## 3 Construction and Assembly
### Fabrication of the Other Elements and Final Assembly  
Figure 8 shows the final prototype: details of the mechanisms are given in Figure 8b and those of the corresponding CAD image in Figure 8a. The frame (exterior structure) was made of extruded aluminium and had a cross-sectional area of 30 \(\times\) 30 mm\({}^{2}\). It is also worth noting that the mechanical spindle system (\"scissor\" configuration) was located on the left of the prototype. Furthermore, it is important to note that there were two additional components: the motor holder and the motor axis adapter. All these elements were first designed and then 3D-printed.  
Figure 9 shows details of the scissor-mechanism rods that allow separating or approaching the individual concentrators. A 3D-printed white component located at the edge of the top concentrator that had the two photoresistors mentioned above for solar-tracking purposes and a shading element can be seen.  
Figure 8: (**a**) The designed and (**b**) the fabricated prototype.  
Figure 9: The mechanical spindle system with the “scissor” configuration.  
Figure 10 shows all parts of the proposed system that produced the rotation of the concentrators to track the solar altitude. The motor holder structure was attached to the main frame, and there were different options to hold the motor in place. It is important to note that this prototype did not have the final dimensions and will be further optimised to reduce the space occupied. From right to left, the first element of Figure 10 is the motor (component no. 1). This was a stepper motor similar to the one utilised for the translational motion produced by RS (model 892-8732). The motor was fixed to the structure by means of a square printed PLA (polymactic acid) (Figure 10: no. 2). The motor shaft and the spindle were coupled by means of a PLA-printed element, white in colour (Figure 10: no. 3). The spindle consisted of a metric six-threaded rod (Figure 10: no. 4). The component no. 5 (Figure 10) is the nut support of the spindle nut mechanism. Figure 10 shows how the piece printed in PLA houses the nut. This piece was joined by four screws and was connected to an aluminium guide (Figure 10: no. 6). The guide groove was fabricated using the previously mentioned numerical control machine. In order to guarantee that the movement produced by the nut spindle mechanism was equally transmitted to each part of the guide, three support elements were incorporated. These components are indicated by circles (Figure 10: no. 7). Two of them were fixed to the extruded-aluminium components. More specifically, a bolt was threaded into the guide and fixed by means of a piece printed in PLA (grey in colour) that housed a linear bearing. When testing the movement, unwanted movement was observed. To cope with this problem, a third bolt was added. This bolt was fixed to the frame by means of a piece printed in PLA (grey in colour) with a linear bearing. Lastly, the elements no. 8 (Figure 10) are the eccentric connecting rods that connected the guide with the axle of the cylinders and caused rotation. These components were made of grey PLA, and the axle (or pivot) that moved in the guide had a bolt. This configuration minimised friction related to movement. Additionally, the guide was lubricated with graphite powder.  
Figure 10: Details of the rotation-mechanism elements: components 1–8.