This phase establishes the foundational infrastructure for autonomous UAV control using PX4 SITL (Software-In-The-Loop) and MAVSDK-Python. It establishes reliable MAVLink communication, monitor vehicle health telemetry, and execute closed-loop flight state transitions (Arm, Takeoff, Hover, Land).
Flight Stack: PX4 Autopilot (Running on Raspberry Pi / Linux)
API: MAVSDK-Python (pip install mavsdk asyncio)
GCS: QGroundControl (Running on Host Mac/PC)
Note
To get PX4 Up and Running and Connected to Mac -> Refer this Article
Running the simulator on a remote machine (Raspberry Pi) and the execution script on a host machine (Mac). I Faced some problems while using the PX4 broadcast parameters and had port collisions with QGroundControl (which aggressively hogs port 14550).
So to run both QGC and the Python script simultaneously, I utilise Direct IP Targeting to create a private MAVLink stream.
The Routing Bypass -
Instead of modifying broadcast parameters, I simply route a secondary MAVLink instance directly to the host machine's IP address using a custom port (14555), leaving 14550 free for QGC.
This phase contains two scripts demonstrating different levels of control logic.
-
phase_0_simple.py (Open-Loop / Timed) A "fire-and-forget" script. It polls the core.connection_state() and telemetry.health() streams to ensure the EKF is settled and a GPS lock is achieved (is_global_position_ok and is_armable). It then commands a takeoff, sleeps the Python thread for 10 seconds, and commands a landing.
-
phase_0_enhanced.py (Closed-Loop / Telemetry Feedback) A closed-loop profile. Instead of relying on blind timers, it actively monitors the drone.telemetry.position() stream.
Modifies the default PX4 takeoff altitude to Maximum Altitude.
Actively polls position.relative_altitude_m.
Dynamically triggers the hold() command only when the physical telemetry proves the vehicle has crossed the threshold.
Flight Review Log: PX4 Logs
Project Working Snippet -
Command Sequence -
# 1. Login
ssh [email protected]
# 2. Fix Wi-Fi Regulation (Run every boot)
sudo iw reg set IN
# 3. Enter Directory
cd PX4-Autopilot
# 4. Start Simulation (Headless)
HEADLESS=1 make px4_sitl jmavsim
# 5. Connection Bind to Mac (pxh>)
mavlink start -u 14581 -o 14555 -t <MAC_IP> -m onboard
# 6. Open QGroundControl in Mac
# 7. Run Program in Mac -
uv run phase_0_enhanced.py
Workflow -
%%{init: { 'theme': 'base', 'themeVariables': { 'textColor': '#000000', 'actorTextColor': '#000000', 'signalTextColor': '#000000', 'noteTextColor': '#000000', 'labelTextColor': '#000000', 'loopTextColor': '#000000', 'sectionTextColor': '#000000', 'activationBorderColor': '#000000' } } }%%
sequenceDiagram
autonumber
%% Use Actor/Participant aliases for cleaner logic
actor U as User (Mac)
participant MT as Mac Terminal
participant PT as Pi Terminal (SSH)
participant PX4 as PX4 SITL (Pi)
participant QGC as QGroundControl (Mac)
participant PY as MAVSDK Script (Mac)
%% Phase 1
rect rgb(230, 240, 255)
Note over U, PT: Phase 1: Environment Setup
U->>MT: ssh [email protected]
activate MT
MT->>PT: Establish SSH Connection
activate PT
PT-->>MT: Connection Established
U->>PT: sudo iw reg set IN
PT-->>U: Wi-Fi Region Updated (India)
end
%% Phase 2
rect rgb(240, 240, 240)
Note over U, QGC: Phase 2: Simulation & Networking
U->>PT: HEADLESS=1 make px4_sitl jmavsim
activate PX4
PT->>PX4: Spawn Headless Simulator
PX4-->>PT: pxh> prompt ready
Note right of PX4: Broadcast active on 14550
U->>QGC: Open Application
activate QGC
PX4->>QGC: MAVLink auto-connects (14550)
U->>PT: mavlink start -u 14581 -o 14555 -t <MAC_IP>
PT->>PX4: Create private MAVLink stream
PX4-->>U: UDP stream to Mac (Port 14555)
end
%% Phase 3
rect rgb(230, 255, 230)
Note over U, PY: Phase 3: Mission Execution
U->>MT: uv run phase_0_enhanced.py
activate PY
MT->>PY: Spawn Python Process
PY->>PX4: Connect via udpin://0.0.0.0:14555
PX4-->>PY: Handshake & Telemetry
Note left of PX4: Wait for Armable/GPS
PY->>PX4: Command: Arm & Takeoff
PX4-->>PY: Altitude Telemetry
PY->>PX4: Command: Land
PX4-->>PY: Disarm detected
PY-->>MT: Clean Exit
deactivate PY
deactivate QGC
deactivate PX4
deactivate PT
deactivate MT
end