navx-mxp AHRS.getAngle() method

Technical Sensors
1

according to the documentation in the code for the AHRS.getAngle() method: the return value should be “continuous”, so if the robot transitions in the positive direction past 359.9999 degrees, it should return 360 and so on. but according to our experiments, this is not true. the getAngle() method never returns any value >= 360 or <= -360. is there some parameter we need to set to get this behavior?

2

Let me take a look into it, sounds like a bug. Are you using Java?

3

yes, using Java.

4

Thanks for helping us find this issue; an updated navX-MXP build is now available which fixes this issue in the Java library.

5

thanks for getting a fix out this quickly. unfortunately we did not have the time to test the new library and for now we have a method that normalizes the angle so we can get around this. i’m hoping to be able to look at this later in the week and get back to you.

thanks,

bill

6

What’s your method?

7

this is for our pid controller that rotates the robot to a heaing. in our code we now always set a target of 0 ie PIDcontroller.setSetpoint(0)

for the PIDsource we do the following:

public double pidGet() {
double gyroAngle = m_navX.getAngle();

		//adding math to normalize the heading for a target of 0
		//always
		double diff = gyroAngle - m_headingToTurnTo;
		if(diff &lt;= -180){
			diff += 360;
		} else if(diff &gt; 180){
			diff -= 360;
		}
		
		return(diff);

}

the term normalize may be incorrect, but i couldn’t come up with a better way to explain it.

unfortunately, trying to use this to tune the PID controller in test mode is rather difficult, but it does work in our code for commands to turn the robot to a specific heading. well, at least the robot doesn’t just continuously spin as it was when we set a heading that caused the robot to spin past an angle of 0 or 360…

8

oops, it should be

value >= 360 or value < 0