Cinemática de direção diferencial¶

The DifferentialDriveKinematics class is a useful tool that converts between a ChassisSpeeds object and a DifferentialDriveWheelSpeeds object, which contains velocities for the left and right sides of a differential drive robot.

Construindo o objeto cinemático¶

The DifferentialDriveKinematics object accepts one constructor argument, which is the track width of the robot. This represents the distance between the two sets of wheels on a differential drive.

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.

Convertendo Speeds Do Chassi Em Speeds Das Rodas¶

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
wpi::DifferentialDriveKinematics kinematics{27_in};
// Example chassis speeds: 2 meters per second linear velocity,
// 1 radian per second angular velocity.
wpi::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 inches_to_meters
# Creating my kinematics object: track width of 27 inches
kinematics = DifferentialDriveKinematics(Units.inches_to_meters(27.0))
# Example chassis speeds: 2 meters per second linear velocity,
# 1 radian per second angular velocity.
chassis_speeds = ChassisSpeeds(2.0, 0, 1.0)
# Convert to wheel speeds
wheel_speeds = kinematics.toWheelSpeeds(chassis_speeds)
# Left velocity
left_velocity = wheel_speeds.left
# Right velocity
right_velocity = wheel_speeds.right

Convertendo Speeds Das Rodas para Speeds Do Chassi¶

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
wpi::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.
wpi::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 inches_to_meters
# Creating my kinematics object: track width of 27 inches
kinematics = DifferentialDriveKinematics(inches_to_meters(27.0))
# Example differential drive wheel speeds: 2 meters per second
# for the left side, 3 meters per second for the right side.
wheel_speeds = DifferentialDriveWheelSpeeds(2.0, 3.0)
# Convert to chassis speeds.
chassis_speeds = kinematics.toChassisSpeeds(wheel_speeds)
# Linear velocity
linear_velocity = chassis_speeds.vx
# Angular velocity
angular_velocity = chassis_speeds.omega