Differential Drive Simulation

package edu.wpi.first.wpilibj.examples.simpledifferentialdrivesimulation;

import edu.wpi.first.math.controller.LTVUnicycleController;
import edu.wpi.first.math.filter.SlewRateLimiter;
import edu.wpi.first.math.geometry.Pose2d;
import edu.wpi.first.math.geometry.Rotation2d;
import edu.wpi.first.math.kinematics.ChassisSpeeds;
import edu.wpi.first.math.trajectory.Trajectory;
import edu.wpi.first.math.trajectory.TrajectoryConfig;
import edu.wpi.first.math.trajectory.TrajectoryGenerator;
import edu.wpi.first.wpilibj.TimedRobot;
import edu.wpi.first.wpilibj.Timer;
import edu.wpi.first.wpilibj.XboxController;
import java.util.List;

public class Robot extends TimedRobot {
  private final XboxController m_controller = new XboxController(0);

  // Slew rate limiters to make joystick inputs more gentle; 1/3 sec from 0 to 1.
  private final SlewRateLimiter m_speedLimiter = new SlewRateLimiter(3);
  private final SlewRateLimiter m_rotLimiter = new SlewRateLimiter(3);

  private final Drivetrain m_drive = new Drivetrain();
  private final LTVUnicycleController m_feedback = new LTVUnicycleController(0.020);
  private final Timer m_timer = new Timer();
  private final Trajectory m_trajectory;

  public Robot() {
    m_trajectory =
        TrajectoryGenerator.generateTrajectory(
            new Pose2d(2, 2, Rotation2d.kZero),
            List.of(),
            new Pose2d(6, 4, Rotation2d.kZero),
            new TrajectoryConfig(2, 2));
  }

  @Override
  public void robotPeriodic() {
    m_drive.periodic();
  }

  @Override
  public void autonomousInit() {
    m_timer.restart();
    m_drive.resetOdometry(m_trajectory.getInitialPose());
  }

  @Override
  public void autonomousPeriodic() {
    double elapsed = m_timer.get();
    Trajectory.State reference = m_trajectory.sample(elapsed);
    ChassisSpeeds speeds = m_feedback.calculate(m_drive.getPose(), reference);
    m_drive.drive(speeds.vxMetersPerSecond, speeds.omegaRadiansPerSecond);
  }

  @Override
  public void teleopPeriodic() {
    // Get the x speed. We are inverting this because Xbox controllers return
    // negative values when we push forward.
    double xSpeed = -m_speedLimiter.calculate(m_controller.getLeftY()) * Drivetrain.kMaxSpeed;

    // Get the rate of angular rotation. 
    double rot = -m_rotLimiter.calculate(m_controller.getRightX()) * Drivetrain.kMaxAngularSpeed;
    m_drive.drive(xSpeed, rot);
  }

  @Override
  public void simulationPeriodic() {
    m_drive.simulationPeriodic();
  }
}

package edu.wpi.first.wpilibj.examples.simpledifferentialdrivesimulation;

import edu.wpi.first.math.controller.PIDController;
import edu.wpi.first.math.controller.SimpleMotorFeedforward;
import edu.wpi.first.math.geometry.Pose2d;
import edu.wpi.first.math.kinematics.ChassisSpeeds;
import edu.wpi.first.math.kinematics.DifferentialDriveKinematics;
import edu.wpi.first.math.kinematics.DifferentialDriveOdometry;
import edu.wpi.first.math.kinematics.DifferentialDriveWheelSpeeds;
import edu.wpi.first.math.system.plant.DCMotor;
import edu.wpi.first.math.system.plant.LinearSystemId;
import edu.wpi.first.wpilibj.AnalogGyro;
import edu.wpi.first.wpilibj.Encoder;
import edu.wpi.first.wpilibj.motorcontrol.PWMSparkMax;
import edu.wpi.first.wpilibj.simulation.AnalogGyroSim;
import edu.wpi.first.wpilibj.simulation.DifferentialDrivetrainSim;
import edu.wpi.first.wpilibj.simulation.EncoderSim;
import edu.wpi.first.wpilibj.smartdashboard.Field2d;
import edu.wpi.first.wpilibj.smartdashboard.SmartDashboard;

public class Drivetrain {
  public static final double kMaxSpeed = 3.0;  // meters per second
  public static final double kMaxAngularSpeed = Math.PI;  // 1/2 rotation per second

  private static final double kTrackWidth = 0.381 * 2;
  private static final double kWheelRadius = 0.0508;

