# Multi-Criteria Optimization of an Innovative Suspension System for Race Cars
## 5 Development and Testing of the Physical (Experimental) Prototype  
The process of modeling, simulation, and optimization in a virtual environment, the results of which are presented in Figure 25 in the form of the full-vehicle virtual prototype, preceded the implementation of the physical prototype, a subject addressed from here on. In order to develop the physical prototype, the following steps were taken: Embodiment design of the full-vehicle suspension system, starting from which the execution and assembly drawings were generated; executing or acquisitioning the components; assembling the components; acquisition and mounting the data monitoring system (sensors). The physical prototype of the proposed suspension system was implemented and tested with the help of BlueStreamline, the Formula Student team of the Transilvania University of Brasov (Figure 26). The data acquisition system used to measure damper travel consisted of two short distance sensors (sharp), an Arduino MEGA 2560 development board, a breadboard, and a SD memory card socket. The programming language used by the microcontroller was C#. The data acquisition system used to measure the forces transmitted in the chassis consists of an AQ-1 data logger, which had a built-in force sensor that was mounted on the chassis near its center of mass. The data thus collected were transferred for postprocessing into EXCEL. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **Four-Bar** & **New Solution** & **Four-Bar** & **New Solution** \\ \hline  & \multicolumn{2}{c}{**Front**} & \multicolumn{2}{c}{**Rear**} \\ \hline Roll center height [mm] & 250 & 246 & 280 & 290 \\ Caster center height [mm] & 150 & 147 & 190 & 188 \\ Anti-dive/squat [\%] & 50 & 49 & 65 & 67 \\ \hline Camber [deg] & 1.5 & & 1 & \\ Toe [deg] & 0.7 & & 0.5 & \\ Kingpin angle [deg] & \(-\)3.9 & & \(-\)4.07 & \\ Steering axis offset [mm] & 3.1 & & 0 & \\ Scrub radius [mm] & 30.75 & & 2 & \\ Caster trail [mm] & 17.25 & & 8 & \\ Track width at wheel center [mm] & 1210 & & 1150 & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Suspension system characteristics. Figure 25: Full-vehicle virtual prototype of the Formula Student single seater. In order to evaluate the dynamic behavior of the single-seater prototype, several tests were carried out, which were similar to those the single seater would have to pass through in the competitions. Further, the results obtained in the case of the left-right cornering and passing over vibrators, as well as a skid pad type event, were presented. The tests were performed on the starting circuit from Prejmer (Figure 27). For the overpass vibrators' test, all the corresponding vibrators of all corners must be reached. This test aimed to check the speed response (reaction) of the suspension system (Figure 28), and the way it supports lateral forces (Figure 29). According to the diagrams shown in Figure 29, it is possible to observe the shift of loading forces that act on the car from on one side to the other (left-right) at the time of turning, in both wide and tight corners. At the same time, a linear behavior was observed in the suspension system, which induced a good handling of the car and reduced the necessary corrections in the steering wheel while turning. Figure 28: Front spring and damper movement—circuit lap. Figure 26: The Formula Student single seater equipped with the proposed suspension. The skid pad type event was carried out in an especially arranged track that mimicked the Formula Student layout shown in Figure 30. The diagrams in Figure 31 show the movement of the front axle spring and damper assembly during constant cornering (left and right). By analyzing the results from Figure 31 (maximum damper travel of \(+/-20\) mm) and Figure 28 (maximum damper travel of \(+/-30\) mm), it is clearly seen that the suspension did not reach its end stops during the skid pad event.