Package edu.wpi.first.math.kinematics

Class MecanumDriveKinematics

java.lang.Object

edu.wpi.first.math.kinematics.MecanumDriveKinematics

All Implemented Interfaces:

Interpolator<MecanumDriveWheelPositions>, Kinematics<MecanumDriveWheelSpeeds,MecanumDriveWheelPositions>, ProtobufSerializable, StructSerializable, WPISerializable

public class MecanumDriveKinematics
extends Object
implements Kinematics<MecanumDriveWheelSpeeds,MecanumDriveWheelPositions>, ProtobufSerializable, StructSerializable

Helper class that converts a chassis velocity (dx, dy, and dtheta components) into individual wheel speeds.

The inverse kinematics (converting from a desired chassis velocity to individual wheel speeds) uses the relative locations of the wheels with respect to the center of rotation. The center of rotation for inverse kinematics is also variable. This means that you can set your center of rotation in a corner of the robot to perform special evasion maneuvers.

Forward kinematics (converting an array of wheel speeds into the overall chassis motion) is performs the exact opposite of what inverse kinematics does. Since this is an overdetermined system (more equations than variables), we use a least-squares approximation.

The inverse kinematics: [wheelSpeeds] = [wheelLocations] * [chassisSpeeds] We take the Moore-Penrose pseudoinverse of [wheelLocations] and then multiply by [wheelSpeeds] to get our chassis speeds.

Forward kinematics is also used for odometry -- determining the position of the robot on the field using encoders and a gyro.

Field Summary

Fields

Modifier and Type	Field	Description
static final MecanumDriveKinematicsProto	proto	MecanumDriveKinematics protobuf for serialization.
static final MecanumDriveKinematicsStruct	struct	MecanumDriveKinematics struct for serialization.

Constructor Summary

Constructors

Constructor	Description
MecanumDriveKinematics(Translation2d frontLeftWheelMeters, Translation2d frontRightWheelMeters, Translation2d rearLeftWheelMeters, Translation2d rearRightWheelMeters)	Constructs a mecanum drive kinematics object.

Method Summary

Modifier and Type	Method	Description
MecanumDriveWheelPositions	copy(MecanumDriveWheelPositions positions)	Returns a copy of the wheel positions object.
void	copyInto(MecanumDriveWheelPositions positions, MecanumDriveWheelPositions output)	Copies the value of the wheel positions object into the output.
Translation2d	getFrontLeft()	Returns the front-left wheel translation.
Translation2d	getFrontRight()	Returns the front-right wheel translation.
Translation2d	getRearLeft()	Returns the rear-left wheel translation.
Translation2d	getRearRight()	Returns the rear-right wheel translation.
MecanumDriveWheelPositions	interpolate(MecanumDriveWheelPositions startValue, MecanumDriveWheelPositions endValue, double t)	Perform interpolation between two values.
ChassisSpeeds	toChassisSpeeds(MecanumDriveWheelSpeeds wheelSpeeds)	Performs forward kinematics to return the resulting chassis state from the given wheel speeds.
Twist2d	toTwist2d(MecanumDriveWheelPositions wheelDeltas)	Performs forward kinematics to return the resulting Twist2d from the given wheel deltas.
Twist2d	toTwist2d(MecanumDriveWheelPositions start, MecanumDriveWheelPositions end)	Performs forward kinematics to return the resulting Twist2d from the given change in wheel positions.
MecanumDriveWheelSpeeds	toWheelSpeeds(ChassisSpeeds chassisSpeeds)	Performs inverse kinematics.
MecanumDriveWheelSpeeds	toWheelSpeeds(ChassisSpeeds chassisSpeeds, Translation2d centerOfRotationMeters)	Performs inverse kinematics to return the wheel speeds from a desired chassis velocity.

Methods inherited from class java.lang.Object

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

Field Details

proto

public static final MecanumDriveKinematicsProto proto

MecanumDriveKinematics protobuf for serialization.

struct

public static final MecanumDriveKinematicsStruct struct

MecanumDriveKinematics struct for serialization.

Constructor Details

MecanumDriveKinematics

public MecanumDriveKinematics(Translation2d frontLeftWheelMeters,
 Translation2d frontRightWheelMeters,
 Translation2d rearLeftWheelMeters,
 Translation2d rearRightWheelMeters)

Constructs a mecanum drive kinematics object.

