## 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)
This ratio can be used to quantify the minimum spatial needs of the two tests after having defined the biggest machine that will be possible to test with the rig under development;
* The required technical features, particularly with regards to the shape of the support plane, are different; the static tests require a simple and flat 'tiltable' plane, whereas the dynamic tests also require the creation of an edge on such plane;* Both types of test require a common feature of the system, i.e., the plane on which the vehicles are placed and made to travel. This must offer the possibility of being tilted with respect to the support plane of the whole system. The requirements of the test platform in terms of indicative size, movement capability (maximum tilting angle) and applied loads (in this case: the maximum allowable mass of the agricultural machines to be tested) should be drawn from market surveys or technical databases. Indeed, with such sources of information it is possible to accurately identify the technical requirements and a possible market of reference. Limiting agricultural machinery to tractors only, an indication of the maximum angle of inclination, which future installations must be able to guarantee to experimenters, may emerge from the analysis of the technical characteristics of existing tractors--e.g., those in OECD test reports--and if necessary limited to a maximum power or dimension class. For example, the following graphs (Figure 6) show the lateral and longitudinal stability angles of tractors tested from 1960 to 2014, calculated from the data collected during the tests according to OECD codes 1 and 2: in particular, the CoG height from the ground, the distance of the CoG from the rear axle, and the lateral shift of the CoG to the left were used [72]. The sample of tractors used for this survey (1438 tractors), although not coinciding with the entire population of tractors produced in the reference period, is still representative of world production quotas in the different years (the largest manufacturers and with more models per manufacturer are considered) and can therefore be used to make effective considerations for the present purpose. Figure 5: Some stability tests that the new test rig should be able to perform: (**a**) static test of lateral rollover (point of view–pow–from the back of the tractor); (**b**) static test of global stability (pov from above); (**c**) static test of global static load transfer (pov from the back of the tractor); (**d**) dynamic test of global stability on a flat and tilted plane (pov from above). Observing the graphs of Figure 6 reporting all the data (which are particularly useful to identify the outliers), with regards to the static overturning angles it may be noted that:  
* a test rig capable of tilting at least 50\({}^{\circ}\) is sufficient to test the static lateral stability of practically all the tractors produced to this day, since a maximum angle of more than 50\({}^{\circ}\) (more precisely, 50.1\({}^{\circ}\)) has been recorded for only 2 tractors out of 1438, i.e., for the 0.14% of the total;
* a platform capable of tilting 55\({}^{\circ}\) is sufficient to test the static longitudinal stability of most tractors produced to this day, since a maximum angle greater than 55\({}^{\circ}\) has been recorded for only 21 tractors out of 1438 (1.5% of the total), none more recent than 1999; bringing the maximum angle of inclination to 57.5\({}^{\circ}\) would leave out only 7 tractors (0.5%). Similar considerations can be made also for the maximum mass of the vehicles to be tested on the rig. In this case the decision can involve the dimensional class of such tractors, intentionally ignoring the largest tractors from the price lists of various manufacturers, which are anyhow also the rarest on the market. For example, considering a maximum testable mass of 6400 kg theoretically allows to test all 4 WD tractors in the medium range, i.e., with a maximum power of about 110 kW/148 HP (calculated by using a mass-to-power coefficient of 60 kg kW\({}^{-1}\)).