ROS Noetic Robot Motor Control & Teleoperation (Keyboard + Xbox Controller)

This guide documents the complete real-world process I followed to drive a 4WD robot using ROS Noetic on Raspberry Pi. It starts after installing Ubuntu 20.04 and ROS Noetic and ends with smooth motor control using both keyboard and Xbox Wireless Controller.

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1. Hardware & Software Used

Hardware

• Raspberry Pi (Ubuntu 20.04)
• 4WD Robot Chassis
• L298N Motor Driver
• Xbox Wireless Controller (Bluetooth)

Software

• Ubuntu 20.04 (Focal)
• ROS Noetic
• Python 3
• pygame
• BlueZ (Bluetooth)

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2. ROS Workspace Setup

mkdir -p ~/catkin_ws/src
cd ~/catkin_ws
catkin_make
source devel/setup.bash

Add this to ~/.bashrc so ROS always loads:

source /opt/ros/noetic/setup.bash
source ~/catkin_ws/devel/setup.bash

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3. Motor Driver ROS Node (Forward / Backward / Left / Right)

This node converts /cmd_vel into GPIO signals for an L298N motor driver.

#!/usr/bin/env python3
import rospy
from geometry_msgs.msg import Twist
import RPi.GPIO as GPIO

ENA = 18
IN1 = 17
IN2 = 27
ENB = 13
IN3 = 22
IN4 = 23

GPIO.setmode(GPIO.BCM)
GPIO.setwarnings(False)

for pin in [ENA, IN1, IN2, ENB, IN3, IN4]:
    GPIO.setup(pin, GPIO.OUT)

pwmA = GPIO.PWM(ENA, 100)
pwmB = GPIO.PWM(ENB, 100)
pwmA.start(0)
pwmB.start(0)

def stop():
    for pin in [IN1, IN2, IN3, IN4]:
        GPIO.output(pin, GPIO.LOW)
    pwmA.ChangeDutyCycle(0)
    pwmB.ChangeDutyCycle(0)

def callback(msg):
    linear = msg.linear.x
    angular = msg.angular.z

    left = linear - angular
    right = linear + angular

    GPIO.output(IN1, GPIO.HIGH if left > 0 else GPIO.LOW)
    GPIO.output(IN2, GPIO.LOW if left > 0 else GPIO.HIGH)

    GPIO.output(IN3, GPIO.HIGH if right > 0 else GPIO.LOW)
    GPIO.output(IN4, GPIO.LOW if right > 0 else GPIO.HIGH)

    pwmA.ChangeDutyCycle(min(abs(left) * 100, 100))
    pwmB.ChangeDutyCycle(min(abs(right) * 100, 100))

rospy.init_node("motor_driver_node")
rospy.Subscriber("/cmd_vel", Twist, callback)
rospy.on_shutdown(stop)
rospy.spin()

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4. Keyboard Control Node (Day 4)

This node allows robot control using keyboard keys:

• W → Forward
• S → Backward
• A → Left
• D → Right

#!/usr/bin/env python3
import rospy
from geometry_msgs.msg import Twist
import sys, select, termios, tty

move = {
    'w': (1, 0),
    's': (-1, 0),
    'a': (0, 1),
    'd': (0, -1)
}

def getKey():
    tty.setraw(sys.stdin.fileno())
    r, _, _ = select.select([sys.stdin], [], [], 0.1)
    key = sys.stdin.read(1) if r else ''
    termios.tcsetattr(sys.stdin, termios.TCSADRAIN, settings)
    return key

settings = termios.tcgetattr(sys.stdin)

rospy.init_node("keyboard_teleop")
pub = rospy.Publisher("/cmd_vel", Twist, queue_size=1)
twist = Twist()

try:
    while not rospy.is_shutdown():
        key = getKey()
        if key in move:
            twist.linear.x = move[key][0]
            twist.angular.z = move[key][1]
        else:
            twist.linear.x = 0
            twist.angular.z = 0
        pub.publish(twist)
finally:
    twist.linear.x = 0
    twist.angular.z = 0
    pub.publish(twist)

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5. Xbox Wireless Controller (Bluetooth Pairing)

bluetoothctl
power on
agent on
default-agent
scan on

Put controller into pairing mode (Xbox + Pair button):

pair XX:XX:XX:XX:XX:XX
trust XX:XX:XX:XX:XX:XX
connect XX:XX:XX:XX:XX:XX

LED becomes solid → paired.

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6. Xbox Teleop (Headless Fix)

Because Raspberry Pi runs headless, pygame needs a dummy display.

import os
os.environ["SDL_VIDEODRIVER"] = "dummy"

Initialize pygame safely:

pygame.init()
pygame.display.init()
pygame.display.set_mode((1,1))
pygame.joystick.init()

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7. Running the System

Terminal 1

roscore

Terminal 2

rosrun my_4wd_robot motor_driver_node.py

Terminal 3 (Keyboard)

rosrun keyboard_teleop keyboard_teleop.py

Terminal 3 (Xbox)

rosrun xbox_teleop xbox_teleop_node.py

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8. Validation

rostopic echo /cmd_vel

Joystick or keyboard movement should reflect in velocity values.

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9. Final Result

• Stable Bluetooth
• Smooth motor control
• Keyboard + Xbox working
• Headless-safe ROS setup

The robot drives like butter.

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10. Next Upgrades

• Deadman safety switch
• Speed modes
• Launch files
• Auto-start on boot

This guide documents a real debugging journey, not theory.