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control of 360 degree servos

Former Member

Hi

 

i wonder how i would control a 360 degree servos from a python script?

 

there are lot of guides on 180 degree servos

 

most of them from adafruit... have nothing against them but i like to not be dependent on external libs

 

 

i'm going to use this in a fully automatic tracker.... the tracker will be used to track high altitude baloons (30+ km)

 

 

/bo

  • 0 in reply to shabaz

    hi

     

    i got back to this.. i opted for the adafruit lib

     

    what excatly do i need to do so i can just tell it a angle between 1 and 360 ?

     

    you said something about "the pulse width needs to be between 800 and 2200usec for a rotation of 2160 degrees" ??

  • 0 in reply to Former Member

    It means just use approx one fifth of the range, since the span +-116usec is approx one-fifth of +-500usec.

    I've not used the adafruit library or tried to control a servo with the BBB.

    If you library (say) takes a value between 0 and 180 to represent 180 degrees of a normal servo (with a value of 90 being the center), then for your servo you need to use a value between about 72 to 108 to represent 0 to 360 degrees.

    Notice this is not very granular (as mentioned in post#1, it won't be very high-res with such a servo).

    If you wanted it more granular you'd need to delve into the driver code and adapt to use a higher-res PWM (e.g. 10-bit or more) - I don't know what the adafruit library uses.

    Furthermore, even if you did this, I doubt you'd get much better granularity because the servo has hysteresis.

    I suspect getting anything remotely close to 1 degree resolution with that servo will not be possible - I'm just guessing though, I've not tried it.

     

    EDIT: This randomly chosen servo has a dead band specification of 8usec. So, if the pulse width has a possible span of 1000usec for 0 to 180 degrees, you can see that the actual granularity that you can use to position this random servo is not much.. (ok for RC models of course).