[wpilib] Add RamseteController examples (#2553)

This is different from the RamseteCommand examples in that they don't use the command-based library.

wpilibcExamples/src/main/cpp/examples/RamseteController/cpp/Drivetrain.cpp

@@ -0,0 +1,37 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2019-2020 FIRST. All Rights Reserved.                        */
+/* Open Source Software - may be modified and shared by FRC teams. The code   */
+/* must be accompanied by the FIRST BSD license file in the root directory of */
+/* the project.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#include "Drivetrain.h"
+
+void Drivetrain::SetSpeeds(const frc::DifferentialDriveWheelSpeeds& speeds) {
+  const auto leftFeedforward = m_feedforward.Calculate(speeds.left);
+  const auto rightFeedforward = m_feedforward.Calculate(speeds.right);
+  const double leftOutput = m_leftPIDController.Calculate(
+      m_leftEncoder.GetRate(), speeds.left.to<double>());
+  const double rightOutput = m_rightPIDController.Calculate(
+      m_rightEncoder.GetRate(), speeds.right.to<double>());
+
+  m_leftGroup.SetVoltage(units::volt_t{leftOutput} + leftFeedforward);
+  m_rightGroup.SetVoltage(units::volt_t{rightOutput} + rightFeedforward);
+}
+
+void Drivetrain::Drive(units::meters_per_second_t xSpeed,
+                       units::radians_per_second_t rot) {
+  SetSpeeds(m_kinematics.ToWheelSpeeds({xSpeed, 0_mps, rot}));
+}
+
+void Drivetrain::UpdateOdometry() {
+  m_odometry.Update(m_gyro.GetRotation2d(),
+                    units::meter_t(m_leftEncoder.GetDistance()),
+                    units::meter_t(m_rightEncoder.GetDistance()));
+}
+
+void Drivetrain::ResetOdometry(const frc::Pose2d& pose) {
+  m_odometry.ResetPosition(pose, m_gyro.GetRotation2d());
+}
+
+frc::Pose2d Drivetrain::GetPose() const { return m_odometry.GetPose(); }

wpilibcExamples/src/main/cpp/examples/RamseteController/cpp/Robot.cpp

@@ -0,0 +1,89 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2019-2020 FIRST. All Rights Reserved.                        */
+/* Open Source Software - may be modified and shared by FRC teams. The code   */
+/* must be accompanied by the FIRST BSD license file in the root directory of */
+/* the project.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#include <frc/SlewRateLimiter.h>
+#include <frc/TimedRobot.h>
+#include <frc/XboxController.h>
+#include <frc/controller/RamseteController.h>
+#include <frc/trajectory/TrajectoryGenerator.h>
+#include <frc2/Timer.h>
+
+#include "Drivetrain.h"
+
+class Robot : public frc::TimedRobot {
+ public:
+  void AutonomousInit() override {
+    // Start the timer.
+    m_timer.Start();
+
+    // Reset the drivetrain's odometry to the starting pose of the trajectory.
+    m_drive.ResetOdometry(m_trajectory.InitialPose());
+  }
+
+  void AutonomousPeriodic() override {
+    // Update odometry.
+    m_drive.UpdateOdometry();
+
+    if (m_timer.Get() < m_trajectory.TotalTime()) {
+      // Get the desired pose from the trajectory.
+      auto desiredPose = m_trajectory.Sample(m_timer.Get());
+
+      // Get the reference chassis speeds from the Ramsete Controller.
+      auto refChassisSpeeds =
+          m_ramseteController.Calculate(m_drive.GetPose(), desiredPose);
+
+      // Set the linear and angular speeds.
+      m_drive.Drive(refChassisSpeeds.vx, refChassisSpeeds.omega);
+    } else {
+      m_drive.Drive(0_mps, 0_rad_per_s);
+    }
+  }
+
+  void TeleopPeriodic() override {
+    // Get the x speed. We are inverting this because Xbox controllers return
+    // negative values when we push forward.
+    const auto xSpeed = -m_speedLimiter.Calculate(
+                            m_controller.GetY(frc::GenericHID::kLeftHand)) *
+                        Drivetrain::kMaxSpeed;
+
+    // Get the rate of angular rotation. We are inverting this because we want a
+    // positive value when we pull to the left (remember, CCW is positive in
+    // mathematics). Xbox controllers return positive values when you pull to
+    // the right by default.
+    const auto rot = -m_rotLimiter.Calculate(
+                         m_controller.GetX(frc::GenericHID::kRightHand)) *
+                     Drivetrain::kMaxAngularSpeed;
+
+    m_drive.Drive(xSpeed, rot);
+  }
+
+ private:
+  frc::XboxController m_controller{0};
+
+  // Slew rate limiters to make joystick inputs more gentle; 1/3 sec from 0
+  // to 1.
+  frc::SlewRateLimiter<units::scalar> m_speedLimiter{3 / 1_s};
+  frc::SlewRateLimiter<units::scalar> m_rotLimiter{3 / 1_s};
+
+  Drivetrain m_drive;
+
+  // An example trajectory to follow.
+  frc::Trajectory m_trajectory = frc::TrajectoryGenerator::GenerateTrajectory(
+      frc::Pose2d(0_m, 0_m, 0_rad),
+      {frc::Translation2d(1_m, 1_m), frc::Translation2d(2_m, -1_m)},
+      frc::Pose2d(3_m, 0_m, 0_rad), frc::TrajectoryConfig(3_fps, 3_fps_sq));
+
+  // The Ramsete Controller to follow the trajectory.
+  frc::RamseteController m_ramseteController;
+
+  // The timer to use during the autonomous period.
+  frc2::Timer m_timer;
+};
+
+#ifndef RUNNING_FRC_TESTS
+int main() { return frc::StartRobot<Robot>(); }
+#endif

