ROS2 Dependencies Made Simple: The Complete Beginner’s Guide

Introduction

One of the most common problems in robotics development is missing dependencies. You clone a ROS2 package, try to build it, and errors start flooding your terminal. For beginners, this can feel like a dead end but it doesn’t have to be.

In this guide, we’ll break down ROS2 dependencies in plain English. We’ll show you how to install everything you need in one go, how to avoid repetitive errors, and how to make your projects reusable for others. Using TurtleBot3 a popular learning platform we’ll walk through real examples of fixing errors, installing dependencies automatically, and structuring your workspace for success.

Why Dependencies Matter in Robotics

Think of your ROS2 package as a recipe. The source code is your instructions, but the ingredients are your dependencies without them, nothing works.

For example, if your TurtleBot3 package needs dynamixel_sdk to communicate with motors, your build will fail until that package is installed. Good developers don’t just solve the problem for themselves they document and organize dependencies so anyone can run the project without extra help.

Here’s a detailed look at the types of dependencies you’ll encounter:

Type	Installed With	Example	When to Use
Binary packages	sudo apt-get install	ros-humble-dynamixel-sdk	Stable packages from official repositories.
Python packages	pip install or requirements.txt	numpy, rclpy	Python-specific dependencies.
Source repositories	VCS (.repos files)	Specific GitHub branch	Latest features or versions not in apt.
Custom builds	Manual clone + build	PCL library	When no prebuilt or VCS option exists.

Dependencies ensure your robotics code can be shared, maintained, and improved by others. Neglecting them means your project will only work on your machine.

Setting Up a ROS2 Workspace

Before working with TurtleBot3 or any other ROS2 package, create a workspace:

# Create workspace and source directory

mkdir -p ~/ros2_ws/src

cd ~/ros2_ws/src

# Clone TurtleBot3 repository

git clone https://github.com/ROBOTIS-GIT/turtlebot3.git

# Move to workspace root and build

cd ~/ros2_ws

colcon build

When you run colcon build, you might immediately get errors about missing packages. This is normal it’s ROS2’s way of telling you what’s missing.

Fixing Missing Binary Dependencies

Suppose your build fails with:

CMake Error: find_package(dynamixel_sdk) not found

Install it manually:

sudo apt-get update

sudo apt-get install ros-humble-dynamixel-sdk

Try building again:

colcon build

If you see another error such as turtlebot3_msgs missing:

sudo apt-get install ros-humble-turtlebot3-msgs

But doing this one package at a time is slow and frustrating. For larger projects with dozens or hundreds of dependencies, it’s unmanageable.

Installing All Dependencies Automatically with Rosdep

ROS2 provides rosdep, a tool that installs every dependency at once. First, initialize it (only once per system):

sudo rosdep init

rosdep update

Then install all dependencies in your workspace:

rosdep install --from-paths src --ignore-src -r -y

For full instructions and advanced options, see the Official ROS 2 Rosdep Documentation (ROS.org is the authoritative source for ROS2).

Command Breakdown

• –from-paths src: Search for all package.xml files in the src folder.
  
• –ignore-src: Don’t reinstall packages you already cloned.
  
• -r: Continue even if some packages fail.
  
• -y: Say “yes” to all installation prompts automatically.
  

This approach is much faster, especially for big projects like Navigation2 or Cartographer. For deeper instructions, visit the Official ROS2 Rosdep Tutorial.

Understanding package.xml in ROS2

The package.xml file is where dependencies are declared. Here’s an example from TurtleBot3:

<depend>ros-humble-dynamixel-sdk</depend>
<depend>ros-humble-turtlebot3-msgs</depend>

When you run rosdep, it reads these lines and installs the required packages automatically. If you forget to add a dependency to package.xml, others won’t be able to build your project without troubleshooting. Keeping this file accurate is critical for reproducibility.

Python-Specific Dependencies

For ROS2 nodes written in Python, you might also see a requirements.txt file. Example:

rclpy
numpy

Install these packages with:

pip install -r requirements.txt

Always include a requirements.txt in your repository if your project uses Python libraries.

