Ultimate 4WD Robot Teleoperation Guide

This guide takes you from zero to a fully working 4WD robot using Raspberry Pi + ROS Noetic, controlled via keyboard or Xbox Controller with speed modes and auto-start capability.

---

Day 1: Raspberry Pi Setup

• Install Ubuntu 20.04 on Raspberry Pi using Raspberry Pi Imager.
• Enable SSH:

  sudo systemctl enable ssh
  sudo systemctl start ssh

• Update packages:

  sudo apt update
  sudo apt upgrade -y

• Install Python and essential tools:

  sudo apt install python3-pip python3-venv git -y

---

Day 2: Installing ROS Noetic

• Add ROS repository:

  sudo sh -c 'echo "deb http://packages.ros.org/ros/ubuntu focal main" > /etc/apt/sources.list.d/ros-latest.list'
  sudo apt install curl -y
  curl -s https://raw.githubusercontent.com/ros/rosdistro/master/ros.asc | sudo apt-key add -

• Install ROS Noetic Desktop Full:

  sudo apt update
  sudo apt install ros-noetic-desktop-full -y

• Initialize rosdep:

  sudo rosdep init
  rosdep update

• Add ROS setup to bash:

  echo "source /opt/ros/noetic/setup.bash" >> ~/.bashrc
  source ~/.bashrc

---

Day 3: Motor Driver Node

• Create workspace:

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

• Create motor driver node:

  cd ~/catkin_ws/src
  mkdir my_4wd_robot
  cd my_4wd_robot
  mkdir scripts
  nano scripts/motor_driver_node.py

  Paste the code:

  #!/usr/bin/env python3
  import rospy
  from geometry_msgs.msg import Twist
  import RPi.GPIO as GPIO
  
  LEFT_FORWARD = 17
  LEFT_BACKWARD = 27
  RIGHT_FORWARD = 22
  RIGHT_BACKWARD = 23
  
  GPIO.setmode(GPIO.BCM)
  GPIO.setup([LEFT_FORWARD, LEFT_BACKWARD, RIGHT_FORWARD, RIGHT_BACKWARD], GPIO.OUT)
  
  def move(linear, angular):
      if linear > 0:
          GPIO.output(LEFT_FORWARD, True)
          GPIO.output(RIGHT_FORWARD, True)
      elif linear < 0:
          GPIO.output(LEFT_BACKWARD, True)
          GPIO.output(RIGHT_BACKWARD, True)
      else:
          GPIO.output([LEFT_FORWARD, LEFT_BACKWARD, RIGHT_FORWARD, RIGHT_BACKWARD], False)
  
  def callback(msg):
      linear = msg.linear.x
      angular = msg.angular.z
      move(linear, angular)
  
  rospy.init_node('motor_driver_node')
  sub = rospy.Subscriber('/cmd_vel', Twist, callback)
  rospy.spin()

• Make executable:

  chmod +x scripts/motor_driver_node.py

• Test node:

  roscore
  rosrun my_4wd_robot motor_driver_node.py

---

Day 4: Keyboard Teleoperation

• Install keyboard teleop:

  cd ~/catkin_ws/src
  git clone https://github.com/ros-teleop/teleop_twist_keyboard.git
  cd teleop_twist_keyboard
  sudo python3 setup.py install

• Run keyboard teleop:

  rosrun teleop_twist_keyboard teleop_twist_keyboard.py
  rostopic echo /cmd_vel

• Robot moves with arrow keys. Forward/backward and left/right verified.

---

Day 5: Xbox Controller Teleoperation

• Pair Xbox controller via Bluetooth:

  bluetoothctl
  power on
  agent on
  default-agent
  scan on
  pair XX:XX:XX:XX:XX:XX
  trust XX:XX:XX:XX:XX:XX
  connect XX:XX:XX:XX:XX:XX
  quit

• Install xpadneo driver:

  sudo apt install dkms
  sudo modprobe hid_xpadneo

• Create xbox teleop node and paste full Day 5 code (headless-safe, speed modes, sensitivity):

  cd ~/catkin_ws/src/xbox_teleop/src
  nano xbox_teleop_node.py
  chmod +x xbox_teleop_node.py

• Test launch:

  roslaunch my_4wd_robot robot_bringup.launch
  rosnode list
  rostopic echo /cmd_vel

---

Day 6: Auto-Connect & Production Hardening

• Create launch file:

  nano ~/catkin_ws/src/my_4wd_robot/launch/robot_bringup.launch

  Paste:

  <launch>
    <node pkg="my_4wd_robot" type="motor_driver_node.py" name="motor_driver_node" output="screen" />
    <node pkg="xbox_teleop" type="xbox_teleop_node.py" name="xbox_teleop" output="screen" />
  </launch>

• Rebuild workspace:

  cd ~/catkin_ws
  catkin_make
  source devel/setup.bash

• Create systemd service for auto-start:

  sudo nano /etc/systemd/system/robot_bringup.service

  Paste:

  [Unit]
  Description=Robot Auto Bringup
  After=network.target bluetooth.target
  
  [Service]
  Type=simple
  User=ubuntu
  WorkingDirectory=/home/ubuntu/catkin_ws
  ExecStart=/opt/ros/noetic/bin/roslaunch my_4wd_robot robot_bringup.launch
  Restart=always
  Environment="DISPLAY=:0"
  
  [Install]
  WantedBy=multi-user.target

• Enable & start:

  sudo systemctl daemon-reload
  sudo systemctl enable robot_bringup.service
  sudo systemctl start robot_bringup.service

• Verify:

  rosnode list
  rostopic echo /cmd_vel

  Joystick forward/backward → moves Left/right → correct turns A/B/Y → speed modes More pressure → faster movement

---

Next Steps

• Add deadman button (robot moves only while pressed)
• Auto-stop on controller disconnect
• Status LED or log
• Tune speed modes and joystick sensitivity

Congratulations! You now have a fully working 4WD robot with:

• Keyboard & Xbox controller control
• Speed modes & sensitivity curves
• Auto-start after power ON
• Ready for production-level testing with safety improvements