Design and analysis of a compliant variable-diameter mechanism used in variable-diameter wheels for lunar rover

Variable-diameter wheels have two limited working statuses: the unfolded limit rimless wheel and the folded rigid circular wheel. These can solve the contradiction between tractive performance and the limited spacecraft volume of the lunar rover. The variable-diameter mechanism proposed here is the most critical part. It allows the wheel to transform its structure using expansion-retraction motion and to possess excellent running performance. A novel compliant mechanism configuration with helical torsion springs is introduced, along with its mechanism principles. Based on two extreme wheel statuses, a two-position motion generation using nonlinear optimization synthesis is used to determine the dimensional parameters of the mechanism. The load-deflection behavior is derived by developing a pseudo-rigid-body model for the mechanism. Load-deflection relationships obtained from the pseudo-rigid-body model are compared with the results of finite element analysis (FEA) simulations. The results show that the predictions made by the pseudo-rigid-body model (PRBM) are in good agreement. Overall, the design and analysis approaches proposed here are applicable for variable-diameter mechanisms. In addition, the load-deflection relationships presented can provide theoretical references for the variable control of the wheel diameter.