Installing from Source Using VCS

Some libraries don’t have apt packages or need specific versions. TurtleBot3 includes a .repos file to handle this:

# Import and clone dependencies from a .repos file
vcs import src < src/turtlebot3/turtlebot3.repos

This clones the listed repositories and their specified branches into your workspace. Use VCS when apt packages are outdated or unavailable, and refer to the Colcon VCS Import tutorial for step-by-step instructions on managing source-based dependencies.

Build Order and Selective Building

Build order matters. If you try to build only one package without its dependencies, you’ll see errors. Example:

colcon build --packages-select turtlebot3_node

If dynamixel_sdk isn’t built first, this will fail. Fix it by building the dependency first:

colcon build --packages-select dynamixel_sdk
colcon build --packages-select turtlebot3_node

Or just build everything at once:

colcon build

Selective building is useful for debugging or when you don’t want to rebuild the entire workspace.

Running TurtleBot3 Navigation

Once everything is installed and built, source your workspace and launch TurtleBot3 Navigation:

source install/setup.bash
ros2 launch turtlebot3_navigation2 navigation2.launch.py

ROS2 will ask for your TurtleBot3 model:

Burger

If dependencies are installed correctly, the navigation stack will launch without “package not found” errors.

Best Practices for Managing Dependencies

1. Keep your package.xml updated whenever you add or remove libraries.
   
2. Use rosdep to install everything instead of manual apt commands.
   
3. Include .repos files if you rely on GitHub branches or unreleased features.
   
4. Provide a requirements.txt for Python dependencies.
   
5. Document everything in a README so others can run your project quickly.
   
6. Use version control for .repos files to prevent mismatched branches.
   
7. Rebuild cleanly after big dependency changes:

rm -rf build install log
colcon build

         Common Dependency Errors and Fixes

Error	Cause	Fix
find_package() not found	Missing binary dependency	Install with sudo apt-get install or rosdep.
ModuleNotFoundError: No module	Missing Python package	pip install -r requirements.txt.
Build order error	Dependent package not yet built	Build the dependency first or use colcon build.
Wrong version installed	Mismatch between branches or distro	Use VCS with correct branch or specify exact version.

Troubleshooting Large Projects

• Check your ROS2 distribution: Make sure your workspace matches (e.g., Humble vs. Galactic).
  

Use verbose builds:

colcon build --event-handlers console_direct+

•  This gives more detail about which dependency failed.
  
• Update regularly: Dependencies may get patched or renamed between ROS2 releases.
  
• Ask the community: The ROS2 Discourse is a great place for help.
  

FAQs

Q1: What is rosdep and why should I use it?
Rosdep automatically installs all required system packages for your ROS2 workspace. It saves you from manually hunting for missing dependencies.

Q2: Do I need to run rosdep every time I build?
No, only when you add new packages or clone a new repository.

Q3: Can I use rosdep for Python dependencies?
No, rosdep does not install pip packages. Use a requirements.txt file for Python libraries.

Q4: What’s the difference between apt and VCS installations?

• apt: Installs precompiled binaries (faster, stable).
  
• VCS: Clones and builds from source (flexible, latest features).
  

Q5: How can I share my project with others?
Include:

• Updated package.xml for every package.
  
• .repos file for source dependencies.
  
• requirements.txt for Python.
  
• A clear README with build and run instructions.
  

Q6: Why does my build fail even after installing everything?
Possible reasons: incorrect ROS2 version, wrong build order, outdated packages, or missing Python dependencies. Clean your build and try again.

Conclusion

Dependencies are the backbone of every ROS2 project. Missing or poorly documented dependencies waste time and frustrate anyone using your code. By using tools like rosdep, VCS, and requirements.txt, and by maintaining an accurate package.xml, you make your robotics projects reproducible and easy to share.

TurtleBot3 is a great example of a well-documented package: everything you need is clearly listed, and you can run its navigation stack on almost any ROS2 system without headaches. Follow these practices, and your own projects will be just as smooth for future developers.

With proper dependency management, you’ll spend less time troubleshooting and more time building robots that actually work.

Want hands-on guidance? Explore our Robotisim learning paths to master ROS2 dependencies and build reliable robotics projects.