Add kinematics suite (#1787)

Co-authored-by: Tyler Veness <calcmogul@gmail.com>
Co-authored-by: Matt <matthew.morley.ca@gmail.com>

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

@@ -0,0 +1,32 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2019 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"
+
+frc::DifferentialDriveWheelSpeeds Drivetrain::GetSpeeds() const {
+  return {units::meters_per_second_t(m_leftEncoder.GetRate()),
+          units::meters_per_second_t(m_rightEncoder.GetRate())};
+}
+
+void Drivetrain::SetSpeeds(const frc::DifferentialDriveWheelSpeeds& speeds) {
+  const auto leftOutput = m_leftPIDController.Calculate(
+      m_leftEncoder.GetRate(), speeds.left.to<double>());
+  const auto rightOutput = m_rightPIDController.Calculate(
+      m_rightEncoder.GetRate(), speeds.right.to<double>());
+
+  m_leftGroup.Set(leftOutput);
+  m_rightGroup.Set(rightOutput);
+}
+
+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(GetAngle(), GetSpeeds());
+}

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

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+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2019 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/TimedRobot.h>
+#include <frc/XboxController.h>
+
+#include "Drivetrain.h"
+
+class Robot : public frc::TimedRobot {
+ public:
+  void AutonomousPeriodic() override {
+    TeleopPeriodic();
+    m_drive.UpdateOdometry();
+  }
+
+  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_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_controller.GetX(frc::GenericHID::kRightHand) *
+                     Drivetrain::kMaxAngularSpeed;
+
+    m_drive.Drive(xSpeed, rot);
+  }
+
+ private:
+  frc::XboxController m_controller{0};
+  Drivetrain m_drive;
+};
+
+#ifndef RUNNING_FRC_TESTS
+int main() { return frc::StartRobot<Robot>(); }
+#endif

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

@@ -0,0 +1,79 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2019 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 <units/units.h>
+
+#include <frc/AnalogGyro.h>
+#include <frc/Encoder.h>
+#include <frc/Spark.h>
+#include <frc/SpeedControllerGroup.h>
+#include <frc/controller/PIDController.h>
+#include <frc/kinematics/DifferentialDriveKinematics.h>
+#include <frc/kinematics/DifferentialDriveOdometry.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);
+  }
+
+  /**
+   * Get the robot angle as a Rotation2d.
+   */
+  frc::Rotation2d GetAngle() const {
+    // Negating the angle because WPILib Gyros are CW positive.
+    return frc::Rotation2d(units::degree_t(-m_gyro.GetAngle()));
+  }
+
+  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
+
+  frc::DifferentialDriveWheelSpeeds GetSpeeds() const;
+  void SetSpeeds(const frc::DifferentialDriveWheelSpeeds& speeds);
+  void Drive(units::meters_per_second_t xSpeed,
+             units::radians_per_second_t rot);
+  void UpdateOdometry();
+
+ private:
+  static constexpr units::meter_t kTrackWidth = 0.381_m * 2;
+  static constexpr double kWheelRadius = 0.0508;  // meters
+  static constexpr int kEncoderResolution = 4096;
+
+  frc::Spark m_leftMaster{1};
+  frc::Spark m_leftFollower{2};
+  frc::Spark m_rightMaster{3};
+  frc::Spark m_rightFollower{4};
+
+  frc::SpeedControllerGroup m_leftGroup{m_leftMaster, m_leftFollower};
+  frc::SpeedControllerGroup m_rightGroup{m_rightMaster, m_rightFollower};
+
+  frc::Encoder m_leftEncoder{0, 1};
+  frc::Encoder m_rightEncoder{0, 1};
+
+  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_kinematics};
+};