From simulation to a real drone

Get the project

Each drone has a ready-made project, laid out like the Quickstart's:

git clone https://github.com/aerostack2/project_crazyflie.git
cd project_crazyflie

The windows of the tmux session are the same as in simulation. Only the platform window runs something else, the driver that talks to the drone.

Tell the project about your drone

Everything for the drones is in config/config.yaml. Its first part applies to every drone, and the end has one section per drone, named after its namespace.

drone0:
  platform:
    ros__parameters:
      uri: radio://0/80/2M/E7E7E7E701

/**:
  state_estimator:
    ros__parameters:
      plugin_name: "raw_odometry"

Notice what isn't there. There's no use_sim_time, so every node runs on the computer's clock, and no base_frame_id, so the drone's body frame is the usual drone0/base_link. The motion controller is the PID speed controller, as in simulation, with gains for this drone in config/pid_speed_controller.yaml.

Start the drone and the ground station

Turn the drone on, put it on the floor where the mission starts, and start its stack:

./launch_as2.bash

In a second terminal, start the ground station with the keyboard teleoperation:

./launch_ground_station.bash -t

The Tello's ground station also starts the OptiTrack driver from mocap4ros2, with the server address in config_ground_station/mocap4r2_optitrack.yaml, and -m leaves it out. The Crazyflie's does it the other way round, and only starts it with -m. Add -v to either for RViz.

Watch the platform window of the drone's session. The Crazyflie platform waits until the radio link connects, and the Tello platform stops if the Tello doesn't answer.

Check where the drone thinks it is

Run state.py from A mission in Python. It doesn't arm or fly. Run it again after moving the drone by hand a little, then put it back:

python3 state.py

The position should follow the drone, in metres, with z close to 0 on the floor. Positions are in earth, like in simulation, but where its origin lies now depends on the source. Every point of the mission is measured from there, so know where it is before you send the drone anywhere.

If the position doesn't change, don't fly. The estimator isn't getting the drone's position.

Fly by hand first

Click the keyboard teleoperation window and press t to take off. Move the drone a step with the arrows, then press l to land. This checks the whole stack with you in control, as in Fly by hand.

Shrink the mission

Copy my_mission.py into the project folder. Keep its structure, with the flight in fly and the landing in finally, but make it fit your flying space. The simulated mission flies 4 m across and starts a flight toward a point 10 m away, which won't fit indoors. A 1 × 1 m square at 1 m, at 0.3 m/s:

import rclpy
from as2_python_api.drone_interface import DroneInterface


def fly(drone: DroneInterface) -> None:
    """Fly the mission. Raises an error if a behavior fails."""
    if not drone.arm() or not drone.offboard():
        raise RuntimeError("Couldn't arm or switch to offboard")

    if not drone.takeoff(height=1.0, speed=0.3):
        raise RuntimeError("Take off failed")

    # A 1 x 1 m square at 1 m, slowly
    drone.go_to(1.0, 0.0, 1.0, speed=0.3)
    drone.go_to.go_to_point_path_facing([1.0, 1.0, 1.0], speed=0.3)
    path = [[0.0, 1.0, 1.0], [0.0, 0.0, 1.0]]
    drone.follow_path.follow_path_with_path_facing(path, speed=0.3)


rclpy.init()
drone = DroneInterface(drone_id="drone0")

try:
    fly(drone)
finally:
    # Whatever happened, land and hand control back
    drone.land(speed=0.3)
    drone.manual()
    drone.shutdown()
    rclpy.shutdown()

• drone_id is still drone0, the namespace in config/config.yaml. Rename one, rename both.
• DroneInterface has no use_sim_time=True. Without a simulation there's no simulated clock, so leave it out, which is the default.
• Everything else is the same API, the same behaviors and the same try and finally.

The script runs unchanged in the multirotor simulator, so fly it there first.

Fly it

Stand clear, with the keyboard teleoperation window ready, and run it:

python3 my_mission.py

The drone takes off, flies the square and lands where it started. If something goes wrong, use the emergency stop below rather than waiting for the script.

Stop everything

Land the drone first. Then:

./stop_tmuxinator.bash

This closes the drone and ground station sessions. Turn the drone off before picking it up.