Differential Drive Kinematics

import com.arcrobotics.ftclib.kinematics.wpilibkinematics.DifferentialDriveKinematics

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.

Constructing the Kinematics Object

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

Note: The trackwidth must be in meters.

Converting Chassis Speeds to Wheel Speeds

The toWheelSpeeds(ChassisSpeeds speeds) 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.

// Creating my kinematics object: track width of 15 inches
DifferentialDriveKinematics kinematics =
  new DifferentialDriveKinematics(15.0 / 254.0);

// Example chassis speeds: 2 meters per second linear velocity,
// 1 radian per second angular velocity.
ChassisSpeeds 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;

Converting Wheel Speeds to Chassis Speeds

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

// Creating my kinematics object: track width of 15 inches
DifferentialDriveKinematics kinematics =
  new DifferentialDriveKinematics(15.0 / 254.0);

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