Odométrie avec l’entraînement de type Mécanum

Un utilisateur peut utiliser les classes de cinématique d’entraînement de Mecanum afin d’effectuer l” Odométrie. WPILib contient une classe MecanumDriveOdometry qui peut être utilisée pour suivre la position d’un robot avec entraînement Mécanum sur le terrain de jeu.

Note

Étant donné que cette méthode n’utilise que des encodeurs et un gyroscope, l’estimation de la position du robot sur le terrain de jeu dérivera avec le temps, d’autant plus que votre robot va entrer en contact avec des objets ou d’autres robots pendant le jeu. Cependant, l’odométrie est généralement très précise pendant la période autonome.

Création de l’objet odométrie

The MecanumDriveOdometry class constructor requires three mandatory arguments and one optional argument.

The mandatory arguments are:

  • The kinematics object that represents your mecanum drive (as a MecanumDriveKinematics instance)

  • The angle reported by your gyroscope (as a Rotation2d)

  • The initial positions of the wheels (as MecanumDriveWheelPositions). In Java / Python, this must be constructed with each wheel position in meters. In C++, the units library must be used to represent your wheel positions.

The fourth optional argument is the starting pose of your robot on the field (as a Pose2d). By default, the robot will start at x = 0, y = 0, theta = 0.

Note

0 degrees / radians represents the robot angle when the robot is facing directly toward your opponent’s alliance station. As your robot turns to the left, your gyroscope angle should increase. The Gyro interface supplies getRotation2d/GetRotation2d that you can use for this purpose. See Coordinate System for more information about the coordinate system.

// Locations of the wheels relative to the robot center.
Translation2d m_frontLeftLocation = new Translation2d(0.381, 0.381);
Translation2d m_frontRightLocation = new Translation2d(0.381, -0.381);
Translation2d m_backLeftLocation = new Translation2d(-0.381, 0.381);
Translation2d m_backRightLocation = new Translation2d(-0.381, -0.381);
// Creating my kinematics object using the wheel locations.
MecanumDriveKinematics m_kinematics = new MecanumDriveKinematics(
  m_frontLeftLocation, m_frontRightLocation, m_backLeftLocation, m_backRightLocation
);
// Creating my odometry object from the kinematics object and the initial wheel positions.
// Here, our starting pose is 5 meters along the long end of the field and in the
// center of the field along the short end, facing the opposing alliance wall.
MecanumDriveOdometry m_odometry = new MecanumDriveOdometry(
  m_kinematics,
  m_gyro.getRotation2d(),
  new MecanumDriveWheelPositions(
    m_frontLeftEncoder.getDistance(), m_frontRightEncoder.getDistance(),
    m_backLeftEncoder.getDistance(), m_backRightEncoder.getDistance()
  ),
  new Pose2d(5.0, 13.5, new Rotation2d())
);

// Locations of the wheels relative to the robot center.
frc::Translation2d m_frontLeftLocation{0.381_m, 0.381_m};
frc::Translation2d m_frontRightLocation{0.381_m, -0.381_m};
frc::Translation2d m_backLeftLocation{-0.381_m, 0.381_m};
frc::Translation2d m_backRightLocation{-0.381_m, -0.381_m};
// Creating my kinematics object using the wheel locations.
frc::MecanumDriveKinematics m_kinematics{
  m_frontLeftLocation, m_frontRightLocation,
  m_backLeftLocation, m_backRightLocation
};
// Creating my odometry object from the kinematics object. Here,
// our starting pose is 5 meters along the long end of the field and in the
// center of the field along the short end, facing forward.
frc::MecanumDriveOdometry m_odometry{
  m_kinematics,
  m_gyro.GetRotation2d(),
  frc::MecanumDriveWheelPositions{
    units::meter_t{m_frontLeftEncoder.GetDistance()},
    units::meter_t{m_frontRightEncoder.GetDistance()},
    units::meter_t{m_backLeftEncoder.GetDistance()},
    units::meter_t{m_backRightEncoder.GetDistance()}
  },
  frc::Pose2d{5_m, 13.5_m, 0_rad}};

