Planetary rovers may traverse terrains with complex geometries and variable physical properties, but their mobility behaviors are complicated and difficult to simulate precisely. This article focuses on high-fidelity dynamic modeling and simulation for a type of rovers that incorporate single-input-multi-output joints to enhance terrain adaptability, which has been used on China's Tianwen-1 Mars rover. A novel multibody dynamic model and its solutions are derived first with consideration of single-input-multi-output joints. Then, a unified terramechanics model is proposed, considering variable terrain surfaces and covering rover's motion states of skidding, slipping, and steering, solved the problem of simulation instability caused by model switching between soft and hard terrains. As the contact areas of wheels with various terrains and resultant sinkage are dominant factors to ensure fidelity but difficult to determine, a new terrain modeling method for calculating contact area and wheel sinkage is developed using digital elevation map with physical properties. A simulation system is developed, integrating all the above models, and verified with physical experiments and commercial software. The relative simulation errors that have been achieved are less than 5.9% for bogie angles, 6.1% for drawbar pull, and 3.4% for slip ratios, demonstrating high fidelity simulation results.

This paper presents a trajectory optimization formulation for planning dynamic trajectories of a six-degree-of-freedom (six-DOF) cable-suspended parallel robot (CSPR) that extend beyond the static workspace. The optimization is guided by low-dimensional dynamic models to overcome the local minima and accelerate the exploration of the narrow feasible state space. The dynamic similarity between the six-DOF CSPR and the three-DOF point-mass CSPR is discussed with the analyses of their feasible force polyhedra. Finally, the transition trajectories of a three-DOF CSPR are used as the initial guess of the translational part of the six-DOF motion. With the proposed approach, highly dynamic motions for a six-DOF CSPR are efficiently generated with multiple oscillations. The feasibility is demonstrated by point-to-point and periodic trajectories in the physics simulation.

Compared with conventional robots, soft structures such as living octopus arms and various soft-robot arms have more degrees of freedom (DOFs) and greater flexibility. Soft robot arms have a considerable range of applications. However, it is arduous to establish a mechanical model for them, because of the hyper-redundant DOFs, and the hyperelasticity and nonlinearity of the soft material. In this study, to investigate the deformation of soft octopus robot arms, the simplified closed-form analytical equations for the curvature and torsion were derived according to the Cosserat theory. A closed-form model for axial constriction was developed. The analytical equations were experimentally validated, and a dynamical simulation of the multi-flexible bodies was performed for a cable-driven soft-robot arm inspired by the octopus. The results show satisfactory accuracy.

Wheeled exploration robots are prone to slip during locomotion on deformable rough planetary terrain, which leads to loss of velocity and extra consumption of energy. Experimental results show that the power required for driving a wheel is an increasing function of its slip ratio; further, the tractive efficiency decreases rapidly after it reaches a peak value when the slip ratio is between 0.05 and 0.2. In this study, wheel-soil interaction terramechanics, which considers the slip ratio as an important state variable, is applied to analyze the quasi-static equations of a planar robot system. The slip ratios of wheels are controllable, but the degree of freedom is the number of wheels minus 1. A generalized algorithm for distributing the slip ratios of all the wheels of a robot to optimize the energy consumption is presented. Experimental and simulation results show that the “equal slip ratio” is at least a sub-optimal solution for optimizing energy consumption. Further, a more robust control method has been developed; this methods aims to equalize the slip ratios of all the wheels while maintaining a constant body velocity on rough terrains, without solving the values of the slip ratios. This method is verified by controlling a virtual four-wheeled robot using dynamics simulations.