[examples] Add differential drive snippets (#8927)

Shows tank, arcade, and curvature for wpilib-docs

wpilibjExamples/example_projects.bzl

@@ -59,6 +59,7 @@ SNIPPET_FOLDERS = [
     "analogpotentiometer",
     "apriltagsvision",
     "canpdp",
+    "differentialdrive",
     "digitalcommunication",
     "digitalinput",
     "dutycycleencoder",

wpilibjExamples/src/main/java/org/wpilib/snippets/differentialdrive/Robot.java

@@ -0,0 +1,44 @@
+// 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.
+
+package org.wpilib.snippets.differentialdrive;
+
+import org.wpilib.drive.DifferentialDrive;
+import org.wpilib.driverstation.Gamepad;
+import org.wpilib.framework.TimedRobot;
+import org.wpilib.hardware.motor.PWMSparkMax;
+
+/**
+ * DifferentialDrive snippets for wpilib-docs. Runs the motors with tank drive, arcade drive, and
+ * curvature drive.
+ * https://docs.wpilib.org/en/stable/docs/software/hardware-apis/motors/wpi-drive-classes.html
+ */
+public class Robot extends TimedRobot {
+  private final PWMSparkMax leftMotor = new PWMSparkMax(0);
+  private final PWMSparkMax rightMotor = new PWMSparkMax(1);
+  private final DifferentialDrive robotDrive =
+      new DifferentialDrive(leftMotor::setThrottle, rightMotor::setThrottle);
+  private final Gamepad driverController = new Gamepad(0);
+
+  /** Called once at the beginning of the robot program. */
+  public Robot() {
+    // 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.
+    rightMotor.setInverted(true);
+  }
+
+  @Override
+  public void teleopPeriodic() {
+    // Tank drive with a given left and right rates
+    robotDrive.tankDrive(-driverController.getLeftY(), -driverController.getRightY());
+    // Arcade drive with a given forward and turn rate
+    robotDrive.arcadeDrive(-driverController.getLeftY(), -driverController.getLeftX());
+    // Curvature drive with a given forward and turn rate, as well as a button for turning in-place.
+    robotDrive.curvatureDrive(
+        -driverController.getLeftY(),
+        -driverController.getLeftX(),
+        driverController.getFaceUpButton());
+  }
+}

wpilibjExamples/src/main/java/org/wpilib/snippets/snippets.json

@@ -332,5 +332,16 @@
     "foldername": "solenoid",
     "gradlebase": "java",
     "robotclass": "Robot"
+  },
+  {
+    "name": "Differential Drive",
+    "description": "Show differential drive control with tank, arcade, and curvature drive in teleop",
+    "tags": [
+      "Differential Drive",
+      "Gamepad"
+    ],
+    "foldername": "differentialdrive",
+    "gradlebase": "java",
+    "robotclass": "Robot"
   }
 ]