Betaflight

Fly racing-style drones with a Betaflight flight controller, sending RC commands over MSP.

Deprecated

The Betaflight platform is no longer maintained. It isn't built in Aerostack2's CI, it was only tested on ROS 2 Humble, and it may be removed in a future release. It's documented here for existing setups.

The Betaflight platform flies drones whose flight controller runs Betaflight, the firmware used on racing and freestyle drones. A companion computer, such as a Jetson, is wired to one of the flight controller's UARTs and sends it RC channel values over the MSP protocol, as if it were the pilot's radio. It was tested with Betaflight 4.4 and 4.5.

Betaflight only stabilizes rates, so the platform accepts body rates and thrust and nothing else. It reports the IMU and the battery but no position, which has to come from another source.

Install

The platform needs the msp library. Clone both into your workspace:

cd ~/aerostack2_ws/src
git clone https://github.com/aerostack2/as2_platform_betaflight.git
git clone https://github.com/CVAR-A2RL/msp.git
cd ~/aerostack2_ws
rosdep install --from-paths src --ignore-src -y
colcon build --symlink-install

Set up Betaflight

Connect the flight controller over USB and open the Betaflight configurator. Save after each screen.

Ports

Enable Configuration/MSP on the UART the companion computer is wired to, and Serial Rx on the UART of your radio receiver.

Rates

On PID Tuning, under Rateprofile Settings, set the RC Rate of roll, pitch and yaw to 1.80 and every other field to 0. That gives straight lines from −360 to 360 deg/s, which is what the platform's default rate limits expect.

Modes

Assign ARM to AUX 1, and ANGLE to a switch for flying with the radio. Then let MSP override the first four channels, the sticks, from the CLI:

set msp_override_channels_mask=15
save

A new MSP OVERRIDE mode appears on the Modes screen. Put it on the same switch as ANGLE, on the opposite position. With the switch on MSP OVERRIDE the companion computer flies the sticks, and flipping it back gives control to the pilot.

Failsafe

Set the failsafe switch action to Kill, and assign the FAILSAFE mode to a switch, so the pilot can always stop the motors.

Board alignment, the receiver protocol and the motor mixer depend on your drone. Check them on the Configuration, Receiver and Motors screens.

Launch

ros2 launch as2_platform_betaflight as2_platform_betaflight_launch.py namespace:=drone0

The platform configuration file sets the serial link, the rates of each MSP stream and the command limits. These are the values you'll most likely change:

Parameter	Default	What it does
`device`	`/dev/ttyTHS1`	The serial port wired to the flight controller
`baudrate`	115200	The serial baud rate
`imu.frequency`	0	How often the IMU is read, in Hz. 0 turns it off
`battery_hz`	0	How often the battery is read, in Hz. 0 turns it off
`thrust.max`	44.0	The thrust in newtons that maps to full throttle
`limit_thrust_percent`	0.6	The highest throttle the platform sends, as a fraction
`use_thrust_map`	false	Map thrust to throttle with a polynomial instead of linearly

With the defaults, no sensor is read. Set imu.frequency and battery_hz above 0 to publish sensor_measurements/imu and sensor_measurements/battery. For high IMU rates, raise serial_update_rate_hz in the Betaflight CLI too.

With the rest of the stack

The platform only accepts body rates with a yaw rate, so use a controller that produces them, like the differential flatness or the geometric controller. The PID speed controller can't drive it.

The drone's position has to come from outside, for example from motion capture through the ground_truth estimator or from another odometry source through raw_odometry.

Things to know

The platform streams RC values all the time, whatever the platform state.
Switching to offboard does nothing on the drone. The pilot hands over control with the MSP OVERRIDE switch.
The kill switch sets every channel low and the kill channel high, and keeps sending that until the node is restarted.

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