# Design and Experiment of a Passive Vibration Isolator for Small Unmanned Aerial Vehicles
## 5 Conclusions  
In this paper, a vibration isolator suitable for 1.7 kg class optical equipment was developed, and a testing methodology was presented. The first natural frequency of the drone was simulated using a fixed-fixed beam (WDH: 30 \(\times\) 3 \(\times\) 540 [mm]) as an equivalent model. The vibration test using the fixed-fixed beam assessed damping within the operational frequency band of 40-85 Hz, based on criteria such as damping amount, damping ratio, and damping performance. The analysis of damping characteristics showed that while stiffness levels of 30, 50, and 70 exhibited similar damping amounts and performance in Section 1, stiffness 70 demonstrated the highest damping amount and performance in Section 2. Furthermore, within the operational frequency band, stiffness 70 had the fewest resonance frequencies, leading to the selection of the vibration isolator with a stiffness of 70. The test method using a fixed-fixed beam has the advantage of being able to simulate various drone vibration environments with simple modifications to boundary conditions, resulting in lower costs and time requirements compared to actual drone flight tests.  
In future research, we will verify the damping performance of vibration isolators based on the vibration transmissibility considering the natural frequencies of optical equipment. Additionally, the damping characteristics of vibration isolators will be evaluated under various temperature conditions. Further experiments involving different types of drones and equipment will also be conducted to enhance the versatility of the system.  
Conceptualization, D.-G.K.; methodology, D.-G.K. and C.-H.K.; validation, D.-G.K., C.-H.K. and H.-S.P.; formal analysis, D.-G.K. and S.-W.S.; investigation, H.-S.P.; data curation, S.-WS.; writing--original draft preparation, C.-H.K. and H.-S.P.; writing--review and editing, D.-G.K., C.-H.K. and H.-S.P.; visualization, D.-G.K.; supervision, D.-G.K.; project administration, D.-G.K.; funding acquisition, D.-G.K. All authors have read and agreed to the published version of the manuscript.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **Section** & **Hardness of 30** & **Hardness of 50** & **Hardness of 70** \\ \hline Random & Section 1 & 22.39 & 22.96 & 22.65 \\ vibration test & Section 2 & 198.61 & 527.04 & 453.94 \\ \hline \hline \end{tabular}
\end{table}
Table 8: Damping performance of each vibration isolator (performance unit = ratio).  
\begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Section** & **Damping Ratio of 30** & **Damping Ratio of 50** & **Damping Ratio of 70** \\ \hline Random & Section 1 & 2.2\% & 1.8\% & 1.8\% \\ vibration test & Section 2 & 1.9\% & 1.8\% & 1.9\% \\ \hline \hline \end{tabular}
\end{table}
Table 9: Damping ratio of each vibration isolator.  
Funding: This research was financially supported by the Institute of Civil Military Technology Cooperation funded by the Defense Acquisition Program Administration and Ministry of Trade Industry and Energy of Korean government under grant No. 19 CM5160.  
**Data Availability Statement:** The data used to support the findings of this study are included within the article.  
**Conflicts of Interest:** The authors declare no conflicts of interest.