 Welcome to our step-by-step presentation aimed at helping you build your drone. Before you start, we recommend that you read this disclaimer. This document is intended to explain some of the principles behind multi-copters and flight controller units in order to help you use the STEVALFCU001V1 reference board and modify it for specific purposes. But it would not be considered an exhaustive introduction to the drone world. Please note that flying a multi-copter may be dangerous for both the pilot and others nearby if basic flight conditions rules are not respected. Furthermore, you should check the rules and regulations specified by your country's Civil Aviation Authority or a similar authority and respect no fly zones. An unmanned aircraft system or UAS, sometimes called a drone, is an aircraft without a human pilot on board. Instead, the UAS is controlled by an operator on the ground. A multi-copter or multi-rotor is a rotor craft with more than two rotors. Whereas two rotor helicopters are complex to build because they need variable pitch rotors, whose pitch varies as the blade rotates for flight stability and control. Multi-copters use fixed pitch blades. Control of the multi-copter is obtained simply by varying the relative speed of each rotor to change the thrust and torque produced by each. A quadcopter is a four-rotor multi-copter. Considering we are looking at the drone from the top, we can see its front direction as in the picture. M1 and M3 motors rotate in clockwise mode, whereas M2 and M4 rotate in counterclockwise mode. When all four motors rotate with the same angular velocity, the drone moves in the Z direction, and its angular respect to yaw remains zero, so there is no need for a tail rotor as with conventional helicopters. From left to right, we have three examples showing how the motor rotations are correlated with respect to the drone ascent. In fact, when all the four motors rotate with the same angular speed, the drone adjusts its altitude or hovers. When the angular speeds are greater on counterclockwise motors, the drone rotates clockwise around the yaw axis. On the right, we have an example where more thrust is applied on a single motor, and its opposing motor, on the diagonal, is slowed down. In this way, the drone rotates around the M1-M3 diagonal. There are several frames of different sizes and materials available on the market. For our simplest control algorithm, reference firmware available with ST-EVAL-FCU001V1, the motors and propellers should be placed in equidistant intervals. The main algorithm for flight control usually runs on a 32-bit microcontroller, which either directly controls the speed of each motor or communicates to them via an external electronic speed controller. In order to stabilize the drone, the data coming from the accelerometer and gyroscope sensors are analyzed, while the pressure sensor may be used for altitude control. It is possible to control drones with smartphones and or RIMACONs, specific for multi-copters. These are generally preferred by users because they offer better flight control sensitivity, whereas a smartphone app is cheaper. Each RIMACON has a receive unit that must be connected to the FCU. For drones, LiPo lithium polymer batteries are commonly used. Depending on the size of the drone and motors, one, two or three cell batteries are selected, with different current capabilities and sizes. This kind of battery must be used with particular care because they can be damaged and even explode if overcharged or short-circuited. Electronic speed controller ESC is used to drive a three-phase DC brushless motor in sensorless mode. Generally, it receives an input signal up to 500 hertz PWM from the FCU, with a pulse width varying from 1ms motor off to 2ms motor full speed. The ESC is also connected directly to the battery, representing the V-Bus for driving the motor. Most of them incorporate a so-called BEC, Battery Eliminator Circuit. Basically, a DC-DC converter to give the supply voltage to the FCU. It is possible to control drones with smartphones or RIMACONs. ST has developed an Android application to pilot the ST eval FCU-001-V1. The ST drone app with BLE connection has a layout similar to mechanical RIMACONs commonly used. By modifying the settings, it is possible to customize the interface to each user's preferences. The source code is open source and available on github.com. The Euler angles are very useful to represent the orientation of a quadcopter or other flying vehicle in the air and are used for the basic PID control algorithm of the FCU. The main goal of the FCU algorithm is to move from source angles to destination angles, estimating the Euler angles, alpha, beta, and gamma, and so balancing the drone. The items listed here represent possible assembly items for a small drone and have already been tested with the current firmware version developed by ST, demonstrating stable flight performance. Warning! You may choose different items, but you will need to ensure any necessary firmware adjustments. The ST eval FCU001-V1 must be mounted in the center of the drone equidistant from the four motors. The board must be mounted as