Assessment: ROS 2 Package Development

Overview

This assessment evaluates your ability to design and implement a complete ROS 2 package for robotic control. You'll create a multi-node system that demonstrates core ROS 2 concepts including nodes, topics, services, actions, and launch files.

Learning Objectives

By completing this assessment, you will demonstrate:

Proficiency in ROS 2 package structure and build systems
Ability to create and configure multiple communicating nodes
Understanding of ROS 2 communication patterns (topics, services, actions)
Skill in writing launch files for complex systems
Knowledge of parameter management and configuration

Project Requirements

Task: Robotic Arm Controller

Create a ROS 2 package that controls a simulated robotic arm with the following capabilities:

1. Package Structure

ros2_arm_controller/
├── package.xml
├── CMakeLists.txt (C++) or setup.py (Python)
├── launch/
│   ├── arm_controller.launch.py
│   └── simulation.launch.py
├── config/
│   ├── arm_params.yaml
│   └── controllers.yaml
├── src/ (or ros2_arm_controller/ for Python)
│   ├── arm_controller_node.cpp/py
│   ├── trajectory_planner_node.cpp/py
│   ├── safety_monitor_node.cpp/py
│   └── gripper_controller_node.cpp/py
├── msg/
│   └── JointCommand.msg
├── srv/
│   └── PlanTrajectory.srv
├── action/
│   └── MoveToTarget.action
└── README.md

2. Required Nodes

a) Arm Controller Node

Responsibilities:

Subscribe to joint command topics
Publish joint states
Execute motion commands
Enforce joint limits

Interface:

# Publishers
/arm/joint_states (sensor_msgs/JointState)

# Subscribers
/arm/joint_commands (your_package/JointCommand)

# Parameters
- joint_limits: [min, max] for each joint
- control_rate: Hz
- max_velocity: rad/s
- max_acceleration: rad/s^2

b) Trajectory Planner Node

Responsibilities:

Plan smooth trajectories between poses
Provide trajectory planning service
Interpolate waypoints

Interface:

# Services
/arm/plan_trajectory (your_package/PlanTrajectory)
  Request:
    - geometry_msgs/Pose target_pose
    - float64 max_velocity
    - float64 max_acceleration
  Response:
    - trajectory_msgs/JointTrajectory trajectory
    - bool success
    - string message

# Publishers
/arm/planned_trajectory (trajectory_msgs/JointTrajectory)

c) Safety Monitor Node

Responsibilities:

Monitor joint states for safety violations
Emergency stop capability
Workspace boundary enforcement

Interface:

# Subscribers
/arm/joint_states (sensor_msgs/JointState)

# Publishers
/arm/safety_status (std_msgs/Bool)
/arm/safety_alerts (std_msgs/String)

# Services
/arm/emergency_stop (std_srvs/Trigger)

# Parameters
- workspace_bounds: [x_min, x_max, y_min, y_max, z_min, z_max]
- joint_velocity_limits: [max_vel] for each joint

d) Gripper Controller Node

Responsibilities:

Control gripper open/close
Monitor grasp force
Provide action interface for pick/place

Interface:

# Action Server
/arm/gripper/move (your_package/MoveToTarget)
  Goal:
    - string command (open/close/grasp)
    - float64 target_position
    - float64 max_effort
  Feedback:
    - float64 current_position
    - float64 current_effort
  Result:
    - bool success
    - string message

# Publishers
/arm/gripper/state (sensor_msgs/JointState)

3. Custom Messages

JointCommand.msg

Header header
string[] joint_names
float64[] positions
float64[] velocities
float64[] efforts

PlanTrajectory.srv

# Request
geometry_msgs/Pose target_pose
float64 max_velocity
float64 max_acceleration
---
# Response
trajectory_msgs/JointTrajectory trajectory
bool success
string message

MoveToTarget.action

# Goal
string command
float64 target_position
float64 max_effort
---
# Result
bool success
string message
---
# Feedback
float64 current_position
float64 current_effort
float64 progress_percentage

4. Launch Files

arm_controller.launch.py

from launch import LaunchDescription
from launch_ros.actions import Node
from launch.actions import DeclareLaunchArgument
from launch.substitutions import LaunchConfiguration

def generate_launch_description():
    return LaunchDescription([
        # Declare arguments
        DeclareLaunchArgument(
            'config_file',
            default_value='arm_params.yaml',
            description='Configuration file'
        ),

        # Arm controller node
        Node(
            package='ros2_arm_controller',
            executable='arm_controller_node',
            name='arm_controller',
            parameters=[LaunchConfiguration('config_file')],
            output='screen'
        ),

        # Trajectory planner node
        Node(
            package='ros2_arm_controller',
            executable='trajectory_planner_node',
            name='trajectory_planner',
            output='screen'
        ),

        # Safety monitor node
        Node(
            package='ros2_arm_controller',
            executable='safety_monitor_node',
            name='safety_monitor',
            output='screen'
        ),

        # Gripper controller node
        Node(
            package='ros2_arm_controller',
            executable='gripper_controller_node',
            name='gripper_controller',
            output='screen'
        ),
    ])

