[examples] Add flywheel bang-bang controller example (#4071)

Co-authored-by: Tyler Veness <calcmogul@gmail.com>

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

@@ -0,0 +1,104 @@
+// Copyright (c) FIRST and other WPILib contributors.
+// Open Source Software; you can modify and/or share it under the terms of
+// the WPILib BSD license file in the root directory of this project.
+
+#include <frc/Encoder.h>
+#include <frc/Joystick.h>
+#include <frc/TimedRobot.h>
+#include <frc/controller/BangBangController.h>
+#include <frc/controller/SimpleMotorFeedforward.h>
+#include <frc/motorcontrol/PWMSparkMax.h>
+#include <frc/simulation/EncoderSim.h>
+#include <frc/simulation/FlywheelSim.h>
+#include <frc/smartdashboard/SmartDashboard.h>
+#include <units/moment_of_inertia.h>
+
+/**
+ * This is a sample program to demonstrate the use of a BangBangController with
+ * a flywheel to control speed.
+ */
+class Robot : public frc::TimedRobot {
+ public:
+  /**
+   * Controls flywheel to a set speed (RPM) controlled by a joystick.
+   */
+  void TeleopPeriodic() override {
+    // Scale setpoint value between 0 and maxSetpointValue
+    units::radians_per_second_t setpoint =
+        units::math::max(0_rpm, m_joystick.GetRawAxis(0) * kMaxSetpointValue);
+
+    // Set setpoint and measurement of the bang-bang controller
+    units::volt_t bangOutput =
+        m_bangBangControler.Calculate(m_encoder.GetRate(), setpoint.value()) *
+        12_V;
+
+    // Controls a motor with the output of the BangBang controller and a
+    // feedforward. The feedforward is reduced slightly to avoid overspeeding
+    // the shooter.
+    m_flywheelMotor.SetVoltage(bangOutput +
+                               0.9 * m_feedforward.Calculate(setpoint));
+  }
+
+  void RobotInit() override {
+    // Add bang-bang controler to SmartDashboard and networktables.
+    frc::SmartDashboard::PutData("BangBangControler", &m_bangBangControler);
+  }
+
+  /**
+   * Update our simulation. This should be run every robot loop in simulation.
+   */
+  void SimulationPeriodic() override {
+    // To update our simulation, we set motor voltage inputs, update the
+    // simulation, and write the simulated velocities to our simulated encoder
+    m_flywheelSim.SetInputVoltage(
+        m_flywheelMotor.Get() *
+        units::volt_t{frc::RobotController::GetInputVoltage()});
+    m_flywheelSim.Update(0.02_s);
+    m_encoderSim.SetRate(m_flywheelSim.GetAngularVelocity().value());
+  }
+
+ private:
+  static constexpr int kMotorPort = 0;
+  static constexpr int kEncoderAChannel = 0;
+  static constexpr int kEncoderBChannel = 1;
+
+  // Max setpoint for joystick control
+  static constexpr units::radians_per_second_t kMaxSetpointValue = 6000_rpm;
+
+  // Joystick to control setpoint
+  frc::Joystick m_joystick{0};
+
+  frc::PWMSparkMax m_flywheelMotor{kMotorPort};
+  frc::Encoder m_encoder{kEncoderAChannel, kEncoderBChannel};
+
+  frc::BangBangController m_bangBangControler;
+
+  // Gains are for example purposes only - must be determined for your own
+  // robot!
+  static constexpr units::volt_t kFlywheelKs = 0.0001_V;
+  static constexpr decltype(1_V / 1_rad_per_s) kFlywheelKv = 0.000195_V / 1_rpm;
+  static constexpr decltype(1_V / 1_rad_per_s_sq) kFlywheelKa =
+      0.0003_V / 1_rev_per_m_per_s;
+  frc::SimpleMotorFeedforward<units::radians> m_feedforward{
+      kFlywheelKs, kFlywheelKv, kFlywheelKa};
+
+  // Simulation classes help us simulate our robot
+
+  // Reduction between motors and encoder, as output over input. If the flywheel
+  // spins slower than the motors, this number should be greater than one.
+  static constexpr double kFlywheelGearing = 1.0;
+
+  // 1/2 MR²
+  static constexpr units::kilogram_square_meter_t kFlywheelMomentOfInertia =
+      0.5 * 1.5_lb * 4_in * 4_in;
+
+  frc::sim::FlywheelSim m_flywheelSim{frc::DCMotor::NEO(1), kFlywheelGearing,
+                                      kFlywheelMomentOfInertia};
+  frc::sim::EncoderSim m_encoderSim{m_encoder};
+};
+
+#ifndef RUNNING_FRC_TESTS
+int main() {
+  return frc::StartRobot<Robot>();
+}
+#endif

wpilibcExamples/src/main/cpp/examples/examples.json

@@ -865,5 +865,17 @@
     "foldername": "SwerveDrivePoseEstimator",
     "gradlebase": "cpp",
     "commandversion": 2
+  },
+  {
+    "name": "Flywheel BangBangController",
+    "description": "A sample program to demonstrate the use of a BangBangController with a flywheel to control RPM",
+    "tags": [
+      "Flywheel",
+      "Simulation",
+      "Joystick"
+    ],
+    "foldername": "FlywheelBangBangController",
+    "gradlebase": "cpp",
+    "commandversion": 2
   }
 ]