wpilibcExamples/src/main/cpp/examples/RamseteController/include/Drivetrain.h

@@ -0,0 +1,80 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2019-2020 FIRST. All Rights Reserved.                        */
+/* Open Source Software - may be modified and shared by FRC teams. The code   */
+/* must be accompanied by the FIRST BSD license file in the root directory of */
+/* the project.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#pragma once
+
+#include <frc/AnalogGyro.h>
+#include <frc/Encoder.h>
+#include <frc/PWMVictorSPX.h>
+#include <frc/SpeedControllerGroup.h>
+#include <frc/controller/PIDController.h>
+#include <frc/controller/SimpleMotorFeedforward.h>
+#include <frc/kinematics/DifferentialDriveKinematics.h>
+#include <frc/kinematics/DifferentialDriveOdometry.h>
+#include <units/angular_velocity.h>
+#include <units/length.h>
+#include <wpi/math>
+
+/**
+ * Represents a differential drive style drivetrain.
+ */
+class Drivetrain {
+ public:
+  Drivetrain() {
+    m_gyro.Reset();
+    // 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 * wpi::math::pi * kWheelRadius /
+                                      kEncoderResolution);
+    m_rightEncoder.SetDistancePerPulse(2 * wpi::math::pi * kWheelRadius /
+                                       kEncoderResolution);
+
+    m_leftEncoder.Reset();
+    m_rightEncoder.Reset();
+  }
+
+  static constexpr units::meters_per_second_t kMaxSpeed =
+      3.0_mps;  // 3 meters per second
+  static constexpr units::radians_per_second_t kMaxAngularSpeed{
+      wpi::math::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;
+
+ private:
+  static constexpr units::meter_t kTrackWidth = 0.381_m * 2;
+  static constexpr double kWheelRadius = 0.0508;  // meters
+  static constexpr int kEncoderResolution = 4096;
+
+  frc::PWMVictorSPX m_leftLeader{1};
+  frc::PWMVictorSPX m_leftFollower{2};
+  frc::PWMVictorSPX m_rightLeader{3};
+  frc::PWMVictorSPX m_rightFollower{4};
+
+  frc::SpeedControllerGroup m_leftGroup{m_leftLeader, m_leftFollower};
+  frc::SpeedControllerGroup m_rightGroup{m_rightLeader, m_rightFollower};
+
+  frc::Encoder m_leftEncoder{0, 1};
+  frc::Encoder m_rightEncoder{2, 3};
+
+  frc2::PIDController m_leftPIDController{1.0, 0.0, 0.0};
+  frc2::PIDController m_rightPIDController{1.0, 0.0, 0.0};
+
+  frc::AnalogGyro m_gyro{0};
+
+  frc::DifferentialDriveKinematics m_kinematics{kTrackWidth};
+  frc::DifferentialDriveOdometry m_odometry{m_gyro.GetRotation2d()};
+
+  // 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};
+};

wpilibcExamples/src/main/cpp/examples/examples.json

@@ -532,5 +532,15 @@
     "foldername": "DriveDistanceOffboard",
     "gradlebase": "cpp",
     "commandversion": 2
+  },
+  {
+    "name": "RamseteController",
+    "description": "An example robot demonstrating the use of RamseteController.",
+    "tags": [
+      "RamseteController"
+    ],
+    "foldername": "RamseteController",
+    "gradlebase": "cpp",
+    "commandversion": 2
   }
 ]