Add mecanum-bot example (#92)

Author: fletch3555

mecanum-bot/drivetrain.py

@@ -0,0 +1,133 @@
+#
+# 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 wpilib.drive
+import wpimath.controller
+import wpimath.geometry
+from wpimath.kinematics import ChassisSpeeds
+import wpimath.units
+
+import math
+
+
+class Drivetrain:
+    """Represents a differential drive style drivetrain."""
+
+    kMaxSpeed = 3.0  # 3 meters per second
+    kMaxAngularSpeed = math.pi  # 1/2 rotation per second
+
+    def __init__(self):
+        self.frontLeftMotor = wpilib.PWMSparkMax(1)
+        self.frontRightMotor = wpilib.PWMSparkMax(2)
+        self.backLeftMotor = wpilib.PWMSparkMax(3)
+        self.backRightMotor = wpilib.PWMSparkMax(4)
+
+        self.frontLeftEncoder = wpilib.Encoder(0, 1)
+        self.frontRightEncoder = wpilib.Encoder(2, 3)
+        self.backLeftEncoder = wpilib.Encoder(4, 5)
+        self.backRightEncoder = wpilib.Encoder(6, 7)
+
+        frontLeftLocation = wpimath.geometry.Translation2d(0.381, 0.381)
+        frontRightLocation = wpimath.geometry.Translation2d(0.381, -0.381)
+        backLeftLocation = wpimath.geometry.Translation2d(-0.381, 0.381)
+        backRightLocation = wpimath.geometry.Translation2d(-0.381, -0.381)
+
+        self.frontLeftPIDController = wpimath.controller.PIDController(1, 0, 0)
+        self.frontRightPIDController = wpimath.controller.PIDController(1, 0, 0)
+        self.backLeftPIDController = wpimath.controller.PIDController(1, 0, 0)
+        self.backRightPIDController = wpimath.controller.PIDController(1, 0, 0)
+
+        self.gyro = wpilib.AnalogGyro(0)
+
+        self.kinematics = wpimath.kinematics.MecanumDriveKinematics(
+            frontLeftLocation, frontRightLocation, backLeftLocation, backRightLocation
+        )
+
+        self.odometry = wpimath.kinematics.MecanumDriveOdometry(
+            self.kinematics, self.gyro.getRotation2d(), self.getCurrentDistances()
+        )
+
+        # Gains are for example purposes only - must be determined for your own robot!
+        self.feedforward = wpimath.controller.SimpleMotorFeedforwardMeters(1, 3)
+
+        self.gyro.reset()
+
+        # 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.frontRightMotor.setInverted(True)
+        self.backRightMotor.setInverted(True)
+
+    def getCurrentState(self) -> wpimath.kinematics.MecanumDriveWheelSpeeds:
+        """Returns the current state of the drivetrain."""
+        return wpimath.kinematics.MecanumDriveWheelSpeeds(
+            self.frontLeftEncoder.getRate(),
+            self.frontRightEncoder.getRate(),
+            self.backLeftEncoder.getRate(),
+            self.backRightEncoder.getRate(),
+        )
+
+    def getCurrentDistances(self) -> wpimath.kinematics.MecanumDriveWheelPositions:
+        """Returns the current distances measured by the drivetrain."""
+        pos = wpimath.kinematics.MecanumDriveWheelPositions()
+
+        pos.frontLeft = self.frontLeftEncoder.getDistance()
+        pos.frontRight = self.frontRightEncoder.getDistance()
+        pos.rearLeft = self.backLeftEncoder.getDistance()
+        pos.rearRight = self.backRightEncoder.getDistance()
+
+        return pos
+
+    def setSpeeds(self, speeds: wpimath.kinematics.MecanumDriveWheelSpeeds):
+        """Sets the desired speeds for each wheel."""
+        frontLeftFeedforward = self.feedforward.calculate(speeds.frontLeft)
+        frontRightFeedforward = self.feedforward.calculate(speeds.frontRight)
+        backLeftFeedforward = self.feedforward.calculate(speeds.rearLeft)
+        backRightFeedforward = self.feedforward.calculate(speeds.rearRight)
+
+        frontLeftOutput = self.frontLeftPIDController.calculate(
+            self.frontLeftEncoder.getRate(), speeds.frontLeft
+        )
+        frontRightOutput = self.frontRightPIDController.calculate(
+            self.frontRightEncoder.getRate(), speeds.frontRight
+        )
+        backLeftOutput = self.frontLeftPIDController.calculate(
+            self.backLeftEncoder.getRate(), speeds.rearLeft
+        )
+        backRightOutput = self.frontRightPIDController.calculate(
+            self.backRightEncoder.getRate(), speeds.rearRight
+        )
+
+        self.frontLeftMotor.setVoltage(frontLeftOutput + frontLeftFeedforward)
+        self.frontRightMotor.setVoltage(frontRightOutput + frontRightFeedforward)
+        self.backLeftMotor.setVoltage(backLeftOutput + backLeftFeedforward)
+        self.backRightMotor.setVoltage(backRightOutput + backRightFeedforward)
+
+    def drive(
+        self,
+        xSpeed: float,
+        ySpeed: float,
+        rot: float,
+        fieldRelative: bool,
+        periodSeconds: float,
+    ):
+        """Method to drive the robot using joystick info."""
+        mecanumDriveWheelSpeeds = self.kinematics.toWheelSpeeds(
+            ChassisSpeeds.discretize(
+                ChassisSpeeds.fromFieldRelativeSpeeds(
+                    xSpeed, ySpeed, rot, self.gyro.getRotation2d()
+                )
+                if fieldRelative
+                else ChassisSpeeds(xSpeed, ySpeed, rot),
+                periodSeconds,
+            )
+        )
+        mecanumDriveWheelSpeeds.desaturate(self.kMaxSpeed)
+        self.setSpeeds(mecanumDriveWheelSpeeds)
+
+    def updateOdometry(self):
+        """Updates the field-relative position."""
+        self.odometry.update(self.gyro.getRotation2d(), self.getCurrentDistances())