Parameters:

frontLeftWheelMeters - The location of the front-left wheel relative to the physical center of the robot.

frontRightWheelMeters - The location of the front-right wheel relative to the physical center of the robot.

rearLeftWheelMeters - The location of the rear-left wheel relative to the physical center of the robot.

rearRightWheelMeters - The location of the rear-right wheel relative to the physical center of the robot.

Method Details

toWheelSpeeds

public MecanumDriveWheelSpeeds toWheelSpeeds(ChassisSpeeds chassisSpeeds,
 Translation2d centerOfRotationMeters)

Performs inverse kinematics to return the wheel speeds from a desired chassis velocity. This method is often used to convert joystick values into wheel speeds.

This function also supports variable centers of rotation. During normal operations, the center of rotation is usually the same as the physical center of the robot; therefore, the argument is defaulted to that use case. However, if you wish to change the center of rotation for evasive maneuvers, vision alignment, or for any other use case, you can do so.

Parameters:

chassisSpeeds - The desired chassis speed.

centerOfRotationMeters - The center of rotation. For example, if you set the center of rotation at one corner of the robot and provide a chassis speed that only has a dtheta component, the robot will rotate around that corner.

Returns:

The wheel speeds. Use caution because they are not normalized. Sometimes, a user input may cause one of the wheel speeds to go above the attainable max velocity. Use the MecanumDriveWheelSpeeds.desaturate(double) function to rectify this issue.

toWheelSpeeds

public MecanumDriveWheelSpeeds toWheelSpeeds(ChassisSpeeds chassisSpeeds)

Performs inverse kinematics. See toWheelSpeeds(ChassisSpeeds, Translation2d) for more information.

Specified by:

toWheelSpeeds in interface Kinematics<MecanumDriveWheelSpeeds,MecanumDriveWheelPositions>

Parameters:

chassisSpeeds - The desired chassis speed.

Returns:

The wheel speeds.

toChassisSpeeds

public ChassisSpeeds toChassisSpeeds(MecanumDriveWheelSpeeds wheelSpeeds)

Performs forward kinematics to return the resulting chassis state from the given wheel speeds. This method is often used for odometry -- determining the robot's position on the field using data from the real-world speed of each wheel on the robot.

Specified by:

toChassisSpeeds in interface Kinematics<MecanumDriveWheelSpeeds,MecanumDriveWheelPositions>

Parameters:

wheelSpeeds - The current mecanum drive wheel speeds.

Returns:

The resulting chassis speed.

toTwist2d

public Twist2d toTwist2d(MecanumDriveWheelPositions start,
 MecanumDriveWheelPositions 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<MecanumDriveWheelSpeeds,MecanumDriveWheelPositions>

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(MecanumDriveWheelPositions wheelDeltas)

Performs forward kinematics to return the resulting Twist2d from the given wheel 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:

wheelDeltas - The distances driven by each wheel.

Returns:

The resulting Twist2d.

getFrontLeft

public Translation2d getFrontLeft()

Returns the front-left wheel translation.

Returns:

The front-left wheel translation.

getFrontRight

public Translation2d getFrontRight()

Returns the front-right wheel translation.

Returns:

The front-right wheel translation.

getRearLeft

public Translation2d getRearLeft()

Returns the rear-left wheel translation.

Returns:

The rear-left wheel translation.

getRearRight

public Translation2d getRearRight()

Returns the rear-right wheel translation.

Returns:

The rear-right wheel translation.

copy

public MecanumDriveWheelPositions copy(MecanumDriveWheelPositions positions)

Description copied from interface: Kinematics

Returns a copy of the wheel positions object.

Specified by:

copy in interface Kinematics<MecanumDriveWheelSpeeds,MecanumDriveWheelPositions>

Parameters:

positions - The wheel positions object to copy.

Returns:

A copy.

copyInto

public void copyInto(MecanumDriveWheelPositions positions,
 MecanumDriveWheelPositions output)

Description copied from interface: Kinematics

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

Specified by:

copyInto in interface Kinematics<MecanumDriveWheelSpeeds,MecanumDriveWheelPositions>

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 MecanumDriveWheelPositions interpolate(MecanumDriveWheelPositions startValue,
 MecanumDriveWheelPositions endValue,
 double t)

Description copied from interface: Interpolator

Perform interpolation between two values.

Specified by:

interpolate in interface Interpolator<MecanumDriveWheelPositions>

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.