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// Copyright (c) FIRST and other WPILib contributors.
// Open Source Software; you can modify and/or share it under the terms of
// the WPILib BSD license file in the root directory of this project.
#pragma once
#include <gcem.hpp>
#include <wpi/MathExtras.h>
#include "units/angle.h"
#include "units/length.h"
#include "units/time.h"
#include "units/voltage.h"
#include "wpimath/MathShared.h"
namespace frc {
/**
* A helper class that computes feedforward voltages for a simple
* permanent-magnet DC motor.
*/
template <class Distance>
requires units::length_unit<Distance> || units::angle_unit<Distance>
class SimpleMotorFeedforward {
public:
using Velocity =
units::compound_unit<Distance, units::inverse<units::seconds>>;
using Acceleration =
units::compound_unit<Velocity, units::inverse<units::seconds>>;
using kv_unit = units::compound_unit<units::volts, units::inverse<Velocity>>;
using ka_unit =
units::compound_unit<units::volts, units::inverse<Acceleration>>;
/**
* Creates a new SimpleMotorFeedforward with the specified gains.
*
* @param kS The static gain, in volts.
* @param kV The velocity gain, in volt seconds per distance.
* @param kA The acceleration gain, in volt seconds² per distance.
* @param dt The period in seconds.
* @throws IllegalArgumentException for kv < zero.
* @throws IllegalArgumentException for ka < zero.
* @throws IllegalArgumentException for period ≤ zero.
*/
constexpr SimpleMotorFeedforward(
units::volt_t kS, units::unit_t<kv_unit> kV,
units::unit_t<ka_unit> kA = units::unit_t<ka_unit>(0),
units::second_t dt = 20_ms)
: kS(kS), kV(kV), kA(kA), m_dt(dt) {
if (kV.value() < 0) {
wpi::math::MathSharedStore::ReportError(
"kV must be a non-negative number, got {}!", kV.value());
this->kV = units::unit_t<kv_unit>{0};
wpi::math::MathSharedStore::ReportWarning("kV defaulted to 0.");
}
if (kA.value() < 0) {
wpi::math::MathSharedStore::ReportError(
"kA must be a non-negative number, got {}!", kA.value());
this->kA = units::unit_t<ka_unit>{0};
wpi::math::MathSharedStore::ReportWarning("kA defaulted to 0.");
}
if (dt <= 0_ms) {
wpi::math::MathSharedStore::ReportError(
"period must be a positive number, got {}!", dt.value());
this->m_dt = 20_ms;
wpi::math::MathSharedStore::ReportWarning("period defaulted to 20 ms.");
}
}
/**
* Calculates the feedforward from the gains and setpoints assuming continuous
* control.
*
* @param velocity The velocity setpoint.
* @param acceleration The acceleration setpoint.
* @return The computed feedforward, in volts.
* @deprecated Use the current/next velocity overload instead.
*/
[[deprecated("Use the current/next velocity overload instead.")]]
constexpr units::volt_t Calculate(
units::unit_t<Velocity> velocity,
units::unit_t<Acceleration> acceleration) const {
return kS * wpi::sgn(velocity) + kV * velocity + kA * acceleration;
}
/**
* Calculates the feedforward from the gains and velocity setpoint assuming
* discrete control. Use this method when the velocity setpoint does not
* change.
*
* @param velocity The velocity setpoint.
* @return The computed feedforward, in volts.
*/
constexpr units::volt_t Calculate(units::unit_t<Velocity> velocity) const {
return Calculate(velocity, velocity);
}
/**
* Calculates the feedforward from the gains and setpoints assuming discrete
* control.
*
* <p>Note this method is inaccurate when the velocity crosses 0.
*
* @param currentVelocity The current velocity setpoint.
* @param nextVelocity The next velocity setpoint.
* @return The computed feedforward, in volts.
