## 3 Prototype Description and Implementation
### Prototyping of Hardware Components
A PPM signal is nothing more than a series of PWM signals transmitted through the same cable one after the other. The transmitter module has a built-in T-shaped antenna. These types of antennas are used for the transmission of medium and long wavelength signals. c. RC receiver (on board the UAV): CrossFire Nano Rx [44]. It is a small-sized receiver of great usefulness due to its small size, in addition to the robustness and range it offers. The normal course of action would be for it to implement the TBS Crossfire (CRSF) protocol, but given the impossibility of doing so, it is also compatible with PPM. The radio control receiver has another T-shaped antenna that will be placed on one of the legs of the drone. 5. Rotors: the rotors that have been selected for the prototype are the MN2212 18 model from the manufacturer T-Motor. They are specific for UAVs used to travel long distances and usable in, at least, medium sized-UAVs. In case of this UAV, the rotors have 920 KV (KV refers to the constant revolutions of a rotor per Volt, that is to say, the revolutions per minute that the rotor offers when 1 Volt of voltage is applied). While its maximum speed is not as high as what racing drone motors can offer, it is torquier and will lift the UAV with ease. Additionally, motors with a lower KV have a smoother ride. 6. ESC (Electronic Speed Control): a speed variator or electronic power controller has as its fundamental purpose to vary the speed of an electric motor, along with the direction of rotation. Typically, the UAV controller sends a PWM signal to the ESC with variations of 1 to 2 ms. If the value is 1 ms, the motor will be stopped. If it is 1.5 ms it will be at half power and at 2 ms it will be at 100% power. For the implementation of the requirement-compliant UAV, four variators of 30 Amperes each have been chosen. There are several ESC features that must be considered, like the maximum current that an ESC can deliver to the motor, the size of the propellers, the number of battery cells or the type of motor that is being used in the UAV. 7. Finder: while it is an accessory not essential for the operation of the aircraft, it can be very useful for the operator when an UAV has an accident (i.e., the UAV falls into an area with high vegetation and becomes difficult to locate). In the environment where the deployment will be made there are areas with cereals, tall grass, bushes, etc. Therefore, it will be necessary to integrate the finder in our aircraft. This finder is connected to one of the PWM channels that the Navio2 has and is activated through a switch in the transmitter. The chosen Finder is the JHE42B S model [44]; it has an extra battery that gives it a few minutes of duration if the UAV battery runs out of power. It is also possible to use the sound emitted by its buzzer to guide the sheep in the desired direction, although they may ignore it once they get used to it. 8. Battery: the battery mounted by the aircraft must have enough autonomy for the UAV to travel to the desired area and be able to make the return trip. The deployment that has been performed works with relatively long distances (2-3 km), so a battery with a higher capacity than those regularly used is required. The choice made is a LiPo battery (Lithium Polymer). This type of battery has been selected due to its energy storage capacity, in addition to the fact that it offers a high discharge rate, something very necessary for multi-rotors. The battery has 4 cells of 3.7 Volts each, so its nominal voltage is 14.8 Volts. It has a discharge capacity of 25 C and a capacity of 6750 milliamperes, enough to cover the distances used in the deployment for testing purposes. Cs of a LiPo battery refer to the rate of discharge. It stands for the capacity of a battery, usually measured in Ampere hours or Ah. The higher the C of a battery, the shorter its life and the higher the speed it can achieve. In this case, being 25 C, there is a balance between battery life and the maximum speed that the aircraft can reach.