Étape 2 : Saisie des constantes calculées

Note

En C++, il est important que les constantes de la commande prédictive soient saisies dans le type d’unité approprié. Pour plus d’informations sur les unités C++, voir La librairie d’unités C++.

Maintenant que nous avons nos constantes système, il est temps de les placer dans notre code. L’emplacement recommandé pour cela est le fichier Constants de la structure de projet basée sur des commandes standard.

The relevant parts of the constants file from the RamseteCommand Example Project (Java, C++) can be seen below.

Gains Prédicitif/Rétroactif

Tout d’abord, nous devons entrer les gains d’anticipation et de rétroaction que nous avons obtenus à partir de l’outil d’identification.

Note

Les gains prédictif et rétroactif ne se transfèrent pas, en général, entre les robots. Aussi, n’utilisez pas les gains de ce tutoriel sur votre propre robot.

JAVA

    // These are example values only - DO NOT USE THESE FOR YOUR OWN ROBOT!
    // These characterization values MUST be determined either experimentally or theoretically
    // for *your* robot's drive.
    // The Robot Characterization Toolsuite provides a convenient tool for obtaining these
    // values for your robot.
    public static final double ksVolts = 0.22;
    public static final double kvVoltSecondsPerMeter = 1.98;
    public static final double kaVoltSecondsSquaredPerMeter = 0.2;

    // Example value only - as above, this must be tuned for your drive!
    public static final double kPDriveVel = 8.5;

C++

// These are example values only - DO NOT USE THESE FOR YOUR OWN ROBOT!
// These characterization values MUST be determined either experimentally or
// theoretically for *your* robot's drive. The Robot Characterization
// Toolsuite provides a convenient tool for obtaining these values for your
// robot.
inline constexpr auto ks = 0.22_V;
inline constexpr auto kv = 1.98 * 1_V * 1_s / 1_m;
inline constexpr auto ka = 0.2 * 1_V * 1_s * 1_s / 1_m;

// Example value only - as above, this must be tuned for your drive!
inline constexpr double kPDriveVel = 8.5;

DifferentialDriveKinematics

En outre, nous devons créer une instance de la classe DifferentialDriveKinematics , qui nous permet d’utiliser la trackwidth (c’est-à-dire la distance horizontale entre les roues) du robot pour la conversion des vitesses du châssis aux vitesses des roues. Comme partout ailleurs, nous gardons nos unités en mètres.

JAVA

    public static final double kTrackwidthMeters = 0.69;
    public static final DifferentialDriveKinematics kDriveKinematics =
        new DifferentialDriveKinematics(kTrackwidthMeters);

C++

inline constexpr auto kTrackwidth = 0.69_m;
extern const frc::DifferentialDriveKinematics kDriveKinematics;

Vitesse/accélération max sur la trajectoire

Nous devons également décider d’une accélération nominale max et d’une vitesse maximale du robot pendant le suivi de la trajectoire. La valeur maximale de la vitesse doit être choisie légèrement en dessous de la vitesse libre nominale du robot. En raison de l’utilisation ultérieure du DifferentialDriveVoltageConstraint, la valeur maximale de l’accélération n’est pas extrêmement cruciale.

Avertissement

Max velocity and acceleration, as defined here, are applied only during trajectory generation. They do not limit the RamseteCommand itself, which may give values to the DriveSubsystem that can cause the robot to greatly exceed these velocities and accelerations.

JAVA

    public static final double kMaxSpeedMetersPerSecond = 3;
    public static final double kMaxAccelerationMetersPerSecondSquared = 1;

C++

inline constexpr auto kMaxSpeed = 3_mps;
inline constexpr auto kMaxAcceleration = 1_mps_sq;

Paramètres Ramsete

Finally, we must include a pair of parameters for the RAMSETE controller. The values b and zeta shown below should work well for most robots, provided distances have been correctly measured in meters.

Larger values of b make convergence more aggressive like a proportional term whereas larger values of zeta provide more damping in the response. These controller gains only dictate how the controller will output adjusted velocities. It does NOT affect the actual velocity tracking of the robot. This means that these controller gains are generally robot-agnostic.

Note

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. As such, a zero-argument constructor for RamseteController exists with gains defaulted to these values.

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;

C++

// Reasonable baseline values for a RAMSETE follower in units of meters and
// seconds
inline constexpr auto kRamseteB = 2.0 * 1_rad * 1_rad / (1_m * 1_m);
inline constexpr auto kRamseteZeta = 0.7 / 1_rad;