Cinemática de accionamiento diferencial

La clase DifferentialDriveKinematics es una herramienta útil que convierte entre un objeto ChassisSpeeds y un objeto DifferentialDriveWheelSpeeds, que contiene velocidades para los lados izquierdo y derecho de un robot de accionamiento diferencial.

Construyendo el objeto de cinemática

El objeto DifferentialDriveKinematics acepta un argumento constructor, que es el ancho de pista del robot. Esto representa la distancia entre los dos juegos de ruedas en una transmisión diferencial.

Nota

In Java and Python, the track width must be in meters. In C++, the units library can be used to pass in the track width using any length unit.

Conversión de velocidades del chasis a velocidades de las ruedas

The toWheelSpeeds(ChassisSpeeds speeds) (Java / Python) / ToWheelSpeeds(ChassisSpeeds speeds) (C++) method should be used to convert a ChassisSpeeds object to a DifferentialDriveWheelSpeeds object. This is useful in situations where you have to convert a linear velocity (vx) and an angular velocity (omega) to left and right wheel velocities.

JAVA

// Creating my kinematics object: track width of 27 inches
DifferentialDriveKinematics kinematics =
  new DifferentialDriveKinematics(Units.inchesToMeters(27.0));

// Example chassis speeds: 2 meters per second linear velocity,
// 1 radian per second angular velocity.
var chassisSpeeds = new ChassisSpeeds(2.0, 0, 1.0);

// Convert to wheel speeds
DifferentialDriveWheelSpeeds wheelSpeeds = kinematics.toWheelSpeeds(chassisSpeeds);

// Left velocity
double leftVelocity = wheelSpeeds.leftMetersPerSecond;

// Right velocity
double rightVelocity = wheelSpeeds.rightMetersPerSecond;

C++

// Creating my kinematics object: track width of 27 inches
frc::DifferentialDriveKinematics kinematics{27_in};

// Example chassis speeds: 2 meters per second linear velocity,
// 1 radian per second angular velocity.
frc::ChassisSpeeds chassisSpeeds{2_mps, 0_mps, 1_rad_per_s};

// Convert to wheel speeds. Here, we can use C++17's structured bindings
// feature to automatically split the DifferentialDriveWheelSpeeds
// struct into left and right velocities.
auto [left, right] = kinematics.ToWheelSpeeds(chassisSpeeds);

PYTHON

from wpimath.kinematics import DifferentialDriveKinematics
from wpimath.kinematics import ChassisSpeeds
from wpimath.units import inchesToMeters

# Creating my kinematics object: track width of 27 inches
kinematics = DifferentialDriveKinematics(Units.inchesToMeters(27.0))

# Example chassis speeds: 2 meters per second linear velocity,
# 1 radian per second angular velocity.
chassisSpeeds = ChassisSpeeds(2.0, 0, 1.0)

# Convert to wheel speeds
wheelSpeeds = kinematics.toWheelSpeeds(chassisSpeeds)

# Left velocity
leftVelocity = wheelSpeeds.left
# Right velocity
rightVelocity = wheelSpeeds.right

Conversión de velocidades de las ruedas a velocidades del chasis

One can also use the kinematics object to convert individual wheel speeds (left and right) to a singular ChassisSpeeds object. The toChassisSpeeds(DifferentialDriveWheelSpeeds speeds) (Java / Python) / ToChassisSpeeds(DifferentialDriveWheelSpeeds speeds) (C++) method should be used to achieve this.

JAVA

// Creating my kinematics object: track width of 27 inches
DifferentialDriveKinematics kinematics =
  new DifferentialDriveKinematics(Units.inchesToMeters(27.0));

// Example differential drive wheel speeds: 2 meters per second
// for the left side, 3 meters per second for the right side.
var wheelSpeeds = new DifferentialDriveWheelSpeeds(2.0, 3.0);

// Convert to chassis speeds.
ChassisSpeeds chassisSpeeds = kinematics.toChassisSpeeds(wheelSpeeds);

// Linear velocity
double linearVelocity = chassisSpeeds.vxMetersPerSecond;

// Angular velocity
double angularVelocity = chassisSpeeds.omegaRadiansPerSecond;

C++

// Creating my kinematics object: track width of 27 inches
frc::DifferentialDriveKinematics kinematics{27_in};

// Example differential drive wheel speeds: 2 meters per second
// for the left side, 3 meters per second for the right side.
frc::DifferentialDriveWheelSpeeds wheelSpeeds{2_mps, 3_mps};

// Convert to chassis speeds. Here we can use C++17's structured bindings
// feature to automatically split the ChassisSpeeds struct into its 3 components.
// Note that because a differential drive is non-holonomic, the vy variable
// will be equal to zero.
auto [linearVelocity, vy, angularVelocity] = kinematics.ToChassisSpeeds(wheelSpeeds);

PYTHON

from wpimath.kinematics import DifferentialDriveKinematics
from wpimath.kinematics import DifferentialDriveWheelSpeeds
from wpimath.units import inchesToMeters

# Creating my kinematics object: track width of 27 inches
kinematics = DifferentialDriveKinematics(inchesToMeters(27.0))

# Example differential drive wheel speeds: 2 meters per second
# for the left side, 3 meters per second for the right side.
wheelSpeeds = DifferentialDriveWheelSpeeds(2.0, 3.0)

# Convert to chassis speeds.
chassisSpeeds = kinematics.toChassisSpeeds(wheelSpeeds)

# Linear velocity
linearVelocity = chassisSpeeds.vx

# Angular velocity
angularVelocity = chassisSpeeds.omega