This report aims to study the viability of using a *Pixhawk* board as the central controller of a model rocket. The system must be able to capture relevant data from sensors, send telemetry information to a ground station, store logs in persistent memory, and trigger parachute systems.
To understand the requirements of the model rocket system, I'll present an overview of a typical flight system for drones, since the architecture is very similar.
In the image above, to translate the system to the context of a rocket, the only component that differs is the **Drone Hardware**. This component represents the elementary drone components, such as the battery, the motors, and the GPS. Thankfully, some of these elementary components are common to both drones and rockets.
As we can see, above the Drone hardware is the *Flight Controller Hardware*. This is the responsibility of the **Pixhawk Board**, which is the object of study. Focusing on the *Pixhawk*, the sensors and components from the layer below (GPS, telemetry modules, etc.) hook into it, forming an essential **hardware hub**. This hub is then used by the *Software layer* to control the drones' basic components.
In terms of hardware, the ground station just needs a telemetry module, identical to the USB module represented in the figure, that will communicate with the antenna in the rocket, using the *MAVLINK* protocol.
In the software layer, resides the user interfaces. The software represented here are essentially GUIs that utilize the *MAVLINK* protocol. Namely, *QGroundControl*, *APM Planner* and *Mission Planner*. The first 2 are for Linux, while the last one is exclusively for Windows.
Additionally, this layer also contains packages that can control vehicles, with the *MAVLINK* protocol through a coding language. In other words, these packages allow you to treat *Ardupilot* and *PX4* as an API to control the vehicle. Here we have represented the package **DroneKit**.
As mentioned above, PX4 is one of the most popular *Flight Controller Software*. For that reason, we will explore it in more detail since its supported features are very similar to *Ardupilot* and the documentation is easier to follow.
### Supported Vehicles
Although PX4 supports a high variety of vehicles, model rockets are not part of that list. Nonetheless, I believe that is not an issue since this list is targeted for the usage of the software as a *Professional Autopilot*, that is, controlling the vehicle's trajectory and moving it as desired. In our use case, that feature isn't required so it should be fine as long as the features mentioned in the [Introduction](##Introduction) are supported.
Fig. 5 - PX4 System Architecture
Note that this architecture is similar to what we wish to achieve, as it contains most of the sensors required for the model rocket. The missing pieces in the diagram are the [*parachute triggering*](https://docs.px4.io/main/en/peripherals/parachute.html) and [*persistent storage*](https://docs.px4.io/main/en/dev_log/logging.html), which are also supported and documented.
There are many *Pixhawk* boards to choose from, such as the [Pixhawk 4](https://docs.px4.io/main/en/flight_controller/pixhawk4.html). The comparison and analysis of the most suitable board should be made in collaboration with the *Electrical Engineering Department*.
It is confirmed that the Pixhawk + PX4 combination supports the sensors and radio systems we are looking for. Anyhow, there are a lot of options to choose from and, once again, contact with the *Electrical Engineering Department* is needed to reach a consensus.
After analyzing this information, *Pixhawk* seems to be a promising board to introduce in our model rocket. However, the current information isn't enough to reach a conclusion. To do so, we must convert this theoretical information into a practical example. Thankfully, the *Software in the Loop* solution mentioned in this report provides a way to simulate the *Pixhawk* and the rocket model. Thus, the next steps involve testing this *PX4* and *Ardupilot* software, to ensure they fit our needs and are capable of adapting to our scenario.
