## 3 Experimental Investigation and Results
### Refinement and Enhancement
To improve the position of the CG of the structure, it was necessary to move the center of gravity towards the front as much as possible, by shifting the side-swing doors to the front of the vehicle. As a guideline for improving the position of the CG of the structure, it is advisable to shift the side-swing door installation towards the front of the vehicle and evaluate the subsequent variation in the center of mass, as shown in Figure 10. Move it three levels from the original position which are 5, 10, and 20 cm, respectively. According to the simulation, the position of the CG of the structure and the forces generated on each leg changed, as shown in Table 3. This causes the mass that each leg bears to shift more towards the front-left direction, which is the direction that improves the balance of the structure. The side-swing door installation position was changed by moving it to the front of the car. It was found that the mass at the position where the leg supports the force decreased at positions G and H by approximately 30%, causing the position of the CG of the structure to change, as shown in Figure 11. The displacement of the center of mass of the structure is directly proportional to the extent to which the side-swing door is moved. Based on the simulation results, it can be concluded that moving the side-swing door installation position 20 cm to the front shifts the position of the center of mass of the structure forward by a distance of 32 cm. Figure 9: Simulation conditions and loads. Due to the results of the simulation of the prototype structure in the previous topic, it was found that the structure still had a very high FOS. It is necessary to reduce the size of some parts of the structure to reduce the weight of the structure and save production costs. Therefore, it was decided to reduce the size of the additional structural steel by changing the size of the square tube (ST) to a C-light lip channel (CL) and using an angle steel bar to fasten it to the structure, as shown in Figure 12. Adjusting the size caused it to lesser affect the load behavior compared to the original model, as shown in Table 3. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Leg Support Position**} & \multicolumn{2}{c}{**Distance of the Forward Shift in the Installation of the Side-Swing Doors Form Original**} \\ \cline{2-5}  & **Original** & **Shift 5 cm.** & **Shift 10 cm.** & **Shift 20 cm.** \\ \hline A & 55 & 55 & 55 & 55 \\ B & 22 & 23 & 23 & 24 \\ C & 32 & 32 & 32 & 32 \\ D & 18 & 18 & 18 & 18 \\ E & 17 & 18 & 20 & 22 \\ F & 81 & 82 & 83 & 85 \\ G & 41 & 44 & 42 & 37 \\ H & 54 & 52 & 52 & 52 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The weight at the leg of the CBF structure affecting the chassis (kg). Figure 11: Changes in (a) percent mass at leg support, and (b) CG position at different distances. Figure 10: The positions of the side-swing doors’ sliding installation design. The structure received a load, along with the side-swing doors that were adjusted by moving the installation position forward by 20 cm, and we found that the structure had collapsed from the load over a distance of 3.1 mm, as shown in Figure 13. In addition, it was found that the maximum stress and strain values were 363 MPa and 1.05 \(\times\) 10\({}^{-3}\) mm/mm, respectively. The position where the maximum strain and stress occurred was on the steel beam used to attach the C-light lip channel beam structure to the main structure, as shown in Figure 14. The aforementioned strain value is in a range that causes the steel to undergo permanent deformation, which poses a significant risk to the structure. In order to prevent damage to the angle steel bar (flat steel) when clamping the top steel beam to the main structure, the thickness of the flat steel used for clamping the beam was simulated to be 1/8 inch or 3.0 mm. The results of the simulation show the maximum force behavior that occurs on the structure, which is presented in Table 4.  
Figure 12: Characteristics of structural improvement.