frc::LTVDifferentialDriveController Class Reference

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

#include <frc/controller/LTVDifferentialDriveController.h>

Public Member Functions
	LTVDifferentialDriveController (const frc::LinearSystem< 2, 2, 2 > &plant, units::meter_t trackwidth, const wpi::array< double, 5 > &Qelems, const wpi::array< double, 2 > &Relems, units::second_t dt)
	Constructs a linear time-varying differential drive controller.
	LTVDifferentialDriveController (LTVDifferentialDriveController &&)=default
	Move constructor.
LTVDifferentialDriveController &	operator= (LTVDifferentialDriveController &&)=default
	Move assignment operator.
bool	AtReference () const
	Returns true if the pose error is within tolerance of the reference.
void	SetTolerance (const Pose2d &poseTolerance, units::meters_per_second_t leftVelocityTolerance, units::meters_per_second_t rightVelocityTolerance)
	Sets the pose error which is considered tolerable for use with AtReference().
DifferentialDriveWheelVoltages	Calculate (const Pose2d &currentPose, units::meters_per_second_t leftVelocity, units::meters_per_second_t rightVelocity, const Pose2d &poseRef, units::meters_per_second_t leftVelocityRef, units::meters_per_second_t rightVelocityRef)
	Returns the left and right output voltages of the LTV controller.
DifferentialDriveWheelVoltages	Calculate (const Pose2d &currentPose, units::meters_per_second_t leftVelocity, units::meters_per_second_t rightVelocity, const Trajectory::State &desiredState)
	Returns the left and right output voltages of the LTV controller.

Detailed Description

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

We precompute gains for important places in our state-space, then interpolate between them with a lookup table to save computational resources.

This controller has a flat hierarchy with pose and wheel velocity references and voltage outputs. This is different from a unicycle controller's nested hierarchy where the top-level controller has a pose reference and chassis velocity command outputs, and the low-level controller has wheel velocity references and voltage outputs. Flat hierarchies are easier to tune in one shot.

See section 8.7 in Controls Engineering in FRC for a derivation of the control law we used shown in theorem 8.7.4.

Constructor & Destructor Documentation

LTVDifferentialDriveController() [1/2]

frc::LTVDifferentialDriveController::LTVDifferentialDriveController ( const frc::LinearSystem< 2, 2, 2 > & plant, units::meter_t trackwidth, const wpi::array< double, 5 > & Qelems, const wpi::array< double, 2 > & Relems, units::second_t dt )

inline

Constructs a linear time-varying differential drive 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

plant	The differential drive velocity plant.
trackwidth	The distance between the differential drive's left and right wheels.
Qelems	The maximum desired error tolerance for each state.
Relems	The maximum desired control effort for each input.
dt	Discretization timestep.

LTVDifferentialDriveController() [2/2]

frc::LTVDifferentialDriveController::LTVDifferentialDriveController ( LTVDifferentialDriveController && )

default

Move constructor.

Member Function Documentation

AtReference()

bool frc::LTVDifferentialDriveController::AtReference ( ) const

inline

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

Calculate() [1/2]

DifferentialDriveWheelVoltages frc::LTVDifferentialDriveController::Calculate	(	const Pose2d &	currentPose,
		units::meters_per_second_t	leftVelocity,
		units::meters_per_second_t	rightVelocity,
		const Pose2d &	poseRef,
		units::meters_per_second_t	leftVelocityRef,
		units::meters_per_second_t	rightVelocityRef )

Returns the left and right output voltages of the LTV controller.

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

Parameters

currentPose	The current pose.
leftVelocity	The current left velocity.
rightVelocity	The current right velocity.
poseRef	The desired pose.
leftVelocityRef	The desired left velocity.
rightVelocityRef	The desired right velocity.

Calculate() [2/2]

DifferentialDriveWheelVoltages frc::LTVDifferentialDriveController::Calculate ( const Pose2d & currentPose, units::meters_per_second_t leftVelocity, units::meters_per_second_t rightVelocity, const Trajectory::State & desiredState )

inline

Returns the left and right output voltages of the LTV controller.

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

Parameters

currentPose	The current pose.
leftVelocity	The left velocity.
rightVelocity	The right velocity.
desiredState	The desired pose, linear velocity, and angular velocity from a trajectory.

operator=()

LTVDifferentialDriveController & frc::LTVDifferentialDriveController::operator= ( LTVDifferentialDriveController && )

default

Move assignment operator.

SetTolerance()

void frc::LTVDifferentialDriveController::SetTolerance ( const Pose2d & poseTolerance, units::meters_per_second_t leftVelocityTolerance, units::meters_per_second_t rightVelocityTolerance )

inline

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

Parameters

poseTolerance	Pose error which is tolerable.
leftVelocityTolerance	Left velocity error which is tolerable.
rightVelocityTolerance	Right velocity error which is tolerable.

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

• frc/controller/LTVDifferentialDriveController.h