*/
constexpr units::volt_t Calculate(
units::unit_t<Velocity> currentVelocity,
units::unit_t<Velocity> nextVelocity) const {
// See wpimath/algorithms.md#Simple_motor_feedforward for derivation
if (kA < decltype(kA)(1e-9)) {
return kS * wpi::sgn(nextVelocity) + kV * nextVelocity;
} else {
double A = -kV.value() / kA.value();
double B = 1.0 / kA.value();
double A_d = gcem::exp(A * m_dt.value());
double B_d = A > -1e-9 ? B * m_dt.value() : 1.0 / A * (A_d - 1.0) * B;
return kS * wpi::sgn(currentVelocity) +
units::volt_t{
1.0 / B_d *
(nextVelocity.value() - A_d * currentVelocity.value())};
}
}
// Rearranging the main equation from the calculate() method yields the
// formulas for the methods below:
/**
* Calculates the maximum achievable velocity given a maximum voltage supply
* 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.
*
* @param maxVoltage The maximum voltage that can be supplied to the motor.
* @param acceleration The acceleration of the motor.
* @return The maximum possible velocity at the given acceleration.
*/
constexpr units::unit_t<Velocity> MaxAchievableVelocity(
units::volt_t maxVoltage,
units::unit_t<Acceleration> acceleration) const {
// Assume max velocity is positive
return (maxVoltage - kS - kA * acceleration) / kV;
}
/**
* Calculates the minimum achievable velocity given a maximum voltage supply
* 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.
*
* @param maxVoltage The maximum voltage that can be supplied to the motor.
* @param acceleration The acceleration of the motor.
* @return The minimum possible velocity at the given acceleration.
*/
constexpr units::unit_t<Velocity> MinAchievableVelocity(
units::volt_t maxVoltage,
units::unit_t<Acceleration> acceleration) const {
// Assume min velocity is positive, ks flips sign
return (-maxVoltage + kS - kA * acceleration) / kV;
}
/**
* Calculates the maximum achievable acceleration given a maximum voltage
* supply 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.
*
* @param maxVoltage The maximum voltage that can be supplied to the motor.
* @param velocity The velocity of the motor.
* @return The maximum possible acceleration at the given velocity.
*/
constexpr units::unit_t<Acceleration> MaxAchievableAcceleration(
units::volt_t maxVoltage, units::unit_t<Velocity> velocity) const {
return (maxVoltage - kS * wpi::sgn(velocity) - kV * velocity) / kA;
}
/**
* Calculates the minimum achievable acceleration given a maximum voltage
* supply 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.
*
* @param maxVoltage The maximum voltage that can be supplied to the motor.
* @param velocity The velocity of the motor.
* @return The minimum possible acceleration at the given velocity.
*/
constexpr units::unit_t<Acceleration> MinAchievableAcceleration(
units::volt_t maxVoltage, units::unit_t<Velocity> velocity) const {
return MaxAchievableAcceleration(-maxVoltage, velocity);
}
/**
* Sets the static gain.
*
* @param kS The static gain.
*/
constexpr void SetKs(units::volt_t kS) { this->kS = kS; }
/**
* Sets the velocity gain.
*
* @param kV The velocity gain.
*/
constexpr void SetKv(units::unit_t<kv_unit> kV) { this->kV = kV; }
/**
* Sets the acceleration gain.
*
* @param kA The acceleration gain.
*/
constexpr void SetKa(units::unit_t<ka_unit> kA) { this->kA = kA; }
/**
* Returns the static gain.
*
* @return The static gain.
*/
constexpr units::volt_t GetKs() const { return kS; }
/**
* Returns the velocity gain.
*
* @return The velocity gain.
*/
constexpr units::unit_t<kv_unit> GetKv() const { return kV; }
/**
* Returns the acceleration gain.
*
* @return The acceleration gain.
*/
constexpr units::unit_t<ka_unit> GetKa() const { return kA; }
/**
* Returns the period.
*
* @return The period.
*/
constexpr units::second_t GetDt() const { return m_dt; }
private:
/** The static gain. */
units::volt_t kS;
/** The velocity gain. */
units::unit_t<kv_unit> kV;
/** The acceleration gain. */
units::unit_t<ka_unit> kA;
/** The period. */
units::second_t m_dt;
};
} // namespace frc