Controlador ramsete

Advertencia

Ramsete Controller has been deprecated. Use LTV Unicycle Controller which has more intuitive tuning.

The Ramsete Controller is a trajectory tracker that is built in to WPILib. This tracker can be used to accurately track trajectories with correction for minor disturbances for differential drivetrains.

Construcción del objeto controlador Ramsete

El controlador Ramsete debe inicializarse con dos ganancias, a saber, b y zeta. Los valores más altos de b hacen que la convergencia sea más agresiva como un término proporcional, mientras que los valores más altos de zeta proporcionan más amortiguación en la respuesta. Estas ganancias del controlador solo dictan cómo el controlador generará velocidades ajustadas. NO afecta el seguimiento de la velocidad real del robot. Esto significa que estas ganancias del controlador son generalmente independientes del robot.

Nota

Las ganancias de 2.0 y 0.7``para ``b y zeta se han probado repetidamente para producir resultados deseables cuando todas las unidades estaban en metros. Como tal, existe un constructor de argumento cero para RamseteController con ganancias predeterminadas a estos valores.

JAVA

// Using the default constructor of RamseteController. Here
// the gains are initialized to 2.0 and 0.7.
RamseteController controller1 = new RamseteController();
// Using the secondary constructor of RamseteController where
// the user can choose any other gains.
RamseteController controller2 = new RamseteController(2.1, 0.8);

C++

// Using the default constructor of RamseteController. Here
// the gains are initialized to 2.0 and 0.7.
frc::RamseteController controller1;
// Using the secondary constructor of RamseteController where
// the user can choose any other gains.
frc::RamseteController controller2{2.1, 0.8};

PYTHON

from wpimath.controller import RamseteController
# Using the default constructor of RamseteController. Here
# the gains are initialized to 2.0 and 0.7.
controller1 = RamseteController()
# Using the secondary constructor of RamseteController where
# the user can choose any other gains.
controller2 = RamseteController(2.1, 0.8)

Obtener velocidades ajustadas

The Ramsete controller returns «adjusted velocities» so that the when the robot tracks these velocities, it accurately reaches the goal point. The controller should be updated periodically with the new reference, which is where it should be at the current time. The reference comprises of a desired pose, desired linear velocity, and desired angular velocity. Furthermore, the current position of the robot should also be updated periodically. The controller uses these four arguments to return the adjusted linear and angular velocity. Users should command their robot to these linear and angular velocities to achieve optimal trajectory tracking.

Nota

The «reference pose» represents the position that the robot should be at a particular timestep when tracking the trajectory. It does NOT represent the final endpoint of the trajectory, which is the goal.

The controller can be updated using the Calculate (C++) / calculate (Java/Python) method. There are two overloads for this method. Both of these overloads accept the current robot position as the first parameter. For the other parameters, one of these overloads takes in the reference as three separate parameters (pose, linear velocity, and angular velocity) whereas the other overload accepts a Trajectory.State object, which contains information about the reference pose. For its ease, users should use the latter method when tracking trajectories.

JAVA

Trajectory.State reference = trajectory.sample(3.4); // sample the trajectory at 3.4 seconds from the beginning
ChassisSpeeds adjustedSpeeds = controller.calculate(currentRobotPose, reference);

C++

const Trajectory::State reference = trajectory.Sample(3.4_s); // sample the trajectory at 3.4 seconds from the beginning
ChassisSpeeds adjustedSpeeds = controller.Calculate(currentRobotPose, reference);

PYTHON

reference = trajectory.sample(3.4)  # sample the trajectory at 3.4 seconds from the beginning
adjustedSpeeds = controller.calculate(currentRobotPose, reference)

These calculations should be performed at every loop iteration, with an updated robot position and reference.

Usando las velocidades ajustadas

Las velocidades ajustadas son del tipo ChassisSpeeds, que contiene un vx (velocidad lineal en la dirección de avance), una vy (velocidad lineal en la dirección lateral) y un omega (velocidad angular alrededor del centro del marco del robot). Debido a que el controlador Ramsete es un controlador para robots no holonómicos (robots que no pueden moverse hacia los lados), el objeto de velocidades ajustadas tiene una vy de cero.

Las velocidades ajustadas de regreso pueden ser convertidas a velocidades para usar utilizando las clases cinemáticas para el tipo de chasis. Por ejemplo, las velocidades ajustadas pueden convertirse en velocidades de derecha e izquierda para un manejo diferencial usando el objeto DifferentialDriveKinematics.

JAVA

ChassisSpeeds adjustedSpeeds = controller.calculate(currentRobotPose, reference);
DifferentialDriveWheelSpeeds wheelSpeeds = kinematics.toWheelSpeeds(adjustedSpeeds);
double left = wheelSpeeds.leftMetersPerSecond;
double right = wheelSpeeds.rightMetersPerSecond;

C++

ChassisSpeeds adjustedSpeeds = controller.Calculate(currentRobotPose, reference);
DifferentialDriveWheelSpeeds wheelSpeeds = kinematics.ToWheelSpeeds(adjustedSpeeds);
auto [left, right] = kinematics.ToWheelSpeeds(adjustedSpeeds);

PYTHON

adjustedSpeeds = controller.calculate(currentRobotPose, reference)
wheelSpeeds = kinematics.toWheelSpeeds(adjustedSpeeds)
left = wheelSpeeds.left
right = wheelSpeeds.right

Because these new left and right velocities are still speeds and not voltages, two PID Controllers, one for each side may be used to track these velocities. Either the WPILib PIDController (C++, Java, Python) can be used, or the Velocity PID feature on smart motor controllers such as the TalonSRX and the SPARK MAX can be used.

Ramsete en el Framework con base comando

Con motivos de facilitar a los usuarios, la clase RamseteCommand está contruida en WPILib. Para un tutorial completo en la implementación de un autónomo que siga un camino usando RamseteCommand, vea Trajectory Tutorial.