[robotpy][examples] Split examples and snippets (#8944)

This also updates the bazel scripts to behave more like the C++ and Java
examples, and updates the copybara scripts to be able to sync up
`mostrobotpy`

robotpyExamples/examples/SimpleDifferentialDriveSimulation/drivetrain.py

@@ -0,0 +1,162 @@
+#
+# 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.
+#
+
+import math
+
+import wpilib
+import wpilib.simulation
+import wpimath
+
+
+class Drivetrain:
+    """Represents a differential drive style drivetrain."""
+
+    # 3 meters per second.
+    kMaxVelocity = 3.0
+    # 1/2 rotation per second.
+    kMaxAngularVelocity = math.pi
+
+    kTrackwidth = 0.381 * 2
+    kWheelRadius = 0.0508
+    kEncoderResolution = -4096
+
+    def __init__(self) -> None:
+        self.leftLeader = wpilib.PWMSparkMax(1)
+        self.leftFollower = wpilib.PWMSparkMax(2)
+        self.rightLeader = wpilib.PWMSparkMax(3)
+        self.rightFollower = wpilib.PWMSparkMax(4)
+
+        self.leftEncoder = wpilib.Encoder(0, 1)
+        self.rightEncoder = wpilib.Encoder(2, 3)
+
+        self.leftPIDController = wpimath.PIDController(8.5, 0, 0)
+        self.rightPIDController = wpimath.PIDController(8.5, 0, 0)
+
+        self.imu = wpilib.OnboardIMU(wpilib.OnboardIMU.MountOrientation.FLAT)
+
+        self.kinematics = wpimath.DifferentialDriveKinematics(self.kTrackwidth)
+        self.odometry = wpimath.DifferentialDriveOdometry(
+            self.imu.getRotation2d(),
+            self.leftEncoder.getDistance(),
+            self.rightEncoder.getDistance(),
+        )
+
+        # Gains are for example purposes only - must be determined for your own
+        # robot!
+        self.feedforward = wpimath.SimpleMotorFeedforwardMeters(1, 3)
+
+        # Simulation classes help us simulate our robot
+        self.leftEncoderSim = wpilib.simulation.EncoderSim(self.leftEncoder)
+        self.rightEncoderSim = wpilib.simulation.EncoderSim(self.rightEncoder)
+        self.fieldSim = wpilib.Field2d()
+        self.drivetrainSystem = wpimath.Models.differentialDriveFromSysId(
+            1.98, 0.2, 1.5, 0.3
+        )
+        self.drivetrainSimulator = wpilib.simulation.DifferentialDrivetrainSim(
+            self.drivetrainSystem,
+            self.kTrackwidth,
+            wpimath.DCMotor.CIM(2),
+            8,
+            self.kWheelRadius,
+        )
+
+        # Subsystem constructor.
+        self.leftLeader.addFollower(self.leftFollower)
+        self.rightLeader.addFollower(self.rightFollower)
+
+        # We need to invert one side of the drivetrain so that positive voltages
+        # result in both sides moving forward. Depending on how your robot's
+        # gearbox is constructed, you might have to invert the left side instead.
+        self.rightLeader.setInverted(True)
+
+        # 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.
+        self.leftEncoder.setDistancePerPulse(
+            2 * math.pi * self.kWheelRadius / self.kEncoderResolution
+        )
+        self.rightEncoder.setDistancePerPulse(
+            2 * math.pi * self.kWheelRadius / self.kEncoderResolution
+        )
+
+        self.leftEncoder.reset()
+        self.rightEncoder.reset()
+
+        self.rightLeader.setInverted(True)
+        wpilib.SmartDashboard.putData("Field", self.fieldSim)
+
+    def setVelocities(
+        self, velocities: wpimath.DifferentialDriveWheelVelocities
+    ) -> None:
+        """Sets velocities to the drivetrain motors."""
+        leftFeedforward = self.feedforward.calculate(velocities.left)
+        rightFeedforward = self.feedforward.calculate(velocities.right)
+        leftOutput = self.leftPIDController.calculate(
+            self.leftEncoder.getRate(), velocities.left
+        )
+        rightOutput = self.rightPIDController.calculate(
+            self.rightEncoder.getRate(), velocities.right
+        )
+
+        self.leftLeader.setVoltage(leftOutput + leftFeedforward)
+        self.rightLeader.setVoltage(rightOutput + rightFeedforward)
+
+    def drive(self, xVelocity: float, rot: float) -> None:
+        """Controls the robot using arcade drive.
+
+        :param xVelocity: the velocity for the x axis
+        :param rot: the rotation
+        """
+        self.setVelocities(
+            self.kinematics.toWheelVelocities(
+                wpimath.ChassisVelocities(xVelocity, 0, rot)
+            )
+        )
+
+    def updateOdometry(self) -> None:
+        """Update robot odometry."""
+        self.odometry.update(
+            self.imu.getRotation2d(),
+            self.leftEncoder.getDistance(),
+            self.rightEncoder.getDistance(),
+        )
+
+    def resetOdometry(self, pose: wpimath.Pose2d) -> None:
+        """Resets robot odometry."""
+        self.drivetrainSimulator.setPose(pose)
+        self.odometry.resetPosition(
+            self.imu.getRotation2d(),
+            self.leftEncoder.getDistance(),
+            self.rightEncoder.getDistance(),
+            pose,
+        )
+
+    def getPose(self) -> wpimath.Pose2d:
+        """Check the current robot pose."""
+        return self.odometry.getPose()
+
+    def simulationPeriodic(self) -> None:
+        """Update our simulation. This should be run every robot loop in simulation."""
+        # To update our simulation, we set motor voltage inputs, update the
+        # simulation, and write the simulated positions and velocities to our
+        # simulated encoder and gyro. We negate the right side so that positive
+        # voltages make the right side move forward.
+        self.drivetrainSimulator.setInputs(
+            self.leftLeader.getThrottle() * wpilib.RobotController.getInputVoltage(),
+            self.rightLeader.getThrottle() * wpilib.RobotController.getInputVoltage(),
+        )
+        self.drivetrainSimulator.update(0.02)
+
+        self.leftEncoderSim.setDistance(self.drivetrainSimulator.getLeftPosition())
+        self.leftEncoderSim.setRate(self.drivetrainSimulator.getLeftVelocity())
+        self.rightEncoderSim.setDistance(self.drivetrainSimulator.getRightPosition())
+        self.rightEncoderSim.setRate(self.drivetrainSimulator.getRightVelocity())
+        # self.gyroSim.setAngle(-self.drivetrainSimulator.getHeading().getDegrees())
+
+    def periodic(self) -> None:
+        """Update odometry - this should be run every robot loop."""
+        self.updateOdometry()
+        self.fieldSim.setRobotPose(self.odometry.getPose())