[wpimath] Replace Speeds with Velocities (#8479)

I left "free speed" alone since that's the technical term for it. In
general, velocity is a vector quantity, and speed is a magnitude (i.e.,
a strictly positive value).

This PR also replaces the speed verbiage in MotorController with duty
cycle.

Fixes #8423.

robotpyExamples/DifferentialDriveBot/drivetrain.py

@@ -12,8 +12,8 @@ import wpimath
 class Drivetrain:
     """Represents a differential drive style drivetrain."""
 
-    kMaxSpeed = 3.0  # meters per second
-    kMaxAngularSpeed = 2 * math.pi  # one rotation per second
+    kMaxVelocity = 3.0  # meters per second
+    kMaxAngularVelocity = 2 * math.pi  # one rotation per second
 
     kTrackwidth = 0.381 * 2  # meters
     kWheelRadius = 0.0508  # meters
@@ -68,35 +68,35 @@ class Drivetrain:
             self.rightEncoder.getDistance(),
         )
 
-    def setSpeeds(self, speeds: wpimath.DifferentialDriveWheelSpeeds) -> None:
-        """Sets the desired wheel speeds.
+    def setVelocities(self, velocities: wpimath.DifferentialDriveWheelVelocities) -> None:
+        """Sets the desired wheel velocities.
 
-        :param speeds: The desired wheel speeds.
+        :param velocities: The desired wheel velocities.
         """
-        leftFeedforward = self.feedforward.calculate(speeds.left)
-        rightFeedforward = self.feedforward.calculate(speeds.right)
+        leftFeedforward = self.feedforward.calculate(velocities.left)
+        rightFeedforward = self.feedforward.calculate(velocities.right)
 
         leftOutput = self.leftPIDController.calculate(
-            self.leftEncoder.getRate(), speeds.left
+            self.leftEncoder.getRate(), velocities.left
         )
         rightOutput = self.rightPIDController.calculate(
-            self.rightEncoder.getRate(), speeds.right
+            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, xSpeed: float, rot: float) -> None:
+    def drive(self, xVelocity: float, rot: float) -> None:
         """Drives the robot with the given linear velocity and angular velocity.
 
-        :param xSpeed: Linear velocity in m/s.
+        :param xVelocity: Linear velocity in m/s.
         :param rot: Angular velocity in rad/s.
         """
-        wheelSpeeds = self.kinematics.toWheelSpeeds(
-            wpimath.ChassisSpeeds(xSpeed, 0.0, rot)
+        wheelVelocities = self.kinematics.toWheelVelocities(
+            wpimath.ChassisVelocities(xVelocity, 0.0, rot)
         )
-        self.setSpeeds(wheelSpeeds)
+        self.setVelocities(wheelVelocities)
 
     def updateOdometry(self) -> None:
         """Updates the field-relative position."""

robotpyExamples/DifferentialDriveBot/robot.py

@@ -19,7 +19,7 @@ class MyRobot(wpilib.TimedRobot):
         self.drive = Drivetrain()
 
         # Slew rate limiters to make joystick inputs more gentle; 1/3 sec from 0 to 1.
-        self.speedLimiter = wpimath.SlewRateLimiter(3)
+        self.velocityLimiter = wpimath.SlewRateLimiter(3)
         self.rotLimiter = wpimath.SlewRateLimiter(3)
 
     def autonomousPeriodic(self) -> None:
@@ -27,11 +27,11 @@ class MyRobot(wpilib.TimedRobot):
         self.drive.updateOdometry()
 
     def teleopPeriodic(self) -> None:
-        # Get the x speed. We are inverting this because Xbox controllers return
+        # Get the x velocity. We are inverting this because Xbox controllers return
         # negative values when we push forward.
-        xSpeed = (
-            -self.speedLimiter.calculate(self.controller.getLeftY())
-            * Drivetrain.kMaxSpeed
+        xVelocity = (
+            -self.velocityLimiter.calculate(self.controller.getLeftY())
+            * Drivetrain.kMaxVelocity
         )
 
         # Get the rate of angular rotation. We are inverting this because we want a
@@ -40,7 +40,7 @@ class MyRobot(wpilib.TimedRobot):
         # the right by default.
         rot = (
             -self.rotLimiter.calculate(self.controller.getRightX())
-            * Drivetrain.kMaxAngularSpeed
+            * Drivetrain.kMaxAngularVelocity
         )
 
-        self.drive.drive(xSpeed, rot)
+        self.drive.drive(xVelocity, rot)