# Reverse Engineering and Topology Optimization for Weight-Reduction of a Bell-Crank
## 5 Results and Discussion
### Design Validation
#### 5.4.3 Experimental Validation of Prototype  
A final validation after manufacturing of the optimized bell crank was carried out using the same laser vibrometer test. The original part was tested again, as well as the optimized part, to confirm that the optimization of the bell crank has been successful and the same testing conditions had been satisfied. Table 3 shows the natural frequency of the original bell crank compared with the optimized prototype. Overall, the optimized prototype showed an increase in natural frequency of 1.5% compared with the original bell crank. Since the difference was within the 5% limit, the optimization task and the machining can be deemed successful.  
The final mass of the optimized bell crank design achieved a weight saving of 2.6% (Table 4). Achieving a reduction in mass of the bell crank not only benefits the overall weight of the sidecar, but also reduces the unsprung mass of the suspension system and, therefore, improves the spring/damper unit efficiency [12]. With a careful design interpretation, the optimized design was able to reduce the density of elements within the design domain, while improving the overall stiffness of the bell crank.  
Moreover, the optimized design achieved a higher value of natural frequency and lower von Mises stress value under the same static load conditions compared with the original part. The resulting topologically optimized bell crank was mounted in the LCF sidecar as shown in Figure 13.  
Figure 12: Prototype of optimal design and CAD comparison.  
\begin{table}
\begin{tabular}{l c c c c} \hline \hline \multirow{2}{*}{**Location**} & **Original Bell Crank, Frequency (Hz)** & \multirow{2}{*}{**Standard Deviation**} & **Optimized Prototype, Frequency (Hz)** & \multirow{2}{*}{**Standard Deviation**} \\ \hline Location 1 & 5055.5 & 1.45 & 5126.6 & 0.70 \\ Location 2 & 5037.5 & 0.70 & 5133.7 & 1.06 \\ Location 3 & 5056.9 & 1.48 & 5119.1 & 0.58 \\ Location 4 & 5087.8 & 1.15 & 5127.0 & 1.40 \\ Location 5 & 5029.6 & 1.41 & 5142.4 & 1.45 \\ \hline Average & 5053.3 & & 5129.  
The modern LCR F1 Sidecar weight is approximately 225 kg, including the engine weight (approximately 50 to 55 kg for current engine specifications). Considering an approximation of 30% to 40% for the sidecar's components (e.g., brake bell, steering, wheel hub and spindle, brake rotor etc.) and further work using the currently proposed methodology that incorporated the topology optimization approach, it was deemed possible that a 5 to 10 kg drop in net weight could be achieved. The methodology described in this paper can be used in mechanical, automotive and aerospace industries for weight reduction design optimization.  
In producing a lightweight product, the present study also contributed to enhancing knowledge of how reverse engineering and non-destructive testing methods can be used effectively for structural topology optimization to solve complex designs without compromising performance and integrity.  
The emerging of additive manufacturing, especially the 3D printing of metallic materials, will enable the possibilities to further optimize and manufacture bell crank with lattice structures [34], and hence, further work could be carried out for topological optimization of complex design, such as the bell crank and other mechanical components, as miniature lattice structures, which leads to even higher weight reduction.