Getting Started with MAVSDK and PX4

In this tutorial, we’ll guide you through the process of getting started with MAVSDK and PX4, using a simulated environment to connect and control a drone.

What You'll Learn

• Connecting MAVSDK to a simulated PX4 instance via TCP.

• Running a small script to take off, hover, and land the drone.

Prerequisites

Before we dive in, ensure you have the following:

• A basic understanding of Python (or another MAVSDK-supported language).

• MAVSDK installed in your development environment.

Let’s get started!

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1. What is MAVSDK?

MAVSDK is an API that simplifies working with MAVLink-enabled drones, offering high-level programming features to control drones using a variety of languages like Python, C++, Swift, and others. It communicates with the drone over MAVLink, a lightweight messaging protocol commonly used in drone systems.

2. What is PX4?

PX4 is an open-source autopilot flight control system for drones and other unmanned vehicles. PX4 can be deployed on real drones or in a simulated environment (which we’ll be using in this tutorial). PX4's simulation is an excellent way to get started without needing physical hardware.

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3. Setting Up Your Environment

To interact with PX4 via MAVSDK, we first need to set up our development environment.

Step 1: Install MAVSDK

You can install the MAVSDK Python library using pip. Open your terminal and run the following command:

pip install mavsdk

Make sure Python is installed and up-to-date on your system before running the command.

Step 2: Access the PX4 Simulation Instance

For this tutorial, we will use a PX4 simulation instance that you can access remotely. The simulation runs on a website server, and we will connect to it via TCP.

The PX4 simulation instance typically runs on TCP port 4560. For this guide, we will assume the server is available at localhost, but in a real scenario, this could be a remote URL provided by the simulation service.

Step 3: Run the PX4 SITL Simulation

If you're running PX4 locally, start the PX4 SITL (Software in the Loop) simulation from your dronesim dashboard. Connect to the remote PX4 instance by specifying its IP and port.

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4. Connecting MAVSDK to the PX4 Simulation

Now that we have the environment ready, let's write a small Python script to connect MAVSDK to the PX4 simulation via TCP.

Example Code: Connecting and Taking Off

Create a Python file, say px4_control.py, and paste the following code:

import asyncio
from mavsdk import System

async def run():
    # Initialize the drone object
    drone = System()
    
    # Connect to the PX4 simulation instance via TCP
    print("Connecting to PX4 Simulation via TCP...")
    await drone.connect(system_address="tcp://127.0.0.1:4560")

    # Wait for the drone to be connected
    print("Waiting for the drone to connect...")
    async for state in drone.core.connection_state():
        if state.is_connected:
            print(f"Drone discovered and connected: {state.uuid}")
            break

    # Check the drone's flight mode
    print("-- Arming the drone")
    await drone.action.arm()

    print("-- Taking off")
    await drone.action.takeoff()

    # Hover for 5 seconds
    await asyncio.sleep(5)

    print("-- Landing")
    await drone.action.land()

    # Wait until the drone has landed
    await asyncio.sleep(5)

if __name__ == "__main__":
    loop = asyncio.get_event_loop()
    loop.run_until_complete(run())

Code Breakdown

1. Import the necessary modules:

   • We import asyncio for managing asynchronous calls and System from MAVSDK to interact with the drone.

2. Connect to the PX4 instance via TCP:

   • The key line here is await drone.connect(system_address="tcp://127.0.0.1:4560"). You will replace 127.0.0.1 with the dronesim simulation server's IP address.

3. Arm the drone:

   • The command await drone.action.arm() is used to arm the drone. This means it’s ready to take off.

4. Take off and hover:

   • After arming, we command the drone to take off with await drone.action.takeoff(). The drone will ascend and hover in place for 5 seconds.

5. Land the drone:

   • After hovering, we command the drone to land using await drone.action.land().

Step 4: Running the Code

Make sure the PX4 simulation is running. Open your terminal, navigate to the folder where you saved the Python script, and run:

python px4_control.py

Once executed, you should see output confirming the connection to the PX4 instance, followed by the drone arming, taking off, hovering, and landing.

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5. Debugging Tips

• Connection Errors: If the script can't connect to the PX4 instance, double-check the system_address. If you’re using a remote server, ensure you're using the correct IP address and port number.

• Arming Failure: If the drone doesn't arm, it could be due to safety or GPS checks. Ensure the simulation environment is set up properly.

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6. Next Steps

Now that you’ve successfully connected to PX4 via MAVSDK and controlled the drone, you can extend this basic example to explore more complex missions, such as waypoint navigation, camera control, or real-time telemetry.

Consider diving into the following topics:

• Autonomous Missions: Learn how to define and execute missions with waypoints.

• Custom Commands: Use MAVSDK to send custom MAVLink commands for more advanced control.

• Real Drone Deployment: Move from the simulator to a real drone setup using PX4 firmware.

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Conclusion

MAVSDK is a powerful tool that simplifies working with drones, and PX4 offers a robust, flexible platform for both simulation and real-world drone applications. By following this tutorial, you now know how to connect to a PX4 simulation via TCP and control a drone using basic commands.

Feel free to experiment with the code, add your own logic, and explore what else you can build with MAVSDK and PX4. Happy coding, and safe flying!