## 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')
#### 3.3.3 Proposal of an Actuation Mechanism (\(\rightarrow\) Step 1.d)  
Thanks to the synoptic table above, the following solution has been outlined: the system to perform the global static stability tests (and hence all other stability tests listed in Section 3.1.2) is a subsystem of the main test rig thought to test the stability of a motionless vehicle (global static stability), and it is configured as a rotating platform ('turntable'). Indeed, combining the tilting angle given by the supporting structure operated by another subsystem (defined in the previous paragraphs; see Section 3.2), with the angular position of the turntable, the longitudinal axis of a vehicle can be positioned at different angles as regards the maximum slope direction. The turntable is an integral part of the platform here described and it can be placed in the lower semi-platform. The turntable surface (above which the vehicle in test is placed) is perfectly aligned with the surface of the lower semi-platform and should be made of the same material (Figure 24, top). When the turntable is not in use for performing any static stability test, it should be locked so that any vehicle performing a dynamic test on the whole extension of the platform can travel also on the turntable surface along circular trajectories (Figure 25). In the same way, if during the dynamic tests there is a need to change the surface properties of the platform by covering it with the removable panels described in Section 3.1.2, it should also be possible to fix the panels onto the turntable. The approximate sizing of the turntable diameter can be performed only after establishing the maximum size of the tractor that can be tested with this system. Since all four wheels of the vehicle should be placed inside the rotation circle of the turntable, the Pythagoras theorem can be applied to the measures of the tractor wheelbase and maximum width, assuming therefore that the geometric center of the tractor is close to the platform center. For example, considering only the New Holland tractors that are currently produced, the diameter should be at least 3174 mm (excluding the models of the T8 series, which are very large) or 4362 mm if including the T8 series. The wide dimensions of the  
Figure 24: Example of positioning of a tractor on the turntable to measure the weight on each individual support as a function of the inclination angle of the platform; the load-cells that support the four quadrants over which the tractor is placed are schematically represented as cylinders. Figure 25: When the platform (**left**: inclined only; **right**: inclined and angled) is used to perform dynamic stability tests, the circular trajectories (shown here with radius: 2500, 3500, 4500, 5500, 6500 mm) to be followed by the vehicle under test tread across the turntable (in blue). t the two-dimensional (10000) tiltable support surface of the platform (each semi-platform has a size of \(8\times 16\) m), the values just found are not a problem and the diameter can be chosen to be of 5000 mm. In order to measure the weight loaded on each tire during a stability test and quantify the load transfer due to the inclination, the surface of the turntable is divided into four independent quadrants, one per each tire (Figure 24, bottom right; Figure 26). Each quadrant is placed on a load-cell that can measure the force exchanged with the supporting structure below, as in the systems realized by [PERSON] et al. [3] and by [PERSON] et al. [48], with the important difference that, in the present case, the turntable and its weighing quadrants can rotate around a vertical axis (Figure 27). The quadrants and the load cells are fixed to an underlying rotating support structure. Although the load cells are placed at a fixed distance from each other (at the vertices of a square and at a distance of 1060 mm from the center, i.e., at the geometric centroid of each quadrant), any vehicle able to position its wheels on the quadrants can be tested.