# Robotized Mobile Platform for Non-Destructive Inspection of Aircraft Structures
## 2 Structural Design and Control System
### Hardware  
The control block for the motors driving the wheels was built on specialized DRV8801 PWP systems from Texas Instruments. These systems were created to control DC motors powered by voltages from 8 to 36 volts. This system was selected, among others, because of its small dimensions, which makes it possible to design a smaller and lighter circuit. The second function block is a serial communication interface system built on the MAX3232 CSE from Analog Devices. It enables the conversion of 3.3 volt logic to the RS232 interface standard with voltages of \(-12\) and \(+12\) V. A larger voltage difference allows data to be transmitted over longer distances and is more resistant to interference. The next block is the MEMS digital accelerometer system from Analog Devices. It is a three-axis accelerometer that can measure accelerations in four ranges, \(\pm 2\) g, \(\pm 4\) g, \(\pm 8\) g, \(\pm 16\) g and in a resolution of 10 bits (0-1023). The power supply voltage range is from 2 to 3.6 V, and communication with the main microprocessor takes place via the I2C serial interface, which uses only two microprocessor ports. Measuring the acceleration value in three axes allows determining the angular position of the vehicle in space. This allows for automatic regulation of the thrust of the propeller drive depending on the angle of the inclined surface on which it is moving. The fourth block is the radio communication system built on the HOPERF RFM75 system. It is a small module in a housing designed for surface mounting with dimensions of 12.8 \(\times\) 16.8 mm. It operates in the ISM band 2400-2483.5 MHz and has the ability to programmatically adjust the output signal power in the range from \(-25\) dBm to 4 dBm. It can transmit data at speeds of 250 Kbps, 1 Mbps or 2 Mbps with the possible length of a single data packet set from 1 to 32 bytes. Communication between this module and the main microprocessor takes place via the SPI interface with a maximum clock frequency of 8 MHz. The fifth block is the Bluetooth radio communication module built into the HC-05 system. Similarly to the previous block, it allows wireless communication in the Bluetooth 2.0 standard. Working in this standard allows for the use of, for example, a phone or tablet with the appropriate application installed as a remote control. The sixth block is the power supply system. It is composed of a linear stabilizer LM1117-3.3, which reduces the input voltage to 3.3 V. This is the voltage at which all semiconductors on the motherboard can be powered. The input of the system is protected by a rectifying diode, which protects the remaining components against reverse voltage polarity. This block also contains capacitors and a choke that filter the input voltage from interference that may come from the BLDC motor controller, brush motors or from the mains converter powering the entire system. The next blocks are the inputs and outputs of signals controlling, among others, the servo mechanism of the head lifting system and the BLDC motor regulator. The last element is the microprocessor block that controls the entire vehicle. It is built on the ATMEGA16A chip from MICROCHIP. This block also includes a quartz resonator with a frequency of 8 MHz, which is the source of the microprocessor clocking signal, and a six-pin connector for uploading the software to the microprocessor's flash memory. The entire system was assembled on a double-sided printed circuit (see Figure 2) with dimensions of 60 \(\times\) 100 mm. The control module (see the scheme in Figure 3) was mounted in the front part of the MP and connected to all other components. The power supply of the MP comes from an external switching power supply with an output voltage of 17 V (no load) and a maximum load capacity of 50 A. It was decided to use a power supply with a higher output voltage due to the losses (voltage drops) between the power supply and the MP.