# Control Methods Comparison for the Real Quadrotor on an Innovative Test Stand
## 3 Experimental Setup and Results  
### The Quadrotor Platform  
The chosen platform for the verification of control techniques was quadrotor DJI F450. The platform by DJI company consists of a main frame, 30A OPTO ESCs and 2212/920 KV motors. This class of motors was chosen because the total produced thrust of all four motors will be twice as much as final weight of the quadrotor (expected to be around 1000 g). The voltage and type of propellers for these motors are recommended by the manufacturer. As power source, the LiPo battery pack was chosen because of its good weight to power ratio. Manufacturer of BLDC motor advise to use 3 or 4 LiPo cells. With 3 LiPo cells, the 2212/920 KV motor was powered with nominal voltage of 11.1 V. Its maximum rotation speed is about 10,000 rpm. Recommended propeller 10\({}^{\prime\prime}\)\(\times\) 45\({}^{\prime\prime}\) with 25.4 cm in diameter lowers this rotation speed to about 7000 rpm with maximum thrust about 800 g. Motor manufacturers usually mention maximum current consumption at this rotational speed, in this case around 10 A. When this value is multiplied by 4, maximum current consumption of the flying platform can be estimated. Current consumption of other electronics could be in this case neglected. With calculated maximum current battery with higher current loading and capacity to maintain required flying time can be chosen. Battery with capacity of 2.2 Ah was chosen, which provides hover time of about 5 min. The battery has 26C current loading, which is about 57 A, and it was enough for evaluation of the proposed controllers. Maximum current consumed by motor also determines the selection of ESC. A 30 A ESC with 30 to 450 Hz frequency response was chosen, which enables to refresh rotation speed of motor more often than conventional 50 Hz ESCs. Figure 7 shows all abovementioned components and their interconnections. The control unit should maintain control, mathematical and other important operations. There are many usable development platforms, but something more powerful than the standard ARDUINO platform and more real-time than the Raspberry Pi platform with a basic operating system was needed. Therefore, the Discovery platform with powerful microcontroller ST32F4 was chosen. This platform runs at 168 MHz rate, it is relatively cheap, easy to program and offers lots of analogue and digital IO pins and communication interfaces as USART, SPI, I2C and so on. The control unit was powered by the LiPo battery via 5 V step-down converter, that transforms battery voltage to necessary voltage of 5 V. The battery is also connected to the ESCs to power all motors. In order to avoid damage to the battery due to an over-discharge, the analogue input (AIn) was wired to read the actual value of the voltage of connected battery. The IMU MPU9150 was used to measure angular speed in the body-fixed frame. The IMU is able to measure all angular speeds and linear acceleration every 1 ms. The orientation from magnetometer is possible to read every 7 ms. The I2C serial bus is used for communication between the control unit and the IMU. Several commercial IMU chips were compared in parameters as noise rejection, low gyroscope drift, measurement ranges, resolution, refresh, etc., and finally the mentioned MPU9150 unit was chosen. The Bluetooth device RN-42 was used to exchange data between the control unit and an external device such as computer. Module RN-42 offers high-speed full-duplex wireless communication link between PC and STM32F4 on the control board. The USART (Universal Synchronous/Asynchronous Receiver and Transmitter) was used to exchange data between the Bluetooth device and the control unit. The ESCs acquires PWM from the digital outputs (DOut) of the control unit, and transforms this signal into 3-phase power waveform that makes the motor rotate at a specific angular speed.