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Payload Package

Payload runs the SAE ground payload in simulation and on Raspberry Pi hardware.

Payload for SAE Advanced Class 2026: - two wheel diff drive payload - front-mounted camera - rear ball caster

Parameters And Controllers

payload generates payload/payload_parameters.hpp from config/payload_params.schema.yaml at build time using generate_parameter_library.

If you are building manually without rosdep, install the generator first:

sudo apt-get install ros-humble-generate-parameter-library

Available controller plugin names: - SimController for Gazebo-backed simulation - GPIOController for Raspberry Pi hardware via pigpio

config/payload_params.schema.yaml defines the supported parameter surface, and config/payload_params.yaml provides the shipped runtime values. payload_params.yaml currently defaults controller to GPIOController. Simulation launch flows override that to SimController, or you can do it manually with controller:=SimController.

Raspberry Pi Hardware Setup (pigpiod)

The GPIOController backend and the hardware test binaries (test_motor, test_servo) require the pigpiod_if2 headers/library at build time and a running pigpiod daemon at runtime. This must be set up on every Pi before running the payload node in hardware mode.

1. Install pigpio from source

pigpio is not available via apt on Ubuntu 22.04. Build and install from source:

cd ~
git clone --depth 1 https://github.com/joan2937/pigpio.git
cd pigpio
cmake . -DBUILD_SHARED_LIBS=ON
make -j$(nproc)
sudo make install
sudo ldconfig

2. Create the systemd service

sudo tee /etc/systemd/system/pigpiod.service > /dev/null << 'EOF'
[Unit]
Description=Daemon required to control GPIO pins via pigpio

[Service]
ExecStart=/usr/local/bin/pigpiod
ExecStop=/bin/systemctl kill pigpiod
Type=forking

[Install]
WantedBy=multi-user.target
EOF

3. Enable and start the daemon

sudo systemctl daemon-reload
sudo systemctl enable pigpiod
sudo systemctl start pigpiod
sudo systemctl status pigpiod

Look for Active: active (running). The daemon will now start automatically on boot.

4. Verify

source install/setup.bash
ros2 run payload test_servo

test_servo should run without sudo and without pigpio_start() failed. test_motor uses the same pigpio runtime path when you are ready to validate motors on hardware.

Each-Session Setup

After the one-time setup, pigpiod should start automatically on boot. A normal hardware bringup looks like:

ssh penn@penn-desktop.local
cd ~/monorepo/controls/sae_2025_ws
python3 -m pip install --user "pydantic>=2,<3"
source install/setup.bash
ros2 launch uav main.launch.py params_file:=$(pwd)/src/uav/launch/launch_params_hardware.yaml

If pigpiod ever stops, restart it with:

sudo systemctl restart pigpiod

Launch

payload.launch.py accepts these launch arguments: - vehicle_name: payload ROS namespace prefix. In simulation, this should match the vehicle identity used by the orchestration layer. Default: payload_0 - controller: optional plugin override. Leave it empty to use config/payload_params.yaml

Examples:

# Hardware / default config
ros2 launch payload payload.launch.py

# Standalone simulation
ros2 launch payload payload.launch.py controller:=SimController

# Alternate vehicle namespace in simulation
ros2 launch payload payload.launch.py vehicle_name:=payload_1 controller:=SimController

Standalone payload.launch.py loads the installed config/payload_params.yaml from the package share directory. It launches payload ROS topics and services under /<vehicle_name>/... so multi-payload orchestration can target each payload independently. If you launch payload through uav main.launch.py, the UAV launch stack handles the mission and camera wiring. On hardware, make sure pigpiod is already running first.