mavlink-interface

The purpose of this repository is to provide a better interface than the c_uart_example that mavlink provides. This interface allows for multithreaded message writing to the interface.

Also included is a position controller class. This is a really simple class that can be used to send both vision_position_estimate and set_position_target_local_ned messages to fully control the desired and current position of the UAV.

Setting Up Repo

git clone https://github.com/rijesha/mavlink-interface
cd mavlink-interface
git submodule init
git submodule update

Setting up the PX4 Compatible Board

Using px4 v1.8.0 the steps to send position data are as follows.

Build the regular release of px4. (https://dev.px4.io/en/setup/building_px4.html) and upload it. Or try to install the latest version available on QGroundControl.

make px4fmu-v2_default
make px4fmu-v2_default upload

• Select a multirotor airframe.
• Change EKF2_AID_MASK to accept vision information. (set value to 24 to completely disable GPS and only use vision)
• Change EKFS_HGT_MODE to Vision.
• Change SYS_COMPANION to 921600.

Power the px4 via battery. I have experienced issues with the local_position_target message when powered via usb.

Making And Running the Example

Set up the serial port name in main.cpp

#define PORT "/dev/ttyUSB0"
#define BAUD 921600

Then build and run the program.

make
./position_controller

Integration of the Mavlink Multithreaded Interface

Setting up the Multithreaded Interface

Multithreaded_Interface mti;
mti.start(PORT, BAUD);

Reading Messages from Mavlink Interface

Reading Last Message received (Polling Mode)

Example for how to read last available message.

auto search = mti.last_messages.find(MAVLINK_MSG_ID_ATTITUDE);
if(search != mti.last_messages.end()) {
    mavlink_attitude_t att;
    mavlink_msg_attitude_decode(&(search->second), &att);
    printf("[Roll Pitch Yaw] = [%f %f %f] \n",att.roll, att.pitch, att.yaw);
}
else {
    std::cout << "Attitude Message not yet Received\n";
}

Binding a message callback function (Interrupt Mode)

The purpose of this mode is to allow a received message to trigger an action.

Create function with the following signature

std::function<void(mavlink_message_t)> // functions returns void and takes in mavlink_message_t

Example callback function with proper signature.

void new_msg_callback(mavlink_message_t message) {
    if (message.msgid == 0){
        cout << "Received HB" << endl;
        mavlink_heartbeat_t heartbeat_msg;
        mavlink_msg_heartbeat_decode(&message, &heartbeat_msg);
    }
}

Binding the callback

mti.bind_new_msg_callback(new_msg_callback);

Writing Messages to Mavlink Interface

Encode and send a mavlink message. See position_controller.cpp for an example.

mavlink_message_t message;
mavlink_msg_command_long_encode(system_id, companion_id, &message, &com);

//Send the message
mti.write_message(message);

Setting Up Periodic Messages

A periodic message class has been made to allow for periodic messages to be sent. positional_controller.cpp has a great example of how to use it.

Setting up Periodic_Message object.

mavlink_message_t current_position_message;
int frequency = 10; // frequency in Hz
Periodic_Message current_position_periodic(*mti, current_position_message, frequency);

Updating the message

current_position_periodic.update_message(current_position_message);

Integration of Position Controller Class

Setup the mti as previously and the setup of position_controller.

Position_Controller p(&mti);

Update current and desired positions

p.update_current_position(x, y, z, yaw);
p.update_desired_position(x, y, z, yaw);

After 100 desired position messages, offboard mode can be enabled.

p.toggle_offboard_control(true); // enable offboard mode
p.toggle_offboard_control(false); // disable offboard mode