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 = units::compound_unit< units::radians_per_second, units::inverse< units::second > >
using	kv_unit = units::compound_unit< units::volts, units::inverse< units::radians_per_second > >
using	ka_unit = units::compound_unit< units::volts, units::inverse< Acceleration > >

Public Member Functions
constexpr	ArmFeedforward ()=default
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))
	Creates a new ArmFeedforward with the specified gains. More...
units::volt_t	Calculate (units::unit_t< Angle > angle, units::unit_t< Velocity > velocity, units::unit_t< Acceleration > acceleration=units::unit_t< Acceleration >(0)) const
	Calculates the feedforward from the gains and setpoints. More...
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. More...
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. More...
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. More...
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. More...

Public Attributes
units::volt_t	kS {0}
units::volt_t	kG {0}
units::unit_t< kv_unit >	kV {0}
units::unit_t< ka_unit >	kA {0}

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

kv_unit

using frc::ArmFeedforward::kv_unit = units::compound_unit<units::volts, units::inverse<units::radians_per_second> >

Velocity

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

Constructor & Destructor Documentation

ArmFeedforward() [1/2]

constexpr frc::ArmFeedforward::ArmFeedforward ( )

constexprdefault

ArmFeedforward() [2/2]

constexpr 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)  )

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.

Member Function Documentation

Calculate()

units::volt_t frc::ArmFeedforward::Calculate ( units::unit_t< Angle >  angle, units::unit_t< Velocity >  velocity, units::unit_t< Acceleration >  acceleration = units::unit_t<Acceleration>(0)  ) const

inline

Calculates the feedforward from the gains and setpoints.

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, in radians per second.
acceleration	The acceleration setpoint, in radians per second².

Returns

The computed feedforward, in volts.

MaxAchievableAcceleration()

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

inline

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  )

inline

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  )

inline

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  )

inline

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.

Member Data Documentation

kA

units::unit_t<ka_unit> frc::ArmFeedforward::kA {0}

kG

units::volt_t frc::ArmFeedforward::kG {0}

kS

units::volt_t frc::ArmFeedforward::kS {0}

kV

units::unit_t<kv_unit> frc::ArmFeedforward::kV {0}

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

• frc/controller/ArmFeedforward.h