# Robotized Mobile Platform for Non-Destructive Inspection of Aircraft Structures
## 2 Structural Design and Control System
### Selection of Components  
At the assumption of building the MP, which will be functional, lightweight, and low-cost, the components were selected upon the availability at the market. To generate thrust of the MP, two types of drives can be used: a classical propeller drive and an EDF. After analyzing 19 types of drives available on the market (pre-selected considering the criteria of the maximal thrust possible to generate by a drive), its current and power consumption, efficiency, and price, the EMAX GT2826/04 drive with the APC 10x5 propeller was selected. It was noticed that EDF drives are characterized by small size and compact construction, however, they can generate much lower thrust and have significantly lower efficiency than classical propeller drives. The selected propeller drive with a propeller can generate a thrust of 3.1 kg at the efficiency of 224.3 W/kg with its own mass of 0.175 kg. The estimated thrust is sufficient under the assumption that the weight of MP will not exceed 2 kg and the friction coefficient of a wheel thread will exceed 0.8. Next, the regulator for the selected brushless direct-current (BLDC) motor was chosen from 10 pre-selected options considering the continuous current value. The chosen regulator was ZTW Beatles-50A BEC, characterized by a continuous current of 50 A and a built-in voltage stabilizer (the so-called BEC system) with a maximum output current of 5.5 A and a voltage of 5 A. This regulator can be used to power the remaining control electronics. Assuming a possibility of turning and changing the direction of MP during inspections, it was decided to design the wheel drive performed by four independently driven and controlled wheels. For this purpose, DC motors integrated with the gear were selected. The parameters taken into account during selection were the output torque calculated in Section 2.1, as well as rotational speed and weight. Considering them, the Pololu 4826 gear motor with a built-in encoder was selected. To fulfill the previously defined assumptions on wheels, the DFRobot wheels with a diameter of 80 mm and a width of 17 mm were used to build the MP. This model was chosen mainly due to availability, low price, and weight, as well as the possibility of removing the treadmill and installing a treadmill made of another material. The power supply for the designed MP was selected considering the electrical power demand of particular components. The most power consumable component is the propeller engine, whose maximum power consumption can reach 700 W at a supply voltage of 14.8 V, while the consumption of other components compared to the latter is negligible. Two options were initially considered:  
* power supply from the vehicle's built-in lithium-polymer battery,
* power supply via a converter from the power grid. In this case, energy is supplied to the vehicle through a two-core cable with an appropriate cross-section. The length of the cable connecting the probe (mounted on the MP) with the flavor detector is 3 m. Therefore, the minimum length of the power supply cable is also 3 m. The weight of a two-core cable with a cross-section of 4 mm\({}^{2}\) (this is due to the current consumption) in a silicone insulation is 0.3 kg. Silicone-insulated cables are characterized by greater flexibility and, due to the higher maximum operating temperature of the insulation, higher current carrying capacity. Batteries made using lithium-polymer technology, weighing approx. 0.3 kg and voltage 14.8 V, have a capacity of approximately 3 Ah. This amount of stored energy allows only for 4 min of operation at the maximum power consumed by the propeller drive. Therefore, considering the short operating time using the built-in battery for power supply, power to the MP will be supplied from an external network converter via a two-core silicone-insulated cable with a cross-section of 4 mm\({}^{2}\). The conditions of inspection taking place in covered hangars also allow using of this type of power supply.