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/SwerveBot/cpp/Drivetrain.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 "Drivetrain.h"
+
+void Drivetrain::Drive(units::meters_per_second_t xSpeed,
+                       units::meters_per_second_t ySpeed,
+                       units::radians_per_second_t rot, bool fieldRelative) {
+  auto states = m_kinematics.ToSwerveModuleStates(
+      fieldRelative ? frc::ChassisSpeeds::FromFieldRelativeSpeeds(
+                          xSpeed, ySpeed, rot, GetAngle())
+                    : frc::ChassisSpeeds{xSpeed, ySpeed, rot});
+
+  m_kinematics.NormalizeWheelSpeeds(&states, kMaxSpeed);
+
+  auto [fl, fr, bl, br] = states;
+
+  m_frontLeft.SetDesiredState(fl);
+  m_frontRight.SetDesiredState(fr);
+  m_backLeft.SetDesiredState(bl);
+  m_backRight.SetDesiredState(br);
+}
+
+void Drivetrain::UpdateOdometry() {
+  m_odometry.Update(GetAngle(), m_frontLeft.GetState(), m_frontRight.GetState(),
+                    m_backLeft.GetState(), m_backRight.GetState());
+}

wpilibcExamples/src/main/cpp/examples/SwerveBot/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 {
+    DriveWithJoystick(false);
+    m_swerve.UpdateOdometry();
+  }
+
+  void TeleopPeriodic() override { DriveWithJoystick(true); }
+
+ private:
+  frc::XboxController m_controller{0};
+  Drivetrain m_swerve;
+
+  void DriveWithJoystick(bool fieldRelative) {
+    // 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 y speed or sideways/strafe speed. We are inverting this because
+    // we want a positive value when we pull to the left. Xbox controllers
+    // return positive values when you pull to the right by default.
+    const auto ySpeed =
+        -m_controller.GetX(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_swerve.Drive(xSpeed, ySpeed, rot, fieldRelative);
+  }
+};
+
+#ifndef RUNNING_FRC_TESTS
+int main() { return frc::StartRobot<Robot>(); }
+#endif

wpilibcExamples/src/main/cpp/examples/SwerveBot/cpp/SwerveModule.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 "SwerveModule.h"
+
+#include <frc/geometry/Rotation2d.h>
+#include <wpi/math>
+
+SwerveModule::SwerveModule(const int driveMotorChannel,
+                           const int turningMotorChannel)
+    : m_driveMotor(driveMotorChannel), m_turningMotor(turningMotorChannel) {
+  // Set the distance per pulse for the drive encoder. We can simply use the
+  // distance traveled for one rotation of the wheel divided by the encoder
+  // resolution.
+  m_driveEncoder.SetDistancePerPulse(2 * wpi::math::pi * kWheelRadius /
+                                     kEncoderResolution);
+
+  // Set the distance (in this case, angle) per pulse for the turning encoder.
+  // This is the the angle through an entire rotation (2 * wpi::math::pi)
+  // divided by the encoder resolution.
+  m_turningEncoder.SetDistancePerPulse(2 * wpi::math::pi / kEncoderResolution);
+
+  // Limit the PID Controller's input range between -pi and pi and set the input
+  // to be continuous.
+  m_turningPIDController.EnableContinuousInput(-wpi::math::pi, wpi::math::pi);
+}
+
+frc::SwerveModuleState SwerveModule::GetState() const {
+  return {units::meters_per_second_t{m_driveEncoder.GetRate()},
+          frc::Rotation2d(units::radian_t(m_turningEncoder.Get()))};
+}
+
+void SwerveModule::SetDesiredState(const frc::SwerveModuleState& state) {
+  // Calculate the drive output from the drive PID controller.
+  const auto driveOutput = m_drivePIDController.Calculate(
+      m_driveEncoder.GetRate(), state.speed.to<double>());
+
+  // Calculate the turning motor output from the turning PID controller.
+  const auto turnOutput = m_turningPIDController.Calculate(
+      m_turningEncoder.Get(),
+      // We have to convert to the meters type here because that's what
+      // ProfiledPIDController wants.
+      units::meter_t(state.angle.Radians().to<double>()));
+
+  // Set the motor outputs.
+  m_driveMotor.Set(driveOutput);
+  m_turningMotor.Set(turnOutput);
+}

