## 3 Application of the Design Approach to the Definition of the Innovative Test Rig
### Design of the Subsystem to Perform the Global Static Stability Tests (i.e., the 'Turntable')  
3.1 Conceptualization of the Mechanism for Operating the System and Illustration of a Possibility for Implementing the Mechanism (\(\rightarrow\) Step 1.c)  
If, as frequently occurs, the attention of a designer of test equipment is focused only on the vehicle to be tested or on the test system but not on both, the creativity of the designer could be limited, thus bringing to conventional solutions only, precisely as observed by [PERSON] [77]. As regards the static stability tests (lateral stability, longitudinal stability, global stability, global load transfer; see Section 3.1.2), for example, the designer could be led to regard the object of the test (here: an agricultural machine) as completely still/immobile on a piece of equipment. All the creative efforts are directed toward the test rig, and particular attention will be diverted to conferring the test rig with all the degrees of freedom required to perform the tests on the vehicle. This way of thinking has brought to the conceptualization of the first 'tiltable' platforms (conventional 'tiltable' platforms), having a single dof necessary to tilt the platform and induce the overturning of the vehicle placed above these, as in the system developed by [PERSON] et al. [3]. A possible evolution of this system would be to equip the test rig with a second possibility of inclination as proposed by [PERSON] et al. [46] to test the stability of a machine also in a direction perpendicular to the first without moving the test subject. This second possibility of inclination could constitute a real second dof of the system as well as not, in the sense that:  
* The second inclination could be alternative to the first (Figure 21), as visible, for example, on dump-trailers having two possibilities of tilting (in these trailers, the body is inclined in one direction or in the other by blocking/unblocking the articulation hinges of interest); in this case, the system would have only one dof at a time (i.e., the inclination), which is activated in two different (perpendicular) directions, one at a time (see Figure 21a,b); two hinges are a revolute pair that can be disassembled (A, C in Figure 21), the third one (B in Figure 21) is instead a ball joint; it is interesting to note that the system can be operated by a single linear actuator, which acts on the only vertex that does not have a hinge (D in Figure 21);
* The second dof could be concurrent to the first dof and constitute a true second dof of the considered system (Figure 22), thus providing tilting directions comprised between the two main directions (i.e., the directions parallel to the longitudinal and transversal axes of the vehicle in test), thus spanning an angle of \(90^{\circ}\); in this case, the system implementing the contemporary double-tilt has two revolute pairs and a ball joint like in the other architecture of Figure 21, but it could be even very complicated; indeed, it is necessary to have an additional, intermediate frame that is the support structure for the second inclination mechanism that operates the plane supporting the vehicle under test. Figure 21: Exemplification of a platform for executing static stability tests having two alternative possibilities of inclination (illustrated in the pictures **a,b**); the locked (i.e., active) hinges are represented in black (A, B in picture a; B, C in picture b), the unlocked hinge is white and the initial positions are indicated within brackets; all possible movements are indicated by the red arrows; the blue arrows indicate the maximum sloping directions; the rectangle positioned in the middle of the ‘tiltable’ platform represents the support polygon of a vehicle in test. Instead, by adopting a holistic point of view, other possibilities can be explored (\(\rightarrow\) step _1.d_) and the final result of the conceptualization process could be even more interesting than the above-described solutions.