# Development of a Novel Variable-Diameter Wheel
## 6 Conclusions  
In this study, the influence of mechanisms on wheel performance was considered for wheel design. The mechanism characteristics are achieved without weakening the wheel's performance. This design guideline has significance for future design and development of deployable wheels. To improve the performance of the existing variable-diameter wheels, we have developed a novel variable-diameter wheel with an innovative compliant mechanism. The proposed wheel uses the same mechanism characteristics as the conventional variable-diameter mechanism but includes more advantages. The wheel's spoke structure eliminates the additional moments acting on the wheel feet during mechanism motion and improves the support stability for the wheel feet. In addition, the wheel leg structure that has three flexure pivots reduces the number of links in the mechanism movement plane, thereby simplifying the kinematic equations for the design and the PRBM for analysis. This structure enables a more compact and reliable mechanism compared with conventional variable-diameter wheels. The presented planetary gear train helps the wheels to continuously adjust in diameter so that the rover can adapt to rough terrains. This feature can improve the rover's obstacle-surmounting capability and stability. In conclusion, the proposed wheel enhances the wheel performance and practicability in real applications. Thus, the new variable-diameter wheel can be utilized not only in planet rovers for rough-terrain planetary explorations but also in earth-based  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{\(\theta_{1}\)} & \multirow{2}{*}{\(\theta_{2}\)} & \multicolumn{3}{c}{\(M_{1}\) (N-mm)} & \multicolumn{3}{c}{\(M_{2}\) (N-mm)} \\ \cline{3-7}  & & **PRBM** & **FEA** & **\%Diff** & **PRBM** & **FEA** & **\%Diff** \\ \hline
103.5\({}^{\circ}\) & 22.5\({}^{\circ}\) & –31,572.65 & –31,880.05 & 0.96\% & 19,340.47 & 19,575.3 & 1.2\% \\
113.5\({}^{\circ}\) & 18.5\({}^{\circ}\) & –54,471.28 & –54,622.25 & 0.28\% & 43,365.75 & 43,428.14 & 0.14\% \\
123.5\({}^{\circ}\) & 14.5\({}^{\circ}\) & –73,162.13 & –73,031.2 & 0.18\% & 63,226.63 & 62,952.67 & 0.44\% \\
133.5\({}^{\circ}\) & 10.5\({}^{\circ}\) & –86,752.77 & –86,267.8 & 0.56\% & 77,993 & 77,375.2 & 0.80\% \\
143.5\({}^{\circ}\) & 6.5\({}^{\circ}\) & –94,515.47 & –93,952.3 & 0.60\% & 86,900.66 & 86,182.82 & 0.83\% \\
151.5\({}^{\circ}\) & 2.5\({}^{\circ}\) & –96,336.40 & –96,104.2 & 0.24\% & 89,592.73 & 89,190.67 & 0.45\% \\ \hline \hline \end{tabular}
\end{table}
Table 3: Comparison of results between modified PRBM and finite element analysis (FEA).  
mobile robots for agriculture and forestry, military applications, rescue operations, and disaster areas. Moreover, the novel wheel is applicable in locomotion systems, especially on unstructured and soft terrains.  
Practical design and analysis approaches for the proposed wheel were also considered. The established kinematic equations were applied to the motion control of the wheel mechanism. The load-deflection relationship was derived from the modified PRBM. The results in Table 3 indicate that the proposed design and analysis tools are suitable for the proposed wheel. The modified PRBM can help operators control changes in the wheel diameter on rigid terrains. Furthermore, the design and analysis methods used in this study are applicable to other deployable wheels.  
[PERSON] and [PERSON] conducted this study and proofread the manuscript together; [PERSON] conceived the idea, designed and analyzed the wheel, and wrote this manuscript; [PERSON] contributed to the FEA for the wheel and proofread the manuscript. This research was funded in part by the National Natural Science Foundation of China under grant number 51675027 and in part by the National Key Technology R&D Program of China under grant number 2016 YFD0700503-1  
The authors declare no conflict of interest.