Class ArmFeedforward

java.lang.Object
org.wpilib.math.controller.ArmFeedforward
All Implemented Interfaces:
ProtobufSerializable, StructSerializable, WPISerializable
public class ArmFeedforward extends Object implements ProtobufSerializable, StructSerializable
A helper class that computes feedforward outputs for a simple arm (modeled as a motor acting against the force of gravity on a beam suspended at an angle).

  • Field Summary

    Fields
    Modifier and Type
    Field
    Description
    static final ArmFeedforwardProto
    proto
    Arm feedforward protobuf for serialization.
    static final ArmFeedforwardStruct
    struct
    Arm feedforward struct for serialization.

  • Constructor Summary

    Constructors
    Constructor
    Description
    ArmFeedforward(double ks, double kg, double kv)
    Creates a new ArmFeedforward with the specified gains.
    ArmFeedforward(double ks, double kg, double kv, double ka)
    Creates a new ArmFeedforward with the specified gains.
    ArmFeedforward(double ks, double kg, double kv, double ka, double dt)
    Creates a new ArmFeedforward with the specified gains and period.

  • Method Summary

    Modifier and Type
    Method
    Description
    double
    calculate(double position, double velocity)
    Calculates the feedforward from the gains and velocity reference assuming continuous control (acceleration is assumed to be zero).
    double
    calculate(double currentAngle, double currentVelocity, double nextVelocity)
    Calculates the feedforward from the gains and references assuming continuous control.
    double
    getDt()
    Returns the period in seconds.
    double
    getKa()
    Returns the acceleration gain in V/(rad/s²).
    double
    getKg()
    Returns the gravity gain in volts.
    double
    getKs()
    Returns the static gain in volts.
    double
    getKv()
    Returns the velocity gain in V/(rad/s).
    double
    maxAchievableAcceleration(double maxVoltage, double angle, double velocity)
    Calculates the maximum achievable acceleration given a maximum voltage supply, a position, and a velocity.
    double
    maxAchievableVelocity(double maxVoltage, double angle, double acceleration)
    Calculates the maximum achievable velocity given a maximum voltage supply, a position, and an acceleration.
    double
    minAchievableAcceleration(double maxVoltage, double angle, double velocity)
    Calculates the minimum achievable acceleration given a maximum voltage supply, a position, and a velocity.
    double
    minAchievableVelocity(double maxVoltage, double angle, double acceleration)
    Calculates the minimum achievable velocity given a maximum voltage supply, a position, and an acceleration.
    void
    setKa(double ka)
    Sets the acceleration gain.
    void
    setKg(double kg)
    Sets the gravity gain.
    void
    setKs(double ks)
    Sets the static gain.
    void
    setKv(double kv)
    Sets the velocity gain.

    Methods inherited from class Object

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

  • Field Details

    • struct

      public static final ArmFeedforwardStruct struct
      Arm feedforward struct for serialization.

    • proto

      public static final ArmFeedforwardProto proto
      Arm feedforward protobuf for serialization.

  • Constructor Details

    • ArmFeedforward

      public ArmFeedforward(double ks, double kg, double kv, double ka, double dt)
      Creates a new ArmFeedforward with the specified gains and period.
      Parameters:
      ks - The static gain in volts.
      kg - The gravity gain in volts.
      kv - The velocity gain in V/(rad/s).
      ka - The acceleration gain in V/(rad/s²).
      dt - The period in seconds.
      Throws:
      IllegalArgumentException - for kv < zero.
      IllegalArgumentException - for ka < zero.
      IllegalArgumentException - for period ≤ zero.

    • ArmFeedforward

      public ArmFeedforward(double ks, double kg, double kv, double ka)
      Creates a new ArmFeedforward with the specified gains. The period is defaulted to 20 ms.
      Parameters:
      ks - The static gain in volts.
      kg - The gravity gain in volts.
      kv - The velocity gain in V/(rad/s).
      ka - The acceleration gain in V/(rad/s²).
      Throws:
      IllegalArgumentException - for kv < zero.
      IllegalArgumentException - for ka < zero.

    • ArmFeedforward

      public ArmFeedforward(double ks, double kg, double kv)
      Creates a new ArmFeedforward with the specified gains. The period is defaulted to 20 ms.
      Parameters:
      ks - The static gain in volts.
      kg - The gravity gain in volts.
      kv - The velocity gain in V/(rad/s).
      Throws:
      IllegalArgumentException - for kv < zero.

  • Method Details

    • setKs

      public void setKs(double ks)
      Sets the static gain.

      This setter is intended for online tuning only. Feedforward gains are assumed constant, so gain scheduling means the system was not correctly modeled.

      Parameters:
      ks - The static gain in volts.

    • setKg

      public void setKg(double kg)
      Sets the gravity gain.

      This setter is intended for online tuning only. Feedforward gains are assumed constant, so gain scheduling means the system was not correctly modeled.

      Parameters:
      kg - The gravity gain in volts.

    • setKv

      public void setKv(double kv)
      Sets the velocity gain.

      This setter is intended for online tuning only. Feedforward gains are assumed constant, so gain scheduling means the system was not correctly modeled.

