CAN Hardware Interface for Piper Robot Arm

This repository contains the ROS 2 hardware interface implementation for controlling the Piper robot arm via CAN bus communication. It provides a complete solution for integrating the Piper arm with ROS 2 control frameworks, including MoveIt2 and servo control.

Repository Structure

can_hardware_interface/
├── can_data_plugins/           # CAN data processing plugins
│   ├── include/can_data_plugins/
│   │   └── piper_feedback/     # Piper-specific feedback handlers
│   └── src/
│       ├── omni_picker/        # Omni picker control
│       ├── piper_ctrl/         # Piper control plugins  
│       ├── piper_feedback/     # Piper feedback plugins
│       └── piper_mit_ctrl/     # MIT control mode plugins
├── piper_bringup/              # Launch files and robot configuration
│   ├── config/
│   ├── launch/
│   │   └── piper_bringup.launch.py  # Main launch file
│   ├── meshes/                 # 3D mesh files for visualization
│   ├── rviz/                   # RViz configuration files
│   └── urdf/                   # Robot description files
│       ├── agilex_piper_macro.urdf.xacro
│       ├── agilex_piper_single.system.xacro
│       ├── agilex_piper_dual.system.xacro
│       └── include/            # ros2_control configurations
└── socket_can_hardware_interface/  # Core CAN interface implementation

Features

🤖 Robot Control Modes

• Position Control: Standard position-based joint control
• MIT Control Mode: Advanced torque control with current feedback
• Mock Hardware: Simulation mode for testing without physical hardware
• Isaac Sim Integration: Support for NVIDIA Isaac Sim
• Gazebo Support: Classic and modern Gazebo simulation

🔌 CAN Communication

• Real-time CAN Interface: Direct CAN bus communication via SocketCAN
• Multi-joint Feedback: Simultaneous monitoring of all 6 joints
• High-speed Feedback: Velocity and effort feedback at high frequencies
• Status Monitoring: Comprehensive arm status and error reporting
• Configurable CAN IDs: Flexible addressing scheme

🎯 Hardware Interfaces

• Position Interface: Joint position command and feedback
• Velocity Interface: Joint velocity feedback
• Effort Interface: Joint torque/effort feedback
• Status Interface: Robot arm status, control modes, and error codes

🏗️ Multi-Robot Support

• Namespace Prefixing: Support for multiple robot instances
• Flexible Configuration: Parameterized robot descriptions
• Dual Robot Setup: Pre-configured dual robot launch files

Quick Start

Prerequisites

• ROS 2 Humble or later
• Ubuntu 22.04 LTS
• CAN interface hardware (for real robot)
• MoveIt2 (for motion planning)

Installation

1. Clone the repository (if not already in workspace):

   cd ~/ros2_ws/src
   git clone <repository_url> can_hardware_interface
   

2. Install dependencies:

   cd ~/ros2_ws
   rosdep install --from-paths src --ignore-src -r -y
   

3. Build the workspace:

   colcon build --packages-select can_data_plugins socket_can_hardware_interface piper_bringup
   source install/setup.bash
   

Usage Examples

🚀 Launch with Mock Hardware (Simulation)

ros2 launch piper_bringup piper_bringup.launch.py use_mock_hardware:=true

🔧 Launch with Real Hardware

# Ensure CAN interface is up
sudo ip link set can1 up type can bitrate 1000000

# Launch with real hardware
ros2 launch piper_bringup piper_bringup.launch.py use_mock_hardware:=false

🎮 Launch with Prefix (Multi-robot)

ros2 launch piper_bringup piper_bringup.launch.py use_mock_hardware:=true prefix:=robot1_

🌐 Launch with Isaac Sim

ros2 launch piper_bringup piper_bringup.launch.py sim_isaac_sim:=true

👥 Dual Robot Setup

ros2 launch piper_bringup piper_bringup_dual.launch.py use_mock_hardware:=true

Configuration

Launch Parameters

The main launch file supports the following parameters:

Parameter	Default	Description
use_mock_hardware	false	Use mock hardware for simulation
mock_sensor_commands	false	Enable mock sensor command interfaces
sim_gazebo_classic	false	Use classic Gazebo simulation
sim_gazebo	false	Use modern Gazebo simulation
sim_isaac_sim	false	Use NVIDIA Isaac Sim
prefix	""	Namespace prefix for multi-robot setups
simulation_controllers	""	Additional simulation controllers

