Package edu.wpi.first.math.kinematics

Class DifferentialDriveKinematics

java.lang.Object

edu.wpi.first.math.kinematics.DifferentialDriveKinematics

All Implemented Interfaces:

Interpolator<DifferentialDriveWheelPositions>, Kinematics<DifferentialDriveWheelSpeeds,DifferentialDriveWheelPositions>, ProtobufSerializable, StructSerializable, WPISerializable

public class DifferentialDriveKinematics
extends Object
implements Kinematics<DifferentialDriveWheelSpeeds,DifferentialDriveWheelPositions>, ProtobufSerializable, StructSerializable

Helper class that converts a chassis velocity (dx and dtheta components) to left and right wheel velocities for a differential drive.

Inverse kinematics converts a desired chassis speed into left and right velocity components whereas forward kinematics converts left and right component velocities into a linear and angular chassis speed.

Field Summary

Fields

Modifier and Type	Field	Description
static final DifferentialDriveKinematicsProto	proto	DifferentialDriveKinematics protobuf for serialization.
static final DifferentialDriveKinematicsStruct	struct	DifferentialDriveKinematics struct for serialization.
final double	trackWidthMeters	Differential drive trackwidth.

Constructor Summary

Constructors

Constructor	Description
DifferentialDriveKinematics(double trackWidthMeters)	Constructs a differential drive kinematics object.
DifferentialDriveKinematics(Distance trackWidth)	Constructs a differential drive kinematics object.

Method Summary

Modifier and Type	Method	Description
DifferentialDriveWheelPositions	copy(DifferentialDriveWheelPositions positions)	Returns a copy of the wheel positions object.
void	copyInto(DifferentialDriveWheelPositions positions, DifferentialDriveWheelPositions output)	Copies the value of the wheel positions object into the output.
DifferentialDriveWheelPositions	interpolate(DifferentialDriveWheelPositions startValue, DifferentialDriveWheelPositions endValue, double t)	Perform interpolation between two values.
ChassisSpeeds	toChassisSpeeds(DifferentialDriveWheelSpeeds wheelSpeeds)	Returns a chassis speed from left and right component velocities using forward kinematics.
Twist2d	toTwist2d(double leftDistanceMeters, double rightDistanceMeters)	Performs forward kinematics to return the resulting Twist2d from the given left and right side distance deltas.
Twist2d	toTwist2d(DifferentialDriveWheelPositions start, DifferentialDriveWheelPositions end)	Performs forward kinematics to return the resulting Twist2d from the given change in wheel positions.
DifferentialDriveWheelSpeeds	toWheelSpeeds(ChassisSpeeds chassisSpeeds)	Returns left and right component velocities from a chassis speed using inverse kinematics.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Details

trackWidthMeters

public final double trackWidthMeters

Differential drive trackwidth.

proto

public static final DifferentialDriveKinematicsProto proto

DifferentialDriveKinematics protobuf for serialization.

struct

public static final DifferentialDriveKinematicsStruct struct

DifferentialDriveKinematics struct for serialization.

Constructor Details

DifferentialDriveKinematics

public DifferentialDriveKinematics(double trackWidthMeters)

Constructs a differential drive kinematics object.

Parameters:

trackWidthMeters - The track width of the drivetrain. Theoretically, this is the distance between the left wheels and right wheels. However, the empirical value may be larger than the physical measured value due to scrubbing effects.

DifferentialDriveKinematics

public DifferentialDriveKinematics(Distance trackWidth)

Constructs a differential drive kinematics object.

Parameters:

trackWidth - The track width of the drivetrain. Theoretically, this is the distance between the left wheels and right wheels. However, the empirical value may be larger than the physical measured value due to scrubbing effects.

Method Details

toChassisSpeeds

public ChassisSpeeds toChassisSpeeds(DifferentialDriveWheelSpeeds wheelSpeeds)

Returns a chassis speed from left and right component velocities using forward kinematics.

Specified by:

toChassisSpeeds in interface Kinematics<DifferentialDriveWheelSpeeds,DifferentialDriveWheelPositions>

Parameters:

wheelSpeeds - The left and right velocities.

Returns:

The chassis speed.

toWheelSpeeds

public DifferentialDriveWheelSpeeds toWheelSpeeds(ChassisSpeeds chassisSpeeds)

Returns left and right component velocities from a chassis speed using inverse kinematics.

Specified by:

toWheelSpeeds in interface Kinematics<DifferentialDriveWheelSpeeds,DifferentialDriveWheelPositions>

Parameters:

chassisSpeeds - The linear and angular (dx and dtheta) components that represent the chassis' speed.

Returns:

The left and right velocities.

toTwist2d

public Twist2d toTwist2d(DifferentialDriveWheelPositions start,
 DifferentialDriveWheelPositions end)

Description copied from interface: Kinematics

Performs forward kinematics to return the resulting Twist2d from the given change in wheel positions. This method is often used for odometry -- determining the robot's position on the field using changes in the distance driven by each wheel on the robot.

Specified by:

toTwist2d in interface Kinematics<DifferentialDriveWheelSpeeds,DifferentialDriveWheelPositions>

Parameters:

start - The starting distances driven by the wheels.

end - The ending distances driven by the wheels.

Returns:

The resulting Twist2d in the robot's movement.

toTwist2d

public Twist2d toTwist2d(double leftDistanceMeters,
 double rightDistanceMeters)

Performs forward kinematics to return the resulting Twist2d from the given left and right side distance deltas. This method is often used for odometry -- determining the robot's position on the field using changes in the distance driven by each wheel on the robot.

Parameters:

leftDistanceMeters - The distance measured by the left side encoder.

rightDistanceMeters - The distance measured by the right side encoder.

Returns:

The resulting Twist2d.

copy

public DifferentialDriveWheelPositions copy(DifferentialDriveWheelPositions positions)

Description copied from interface: Kinematics

Returns a copy of the wheel positions object.

Specified by:

copy in interface Kinematics<DifferentialDriveWheelSpeeds,DifferentialDriveWheelPositions>

Parameters:

positions - The wheel positions object to copy.

Returns:

A copy.

copyInto

public void copyInto(DifferentialDriveWheelPositions positions,
 DifferentialDriveWheelPositions output)

Description copied from interface: Kinematics

Copies the value of the wheel positions object into the output.

Specified by:

copyInto in interface Kinematics<DifferentialDriveWheelSpeeds,DifferentialDriveWheelPositions>

Parameters:

positions - The wheel positions object to copy. Will not be modified.

output - The output variable of the copy operation. Will have the same value as the positions object after the call.

interpolate

public DifferentialDriveWheelPositions interpolate(DifferentialDriveWheelPositions startValue,
 DifferentialDriveWheelPositions endValue,
 double t)

Description copied from interface: Interpolator

Perform interpolation between two values.

Specified by:

interpolate in interface Interpolator<DifferentialDriveWheelPositions>

Parameters:

startValue - The value to start at.

endValue - The value to end at.

t - How far between the two values to interpolate. This should be bounded to [0, 1].

Returns:

The interpolated value.