allwpilib/wpilibcExamples/src/main/cpp/examples/SimpleDifferentialDriveSimulation/include/Drivetrain.hpp

// 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 <numbers>

#include <wpi/hardware/imu/OnboardIMU.hpp>
#include <wpi/hardware/motor/PWMSparkMax.hpp>
#include <wpi/hardware/rotation/Encoder.hpp>
#include <wpi/math/controller/PIDController.hpp>
#include <wpi/math/controller/SimpleMotorFeedforward.hpp>
#include <wpi/math/kinematics/DifferentialDriveKinematics.hpp>
#include <wpi/math/kinematics/DifferentialDriveOdometry.hpp>
#include <wpi/math/system/plant/LinearSystemId.hpp>
#include <wpi/simulation/DifferentialDrivetrainSim.hpp>
#include <wpi/simulation/EncoderSim.hpp>
#include <wpi/smartdashboard/Field2d.hpp>
#include <wpi/smartdashboard/SmartDashboard.hpp>
#include <wpi/units/angle.hpp>
#include <wpi/units/angular_velocity.hpp>
#include <wpi/units/length.hpp>
#include <wpi/units/velocity.hpp>

/**
 * Represents a differential drive style drivetrain.
 */
class Drivetrain {
 public:
  Drivetrain() {
    m_imu.ResetYaw();

    m_leftLeader.AddFollower(m_leftFollower);
    m_rightLeader.AddFollower(m_rightFollower);

    // We need to invert one side of the drivetrain so that positive voltages
    // result in both sides moving forward. Depending on how your robot's
    // gearbox is constructed, you might have to invert the left side instead.
    m_rightLeader.SetInverted(true);

    // Set the distance per pulse for the drive encoders. We can simply use the
    // distance traveled for one rotation of the wheel divided by the encoder
    // resolution.
    m_leftEncoder.SetDistancePerPulse(2 * std::numbers::pi * kWheelRadius /
                                      kEncoderResolution);
    m_rightEncoder.SetDistancePerPulse(2 * std::numbers::pi * kWheelRadius /
                                       kEncoderResolution);

    m_leftEncoder.Reset();
    m_rightEncoder.Reset();

    m_rightLeader.SetInverted(true);

    frc::SmartDashboard::PutData("Field", &m_fieldSim);
  }

  static constexpr units::meters_per_second_t kMaxSpeed =
      3.0_mps;  // 3 meters per second
  static constexpr units::radians_per_second_t kMaxAngularSpeed{
      std::numbers::pi};  // 1/2 rotation per second

  void SetSpeeds(const frc::DifferentialDriveWheelSpeeds& speeds);
  void Drive(units::meters_per_second_t xSpeed,
             units::radians_per_second_t rot);
  void UpdateOdometry();
  void ResetOdometry(const frc::Pose2d& pose);

  frc::Pose2d GetPose() const { return m_odometry.GetPose(); }

  void SimulationPeriodic();
  void Periodic();

 private:
  static constexpr units::meter_t kTrackwidth = 0.381_m * 2;
  static constexpr double kWheelRadius = 0.0508;  // meters
  static constexpr int kEncoderResolution = 4096;

  frc::PWMSparkMax m_leftLeader{1};
  frc::PWMSparkMax m_leftFollower{2};
  frc::PWMSparkMax m_rightLeader{3};
  frc::PWMSparkMax m_rightFollower{4};

  frc::Encoder m_leftEncoder{0, 1};
  frc::Encoder m_rightEncoder{2, 3};

  frc::PIDController m_leftPIDController{8.5, 0.0, 0.0};
  frc::PIDController m_rightPIDController{8.5, 0.0, 0.0};

  frc::OnboardIMU m_imu{frc::OnboardIMU::kFlat};

  frc::DifferentialDriveKinematics m_kinematics{kTrackwidth};
  frc::DifferentialDriveOdometry m_odometry{
      m_imu.GetRotation2d(), units::meter_t{m_leftEncoder.GetDistance()},
      units::meter_t{m_rightEncoder.GetDistance()}};

  // Gains are for example purposes only - must be determined for your own
  // robot!
  frc::SimpleMotorFeedforward<units::meters> m_feedforward{1_V, 3_V / 1_mps};

  // Simulation classes help us simulate our robot
  frc::sim::EncoderSim m_leftEncoderSim{m_leftEncoder};
  frc::sim::EncoderSim m_rightEncoderSim{m_rightEncoder};
  frc::Field2d m_fieldSim;
  frc::LinearSystem<2, 2, 2> m_drivetrainSystem =
      frc::LinearSystemId::IdentifyDrivetrainSystem(
          1.98_V / 1_mps, 0.2_V / 1_mps_sq, 1.5_V / 1_mps, 0.3_V / 1_mps_sq);
  frc::sim::DifferentialDrivetrainSim m_drivetrainSimulator{
      m_drivetrainSystem, kTrackwidth, frc::DCMotor::CIM(2), 8, 2_in};
};