frc::ArmFeedforward Class Reference

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). More...

#include <frc/controller/ArmFeedforward.h>

Public Types
using	Angle = units::radians
using	Velocity = units::radians_per_second
using	Acceleration
using	kv_unit
using	ka_unit

Public Member Functions
constexpr	ArmFeedforward (units::volt_t kS, units::volt_t kG, units::unit_t< kv_unit > kV, units::unit_t< ka_unit > kA=units::unit_t< ka_unit >(0), units::second_t dt=20_ms)
	Creates a new ArmFeedforward with the specified gains.
constexpr units::volt_t	Calculate (units::unit_t< Angle > angle, units::unit_t< Velocity > velocity, units::unit_t< Acceleration > acceleration) const
	Calculates the feedforward from the gains and setpoints assuming continuous control.
units::volt_t	Calculate (units::unit_t< Angle > currentAngle, units::unit_t< Velocity > currentVelocity, units::unit_t< Velocity > nextVelocity, units::second_t dt) const
	Calculates the feedforward from the gains and setpoints assuming continuous control.
constexpr units::volt_t	Calculate (units::unit_t< Angle > currentAngle, units::unit_t< Velocity > currentVelocity) const
	Calculates the feedforward from the gains and setpoint assuming discrete control.
units::volt_t	Calculate (units::unit_t< Angle > currentAngle, units::unit_t< Velocity > currentVelocity, units::unit_t< Velocity > nextVelocity) const
	Calculates the feedforward from the gains and setpoints assuming discrete control.
constexpr units::unit_t< Velocity >	MaxAchievableVelocity (units::volt_t maxVoltage, units::unit_t< Angle > angle, units::unit_t< Acceleration > acceleration)
	Calculates the maximum achievable velocity given a maximum voltage supply, a position, and an acceleration.
constexpr units::unit_t< Velocity >	MinAchievableVelocity (units::volt_t maxVoltage, units::unit_t< Angle > angle, units::unit_t< Acceleration > acceleration)
	Calculates the minimum achievable velocity given a maximum voltage supply, a position, and an acceleration.
constexpr units::unit_t< Acceleration >	MaxAchievableAcceleration (units::volt_t maxVoltage, units::unit_t< Angle > angle, units::unit_t< Velocity > velocity)
	Calculates the maximum achievable acceleration given a maximum voltage supply, a position, and a velocity.
constexpr units::unit_t< Acceleration >	MinAchievableAcceleration (units::volt_t maxVoltage, units::unit_t< Angle > angle, units::unit_t< Velocity > velocity)
	Calculates the minimum achievable acceleration given a maximum voltage supply, a position, and a velocity.
constexpr units::volt_t	GetKs () const
	Returns the static gain.
constexpr units::volt_t	GetKg () const
	Returns the gravity gain.
constexpr units::unit_t< kv_unit >	GetKv () const
	Returns the velocity gain.
constexpr units::unit_t< ka_unit >	GetKa () const
	Returns the acceleration gain.

Detailed Description

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).

Member Typedef Documentation

Acceleration

using frc::ArmFeedforward::Acceleration

Initial value:

 units::compound_unit<units::radians_per_second,
                                            units::inverse<units::second>>

Angle

using frc::ArmFeedforward::Angle = units::radians

ka_unit

using frc::ArmFeedforward::ka_unit

Initial value:

 
      units::compound_unit<units::volts, units::inverse<Acceleration>>

kv_unit

using frc::ArmFeedforward::kv_unit

Initial value:

 
      units::compound_unit<units::volts,
                           units::inverse<units::radians_per_second>>

Velocity

using frc::ArmFeedforward::Velocity = units::radians_per_second

Constructor & Destructor Documentation

ArmFeedforward()

frc::ArmFeedforward::ArmFeedforward ( units::volt_t kS, units::volt_t kG, units::unit_t< kv_unit > kV, units::unit_t< ka_unit > kA = units::unit_t<ka_unit>(0), units::second_t dt = 20_ms )

inlineconstexpr

Creates a new ArmFeedforward with the specified gains.

Parameters

kS	The static gain, in volts.
kG	The gravity gain, in volts.
kV	The velocity gain, in volt seconds per radian.
kA	The acceleration gain, in volt seconds² per radian.
dt	The period in seconds.

Throws:

IllegalArgumentException for kv < zero.

