt the camera up, or the roll dial going the wrong way (remember it's like an aeroplane dial, so it shows the view as if from behind).

    If Pitch is inverted, invert the Axis Top setting (-Z to +Z or vice versa), and if roll is inverted, invert the Axis Right setting. Invert both if necessary.

    That should be it. If you get stuck, let us know how far you get -- and which way round the IMU is mounted on your gimbal - bumpy component side up or down, which way the pins are facing.

    There may only be 12 combinations of settings but it's easy to tie your head in knots. Be methodical, and good luck!
  • I see this is an old thread, but I had this problem after I clicked the Auto button under motor configuration. I solved it by changing Axis TOP to "-Z" in the "sensor" section on the Basic tab, then clicking write, then disconnecting and connecting again,