[wpilibc] Update C++ DiffDriveSim example to match Java (#2839)

wpilibcExamples/src/main/cpp/examples/StateSpaceDifferentialDriveSimulation/include/Constants.h

@@ -0,0 +1,86 @@
+/*----------------------------------------------------------------------------*/
+/* 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/kinematics/DifferentialDriveKinematics.h>
+#include <frc/system/plant/DCMotor.h>
+#include <frc/system/plant/LinearSystemId.h>
+#include <frc/trajectory/constraint/DifferentialDriveKinematicsConstraint.h>
+#include <units/acceleration.h>
+#include <units/angle.h>
+#include <units/length.h>
+#include <units/time.h>
+#include <units/velocity.h>
+#include <units/voltage.h>
+#include <wpi/math>
+
+#pragma once
+
+/**
+ * The Constants header provides a convenient place for teams to hold robot-wide
+ * numerical or bool constants.  This should not be used for any other purpose.
+ *
+ * It is generally a good idea to place constants into subsystem- or
+ * command-specific namespaces within this header, which can then be used where
+ * they are needed.
+ */
+
+namespace DriveConstants {
+constexpr int kLeftMotor1Port = 0;
+constexpr int kLeftMotor2Port = 1;
+constexpr int kRightMotor1Port = 2;
+constexpr int kRightMotor2Port = 3;
+
+constexpr int kLeftEncoderPorts[]{0, 1};
+constexpr int kRightEncoderPorts[]{2, 3};
+constexpr bool kLeftEncoderReversed = false;
+constexpr bool kRightEncoderReversed = true;
+
+constexpr auto kTrackwidth = 0.69_m;
+extern const frc::DifferentialDriveKinematics kDriveKinematics;
+
+constexpr int kEncoderCPR = 1024;
+constexpr auto kWheelDiameter = 6_in;
+constexpr double kEncoderDistancePerPulse =
+    // Assumes the encoders are directly mounted on the wheel shafts
+    (kWheelDiameter.to<double>() * wpi::math::pi) /
+    static_cast<double>(kEncoderCPR);
+
+// These are example values only - DO NOT USE THESE FOR YOUR OWN ROBOT!
+// These characterization values MUST be determined either experimentally or
+// theoretically for *your* robot's drive. The Robot Characterization
+// Toolsuite provides a convenient tool for obtaining these values for your
+// robot.
+constexpr auto ks = 0.22_V;
+constexpr auto kv = 1.98 * 1_V * 1_s / 1_m;
+constexpr auto ka = 0.2 * 1_V * 1_s * 1_s / 1_m;
+
+constexpr auto kvAngular = 1.5 * 1_V * 1_s / 1_rad;
+constexpr auto kaAngular = 0.3 * 1_V * 1_s * 1_s / 1_rad;
+
+extern const frc::LinearSystem<2, 2, 2> kDrivetrainPlant;
+
+// Example values only -- use what's on your physical robot!
+constexpr auto kDrivetrainGearbox = frc::DCMotor::CIM(2);
+constexpr auto kDrivetrainGearing = 8.0;
+
+// Example value only - as above, this must be tuned for your drive!
+constexpr double kPDriveVel = 8.5;
+}  // namespace DriveConstants
+
+namespace AutoConstants {
+constexpr auto kMaxSpeed = 3_mps;
+constexpr auto kMaxAcceleration = 3_mps_sq;
+
+// Reasonable baseline values for a RAMSETE follower in units of meters and
+// seconds
+constexpr double kRamseteB = 2;
+constexpr double kRamseteZeta = 0.7;
+}  // namespace AutoConstants
+
+namespace OIConstants {
+constexpr int kDriverControllerPort = 1;
+}  // namespace OIConstants