from wpimath.geometry import Translation2d
from wpimath.kinematics import MecanumDriveKinematics
from wpimath.kinematics import MecanumDriveOdometry
from wpimath.kinematics import MecanumDriveWheelPositions
from wpimath.geometry import Pose2d
from wpimath.geometry import Rotation2d
# Locations of the wheels relative to the robot center.
frontLeftLocation = Translation2d(0.381, 0.381)
frontRightLocation = Translation2d(0.381, -0.381)
backLeftLocation = Translation2d(-0.381, 0.381)
backRightLocation = Translation2d(-0.381, -0.381)
# Creating my kinematics object using the wheel locations.
self.kinematics = MecanumDriveKinematics(
  frontLeftLocation, frontRightLocation, backLeftLocation, backRightLocation
)
# Creating my odometry object from the kinematics object and the initial wheel positions.
# Here, our starting pose is 5 meters along the long end of the field and in the
# center of the field along the short end, facing the opposing alliance wall.
self.odometry = MecanumDriveOdometry(
  self.kinematics,
  self.gyro.getRotation2d(),
  MecanumDriveWheelPositions(
    self.frontLeftEncoder.getDistance(), self.frontRightEncoder.getDistance(),
    self.backLeftEncoder.getDistance(), self.backRightEncoder.getDistance()
  ),
  Pose2d(5.0, 13.5, Rotation2d())
)

Mise à jour de la pose du robot

The update method of the odometry class updates the robot position on the field. The update method takes in the gyro angle of the robot, along with a MecanumDriveWheelPositions object representing the position of each of the 4 wheels on the robot. This update method must be called periodically, preferably in the periodic() method of a Subsystem. The update method returns the new updated pose of the robot.

@Override
public void periodic() {
  // Get my wheel positions
  var wheelPositions = new MecanumDriveWheelPositions(
    m_frontLeftEncoder.getDistance(), m_frontRightEncoder.getDistance(),
    m_backLeftEncoder.getDistance(), m_backRightEncoder.getDistance());
  // Get the rotation of the robot from the gyro.
  var gyroAngle = m_gyro.getRotation2d();
  // Update the pose
  m_pose = m_odometry.update(gyroAngle, wheelPositions);
}

void Periodic() override {
  // Get my wheel positions
  frc::MecanumDriveWheelPositions wheelPositions{
    units::meter_t{m_frontLeftEncoder.GetDistance()},
    units::meter_t{m_frontRightEncoder.GetDistance()},
    units::meter_t{m_backLeftEncoder.GetDistance()},
    units::meter_t{m_backRightEncoder.GetDistance()}};
  // Get the rotation of the robot from the gyro.
  frc::Rotation2d gyroAngle = m_gyro.GetRotation2d();
  // Update the pose
  m_pose = m_odometry.Update(gyroAngle, wheelPositions);
}

from wpimath.kinematics import MecanumDriveWheelPositions
   def periodic(self):
  # Get my wheel positions
  wheelPositions = MecanumDriveWheelPositions(
    self.frontLeftEncoder.getDistance(), self.frontRightEncoder.getDistance(),
    self.backLeftEncoder.getDistance(), self.backRightEncoder.getDistance())
  # Get the rotation of the robot from the gyro.
  gyroAngle = gyro.getRotation2d()
  # Update the pose
  self.pose = odometry.update(gyroAngle, wheelPositions)

Réinitialisation de la pose de robot

The robot pose can be reset via the resetPosition method. This method accepts three arguments: the current gyro angle, the current wheel positions, and the new field-relative pose.

Important

If at any time, you decide to reset your gyroscope or encoders, the resetPosition method MUST be called with the new gyro angle and wheel positions.

Note

A full example of a mecanum drive robot with odometry is available here: C++ / Java / Python

In addition, the GetPose (C++) / getPoseMeters (Java / Python) methods can be used to retrieve the current robot pose without an update.