[wpilib] Add pose estimators (#2867)

Pose and state estimators can filter latency-compensated global measurements and fuse them with state-space drivetrain model information to estimate robot position. They are drop-in replacements for the existing odometry classes.

Co-authored-by: Declan Freeman-Gleason <declanfreemangleason@gmail.com>
Co-authored-by: Prateek Machiraju <prateek.machiraju@gmail.com>
Co-authored-by: Claudius Tewari <cttewari@gmail.com>
Co-authored-by: Matt <matthew.morley.ca@gmail.com>

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

@@ -0,0 +1,88 @@
+/*----------------------------------------------------------------------------*/
+/* 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/estimator/DifferentialDrivePoseEstimator.h>
+#include <frc/kinematics/DifferentialDriveKinematics.h>
+#include <units/angle.h>
+#include <units/angular_velocity.h>
+#include <units/length.h>
+#include <units/velocity.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.to<double>() / kEncoderResolution);
+    m_rightEncoder.SetDistancePerPulse(
+        2 * wpi::math::pi * kWheelRadius.to<double>() / 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();
+
+ private:
+  static constexpr units::meter_t kTrackWidth = 0.381_m * 2;
+  static constexpr units::meter_t kWheelRadius = 0.0508_m;
+  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};
+
+  // Gains are for example purposes only - must be determined for your own
+  // robot!
+  frc::DifferentialDrivePoseEstimator m_poseEstimator{
+      frc::Rotation2d(),
+      frc::Pose2d(),
+      {0.01, 0.01, 0.01, 0.01, 0.01},
+      {0.1, 0.1, 0.1},
+      {0.1, 0.1, 0.1}};
+
+  // 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};
+};