allwpilib/wpilibc/src/main/native/cpp/simulation/ElevatorSim.cpp

// 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.

#include "frc/simulation/ElevatorSim.h"

#include <wpi/MathExtras.h>

#include "frc/StateSpaceUtil.h"
#include "frc/system/NumericalIntegration.h"
#include "frc/system/plant/LinearSystemId.h"

using namespace frc;
using namespace frc::sim;

ElevatorSim::ElevatorSim(const LinearSystem<2, 1, 1>& plant,
                         const DCMotor& gearbox, double gearing,
                         units::meter_t drumRadius, units::meter_t minHeight,
                         units::meter_t maxHeight,
                         const std::array<double, 1>& measurementStdDevs)
    : LinearSystemSim(plant, measurementStdDevs),
      m_gearbox(gearbox),
      m_drumRadius(drumRadius),
      m_minHeight(minHeight),
      m_maxHeight(maxHeight),
      m_gearing(gearing) {}

ElevatorSim::ElevatorSim(const DCMotor& gearbox, double gearing,
                         units::kilogram_t carriageMass,
                         units::meter_t drumRadius, units::meter_t minHeight,
                         units::meter_t maxHeight,
                         const std::array<double, 1>& measurementStdDevs)
    : LinearSystemSim(LinearSystemId::ElevatorSystem(gearbox, carriageMass,
                                                     drumRadius, gearing),
                      measurementStdDevs),
      m_gearbox(gearbox),
      m_drumRadius(drumRadius),
      m_minHeight(minHeight),
      m_maxHeight(maxHeight),
      m_gearing(gearing) {}

bool ElevatorSim::HasHitLowerLimit(const Eigen::Matrix<double, 2, 1>& x) const {
  return x(0) < m_minHeight.to<double>();
}

bool ElevatorSim::HasHitUpperLimit(const Eigen::Matrix<double, 2, 1>& x) const {
  return x(0) > m_maxHeight.to<double>();
}

units::meter_t ElevatorSim::GetPosition() const {
  return units::meter_t{m_y(0)};
}

units::meters_per_second_t ElevatorSim::GetVelocity() const {
  return units::meters_per_second_t{m_x(1)};
}

units::ampere_t ElevatorSim::GetCurrentDraw() const {
  // I = V / R - omega / (Kv * R)
  // Reductions are greater than 1, so a reduction of 10:1 would mean the motor
  // is spinning 10x faster than the output.

  // v = r w, so w = v / r
  units::meters_per_second_t velocity{m_x(1)};
  units::radians_per_second_t motorVelocity =
      velocity / m_drumRadius * m_gearing * 1_rad;

  // Perform calculation and return.
  return m_gearbox.Current(motorVelocity, units::volt_t{m_u(0)}) *
         wpi::sgn(m_u(0));
}

void ElevatorSim::SetInputVoltage(units::volt_t voltage) {
  SetInput(frc::MakeMatrix<1, 1>(voltage.to<double>()));
}

Eigen::Matrix<double, 2, 1> ElevatorSim::UpdateX(
    const Eigen::Matrix<double, 2, 1>& currentXhat,
    const Eigen::Matrix<double, 1, 1>& u, units::second_t dt) {
  auto updatedXhat = RKF45(
      [&](const Eigen::Matrix<double, 2, 1>& x,
          const Eigen::Matrix<double, 1, 1>& u_)
          -> Eigen::Matrix<double, 2, 1> {
        return m_plant.A() * x + m_plant.B() * u_ + MakeMatrix<2, 1>(0.0, -9.8);
      },
      currentXhat, u, dt);
  // Check for collision after updating x-hat.
  if (HasHitLowerLimit(updatedXhat)) {
    return MakeMatrix<2, 1>(m_minHeight.to<double>(), 0.0);
  }
  if (HasHitUpperLimit(updatedXhat)) {
    return MakeMatrix<2, 1>(m_maxHeight.to<double>(), 0.0);
  }
  return updatedXhat;
}