LTVDifferentialDriveController

class wpimath.controller.LTVDifferentialDriveController(plant: wpimath._controls._controls.system.LinearSystem_2_2_2, trackwidth: wpimath.units.meters, Qelems: Tuple[float, float, float, float, float], Relems: Tuple[float, float], dt: wpimath.units.seconds)

Bases: pybind11_object

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 Ramsete 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. Furthermore, this controller is more optimal in the “least-squares error” sense than a controller based on Ramsete.

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

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. @throws std::domain_error if max velocity of plant with 12 V input <= 0 m/s or >= 15 m/s.

atReference() → bool

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

calculate(*args, **kwargs)

Overloaded function.

  1. calculate(self: wpimath._controls._controls.controller.LTVDifferentialDriveController, currentPose: wpimath.geometry._geometry.Pose2d, leftVelocity: wpimath.units.meters_per_second, rightVelocity: wpimath.units.meters_per_second, poseRef: wpimath.geometry._geometry.Pose2d, leftVelocityRef: wpimath.units.meters_per_second, rightVelocityRef: wpimath.units.meters_per_second) -> wpimath._controls._controls.controller.DifferentialDriveWheelVoltages

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.

  1. calculate(self: wpimath._controls._controls.controller.LTVDifferentialDriveController, currentPose: wpimath.geometry._geometry.Pose2d, leftVelocity: wpimath.units.meters_per_second, rightVelocity: wpimath.units.meters_per_second, desiredState: wpimath._controls._controls.trajectory.Trajectory.State) -> wpimath._controls._controls.controller.DifferentialDriveWheelVoltages

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.

setTolerance(poseTolerance: wpimath.geometry._geometry.Pose2d, leftVelocityTolerance: wpimath.units.meters_per_second, rightVelocityTolerance: wpimath.units.meters_per_second) → None

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.