**4.2 Additive manufacturing procedure**

A framework for the production of parts for specialised multirotor UAVs using additive manufacturing is presented. It consists of an aircraft design stage in which various software packages can be used for the needs of 3D modelling of parts and

**Figure 11.** *Additive manufacturing procedure.*

*Framework for Design and Additive Manufacturing of Specialised Multirotor UAV Parts DOI: http://dx.doi.org/10.5772/intechopen.102781*

assemblies, and also for simulations. In this research, the SOLIDWORKS software package is used in the design stage. After the process of creating a model is done, triangulation of the 3D CAD model is performed and the model is exported into an STL format. In the prototyping stage, it is necessary to adjust the parameters of the 3D print in accordance with the selected AM technology using associated software, the socalled slicer. The next step is the execution of the g-code by which the given parts are produced. After finishing the print, the parts need to be post-processed (**Figure 11**).

### **4.3 Experimental verification**

Manufactured parts of specialised multirotor UAVs are connected together with other components into functional assemblies. Through the prototyping phase, different test phases were conducted for the two aircraft based on propulsion units with the parameters given in **Table 2**. By assembling and testing individual subsystems, potential design errors can be identified, and improvements offered.

The control subsystem of the experimental aircraft is based on the open-source Pixhawk FC. To operate a fully-actuated aircraft, custom firmware has been developed.


#### **Table 2.**

*Considered multirotor configuration main parameters.*

**Figure 12.**

*Experimental testing of PTX6 configuration in case of attitude control.*

**Figure 13.** *Heavy-lift aircraft propulsion: (a) EPU testing; (b) EPU assembly.*

**Figure 12** shows the indoor testing phase where attitude control experiments were conducted. Indoor testing provides a safe way to set the basic parameters of the control subsystem and set up and test all safety elements. It is also possible to tune the parameters of the control algorithm. After the indoor phase, the remote control of the aircraft was tested in two cases that differ by control inputs from the RC transmitter. The first case is represented with conventional control inputs (thrust, roll, pitch, and yaw), while in the second, control inputs were three forces and yaw moment with respect to body axes.

For the second experimental aircraft, the propulsion unit was tested in different operating regimes at the full power range. Characteristics were obtained (**Figure 9b**) and other parameters, such as heating, were monitored (**Figure 13a**). Given the power of the aircraft, the described framework is used in a wider range of rapid prototyping, which includes cutting carbon plates, which together with printed parts and prefabricated tubes form the rotor arm assembly (**Figure 13b**). In the coming period, it is planned to assemble the propulsion subsystem into a functional assembly so that tests can be carried out as in the case of the first experimental aircraft.