  private final PWMSparkMax m_leftLeader = new PWMSparkMax(1);
  private final PWMSparkMax m_rightLeader = new PWMSparkMax(3);

  private final Encoder m_leftEncoder = new Encoder(0, 1);
  private final Encoder m_rightEncoder = new Encoder(2, 3);

  private final PIDController m_leftPIDController = new PIDController(8.5, 0, 0);
  private final PIDController m_rightPIDController = new PIDController(8.5, 0, 0);

  private final AnalogGyro m_gyro = new AnalogGyro(0);

  private final DifferentialDriveKinematics m_kinematics =
      new DifferentialDriveKinematics(kTrackWidth);
  private final DifferentialDriveOdometry m_odometry =
      new DifferentialDriveOdometry(
          m_gyro.getRotation2d(), m_leftEncoder.getDistance(), m_rightEncoder.getDistance());

  private final SimpleMotorFeedforward m_feedforward = new SimpleMotorFeedforward(1, 3);

  // Simulation classes
  private final AnalogGyroSim m_gyroSim = new AnalogGyroSim(m_gyro);
  private final EncoderSim m_leftEncoderSim = new EncoderSim(m_leftEncoder);
  private final EncoderSim m_rightEncoderSim = new EncoderSim(m_rightEncoder);
  private final Field2d m_fieldSim = new Field2d();
  private final DifferentialDrivetrainSim m_drivetrainSimulator =
      new DifferentialDrivetrainSim(
          LinearSystemId.identifyDrivetrainSystem(1.98, 0.2, 1.5, 0.3),
          DCMotor.getCIM(2),
          8,
          kTrackWidth,
          kWheelRadius,
          null);

  public Drivetrain() {
    m_rightLeader.setInverted(true);
    m_leftEncoder.setDistancePerPulse(2 * Math.PI * kWheelRadius / 4096);
    m_rightEncoder.setDistancePerPulse(2 * Math.PI * kWheelRadius / 4096);
    SmartDashboard.putData("Field", m_fieldSim);
  }

  /** Sets speeds to the drivetrain motors. */
  public void setSpeeds(DifferentialDriveWheelSpeeds speeds) {
    final double leftFeedforward = m_feedforward.calculate(speeds.leftMetersPerSecond);
    final double rightFeedforward = m_feedforward.calculate(speeds.rightMetersPerSecond);
    double leftOutput =
        m_leftPIDController.calculate(m_leftEncoder.getRate(), speeds.leftMetersPerSecond);
    double rightOutput =
        m_rightPIDController.calculate(m_rightEncoder.getRate(), speeds.rightMetersPerSecond);

    m_leftLeader.setVoltage(leftOutput + leftFeedforward);
    m_rightLeader.setVoltage(rightOutput + rightFeedforward);
  }

  public void drive(double xSpeed, double rot) {
    setSpeeds(m_kinematics.toWheelSpeeds(new ChassisSpeeds(xSpeed, 0, rot)));
  }

  public void resetOdometry(Pose2d pose) {
    m_drivetrainSimulator.setPose(pose);
    m_odometry.resetPosition(
        m_gyro.getRotation2d(), m_leftEncoder.getDistance(), m_rightEncoder.getDistance(), pose);
  }

  public Pose2d getPose() {
    return m_odometry.getPoseMeters();
  }

  /** Update our simulation. */
  public void simulationPeriodic() {
    m_drivetrainSimulator.setInputs(
        m_leftLeader.get() * RobotController.getInputVoltage(),
        m_rightLeader.get() * RobotController.getInputVoltage());
    m_drivetrainSimulator.update(0.02);

    m_leftEncoderSim.setDistance(m_drivetrainSimulator.getLeftPositionMeters());
    m_leftEncoderSim.setRate(m_drivetrainSimulator.getLeftVelocityMetersPerSecond());
    m_rightEncoderSim.setDistance(m_drivetrainSimulator.getRightPositionMeters());
    m_rightEncoderSim.setRate(m_drivetrainSimulator.getRightVelocityMetersPerSecond());
    m_gyroSim.setAngle(-m_drivetrainSimulator.getHeading().getDegrees());
  }

  /** Update odometry. */
  public void periodic() {
    m_odometry.update(
        m_gyro.getRotation2d(), m_leftEncoder.getDistance(), m_rightEncoder.getDistance());
    m_fieldSim.setRobotPose(m_odometry.getPoseMeters());
  }
}