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R2M 4WD Differential Drive Bot

Build Status

Branch Build Status
main Main Branch Build
dev Dev Branch Build

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