# Mechanical Design and Testing of Mobile Monitoring Units for Security Systems
## 2 Materials and Methods
### Mobile Monitoring Units
Protection against the influence of water and humidity present in the proximity of terrain is also ensured by the height-adjustable legs. Figure 2: Mobile monitoring unit: (**a**) first design; (**b**) second design. The vertical construction of the mobile monitoring unit is firmly connected to the base and is used for the attachment of various sensors, such as the above-mentioned laser, optical or ultrasonic sensors, FMCW radars and communication units. On the top of this construction, there is a customized platform with two adjustable axes, which is used for the precise adjustment of the solar panel. The precise adjustment of the azimuth and elevation angles of the solar panel is important for the efficient use of sunlight to achieve the maximum efficiency of the solar panel. It is made of high-quality materials to ensure not only precision positioning, but also the necessary stability and related long-term operational life and reliability of the mobile monitoring unit. The overall mechanical design of the mobile monitoring unit can be seen in Figure 3b. It has been carefully designed to be easily transportable and durable. The hexagonal base allows the better utilization of space, and the adjustable legs were designed so that the mobile monitoring unit can be placed on uneven surfaces (Figure 4). The material cost for the construction of one unit, involving profiles, legs, tensioning cables, covers and sealings, is EUR 1045. As the sensor equipment and power supply system are modular, these costs are not fixed and were not included into this calculation. However, as the mechanical design is created from metal parts, another possible problem is lightning. This is because lightning can cause not only impact stresses on the metal construction, but also damage the sensor fixtures fabricated from thermoplastic materials using 3D printers. Also, the sensors and related electronics can be damaged. As the primary purpose of the mobile monitoring security system is to protect groups of people against the spread of viral diseases, its application is assumed in the proximity of buildings. In this case, the protection is secured by lightning rods mounted on the buildings in the proximity of the mobile monitoring units. If we assume its application outside inhabited areas, this problem can be solved by an active lightning system placed in the proximity of the mobile monitoring station. However, as will be seen from the simulation and measurement results, a subsequent third modification of the mobile monitoring unit was necessary to enhance the stiffness of the construction against vibrations that can be caused by external influences, such as, for example, wind gusts. The high stiffness of the construction is necessary due to the correct function of sensors, because many of them are sensitive to vibrations and these vibrations  
Figure 3: Mobile monitoring unit: (**a**) model of construction made from the aluminum profiles, (**b**) manufactured prototype. can result in false warning or alarm situations. Therefore, the mechanical design of the mobile monitoring unit was supplemented by tensioning steel wire cables, the stiffness of which can be adjusted using clamp tensioners.