[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/DifferentialDriveBot/drivetrain.py

@@ -0,0 +1,109 @@
+#
+# 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 wpimath
+
+
+class Drivetrain:
+    """Represents a differential drive style drivetrain."""
+
+    kMaxVelocity = 3.0  # meters per second
+    kMaxAngularVelocity = 2 * math.pi  # one rotation per second
+
+    kTrackwidth = 0.381 * 2  # meters
+    kWheelRadius = 0.0508  # meters
+    kEncoderResolution = 4096  # counts per revolution
+
+    def __init__(self) -> None:
+        self.leftLeader = wpilib.PWMSparkMax(1)
+        self.leftFollower = wpilib.PWMSparkMax(2)
+        self.rightLeader = wpilib.PWMSparkMax(3)
+        self.rightFollower = wpilib.PWMSparkMax(4)
+
+        # Make sure both motors for each side are in the same group
+        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)
+
+        self.leftEncoder = wpilib.Encoder(0, 1)
+        self.rightEncoder = wpilib.Encoder(2, 3)
+
+        self.imu = wpilib.OnboardIMU(wpilib.OnboardIMU.MountOrientation.FLAT)
+
+        self.leftPIDController = wpimath.PIDController(1.0, 0.0, 0.0)
+        self.rightPIDController = wpimath.PIDController(1.0, 0.0, 0.0)
+
+        self.kinematics = wpimath.DifferentialDriveKinematics(self.kTrackwidth)
+
+        # Gains are for example purposes only - must be determined for your own robot!
+        self.feedforward = wpimath.SimpleMotorFeedforwardMeters(1, 3)
+
+        self.imu.resetYaw()
+
+        # 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.odometry = wpimath.DifferentialDriveOdometry(
+            self.imu.getRotation2d(),
+            self.leftEncoder.getDistance(),
+            self.rightEncoder.getDistance(),
+        )
+
+    def setVelocities(
+        self, velocities: wpimath.DifferentialDriveWheelVelocities
+    ) -> None:
+        """Sets the desired wheel velocities.
+
+        :param velocities: The desired wheel velocities.
+        """
+        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
+        )
+
+        # Controls the left and right sides of the robot using the calculated outputs
+        self.leftLeader.setVoltage(leftOutput + leftFeedforward)
+        self.rightLeader.setVoltage(rightOutput + rightFeedforward)
+
+    def drive(self, xVelocity: float, rot: float) -> None:
+        """Drives the robot with the given linear velocity and angular velocity.
+
+        :param xVelocity: Linear velocity in m/s.
+        :param rot: Angular velocity in rad/s.
+        """
+        wheelVelocities = self.kinematics.toWheelVelocities(
+            wpimath.ChassisVelocities(xVelocity, 0.0, rot)
+        )
+        self.setVelocities(wheelVelocities)
+
+    def updateOdometry(self) -> None:
+        """Updates the field-relative position."""
+        self.odometry.update(
+            self.imu.getRotation2d(),
+            self.leftEncoder.getDistance(),
+            self.rightEncoder.getDistance(),
+        )

robotpyExamples/examples/DifferentialDriveBot/robot.py

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+#!/usr/bin/env python3
+#
+# 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 wpimath
+import wpilib
+
+from drivetrain import Drivetrain
+
+
+class MyRobot(wpilib.TimedRobot):
+    def __init__(self) -> None:
+        super().__init__()
+
+        self.controller = wpilib.NiDsXboxController(0)
+        self.drive = Drivetrain()
+
+        # Slew rate limiters to make joystick inputs more gentle; 1/3 sec from 0 to 1.
+        self.velocityLimiter = wpimath.SlewRateLimiter(3)
+        self.rotLimiter = wpimath.SlewRateLimiter(3)
+
+    def autonomousPeriodic(self) -> None:
+        self.teleopPeriodic()
+        self.drive.updateOdometry()
+
+    def teleopPeriodic(self) -> None:
+        # Get the x velocity. We are inverting this because Xbox controllers return
+        # negative values when we push forward.
+        xVelocity = (
+            -self.velocityLimiter.calculate(self.controller.getLeftY())
+            * Drivetrain.kMaxVelocity
+        )
+
+        # 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.
+        rot = (
+            -self.rotLimiter.calculate(self.controller.getRightX())
+            * Drivetrain.kMaxAngularVelocity
+        )
+
+        self.drive.drive(xVelocity, rot)