Design of a Self-Folding Composite Variable-Diameter Wheel Structure based on 4D Printing Technology

The conventional variable-diameter wheel's complex control system and structure seriously affect its mobility and dependability in unstructured terrain. Based on 4-dimensional (4D) printing technology, this work proposes a self-folding composite variable-diameter wheel consisting of a self-folding structure and an outer hub that can self-adjust the wheel diameter under thermal stimulation, avoiding the drawbacks of conventional structures. The structure integrates the control system and variable-diameter mechanical structure using 4D printing. The design and construction of the self-folding structures are introduced, and the mathematical model and design parameters for self-folding motion are obtained using kinematic analysis. Based on the above research and material properties analysis, a programmable morphing structural design and morphing influence investigation based on manufacturing parameters are carried out for the self-folding rod that controls the contraction of this structure. The digital model and prototype have been developed to verify the feasibility of the design and the correctness of the theoretical analysis and to realize the self-adjusting wheel diameter under thermal stimulation.