## 3 Application of the Design Approach to the Definition of the Innovative Test Rig
### Design of the General System ('Test Rig')
#### 3.1.3 Delineation of General Features (\(\rightarrow\) Step 1.c)  
Starting from these last considerations and with the aim of developing an apparatus with the ability to perform both static and dynamic tests, a system (here called 'platform') was developed which is equipped with a wide tilting plane. This plane should allow a vehicle, possibly with a trailer, to travel on its surface following complete circular trajectories (Figure 7), so its dimensions (\(16\times 16\) m, as stated above) originate from the intention of performing the dynamic tests. The possibility to be tilted constitutes the first degree of freedom of the whole system (Figure 8A).  
Figure 7: Overturning forces acting on a vehicle under a dynamic test **(left)** in some significant points of the trajectory (in red); seen from the top of the supporting plane **(right)**; the weight force is in blue, the centrifugal force is in green, the resulting force in the same inclined plane is in red; \(r\) and \(s\) are, respectively, the radial and perpendicular direction to the radius in a generic point.  
The need to generate an edge on the plane implies the need to have a second subsystem for moving part of the plane (second degree of freedom; Figure 8B). In particular, this further subsystem should have the final effect of generating an angle between two parts of the support surface (namely, half-planes or semi-platforms) and to allow the operator the possibility of having the upstream part of the support parallel to the ground or not. Looking at the spatial convenience, the best solution is placing an angulation hinge as wide as the platform width at about halfway along the plane. The two semi-platforms have therefore equal dimensions (see Section 3.2).  
The creation of an edge between the two support half-planes (semi-platforms), to be overcome with the mechanical vehicle under test, is fundamental for the simulation of the exit maneuver of the same mechanical vehicle from an inter-row of a terraced slope in a controlled environment. In particular, this degree of freedom of the structure makes it possible to reproduce the dangerous load transfer that occurs at the same time as the change of support (tires in contact with the support ground; see Figure 9).  
The need to perform the static test at many angles of the vehicle longitudinal axis with respect to the maximum slope direction is a slightly more complex matter. In general, this could also not require another degree of freedom (dof) of the test-equipment. In fact, a hypothetical test of this type can be performed as follows: (1) the vehicle can be moved horizontally on the plane by using its own propulsion system, (2) the plane is tilted until the vehicle reaches an incipient overturning situation, (3) the plane is moved to the horizontal position again, then (4) the vehicle is moved once more into another position on the plane and steps 1 to 3 are repeated. The need to reposition the vehicle several times during a test, however, makes such a solution not practical and urges the designer to provide a faster/easier placement of the vehicle by giving the whole system a further dof (third degree of freedom), thus requiring another sub-system, called 'turntable' (see Section 3.3).  
Figure 8: Side schemes of the platform, with its two degrees of freedom (dofs) in evidence: inclination (**A**) and angulation (**B**).  
Design of the Subsystem to Perform the Dynamic and Static Stability Tests (i.e., the 'Tiltable and Angleable Platform')