What form is the feedback from a continuous rotation servo

Hardware
1

I'm looking at the Feedback 360 Degree - High Speed Continuous Rotation Servo from AdaFruit.

What I don't understand is how the feedback of the current position is "formatted". The details say "PWM positional feedback across entire angular range" but does that get "averaged" in some way into a DC voltage...?

Or do I need to add a low pass filter to do the averaging myself?

Or do I need my software to measure the pulse width?

Or have I misunderstood something?

2

You have to measure the pulse width using Arduino's pulseIn() function.

1 Like
3

Here is a link to a library that may provide the answer to your question.

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4

The Adafruit video mentions that the feedback is from an AS5600 sensor. See the data sheet for the details on the PWM output (page 27)
https://www.mouser.com/datasheet/2/588/AS5600_DS000365_5_00-1877365.pdf

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5

From the servo data sheet:

Screenshot 2024-07-13 at 11.50.29 AM
Screenshot 2024-07-13 at 11.50.29 AM1230×778 94.1 KB

Screenshot 2024-07-13 at 11.50.41 AM
Screenshot 2024-07-13 at 11.50.41 AM1212×436 33 KB

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6

But do I need a libary, can't I just use pulseIn() ? Genuine question, I have no experience with continuous servos...

7

Thanks, so I use pulseIn() with the formula you've shown me? Have I understood?

8

That's the way I see it.

1 Like
9

Finally got round to following your advice an I've implemented this for the Parallax 360 feedback servo, seems to work:

static const double kFeedbackFreq = 910.0 ;
static const double kFeedbackCycleTimeSeconds = 1.0/kFeedbackFreq ;
static const double kFeedbackCycleTimeMicroseconds = kFeedbackCycleTimeSeconds*1000000 ;

int Read_Servo_Angle()
{
    // See how high the pulse is in microseconds
    int iServoPulseFeedbackMicros = pulseIn (ikHoursServoFeedbackPin,HIGH) ;

    // these also depend on your servo...
    const double kDutyCycleMin = 0.027 ;
    const double kDutyCycleMax = 0.971 ;

    // Get a fraction from 0.027 to 0.971
    double DutyCycle1 = iServoPulseFeedbackMicros/kFeedbackCycleTimeMicroseconds ;
    
    // Convert to a fraction from 0.0 to 1.0
    double DutyCycle2 = (DutyCycle1-kDutyCycleMin)/(kDutyCycleMax - kDutyCycleMin) ;

    Serial.print ("DC1=") ; Serial.print (DutyCycle1) ;
    Serial.print (", DC2=") ; Serial.println (DutyCycle2) ;

    // Convert to an angle...
    const double kDegsAngle = 180.0 - (DutyCycle2*360.0) ;

    return int(kDegsAngle+0.5) ;
}