R2M 4WD Differential Drive Bot

Build Status

Branch	Build Status
main
dev

Project Overview

This repository implements a 4-wheel drive (4WD) differential drive robot based on the ROS2 Control framework. It extends the standard diffbot example from ros2_control_demos to support a 4WD configuration with ODrive motor controllers via CAN bus.

System components:

• Four-wheel drive with differential steering mechanism
• ODrive motor controllers with CAN communication protocol
• Docker containers for cross-architecture deployment
• ROS2 Control hardware interface implementation

Setup Instructions

git clone git@github.com:rwu-r2m/r2m_4wd_diff_drive.git && cd r2m_4wd_diff_drive

git submodule update --init

docker compose -f docker/build.yml build

Docker Compose Files

Docker configuration files:

• docker/build.yml: Docker image build configuration
• docker/docker-compose.yml: Simulation environment with mock hardware interfaces
• docker/docker-compose-hardware.yml: Hardware integration with physical motors
• docker/docker-compose-amd64.yml: AMD64 architecture configuration
• docker/docker-compose-arm64.yml: ARM64 architecture configuration

Start without real hardware:

Execute with simulated hardware interface:

# Grant X server access to the container (required for GUI applications)
xhost local:user

docker compose -f docker/docker-compose.yml up

If the simulation GUI fails to start, check that X server permissions are properly set. The xhost local:user command allows the Docker container to access your local X server for displaying GUI applications.

If you can an unauthorized error, try logging out from the docker registry

docker logout ghcr.io

Start with real hardware:

Connect to physical hardware components via CAN interface.

Hardware Setup

1. CAN interface connection: Connect the CAN2USB adapter to the diff-base

2. CAN interface configuration: Set up the Linux CAN interface

   sudo ip link set can0 up type can bitrate 250000

   If interface doesn't exist:

   sudo ip link add dev can0 type can bitrate 250000
   sudo ip link set can0 up

3. Power system initialization:

   • Connect power supply (bike cell)
   • Enable main power switch
   • Verify ODrive controller status LEDs

4. Launch hardware container:

   docker compose -f docker/docker-compose-hardware.yml up

Command Interface

To send velocity commands:

ros2 topic pub --rate 30 /cmd_vel geometry_msgs/msg/TwistStamped "
       twist:
         linear:
           x: 0.2
           y: 0.0
           z: 0.0
         angular:
           x: 0.0
           y: 0.0
           z: 0.3"

Single command format:

ros2 topic pub -1 /cmd_vel geometry_msgs/msg/TwistStamped "{header: {stamp: {sec: 0}, frame_id: 'base_link'}, twist: {linear: {x: 0.2, y: 0.0, z: 0.0}, angular: {x: 0.0, y: 0.0, z: 0.3}}}"

Modifications from Standard Diffbot

Implemented extensions to the original diffbot implementation:

1. 4WD configuration:

   • Independent control of 4 wheel motors
   • Modified controller parameters for multi-wheel configuration per side

2. ODrive integration:

   • CAN bus communication interface
   • odrive_ros2_control hardware_interface plugin implementation

3. Docker implementation:

   • Multi-architecture compatibility (AMD64/ARM64)
   • Separate runtime environments for simulation and hardware testing

4. Parameter modifications:

   • Wheel geometry parameters for 4WD system
   • ODrive-specific CAN bus parameters

Hardware Interface Variants

Mock Hardware Interface

• Simulated motor/encoder feedback
• Command reception without physical hardware
• Used for algorithm testing and development
• No hardware dependencies

Physical Hardware Interface

• ODrive motor controller communication via CAN
• Real-time sensor data acquisition
• Physical motor command transmission
• Full hardware dependencies

Troubleshooting

Odometry Data Missing

Symptom: No odometry data or abnormal motor behavior

Cause: Incorrect ODrive CAN ID configuration

Solution:

• Verify ODrive CAN IDs (ID 0 for left motors, ID 1 for right motors)
• Use ODrive Tool to check/modify CAN configuration

Directional Control Issues

Symptom: Wheels rotating in same direction during turn commands

Solution:

1. Check controller configuration (bringup/config/)
2. Rebuild and restart after parameter modification

Command Execution Failure

Symptom: No response to velocity commands

Causes:

1. Topic mismatch: Verify publishing to /cmd_vel with correct message type
2. Controller state: Verify controller status:

   ros2 control list_controllers

3. Hardware communication: Check ODrive status and CAN communication

CAN Communication Issues

Symptom: Hardware interface errors or timeout

Diagnostics:

• Check interface status:

  ip -details link show can0

• Monitor CAN traffic:

  candump can0

• Reset interface if necessary:

  sudo ip link set can0 down
  sudo ip link set can0 up type can bitrate 250000

References

• ROS2 Control Demos
• ODrive ROS2 Package
• ros2_control Documentation
• Differential Drive Controller Documentation