## 3 Application of the Design Approach to the Definition of the Innovative Test Rig
### Design of the General System ('Test Rig')
#### 3.1.2 Definition of General Requirements (\(\rightarrow\) Step 1.b)  
Therefore, the test rig under development must be able to perform the following tests:  
* Static tests of a vehicle that is placed, motionless, on a sloping support. Its steering components (wheels, central joint) can be oriented as to follow a straight-path trajectory or to perform a steering maneuver. The trials are repeated with several inclinations of the support. If there is some equipment (backhoe, crane boom, arm, etc.) that can assume different positions, the listed tests can be repeated with this equipment fixed in several different positions or moving at different speeds. The static tests can assess:
* lateral stability (\(\rightarrow\) classic test of lateral-rollover; Figure 5a); in this test the longitudinal axis of the vehicle and the maximum slope direction are perpendicular;
* longitudinal stability (\(\rightarrow\) classic test of longitudinal stability, or hopping test); in this test the vehicle longitudinal axis and the maximum slope direction are aligned, and the vehicle front part is uphill;
* global stability (Figure 5b); in this test the vehicle longitudinal axis and the maximum slope direction are angled (any angle between \(-180^{\circ}\) and \(+180^{\circ}\));
* global static load transfer (Figure 5c) and lying down on the downstream tire (real inclination of the frame) for a vehicle in the aforementioned conditions, i.e., at any angle between the vehicle longitudinal axis and the maximum slope direction of the support surface;
* Dynamic tests of a vehicle moving along a circular path with a constant radius and at different constant speeds. The dynamic tests can assess:
* global stability on a flat and tilted plane (Figure 5d); in this test the inclination of the tangent line varies at each point of this circumferential trajectory and it forms an angle comprised between -180\({}^{\circ}\) and +180\({}^{\circ}\) with the platform maximum slope direction;
* global stability on a tilted plane with an edge, i.e., simulating a steering maneuver with a change in the slope (e.g., a tractor entering/exiting from an inter-row). Some of the above-described tests are coded by international norms, especially the tests of static lateral-rollover stability [42; 43]. Others are completely new and could provide much more information concerning the use and the users' safety of agricultural machinery on sloping grounds. According to the presented approach, it could be suitable to analyze the requirements by finding analogies and differences and, therefore, to conceptually subdivide the general test-system into several subsystems, each addressing one or more requirement. A first analysis of the technical requirements of a possible facility leads to the following considerations:  
* The above-mentioned tests have very different requirements in spatial terms; indeed, the dynamic tests require much more space than the static tests due to the need for the vehicle to travel a whole circular path. As a practical rule-of-thumb, it is possible to calculate the test area dimensions starting from the dimensions of the width of the supporting surface of a conventional tractor. The ratio between the minor dimension of the support polygon of the machine and the minimum room of the test area can be approximated by 1 to 5. Indeed, due to the similarities in the proportions and in the maximum wheel-steering angle of all farm tractors, the minimum turning radius is usually about twice the minimum width of a tractor. In the calculation of the minimum manoeuvring space two half widths of the tractor have to be added, thus reaching the factor of 2 \(\times\) 2 + 1 = 5.