      Parameters:
      kv - The velocity gain in V/(rad/s).

    • setKa

      public void setKa(double ka)
      Sets the acceleration gain.

      This setter is intended for online tuning only. Feedforward gains are assumed constant, so gain scheduling means the system was not correctly modeled.

      Parameters:
      ka - The acceleration gain in V/(rad/s²).

    • getKs

      public double getKs()
      Returns the static gain in volts.
      Returns:
      The static gain in volts.

    • getKg

      public double getKg()
      Returns the gravity gain in volts.
      Returns:
      The gravity gain in volts.

    • getKv

      public double getKv()
      Returns the velocity gain in V/(rad/s).
      Returns:
      The velocity gain.

    • getKa

      public double getKa()
      Returns the acceleration gain in V/(rad/s²).
      Returns:
      The acceleration gain.

    • getDt

      public double getDt()
      Returns the period in seconds.
      Returns:
      The period in seconds.

    • calculate

      public double calculate(double position, double velocity)
      Calculates the feedforward from the gains and velocity reference assuming continuous control (acceleration is assumed to be zero).
      Parameters:
      position - The position reference in radians. This angle should be measured from the horizontal (i.e. if the provided angle is 0, the arm should be parallel with the floor). If your encoder does not follow this convention, an offset should be added.
      velocity - The velocity reference in radians per second.
      Returns:
      The computed feedforward.

    • calculate

      public double calculate(double currentAngle, double currentVelocity, double nextVelocity)
      Calculates the feedforward from the gains and references assuming continuous control.
      Parameters:
      currentAngle - The current angle in radians. This angle should be measured from the horizontal (i.e. if the provided angle is 0, the arm should be parallel to the floor). If your encoder does not follow this convention, an offset should be added.
      currentVelocity - The current velocity reference in radians per second.
      nextVelocity - The next velocity reference in radians per second.
      Returns:
      The computed feedforward in volts.

    • maxAchievableVelocity

      public double maxAchievableVelocity(double maxVoltage, double angle, double acceleration)
      Calculates the maximum achievable velocity given a maximum voltage supply, a position, and an acceleration. Useful for ensuring that velocity and acceleration constraints for a trapezoidal profile are simultaneously achievable - enter the acceleration constraint, and this will give you a simultaneously-achievable velocity constraint.
      Parameters:
      maxVoltage - The maximum voltage that can be supplied to the arm.
      angle - The angle of the arm, in radians. This angle should be measured from the horizontal (i.e. if the provided angle is 0, the arm should be parallel with the floor). If your encoder does not follow this convention, an offset should be added.
      acceleration - The acceleration of the arm, in (rad/s²).
      Returns:
      The maximum possible velocity in (rad/s) at the given acceleration and angle.

    • minAchievableVelocity

      public double minAchievableVelocity(double maxVoltage, double angle, double acceleration)
      Calculates the minimum achievable velocity given a maximum voltage supply, a position, and an acceleration. Useful for ensuring that velocity and acceleration constraints for a trapezoidal profile are simultaneously achievable - enter the acceleration constraint, and this will give you a simultaneously-achievable velocity constraint.
      Parameters:
      maxVoltage - The maximum voltage that can be supplied to the arm, in volts.
      angle - The angle of the arm, in radians. This angle should be measured from the horizontal (i.e. if the provided angle is 0, the arm should be parallel with the floor). If your encoder does not follow this convention, an offset should be added.
      acceleration - The acceleration of the arm, in (rad/s²).
      Returns:
      The minimum possible velocity in (rad/s) at the given acceleration and angle.

    • maxAchievableAcceleration

      public double maxAchievableAcceleration(double maxVoltage, double angle, double velocity)
      Calculates the maximum achievable acceleration given a maximum voltage supply, a position, and a velocity. Useful for ensuring that velocity and acceleration constraints for a trapezoidal profile are simultaneously achievable - enter the velocity constraint, and this will give you a simultaneously-achievable acceleration constraint.
      Parameters:
      maxVoltage - The maximum voltage that can be supplied to the arm, in volts.
      angle - The angle of the arm, in radians. This angle should be measured from the horizontal (i.e. if the provided angle is 0, the arm should be parallel with the floor). If your encoder does not follow this convention, an offset should be added.
      velocity - The velocity of the elevator, in (rad/s)
      Returns:
      The maximum possible acceleration in (rad/s²) at the given velocity.

    • minAchievableAcceleration

      public double minAchievableAcceleration(double maxVoltage, double angle, double velocity)
      Calculates the minimum achievable acceleration given a maximum voltage supply, a position, and a velocity. Useful for ensuring that velocity and acceleration constraints for a trapezoidal profile are simultaneously achievable - enter the velocity constraint, and this will give you a simultaneously-achievable acceleration constraint.
      Parameters:
      maxVoltage - The maximum voltage that can be supplied to the arm, in volts.
      angle - The angle of the arm, in radians. This angle should be measured from the horizontal (i.e. if the provided angle is 0, the arm should be parallel with the floor). If your encoder does not follow this convention, an offset should be added.
      velocity - The velocity of the elevator, in (rad/s)
      Returns:
      The maximum possible acceleration in (rad/s²) at the given velocity.