# Differential Drive Kinematics

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 track width of the robot. This represents the distance between the two sets of wheels on a differential drive.

Note

In Java, 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.

## Converting Chassis Speeds to Wheel Speeds

The toWheelSpeeds(ChassisSpeeds speeds) (Java) / 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.

// 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;


## 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) (Java) / ToChassisSpeeds(DifferentialDriveWheelSpeeds speeds) (C++) method should be used to achieve this.

// 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