frc::LTVUnicycleController Class Reference

The linear time-varying unicycle controller has a similar form to the LQR, but the model used to compute the controller gain is the nonlinear unicycle model linearized around the drivetrain's current state. More...

#include <frc/controller/LTVUnicycleController.h>

Public Member Functions
	LTVUnicycleController (units::second_t dt, units::meters_per_second_t maxVelocity=9_mps)
	Constructs a linear time-varying unicycle controller with default maximum desired error tolerances of (x = 0.0625 m, y = 0.125 m, heading = 2 rad) and default maximum desired control effort of (linear velocity = 1 m/s, angular velocity = 2 rad/s).
	LTVUnicycleController (const wpi::array< double, 3 > &Qelems, const wpi::array< double, 2 > &Relems, units::second_t dt, units::meters_per_second_t maxVelocity=9_mps)
	Constructs a linear time-varying unicycle controller.
	LTVUnicycleController (LTVUnicycleController &&)=default
	Move constructor.
LTVUnicycleController &	operator= (LTVUnicycleController &&)=default
	Move assignment operator.
bool	AtReference () const
	Returns true if the pose error is within tolerance of the reference.
void	SetTolerance (const Pose2d &poseTolerance)
	Sets the pose error which is considered tolerable for use with AtReference().
ChassisSpeeds	Calculate (const Pose2d &currentPose, const Pose2d &poseRef, units::meters_per_second_t linearVelocityRef, units::radians_per_second_t angularVelocityRef)
	Returns the linear and angular velocity outputs of the LTV controller.
ChassisSpeeds	Calculate (const Pose2d &currentPose, const Trajectory::State &desiredState)
	Returns the linear and angular velocity outputs of the LTV controller.
void	SetEnabled (bool enabled)
	Enables and disables the controller for troubleshooting purposes.

Detailed Description

The linear time-varying unicycle controller has a similar form to the LQR, but the model used to compute the controller gain is the nonlinear unicycle model linearized around the drivetrain's current state.

This controller is a roughly drop-in replacement for RamseteController with more optimal feedback gains in the "least-squares error" sense.

See section 8.9 in Controls Engineering in FRC for a derivation of the control law we used shown in theorem 8.9.1.

Constructor & Destructor Documentation

LTVUnicycleController() [1/3]

frc::LTVUnicycleController::LTVUnicycleController ( units::second_t dt, units::meters_per_second_t maxVelocity = 9_mps )

explicit

Constructs a linear time-varying unicycle controller with default maximum desired error tolerances of (x = 0.0625 m, y = 0.125 m, heading = 2 rad) and default maximum desired control effort of (linear velocity = 1 m/s, angular velocity = 2 rad/s).

Parameters

dt	Discretization timestep.
maxVelocity	The maximum velocity for the controller gain lookup table.

Throws:

std::domain_error if maxVelocity <= 0 m/s or >= 15 m/s.

LTVUnicycleController() [2/3]

frc::LTVUnicycleController::LTVUnicycleController	(	const wpi::array< double, 3 > &	Qelems,
		const wpi::array< double, 2 > &	Relems,
		units::second_t	dt,
		units::meters_per_second_t	maxVelocity = 9_mps )

Constructs a linear time-varying unicycle controller.

See https://docs.wpilib.org/en/stable/docs/software/advanced-controls/state-space/state-space-intro.html#lqr-tuning for how to select the tolerances.

Parameters

Qelems	The maximum desired error tolerance for each state (x, y, heading).
Relems	The maximum desired control effort for each input (linear velocity, angular velocity).
dt	Discretization timestep.
maxVelocity	The maximum velocity for the controller gain lookup table.

Throws:

std::domain_error if maxVelocity <= 0 m/s or >= 15 m/s.

LTVUnicycleController() [3/3]

frc::LTVUnicycleController::LTVUnicycleController ( LTVUnicycleController && )

default

Move constructor.

Member Function Documentation

AtReference()

bool frc::LTVUnicycleController::AtReference

(

)

const

Returns true if the pose error is within tolerance of the reference.

Calculate() [1/2]

ChassisSpeeds frc::LTVUnicycleController::Calculate	(	const Pose2d &	currentPose,
		const Pose2d &	poseRef,
		units::meters_per_second_t	linearVelocityRef,
		units::radians_per_second_t	angularVelocityRef )

Returns the linear and angular velocity outputs of the LTV controller.

The reference pose, linear velocity, and angular velocity should come from a drivetrain trajectory.

Parameters

currentPose	The current pose.
poseRef	The desired pose.
linearVelocityRef	The desired linear velocity.
angularVelocityRef	The desired angular velocity.

Calculate() [2/2]

ChassisSpeeds frc::LTVUnicycleController::Calculate	(	const Pose2d &	currentPose,
		const Trajectory::State &	desiredState )

Returns the linear and angular velocity outputs of the LTV controller.

The reference pose, linear velocity, and angular velocity should come from a drivetrain trajectory.

Parameters

currentPose	The current pose.
desiredState	The desired pose, linear velocity, and angular velocity from a trajectory.

operator=()

LTVUnicycleController & frc::LTVUnicycleController::operator= ( LTVUnicycleController && )

default

Move assignment operator.

SetEnabled()

void frc::LTVUnicycleController::SetEnabled

(

bool

enabled

)

Enables and disables the controller for troubleshooting purposes.

Parameters

enabled

If the controller is enabled or not.

SetTolerance()

void frc::LTVUnicycleController::SetTolerance

(

const Pose2d &

poseTolerance

)

Sets the pose error which is considered tolerable for use with AtReference().

Parameters

poseTolerance

Pose error which is tolerable.

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The documentation for this class was generated from the following file:

• frc/controller/LTVUnicycleController.h