## 1 Introduction  
Researchers investigating wall-climbing robots looked to nature for inspiration. Around the gecko, researchers studied the gecko's toe and crawling approach to propose some wall-climbing robots. On the basis of numerous studies on the gecko [1; 2; 3; 4; 5; 6], the gecko's adhesion mechanism was proposed, and the relevant wall-climbing robots inspired by the gecko were investigated. [PERSON] et al. [7] assessed a four-legged wall-climbing robot with an elastomer adhesive pad to climb a sloped surface. A novel robot [8] was presented with a shape memory alloy actuator to drive its climbing. A microfiber with an angled mushroom tips [9] array inspired by gecko was manufactured for a novel wall-climbing robot, Waalbot [10; 11]. These studies applied the special structure array inspired by the gecko to the wall-climbing robot. [PERSON] et al. [12; 13; 14; 15] learned from the gecko's pad and body structure to present a gecko-like, wall-climbing robot. A bionic pad of this robot consisted of a microfiber array and four-legged locomotion. The tail was inspired by the gecko's toe and the gecko's climbing gait. [PERSON] et al. [16] proposed a novel wall-climbing robot with a biomimetic gait inspired by the gecko, which adjusted the posture of the robot's foot to stably adhere to the wall. [PERSON] et al. [17; 18] assessed a tank-like, wall-climbing robot with gecko-inspired material on the caterpillar band. This robot climbed on a vertical surface, on the ceiling, or travelled from the vertical surface to the ceiling. In another line of research, a series of studies were presented on wall-climbing robots inspired by animals with claws for traversing rough surfaces. [PERSON] et al. (2019) proposed a model of claws' adherence on rough surfaces and investigated the relation of the dimensions of the claws with respect to the particles. [PERSON] et al. (2019); [PERSON] et al. (2020); [PERSON] et al. (2020) presented a six-legged, wall-climbing robot with alternating tripod gait for climbing a wall with stability. [PERSON] et al. (2020) proposed a RiSE robot with six legs and flexible spines inspired by insects. The robot climbed a 90\({}^{\circ}\) tree in addition to carpted and cork covered stucco surfaces in the quasi-static regime. Then, the foot of this robot was improved to climb on the wall with stability. A new type of the wall-climbing robot ([PERSON] et al., 2020) was assessed and demonstrated better performance. An improved wall-climbing robot ([PERSON] et al., 2020) was proposed with better stability and faster movement. Based on the results presented by [PERSON] et al. (2020) on the behaviors of the cockroach, [PERSON] et al. (2020); [PERSON] et al. (2020); [PERSON] et al. (2020) proposed a bionic, double-legged wall-climbing robot for rough surfaces. Furthermore, quadrupedal wall-climbing robots ([PERSON] et al., 2020; [PERSON] et al., 2020; [PERSON] et al., 2020) were proposed with a lateral leg spring model. [PERSON] (2020) proposed a wheeled wall-climbing robot with bionic feet inspired by Serica orientalis Motschulsky; it was capable of climbing across the transition from horizontal to vertical surfaces. Then, a novel, tracked, wall-climbing robot with bio-inspired spine feet was presented for rough surface ([PERSON] et al., 2020). It can be seen from the literature that the wall-climbing robots studied by many researchers only aim at smooth or rough surfaces and rarely prepare wall-climbing robots that adapt to both smooth and rough surfaces. This paper proposes a novel type of wall-climbing robot with a gear transmission system arm for climbing on the smooth and rough surfaces that absorbs the adhesion characteristics of gecko and cicada. The novel actuating structure consisted of a five-bar link, gear transmission system, and drive source servos. The dynamic characteristics of the gear transmission of the robot were obtained by a numerical model. In the transmission system, the driving gear was driven by the servos, and the two driven gears were fixed with the links.