arduino-with-mavlink

Tutorial that explains connection with a quadrocopter based on APM 2.6 with an Arduino ESP32 board. Project is made like a part of the DroneTeam project.

DroneTeam Project

This repository is a part of DroneTeam project. More about this project you can learn here

My school taking part in this prject you can find here

DronE app

All the code contained here is related to the DronE android app. This app is used with ESP32 for remote control.

DronE repository - Source code. Play Store link - Place where you can download the app.

Getting Started

To start creating briged connection, you have to download the following libraries and software.

Software

This is a mandatory software that you have to include into the project to compile it successfully.

• Arduino - Arduino IDE
• ESP32 - Esp32 arduino library
• Mavlink - Mavlink core library

Sources

Below there are some links with really helpful knowledge. Mostly you will find only the official mavlink documentation which isn't sufficient and clear for begginers.

• Basics - A great document with explanation of the elementary issues of mavlink messages and issues.

• Mavlink common - Official mavlink's list with the all commands. The most important are numbers that stands for the appropriate message.

• Mavlink's code - This article contains step by step entry for coding in mavlink. Highly recommended to read before starting to code.

• Mavlink and arduino - This is a working example of professional usage mavlink protocol in the Arduino environment. Requires a lot of time to understand everything at all.

Code

Mavlink protocol doesn't send any useful information without requesting it. In the examples below you can see working requests. Code must be initiating in an interval.

Variables

Mavlink sends one message at once. You need to declare message variable and length of a packet.

mavlink_message_t msg;
uint8_t buf[MAVLINK_MAX_PACKET_LEN];

Heartbeat

Indicates correct connection. Should be executed firstly.

void mav_heartbeat_pack() {
  mavlink_message_t msg;
  uint8_t buf[MAVLINK_MAX_PACKET_LEN];
  
  /**
   * @brief Pack a heartbeat message
   * @param system_id ID of this system
   * @param component_id ID of this component (e.g. 200 for IMU)
   * @param msg The MAVLink message to compress the data into
   *
   * @param type Type of the MAV (quadrotor, helicopter, etc., up to 15 types, defined in MAV_TYPE ENUM)
   * @param autopilot Autopilot type / class. defined in MAV_AUTOPILOT ENUM
   * @param base_mode System mode bitfield, see MAV_MODE_FLAGS ENUM in mavlink/include/mavlink_types.h
   * @param custom_mode A bitfield for use for autopilot-specific flags.
   * @param system_status System status flag, see MAV_STATE ENUM
   * @return length of the message in bytes (excluding serial stream start sign)
   */
  mavlink_msg_heartbeat_pack(255,0, &msg, type, autopilot_type, system_mode, custom_mode, system_state);
  uint16_t len = mavlink_msg_to_send_buffer(buf, &msg);
  SerialMAV.write(buf, len);
}

Arming

Main mavlink command for changing arming state is a MAV_CMD_COMPONENT_ARM_DISARM. Every MAV_CMD_... you have to send via mavlink_msg_command_long_pack.

void mav_arm_pack(boolean state) {
  mavlink_message_t msg;
  uint8_t buf[MAVLINK_MAX_PACKET_LEN];

  //Arm the drone
  //400 stands for MAV_CMD_COMPONENT_ARM_DISARM
  // 1 an 8'th argument is for ARM (0 for DISARM)
  if(state) {
    //ARM
    mavlink_msg_command_long_pack(0xFF, 0xBE, &msg, 1, 1, 400, 1,1.0,0,0,0,0,0,0);
  }else {
    //DISARM
    mavlink_msg_command_long_pack(0xFF, 0xBE, &msg, 1, 1, 400, 1,0.0,0,0,0,0,0,0);
  }
  uint16_t len = mavlink_msg_to_send_buffer(buf, &msg);
  SerialMAV.write(buf, len);
}

Changing flight mode

The last parameter defines flight mode. Some values you can check below.

• Stablize - 0
• AltHold - 2
• Auto - 3
• Loiter - 5
• Circle - 7

void mav_set_mode() {
  mavlink_message_t msg;
  uint8_t buf[MAVLINK_MAX_PACKET_LEN];
  
  //Set flight mode 'Stabilize'
  mavlink_msg_set_mode_pack(0xFF, 0xBE, &msg, 1, 209, 0);
  uint16_t len = mavlink_msg_to_send_buffer(buf, &msg);
  SerialMAV.write(buf, len);
}

Overriding RC (Radio control) channels

Overriding RC channels you are able to adjust motors speed and severally roll, pitch, throttle, yaw.

void mav_override_rc(int roll, int pitch, int throttle, int yaw) {
  mavlink_message_t msg;
  uint8_t buf[MAVLINK_MAX_PACKET_LEN];

  mavlink_msg_rc_channels_override_pack(0xFF, 0xBE, &msg, 1, 1, roll, pitch, throttle, yaw, 0, 0, 0, 0);
  uint16_t len = mavlink_msg_to_send_buffer(buf, &msg);
  SerialMAV.write(buf, len);
}

Contribution

I would like to thank Ola and Paweł for their support and contribution. They helped me a lot with documenting and looking for the sources.

• Aleksandra Pawłowska - sources, media documentation
• Paweł Modzelewski - documentation, electronic consultation

MIT License

Copyright (c) 2018 Tomasz

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.