Throws:

IllegalArgumentException for ka < zero.

Throws:

IllegalArgumentException for period ≤ zero.

Member Function Documentation

Calculate() [1/4]

units::volt_t frc::ArmFeedforward::Calculate ( units::unit_t< Angle > angle, units::unit_t< Velocity > velocity, units::unit_t< Acceleration > acceleration ) const

inlineconstexpr

Calculates the feedforward from the gains and setpoints assuming continuous control.

Parameters

angle	The angle setpoint, 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.
velocity	The velocity setpoint.
acceleration	The acceleration setpoint.

Returns

The computed feedforward, in volts.

Calculate() [2/4]

units::volt_t frc::ArmFeedforward::Calculate ( units::unit_t< Angle > currentAngle, units::unit_t< Velocity > currentVelocity ) const

inlineconstexpr

Calculates the feedforward from the gains and setpoint assuming discrete control.

Use this method when the velocity does not change.

Parameters

currentAngle	The current angle. 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.

Returns

The computed feedforward in volts.

Calculate() [3/4]

units::volt_t frc::ArmFeedforward::Calculate	(	units::unit_t< Angle >	currentAngle,
		units::unit_t< Velocity >	currentVelocity,
		units::unit_t< Velocity >	nextVelocity ) const

Calculates the feedforward from the gains and setpoints assuming discrete control.

Parameters

currentAngle	The current angle. 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.
nextVelocity	The next velocity.

Returns

The computed feedforward in volts.

Calculate() [4/4]

units::volt_t frc::ArmFeedforward::Calculate ( units::unit_t< Angle > currentAngle, units::unit_t< Velocity > currentVelocity, units::unit_t< Velocity > nextVelocity, units::second_t dt ) const

inline

Calculates the feedforward from the gains and setpoints 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 setpoint.
nextVelocity	The next velocity setpoint.
dt	Time between velocity setpoints in seconds.

Returns

The computed feedforward in volts.

GetKa()

units::unit_t< ka_unit > frc::ArmFeedforward::GetKa ( ) const

inlineconstexpr

Returns the acceleration gain.

Returns

The acceleration gain.

GetKg()

units::volt_t frc::ArmFeedforward::GetKg ( ) const

inlineconstexpr

Returns the gravity gain.

Returns

The gravity gain.

GetKs()

units::volt_t frc::ArmFeedforward::GetKs ( ) const

inlineconstexpr

Returns the static gain.

Returns

The static gain.

GetKv()

units::unit_t< kv_unit > frc::ArmFeedforward::GetKv ( ) const

inlineconstexpr

Returns the velocity gain.

Returns

The velocity gain.

MaxAchievableAcceleration()

units::unit_t< Acceleration > frc::ArmFeedforward::MaxAchievableAcceleration ( units::volt_t maxVoltage, units::unit_t< Angle > angle, units::unit_t< Velocity > velocity )

inlineconstexpr

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.
angle	The angle of the arm. 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.
velocity	The velocity of the arm.

Returns

The maximum possible acceleration at the given velocity and angle.

MaxAchievableVelocity()

units::unit_t< Velocity > frc::ArmFeedforward::MaxAchievableVelocity ( units::volt_t maxVoltage, units::unit_t< Angle > angle, units::unit_t< Acceleration > acceleration )

inlineconstexpr

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. 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.
acceleration	The acceleration of the arm.

Returns

The maximum possible velocity at the given acceleration and angle.

MinAchievableAcceleration()

units::unit_t< Acceleration > frc::ArmFeedforward::MinAchievableAcceleration ( units::volt_t maxVoltage, units::unit_t< Angle > angle, units::unit_t< Velocity > velocity )

inlineconstexpr

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.
angle	The angle of the arm. 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.
velocity	The velocity of the arm.

Returns

The minimum possible acceleration at the given velocity and angle.

MinAchievableVelocity()

units::unit_t< Velocity > frc::ArmFeedforward::MinAchievableVelocity ( units::volt_t maxVoltage, units::unit_t< Angle > angle, units::unit_t< Acceleration > acceleration )

inlineconstexpr

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.
angle	The angle of the arm. 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.
acceleration	The acceleration of the arm.

Returns

The minimum possible velocity at the given acceleration and angle.

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

• frc/controller/ArmFeedforward.h