# Configuration Design and Gait Planning of a Six-Bar Tensegrity Robot
## 1 Introduction  
Recently, deep space exploration has become an important research direction in the aerospace field with the development of science and technology [1, 2, 3]. However, problems such as the high cost of traditional exploration robots, complex landing methods, and a small number of launches are difficult to solve. Therefore, developing new planetary probes is becoming urgent and important. A tensegirty structure is a selfequilibrium system composed of a continuous set of cables and a discrete set of struts, for which the designs are characterized by rigid bodies that are suspended in a balanced tension network of elastic elements; these configurational features make it lightweight, compliant, and impact-resilient under external loads. Therefore, it is an ideal new type of planetary probe to complete dangerous and highly unknown tasks and has become a research hotspot in the fields of aerospace, bridge construction, and special robots recently [4, 5, 6, 7, 8, 9]. As shown in Figure 1, the planning of the exoplanet exploration mission of the six-bar tensegirity robot was proposed in 2015 by the NASA Ames Research Center [10]. Tensegrity structures were originally applied in the field of architecture; the cable-rod structure is a key component of the tensegrity structures. In order to prevent collapse and maintain the ideal shape and stiffness, the key to the cable-rod structure is to keep a certain initial prestress. Therefore, the configuration design and shape optimization of the tensegrity structure are particularly important, for which the force density method [11], the dynamic relaxation method [12], the energy method [13], and iterative algorithms [14] are widely used. [PERSON] et al. [15, 16] proposed a form-finding method for a multistress modal tensegrity structure based on force density and grouping methods, and the spatialpositions of nodes and cables of the tensegrip structure were obtained by minimizing the energy function. [PERSON] et al. [17] proposed a stiffness matrix-based form-finding (SMFF) method for tensegrip structures. This form-finding method easily determines the selfequilibrated and stable configuration of a tensegrip from an arbitrary initial state. [PERSON] et al. [18] proposed a form-finding method for free-form tensegrip structures by TPE minimization using a genetic algorithm and computationally showed that it is possible to perform form-finding for tensegrities using simple calculations when compared to other form-finding methods. Recently, due to the strong flexibility exhibited by the tensegrip structures, more and more researchers focus on its application in the field of space exploration. NASA [19] has developed two types of tensegrip robots for the \"Titan\" planetary exploration program and conducted simulation experiments for application scenarios. [PERSON] et al. [20] designed a six-bar tensegrip robot driven by BMX150 shape memory alloy (SMA) coils, described the topological transition diagram, and proved that the robot prototype has a crawling ability through experiments. [PERSON] et al. [21] designed a six-bar tensegrip robot constructed by soft pneumatic actuators instead of cables, which realized continuous tumbling on a flat surface. [PERSON] et al. [22] developed a tensegrip robot simulation simulator; it was proved that the tensegrip structure could roll according to the predetermined motion trajectory. [PERSON] et al. [23] proposed a six-bar tensioning integral robot and designed and studied the single-step rolling method of the robot through simulation analysis. [PERSON] et al. [24] designed a tensegrip robot and conducted continuous rolling experiments through tumbling gait simulations to obtain the influence of the structural parameters on the robot's rolling. The above research fully proves that the tensegrip robot has strong motion performance. However, gait planning for continuous motion is rarely involved.