flat as possible and well attached to the frame. You can use an adhesive sponge between the frame and the FCU board to minimize mechanical vibration from the motors. The front direction is indicated on the ST eval FCU001-V1 by a small arrow. Current firmware supports the common X configuration shown here, and please note that to use a plus configuration, some modifications to the firmware are needed. To respect the directions and motor placement indicated in the following pages, DC motors should be connected to P1, P2, P4, and P5, following the sequence motor 1, motor 3, motor 2, and motor 4. Warning! A clockwise DC motor can rotate in a counterclockwise direction if plus and minus are reversed, but the brushes are designed for clockwise rotation and prolonged use in the opposite direction to reduce its lifetime. Please do check the documentation of the motor manufacturer for wire color assignment. The ST eval FCU001-V1 is ready to be connected to a standard remote controller like Remicon by using a 4RC channel receive module. The receive module should be connected to the PWM input connector. You should verify that the transmitter is programmed in order to have the 4RC channels assigned as per the following table. The current firmware is compatible with PPM, Pulse Period Modulation Receiver. Note, the above figure refers to a Type II Remicon commonly used for quadcopters. In case of Type I, the commands are switched. A LiPo 1-cell battery can be connected directly to the connector BT1 on ST eval FCU001-V1 board and can be charged via USB thanks to the on-board charger. If it is a 2 or 3-cell battery, it should be connected to the ESC and VBAT should be connected to the 5V Max Input Voltage 5.5V generated by the BEC of the ESC. Warning! A reverse battery protection diode is not mounted. Check carefully before connecting the battery. LiPo batteries can be damaged and even explode if they are short-circuited or overcharged. They should also always be kept in a safe bag when not used or during charging. Please read detailed information from the battery maker or on the internet before handling a LiPo battery. As soon as the battery is discharged after a flight, when there is not enough power to make the drone fly, disconnect the battery from the board immediately. If the battery remains connected and is completely discharged, it will be damaged and you will no longer be able to recharge. To download and debug the firmware on the STM32 F401 MCU, a JTAG with a micro connector SWD should be connected and a voltage should be supplied to the board using a 1S LiPo battery, 3.7V. The following steps must be achieved. 1. A one-cell battery or 3.7V supply voltage by external power supply must be connected. 2. Connect the micro USB cable to avoid discharging the battery. 3. Connect the cable for ST-Link V2 to the SWD micro connector. 4. Optionally, the UART can be used for debug and data logging. After startup, with ST-EVAL-FCU001V1 already mounted on the quadcopter, it is necessary to run a sensor calibration procedure. Place the quadcopter on a flat surface. Press the reset button and move the Remicon control levers to the positions shown in the figure. The ST-EVAL-FCU001V1 will take the flat surface as reference and determine any offsets for the AHRS Euler angle. These offsets must be driven to a value below a certain threshold to avoid flying malfunctions. Note, the same procedure could be performed with the smartphone app by placing the levers in the same position. The first operational tests should be performed without the propellers mounted to verify that connections are correct, the motors function, and the Remicon connection is established. For safety reasons, the drone is initially disarmed. Even if connection with Remicon TX is established and throttle is at full scale, the motors are intentionally not driven. The red LED on the ST-EVAL-FCU001V1 blinks. To allow flight, you must perform an arming procedure. With the current firmware implementation, arming is achieved by moving the Remicon levers to the positions shown in the figure below for at least two seconds. The red LED will stop blinking and remain on. Care must be taken to mount the propeller blades correctly. The propeller is designed according to Bernoulli's principle, where a positive thrust perpendicular to the rotation axis is achieved when the top advances in the sense of rotation. You can recognize CW or CCW orientation by observing the top ribbed direction. CCW blades are also usually marked with an R, reversed. Proceed with your first test flight in an open area with no one in the immediate vicinity after you have followed all the safety procedures during setup and have completed the arming procedure. First, make the drone hover at two meters altitude and ensure that it remains stable. Then proceed with simple flight maneuvers like forming a cross at two to three meters altitude. Be careful. If the drone seems unstable and starts to oscillate, try reducing the PID proportional gain. Refer to the Firmware Description section and PID tuning tutorials on the Internet. For more information, please connect to ST Community and check out our drone zone.