# Ramsete calculations

For ramsete, what does b and zeta do and how do i calculate them? Thanks!

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Thanks for the link, but what does those values change? Does b make the curve flatter?

``````b    Tuning parameter (b < 0) for which larger values make convergence more
aggressive like a proportional term.
zeta Tuning parameter (0 < zeta < 1) for which larger values provide more damping
in response.``````

Thanks for the explanation, but what is that impact on the actual movement of the robot?

m_zeta scales out the curve, making the robot change speed slower. i cant figure out how m_b works, but this is the direct code from wpilib:

``````public ChassisSpeeds calculate(Pose2d currentPose,
Pose2d poseRef,
double linearVelocityRefMeters,
m_poseError = poseRef.relativeTo(currentPose);

final double eX = m_poseError.getTranslation().getX();
final double eY = m_poseError.getTranslation().getY();
final double vRef = linearVelocityRefMeters;

double k = 2.0 * m_zeta * Math.sqrt(Math.pow(omegaRef, 2) + m_b * Math.pow(vRef, 2));

return new ChassisSpeeds(vRef * m_poseError.getRotation().getCos() + k * eX,
0.0,
omegaRef + k * eTheta + m_b * vRef * sinc(eTheta) * eY);
}``````
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These controller gains don’t affect the actual velocity tracking happening; they only affect how the controller outputs. Honestly, for our team, we used the constants from WPILib’s Ramsete example: https://github.com/wpilibsuite/allwpilib/blob/master/wpilibjExamples/src/main/java/edu/wpi/first/wpilibj/examples/ramsetecommand/Constants.java

``````    // Reasonable baseline values for a RAMSETE follower in units of meters and seconds
public static final double kRamseteB = 2;
public static final double kRamseteZeta = 0.7;
``````

And these worked out pretty well.

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With the link, @Sumifairy, I was directing you towards
`Gains of 2.0 and 0.7 for b and zeta have been tested repeatedly to produce desirable results when all units were in meters.`
Or as @mustangtech mentioned, using the default constants should work.

Thanks for the replies! I have one question about their example trajectory that is supposed to go 3 meters “forward” facing 0 degrees at the end but their start is (0,0) and end is (3,0). won’t this be going to the right instead of forward? Thanks!

Headings are measured according to mathematical convention - counterclockwise from the +x axis.

Thanks for the reply! So just to clarify, if i wanted to go forward i would change the X to positive values and side to side is a change in the Y. And then that if i wanted to face left, i would say 90, which would be facing the positive Y axis? This kinda makes sense since we just learned unit circle in trig. Thanks!

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Yes, the standard is exactly the same as the unit circle you’ve learned.

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