CAN Interface Setup

For real hardware operation, configure your CAN interface:

# Load CAN modules
sudo modprobe can
sudo modprobe can_raw
sudo modprobe can_bcm

# Bring up CAN interface
sudo ip link set can1 up type can bitrate 1000000

# Verify interface
ip link show can1
candump can1  # Monitor CAN traffic

Robot Description Configuration

The robot description supports flexible configuration through xacro parameters:

<!-- Basic usage -->
<xacro:agilex_piper name="agilex_piper" parent="base_link">
  <origin xyz="0 0 0" rpy="0 0 0" />
</xacro:agilex_piper>

<!-- With namespace prefix -->
<xacro:agilex_piper name="agilex_piper" parent="base_link" prefix="robot1_">
  <origin xyz="0 0 0" rpy="0 0 0" />
</xacro:agilex_piper>

CAN Protocol Details

📡 CAN Message Structure

The Piper robot uses a structured CAN protocol with specific message IDs:

Status Messages (Read-only)

• 0x2A1 (673): Arm status, control mode, errors
• 0x2A5 (677): Joint 1&2 position feedback
• 0x2A6 (678): Joint 3&4 position feedback
• 0x2A7 (679): Joint 5&6 position feedback

Control Messages (Write)

• 0x151 (337): Motion control configuration
• 0x155 (341): Joint 1&2 position commands
• 0x156 (342): Joint 3&4 position commands
• 0x157 (343): Joint 5&6 position commands
• 0x471 (1137): Arm disable/enable configuration

🔧 Control Modes

Configure control mode in the ros2_control configuration:

<!-- Position-Speed Mode (Normal) -->
<param name="mit_mode">0</param>

<!-- MIT Mode (Advanced Torque Control) -->
<param name="mit_mode">173</param>

Control modes:

• 0x00: Position-speed mode (default)
• 0xAD (173): MIT mode for advanced torque control

🔢 Data Encoding

• Position: 32-bit integer, unit: millidegrees (divide by 1000 * 180/π for radians)
• Velocity: 16-bit integer, unit: millirad/s (divide by 1000 for rad/s)
• Effort: 16-bit integer with joint-specific scaling coefficients

Plugin Architecture

The system uses a modular plugin architecture for CAN data processing:

Available Device Types

• PIPER: Standard Piper robot arm communication
• OMNI_PICKER: Omni picker attachment support

Plugin Categories

• Feedback Plugins: Handle incoming sensor data from robot
• Control Plugins: Send position/velocity commands to robot
• MIT Control Plugins: Advanced torque control mode
• Status Plugins: Monitor system status and errors

Hardware Interface Details

Exported Interfaces

The hardware interface exports the following ROS 2 control interfaces:

Joint Interfaces (for each joint: joint1-joint6)

• position (command & state)
• velocity (state only)
• effort (state only)

System Interfaces

• arm_status/* - Robot arm status information
• joint*_feedback/* - Joint feedback data
• arm_motion_ctrl2/* - Motion control configuration

Multi-Robot Support

When using the prefix parameter, all interfaces are prefixed:

• Joint names: robot1_joint1, robot1_joint2, etc.
• Hardware interfaces: robot1_joint1/position, etc.

Troubleshooting

Common Issues

1. CAN Interface Not Found

   # Check if CAN interface exists
   ip link show can1
   
   # If not, configure it
   sudo ip link set can1 up type can bitrate 1000000
   

2. Permission Denied on CAN Interface

   # Add user to dialout group
   sudo usermod -a -G dialout $USER
   # Re-login for changes to take effect
   

3. Robot Not Responding

   # Check CAN traffic
   candump can1
   
   # Send test frame
   cansend can1 151#0000000000000000
   

4. Joint Limits Exceeded

   • Check joint limit definitions in URDF
   • Verify command values are within acceptable ranges
   • Monitor robot status messages for error codes

Debug Tools

# Monitor CAN traffic
candump can1

# Send raw CAN frames
cansend can1 <ID>#<DATA>

# Check ros2_control status
ros2 control list_hardware_interfaces

# Monitor joint states
ros2 topic echo /joint_states

# Check controller status
ros2 control list_controllers

Development

Adding New Plugins

1. Create plugin class inheriting from base interface
2. Implement required methods for CAN communication
3. Register plugin in CMakeLists.txt
4. Add device configuration to ros2_control URDF