mecanum-bot/robot.py

@@ -0,0 +1,61 @@
+#!/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 wpilib
+import wpilib.drive
+import wpimath.filter
+
+from drivetrain import Drivetrain
+
+
+class MyRobot(wpilib.TimedRobot):
+    def robotInit(self):
+        self.controller = wpilib.XboxController(0)
+        self.mecanum = Drivetrain()
+
+        # Slew rate limiters to make joystick inputs more gentle; 1/3 sec from 0 to 1.
+        self.xspeedLimiter = wpimath.filter.SlewRateLimiter(3)
+        self.yspeedLimiter = wpimath.filter.SlewRateLimiter(3)
+        self.rotLimiter = wpimath.filter.SlewRateLimiter(3)
+
+    def autonomousPeriodic(self):
+        self._driveWithJoystick(False)
+        self.mecanum.updateOdometry()
+
+    def teleopPeriodic(self):
+        self._driveWithJoystick(True)
+
+    def _driveWithJoystick(self, fieldRelative: bool):
+        # Get the x speed. We are inverting this because Xbox controllers return
+        # negative values when we push forward.
+        xSpeed = (
+            -self.xspeedLimiter.calculate(self.controller.getLeftY())
+            * Drivetrain.kMaxSpeed
+        )
+
+        # Get the y speed or sideways/strafe speed. We are inverting this because
+        # we want a positive value when we pull to the left. Xbox controllers
+        # return positive values when you pull to the right by default.
+        ySpeed = (
+            -self.yspeedLimiter.calculate(self.controller.getLeftX())
+            * Drivetrain.kMaxSpeed
+        )
+
+        # 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.kMaxAngularSpeed
+        )
+
+        self.mecanum.drive(xSpeed, ySpeed, rot, fieldRelative, self.getPeriod())
+
+
+if __name__ == "__main__":
+    wpilib.run(MyRobot)

run_tests.sh

@@ -29,6 +29,7 @@ BASE_TESTS="
   hid-rumble
   i2c-communication
   magicbot-simple
+  mecanum-bot
   mecanum-drive
   mecanum-driveXbox
   mechanism2d