**4. Toward heavy-payload multirotor UAV prototype**

This chapter will present the results of individual design phases of a multirotor aircraft that is planned to be used as an integral part of the presented concept of an air robotic system for applications in precision agriculture. Experimental measurements of the considered propulsion units were conducted, on the basis of which payload analysis was performed for several configurations. Based on obtained physical parameters, a model was set up and preliminary simulations were performed, with the help of which it is possible to estimate the energy consumption of a real system.

#### **4.1 Electric propulsion unit characterization**

In order to adequately select aircraft components to ensure the performance of aircraft required for certain tasks (maximum cargo weight, flight speed, flight time, others), it is important to determine the thrust generated by a specific combination of motor and propeller and to determine power consumption. Based on a certain thrust, the maximum load capacity of the aircraft is determined with regard to the defined thrust-to-weight ratio. Based on electricity consumption, more specifically through the relationship between electric current and thrust, it is possible to estimate the maximum flight time depending on the mission. Manufacturers of propulsion elements generally also provide specifications, as previously shown in **Figure 6**; however, these data are not in all cases consistent with actual characteristics. Therefore, for a more precise analysis of the propulsion, it is necessary to perform characterization, and in this paper, the method described in the previous research was used [45] utilizing the experimental test stand RCbenchmark 1780 [46]. **Figure 10** shows the thrust force as a function of the angular velocity of the rotor for the considered propulsion units where the measured experimental characteristics and the characteristics according

**Figure 10.** *Thrust force with respect to rotor angular velocity.*

**Figure 11.** *Electric current with respect to the thrust force.*

to the manufacturer's specifications are shown. Furthermore, **Figure 11** shows the electric current as a function of the thrust force for the purpose of estimating the flight time.
