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/MecanumBot/cpp/Drivetrain.cpp

@@ -0,0 +1,46 @@
+/*----------------------------------------------------------------------------*/
+/* 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::MecanumDriveWheelSpeeds Drivetrain::GetCurrentState() const {
+  return {units::meters_per_second_t(m_frontLeftEncoder.GetRate()),
+          units::meters_per_second_t(m_frontRightEncoder.GetRate()),
+          units::meters_per_second_t(m_backLeftEncoder.GetRate()),
+          units::meters_per_second_t(m_backRightEncoder.GetRate())};
+}
+
+void Drivetrain::SetSpeeds(const frc::MecanumDriveWheelSpeeds& wheelSpeeds) {
+  const auto frontLeftOutput = m_frontLeftPIDController.Calculate(
+      m_frontLeftEncoder.GetRate(), wheelSpeeds.frontLeft.to<double>());
+  const auto frontRightOutput = m_frontRightPIDController.Calculate(
+      m_frontRightEncoder.GetRate(), wheelSpeeds.frontRight.to<double>());
+  const auto backLeftOutput = m_backLeftPIDController.Calculate(
+      m_backLeftEncoder.GetRate(), wheelSpeeds.rearLeft.to<double>());
+  const auto backRightOutput = m_backRightPIDController.Calculate(
+      m_backRightEncoder.GetRate(), wheelSpeeds.rearRight.to<double>());
+
+  m_frontLeftMotor.Set(frontLeftOutput);
+  m_frontRightMotor.Set(frontRightOutput);
+  m_backLeftMotor.Set(backLeftOutput);
+  m_backRightMotor.Set(backRightOutput);
+}
+
+void Drivetrain::Drive(units::meters_per_second_t xSpeed,
+                       units::meters_per_second_t ySpeed,
+                       units::radians_per_second_t rot, bool fieldRelative) {
+  auto wheelSpeeds = m_kinematics.ToWheelSpeeds(
+      fieldRelative ? frc::ChassisSpeeds::FromFieldRelativeSpeeds(
+                          xSpeed, ySpeed, rot, GetAngle())
+                    : frc::ChassisSpeeds{xSpeed, ySpeed, rot});
+  wheelSpeeds.Normalize(kMaxSpeed);
+  SetSpeeds(wheelSpeeds);
+}
+
+void Drivetrain::UpdateOdometry() {
+  m_odometry.Update(GetAngle(), GetCurrentState());
+}

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

@@ -0,0 +1,51 @@
+/*----------------------------------------------------------------------------*/
+/* 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_mecanum.UpdateOdometry();
+  }
+
+  void TeleopPeriodic() override { DriveWithJoystick(true); }
+
+ private:
+  frc::XboxController m_controller{0};
+  Drivetrain m_mecanum;
+
+  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_mecanum.Drive(xSpeed, ySpeed, rot, fieldRelative);
+  }
+};
+
+#ifndef RUNNING_FRC_TESTS
+int main() { return frc::StartRobot<Robot>(); }
+#endif

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

@@ -0,0 +1,75 @@
+/*----------------------------------------------------------------------------*/
+/* 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/Encoder.h>
+#include <frc/Spark.h>
+#include <frc/controller/PIDController.h>
+#include <frc/geometry/Translation2d.h>
+#include <frc/kinematics/MecanumDriveKinematics.h>
+#include <frc/kinematics/MecanumDriveOdometry.h>
+#include <frc/kinematics/MecanumDriveWheelSpeeds.h>
+#include <wpi/math>
+
+/**
+ * Represents a mecanum 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()));
+  }
+
+  frc::MecanumDriveWheelSpeeds GetCurrentState() const;
+  void SetSpeeds(const frc::MecanumDriveWheelSpeeds& wheelSpeeds);
+  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::Spark m_frontLeftMotor{1};
+  frc::Spark m_frontRightMotor{2};
+  frc::Spark m_backLeftMotor{3};
+  frc::Spark m_backRightMotor{4};
+
+  frc::Encoder m_frontLeftEncoder{0, 1};
+  frc::Encoder m_frontRightEncoder{0, 1};
+  frc::Encoder m_backLeftEncoder{0, 1};
+  frc::Encoder m_backRightEncoder{0, 1};
+
+  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};
+
+  frc2::PIDController m_frontLeftPIDController{1.0, 0.0, 0.0};
+  frc2::PIDController m_frontRightPIDController{1.0, 0.0, 0.0};
+  frc2::PIDController m_backLeftPIDController{1.0, 0.0, 0.0};
+  frc2::PIDController m_backRightPIDController{1.0, 0.0, 0.0};
+
+  frc::AnalogGyro m_gyro{0};
+
+  frc::MecanumDriveKinematics m_kinematics{
+      m_frontLeftLocation, m_frontRightLocation, m_backLeftLocation,
+      m_backRightLocation};
+
+  frc::MecanumDriveOdometry m_odometry{m_kinematics};
+};