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PWM pitch control not very linear, and extremely difficult to set the min/max angles accurately
  • David_Hogg
    Hi everyone,

    I'm just setting up my Desire RC 3-axis 32-bit Basecam board and I'm noticing some strange behaviour ...

    Firstly, when tilting from straight forward to straight down, when the gimbal reaches about 80° (so 10° off straight down) the constant tilt speed will suddenly drop to a very slow tilt speed, and it will take some 10 seconds to go from 80° to 90°. Likewise if I've let it settle at 90° and then tilt up to 0°, it will tilt quickly from 90° to 10° and then move very slowly from 10° to 0°!

    Strangely, if I don't let the tilt reach one of its extremities this problem doesn't occur – so if the gimbal is stationary at 0° and I push the tilt lever down to 90° and back to 0° so quickly that the gimbal doesn't have time to move far, it will stop dead at 0°, with no slow down at the end ...


    Secondly, when setting the Min and Max angles for the pitch axis in the GUI, every time I press 'Write' the gimbal ends up at a new starting angle! Eg. I want a Min angle of 0° (straight ahead) and a Max angle of 90° (straight down) so I enter these values and click Write. More often than not, instead of going to 0° it will point upwards or downwards at some random angle! Then pressing Write again will make it assume another angle! Basically it's virtually impossible to set the tilt to go from straight ahead to straight down – due to a combination of both the problems described above ... I finally managed it, but only by setting Min to 15° and Max to 85° or something bizarre, and waiting for the gimbal to finally stop moving at either end!


    Interestingly, the GUI display showing the real-time position of the pitch axis correctly displays the angle of the pitch motor – and it is correctly showing the pitch axis completely ignoring my requests for 0° and 90° Min/Max values – so the controller knows it's moving the axis too far / not far enough at either end!

    Sorry for the waffly explanations, I hope you can understand what I'm describing and can suggest ways of trying to fix these problems?

    Many thanks for your help,

    David
  • MdG_NL
    Hello David,

    I think your Pitch axis needs to be inverted by the Basic Motor settings.
    Better is to use the Auto option, please check the number of your MotorPoles after you have used the auto option !
    Somethimes it's gets wrong during the auto option.

    Regards,
    Marten
  • David_Hogg
    Hi Marten,

    Many thanks for your reply.

    Unfortunately this didn't seem to make any difference. Actually instead of undershooting, inverting the motor direction makes it overshoot (going beyond 90° down and then coming back). I tried auto-detecting but the number of poles were wildly incorrect (17 and 54 for identical roll and pitch motors for example)!

    Do you have any other ideas what might be causing the problem? I'm still puzzled why I can't just enter 0 and 90 in the Min and Max angles for pitch – I'm currently using 15° and 90° to get it to go from straight forward to straight down.

    Many thanks for your help,

    David
  • David_Hogg
    PS. Ok I've just found that if I increase the Pitch value for 'I' it removes the delay ... it's a work-around I guess and the gimbal still seems to behave so I'm happy for now :-)
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