5. Configuration Files

arm_params.yaml

arm_controller:
  ros__parameters:
    joint_names: ['joint_1', 'joint_2', 'joint_3', 'joint_4']
    joint_limits:
      joint_1: [-3.14, 3.14]
      joint_2: [-1.57, 1.57]
      joint_3: [-2.0, 2.0]
      joint_4: [-1.57, 1.57]
    control_rate: 100.0
    max_velocity: 1.0
    max_acceleration: 2.0

safety_monitor:
  ros__parameters:
    workspace_bounds:
      x: [-1.0, 1.0]
      y: [-1.0, 1.0]
      z: [0.0, 2.0]
    joint_velocity_limits: [2.0, 2.0, 3.0, 3.0]
    enable_collision_checking: true

Testing Requirements

Unit Tests

Create unit tests for each node:

import unittest
from ros2_arm_controller import ArmController

class TestArmController(unittest.TestCase):
    def test_joint_limits(self):
        """Test that joint limits are enforced"""
        controller = ArmController()
        # Test joint limit enforcement
        pass

    def test_emergency_stop(self):
        """Test emergency stop functionality"""
        pass

    def test_trajectory_execution(self):
        """Test trajectory following"""
        pass

Integration Tests

import rclpy
from rclpy.node import Node

class TestArmIntegration(unittest.TestCase):
    def test_full_motion(self):
        """Test complete motion from start to goal"""
        # 1. Initialize nodes
        # 2. Send target pose
        # 3. Verify trajectory planning
        # 4. Verify execution
        # 5. Check final position
        pass

    def test_safety_violation(self):
        """Test safety monitor catches violations"""
        pass

Deliverables

1. Source Code

Complete ROS 2 package with all required nodes
Custom messages, services, and actions
Launch files and configuration files

2. Documentation

README with:
- Package description
- Installation instructions
- Usage examples
- Architecture diagram
- API documentation

3. Demonstration

Video or live demo showing:
- Successful trajectory planning and execution
- Gripper control (open/close/grasp)
- Safety monitoring (boundary violation, emergency stop)
- Multiple nodes communicating

4. Test Results

Unit test coverage report (>80%)
Integration test results
Performance metrics (control frequency, latency)

Evaluation Criteria

Criteria	Points	Description
Package Structure	10	Proper ROS 2 package layout, build configuration
Node Implementation	30	All required nodes functioning correctly
Communication	20	Proper use of topics, services, actions
Launch Files	10	Correct launch file configuration
Safety	10	Safety monitoring and emergency stop
Code Quality	10	Clean code, documentation, comments
Testing	10	Unit and integration tests

Total: 100 points

Submission Guidelines

Git Repository: Submit link to git repository containing:
- All source code
- Documentation
- Test files
Demonstration Video: 5-10 minute video showing functionality
Report: PDF document (5-10 pages) including:
- System architecture
- Design decisions
- Challenges encountered
- Test results

Tips for Success

Start Simple: Implement basic node structure first, then add features
Test Early: Write tests as you develop, not at the end
Use ROS 2 Tools: Leverage ros2 topic echo, ros2 service call, etc.
Document: Comment your code and maintain a good README
Version Control: Commit frequently with clear messages

Resources

Extension Challenges (Optional)

For extra credit, implement:

Collision Avoidance: Integrate with obstacle detection
Visual Servoing: Control arm based on camera feedback
Force Control: Implement impedance control for compliant motion
Multi-Arm Coordination: Coordinate two arms for bimanual tasks

Good luck with your ROS 2 project!

Overview​

Learning Objectives​

Project Requirements​

Task: Robotic Arm Controller​

1. Package Structure​

2. Required Nodes​

a) Arm Controller Node​

b) Trajectory Planner Node​

c) Safety Monitor Node​

d) Gripper Controller Node​

3. Custom Messages​

JointCommand.msg​

PlanTrajectory.srv​

MoveToTarget.action​

4. Launch Files​

arm_controller.launch.py​

5. Configuration Files​

arm_params.yaml​

Testing Requirements​

Unit Tests​

Integration Tests​

Deliverables​

1. Source Code​

2. Documentation​

3. Demonstration​

4. Test Results​

Evaluation Criteria​

Submission Guidelines​

Tips for Success​

Resources​

Extension Challenges (Optional)​

Overview

Learning Objectives

Project Requirements

Task: Robotic Arm Controller

1. Package Structure

2. Required Nodes

a) Arm Controller Node

b) Trajectory Planner Node

c) Safety Monitor Node

d) Gripper Controller Node

3. Custom Messages

JointCommand.msg

PlanTrajectory.srv

MoveToTarget.action

4. Launch Files

arm_controller.launch.py

5. Configuration Files

arm_params.yaml

Testing Requirements

Unit Tests

Integration Tests

Deliverables

1. Source Code

2. Documentation

3. Demonstration

4. Test Results

Evaluation Criteria

Submission Guidelines

Tips for Success

Resources

Extension Challenges (Optional)