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

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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.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#pragma once
+
+#include <frc/AnalogGyro.h>
+#include <frc/geometry/Translation2d.h>
+#include <frc/kinematics/SwerveDriveKinematics.h>
+#include <frc/kinematics/SwerveDriveOdometry.h>
+#include <wpi/math>
+
+#include "SwerveModule.h"
+
+/**
+ * Represents a swerve drive style drivetrain.
+ */
+class Drivetrain {
+ public:
+  Drivetrain() { m_gyro.Reset(); }
+
+  /**
+   * 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()));
+  }
+
+  void Drive(units::meters_per_second_t xSpeed,
+             units::meters_per_second_t ySpeed, units::radians_per_second_t rot,
+             bool fieldRelative);
+  void UpdateOdometry();
+
+  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
+
+ private:
+  frc::Translation2d m_frontLeftLocation{+0.381_m, +0.381_m};
+  frc::Translation2d m_frontRightLocation{+0.381_m, -0.381_m};
+  frc::Translation2d m_backLeftLocation{-0.381_m, +0.381_m};
+  frc::Translation2d m_backRightLocation{-0.381_m, -0.381_m};
+
+  SwerveModule m_frontLeft{1, 2};
+  SwerveModule m_frontRight{2, 3};
+  SwerveModule m_backLeft{5, 6};
+  SwerveModule m_backRight{7, 8};
+
+  frc::AnalogGyro m_gyro{0};
+
+  frc::SwerveDriveKinematics<4> m_kinematics{
+      m_frontLeftLocation, m_frontRightLocation, m_backLeftLocation,
+      m_backRightLocation};
+
+  frc::SwerveDriveOdometry<4> m_odometry{m_kinematics};
+};

wpilibcExamples/src/main/cpp/examples/SwerveBot/include/SwerveModule.h

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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.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#pragma once
+
+#include <frc/Encoder.h>
+#include <frc/Spark.h>
+#include <frc/controller/PIDController.h>
+#include <frc/controller/ProfiledPIDController.h>
+#include <frc/kinematics/SwerveModuleState.h>
+#include <wpi/math>
+
+class SwerveModule {
+ public:
+  SwerveModule(int driveMotorChannel, int turningMotorChannel);
+  frc::SwerveModuleState GetState() const;
+  void SetDesiredState(const frc::SwerveModuleState& state);
+
+ private:
+  static constexpr double kWheelRadius = 0.0508;
+  static constexpr int kEncoderResolution = 4096;
+
+  // We have to use meters here instead of radians because of the fact that
+  // ProfiledPIDController's constraints only take in meters per second and
+  // meters per second squared.
+
+  static constexpr units::meters_per_second_t kModuleMaxAngularVelocity =
+      units::meters_per_second_t(wpi::math::pi);  // radians per second
+  static constexpr units::meters_per_second_squared_t
+      kModuleMaxAngularAcceleration = units::meters_per_second_squared_t(
+          wpi::math::pi * 2.0);  // radians per second squared
+
+  frc::Spark m_driveMotor;
+  frc::Spark m_turningMotor;
+
+  frc::Encoder m_driveEncoder{0, 1};
+  frc::Encoder m_turningEncoder{0, 1};
+
+  frc2::PIDController m_drivePIDController{1.0, 0, 0};
+  frc::ProfiledPIDController m_turningPIDController{
+      1.0,
+      0.0,
+      0.0,
+      {kModuleMaxAngularVelocity, kModuleMaxAngularAcceleration}};
+};