## 3 Application of the Design Approach to the Definition of the Innovative Test Rig
### Design of the General System ('Test Rig')
#### 3.2.1 Conceptualization of the Mechanism(s) for Operating the System (\(\rightarrow\) Step 1.c)  
Based on the expressed requirements, the design process of the platform involved the conceptualization of the kinematic mechanism(s) to operate the system. Limiting the number of the rigid links to four, it is necessary to determine how they are interfaced, i.e., how the \"basic system components\" perform their \"fundamental interactions\" [64] to define the kinematic mechanism. With that maximum number of components, there are three different possibilities (Figure 10):  
* Two links only (scheme '2L' of Figure 10), the first one (AB) connected to the ground through a revolute pair (in A), the second one (BC) connected to the first link through another revolute pair  
Figure 9: Transition maneuver of a vehicle from a horizontal surface (yellow) to a lower/inclined surface (white; the blue arrow indicates the slope direction of the inclined plane), analogous to the maneuver of exiting of an inter-row depicted in Figure 1; with a rigid chassis, the tire highlighted in red is not touching any surface; in the proposed test rig each of the two colored surfaces is one of the two semi-platforms. (in B); both of them have an integrated surface on their top used for making a tractor travel (i.e., these two links are just the semi-platforms);
* Three links (scheme '3L' of Figure 10), one of them (AD) is a sort of support structure connected to the ground through a revolute pair (in A); when this link is inclined with respect to the ground, the two links supported by it (AB, BC) are inclined as well; the other two links have an integrated surface on their top used for making a tractor travel (i.e., these two links are the semi-platforms) and can be angled with respect to one another through two revolute pairs (in A and B) and a slider (in C);
* Four links (scheme '4L' of Figure 10), two of them (AB, DE) connected to the ground (in A, E) and forming, together with another link (BD) connected to them through revolute pairs (in B, D), an articulated parallelogram, able to keep horizontal the position of link BD whichever the inclination of AB; there is another link (BC) connected to the link AB through another revolute pair (in B); the links AB and BC have an integrated surface on their top used for making a tractor travel (i.e., these two links are the semi-platforms). As the test rig will have two degrees of freedom, the final project will have (at least) two actuators or rather, two pairs of actuators due to the spatial extension of the installation. Indeed, as a general principle, in the development of a structure, each dof of the system (i.e., considered an independent movement) should correspond to an actuator of some kind. The test configuration of the system is given by fixing the relative positions of the two semi-platforms (AB, BC in Figures 10-13) for the duration of a test, and this can be controlled by acting on:  
* the position of the free end-points of each link (B, C, D) in terms of relative distance from a reference (ground, or other link; see Figure 11, schemes 2L.a-d, Figure 12 schemes 3L.a-d, Figure 13 schemes 4L.a-d), obtained by supporting them (e.g., with linear actuators), and/or
* the inclination of these links (AB, BC, AD, DE) related to a reference (ground, other link; see Figure 11, schemes 2L.b-e, Figure 12 schemes 3L.b-f Figure 13 schemes 4L.b-f), obtained by blocking the revolute pairs (e.g., with a rotary actuator or a linear actuator, connected to the two articulated links so close to the articulation hinge as to act as a rotary actuator). Figure 10: Side schemes of the kinematic mechanisms to operate the platform (the \(y\)-axis is vertical); the semi-platforms are always AB and BC (in black) in all the schemes; other links (AD in scheme **3L**; BD, DE in scheme **4L**) constitute auxiliary structural components (in gray). The schemes presented in Figures 11-13 report each of the solutions described above.