Mobile Robot Project (ROS 1 – Noetic)

Hardware Configuration

Mechanical Structure

• Drive System: Differential drive mobile robot
• Wheelbase: 187mm (center-to-center wheel distance)
• Wheel Specifications:
  • Diameter: 80mm (derived from radius = 0.04m)
  • Motorized wheels: 2
  • Encoder-equipped: Yes (330 CPR encoders)

Sensor Placement

• LiDAR: Top-mounted RPLidar (specific position to be detailed)
• Encoders: Attached to both drive wheels
• Additional Sensors: LED indicator on PIN 25 for system status

Key Mechanical Parameters

• Speed Characteristics:
  • PWM to Speed Ratio: 0.00335 (speed-to-pwm ratio for motor control)
  • Configurable maximum speed limits
• Construction: Rigid chassis with precision-mounted motors for accurate odometry

Electrical Components & Pin Connections

Core Computing Units

• Main Computer: NVIDIA Jetson Nano
  • Power Supply: 5V/4A
  • Network: WiFi/Ethernet (192.168.1.117)
• Microcontroller: Raspberry Pi Pico
  • Operating Voltage: 3.3V
  • Connected via USB to Jetson Nano

Motor System

• Motors: 2x DC Motors with Encoders
  • Operating Voltage: 12V
  • Encoder Resolution: 330 CPR
• Motor Driver: L298N Dual H-Bridge
  • Logic Voltage: 5V
  • Motor Supply: 12V

Sensors

• LiDAR: RPLidar A1
  • Interface: USB
  • Power: 5V
• Encoders: Quadrature Encoders
  • Resolution: 330 CPR
  • Operating Voltage: 3.3V

Pin Connection Table

Component	Pico Pin	Function
Left Motor A	GPIO 2	PWM Control
Left Motor B	GPIO 3	Direction
Right Motor A	GPIO 4	PWM Control
Right Motor B	GPIO 5	Direction
Left Encoder A	GPIO 6	Encoder Phase
Left Encoder B	GPIO 7	Encoder Phase
Right Encoder A	GPIO 8	Encoder Phase
Right Encoder B	GPIO 9	Encoder Phase
Status LED	GPIO 25	System Status

Power Distribution

• Main Battery: 4S LiPo Battery
  • Voltage: 14.8V nominal (16.8V fully charged)
  • Powers: Motors directly, converted for electronics
• Voltage Regulation:
  • Buck Converter: 14.8V → 5V @ 5A
    • Primary output: Jetson Nano power supply
    • Efficiency: >90%

Software Setup

Development Environment Setup

1. Jetson Nano Configuration

• Operating System: Ubuntu 20.04 LTS

• ROS Version: ROS 1 Noetic

• Network Configuration:

  # Add to /etc/hosts
  192.168.1.117   jet 
  192.168.1.110   pc

2. SSH Connection Setup

# From development PC
ssh jetson@192.168.1.117

# Test connection
ping jet
ping pc

# Set ROS environment variables
export ROS_MASTER_URI=http://jet:11311
export ROS_HOSTNAME=jet

(Add those to ~/.bashrc for persistence.)

3. ROS 1 Workspace Setup

# Create catkin workspace
mkdir -p ~/catkin_ws/src
cd ~/catkin_ws
catkin_make

# Source workspace
source devel/setup.bash

4. Raspberry Pi Pico Setup

# Install serial communication tools
sudo apt install python3-serial

# Verify Pico connection
ls /dev/ttyACM*

Debug Steps

1. Communication Check

ls -l /dev/ttyACM0
screen /dev/ttyACM0 115200

2. ROS 1 Network Check

# Test ROS 1 communication
rostopic list
rosnode list

# Check topic data
rostopic echo /cmd_vel
rostopic echo /odom

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Packages and Dependencies

Core ROS 1 Packages

• robot_core: hardware interface + motor control + odometry
• robot_description: URDF, meshes, TFs, visualization

External Dependencies

ROS 1 Packages

# Install required ROS 1 packages
sudo apt install ros-noetic-navigation \
                 ros-noetic-gmapping \
                 ros-noetic-amcl \
                 ros-noetic-rplidar-ros \
                 ros-noetic-joint-state-publisher \
                 ros-noetic-robot-state-publisher \
                 ros-noetic-tf2-tools

Python Dependencies

pip3 install numpy pyserial transforms3d scipy

Version Requirements

• ROS 1: Noetic
• Python: >= 3.8
• OpenCV: >= 4.2

---

How to Run & Debug

Initial Setup

1. Power Up Sequence

1. Connect 4S LiPo battery (check voltage > 14.4V)
2. Wait for Jetson Nano boot sequence (~30s)
3. Verify Pico connection:

ls -l /dev/ttyACM0
sudo chmod 666 /dev/ttyACM0  # If permission denied

2. Network Configuration

# Verify network setup
ip addr show
# Should show eth0 or wlan0 with IP 192.168.1.117

# Test PC connection
ping pc

Launch Sequence

1. Core System

# Terminal 1: Start ROS master
roscore

# Terminal 2: Launch core robot bringup
roslaunch robot_core bringup.launch

2. Sensors

# Terminal 3: Launch LiDAR
roslaunch rplidar_ros rplidar.launch

3. Navigation Stack

# Terminal 4: Start navigation
roslaunch robot_navigation move_base.launch

---

Common Debug Procedures

1. Motor Control Debug

rostopic pub /cmd_vel geometry_msgs/Twist "linear:
  x: 0.1
  y: 0.0
  z: 0.0
angular:
  x: 0.0
  y: 0.0
  z: 0.0"

2. Encoder Feedback

rostopic echo /wheel_ticks
rostopic echo /odom

3. TF Tree

rosrun tf view_frames
evince frames.pdf

---

Troubleshooting

Common Issues

1. Motor Not Responding

   • Check motor power (14.8V line)
   • Verify PWM signals using oscilloscope
   • Check encoder connections

2. Odometry Drift

   • Calibrate wheel radius parameter
   • Verify encoder resolution setting
   • Check wheel slippage

3. Navigation Issues

   • Verify TF tree:

    rosrun tf view_frames
    evince frames.pdf

   • Check costmap updates:

    rostopic echo /move_base/local_costmap/costmap
    rostopic echo /move_base/global_costmap/costmap

Note: Always check battery voltage under load - system may behave erratically at voltages below 14.4V

References & Credits

External Projects

• Nox Robot Project
  • Source: Nox_robot
  • Author: RBinsonB
  • License: MIT
  • Used for: Reference design and inspiration for differential drive implementation
  • Key components adapted:
    • Motor control architecture
    • Odometry calculation methods
    • ROS 1 node structure

Hardware References

• RPLidar A1 Manual: Slamtec Documentation
• Raspberry Pi Pico Datasheet: Raspberry Pi Documentation
• L298N Motor Driver: Component Datasheet