# The Design and Building of a Hexapod Robot with Biomimetic Legs
## 1 Introduction  
The grounds of construction sites or factories are often muddy or scattered with debris. Under such circumstances, wheeled vehicles used for material handling might be easily blockaded by obstacles or experience skidding on the muddy grounds. Hence, this inspires us to pursue the development of a hexapod robot to replace a wheeled vehicle. However, robots are complex and expensive machines, consisting of many actuators, sensors, transmissions, and hardware. Therefore, a method of developing a hexapod robot to reduce the cost by means of using a minimal number of actuators is proposed. In this article, a hexapod robot was conceived, designed, and built. In the development of a legged robot, there are two primary concerns, i.e., how to generate a stable gait, so that the robot can walk without tumbling, and how to perpetually generate stable gaits. Regarding the first concern, [PERSON] and [PERSON] [1; 2] proposed the COG (center of gravity projection) method in 1968, stating that the legged robot is statically stable if the horizontal projection of its COG lies within the support polygon, which is defined as the convex polygon formed by connecting the footprints. [PERSON] [3] generalized the COG method in 1976, proposing the COP (center of pressure) method, where a robot is dynamically stable if the projection of the COG, along the direction of the resultant force acting on the COG, lies within the support polygon. In 1969, [PERSON] and [PERSON] [4; 5] further proposed a method in favor of the biped robot called the ZMP (zero moment point) method, where a robot is stable if the moment about the COP, at its supporting foot, is zero. As to the second concern, many rhythmic movements such as locomotion, respiration, swallowing, etc., in animals, have been found to be produced by a CPG (central pattern generator) [6; 7; 8; 9; 10; 11]. Neuroscientists [12] have employed a variety of techniques, including anatomical, behavioral, physiological methods, etc., to investigate the specific neural circuits and discover the mapping functionin those circuits. One notable study on the locomotion of the salamander [13] proposed the CPG model based on nonlinear oscillators instead of neural network oscillators, presented numerical as well as mechanical simulations, and successfully constructed a salamander-like robot. Some studies [14; 15; 16] have addressed to the locomotion of hexapods with CPG and established mathematical models not only including the rhythmic generator, but also the interlimb coordinator, so that the hexapod can adapt to variant terrains by gait transition. Beyond bio-inspiration, a new trend of research that is noteworthy is the merging of natural and artificial components, which is defined as bio-hybrid organisms [17; 18], also called bio-robots, in which an artificial component or a biological organ is incorporated into an animal or robot, respectively. These studies even investigate how the artificial agent interacts with an animal individual or a population. So far, all studies have relied on electronic circuits or processors to implement the locomotion of legged robots. Computers have always been thought of as nothing more than electronic devices, which is not necessarily the case. Recalling the evolution of computer science, the earlier computing devices, called calculators, invented by [PERSON] of France (1642) and [PERSON] of Germany (1671), were built with the technology of gears. In fact, they were mechanical calculators, where data was represented through gear positioning and entered mechanically, by adjusting the initial gear positions. The output of the calculators was achieved by observing the final gear positions. Therefore, mechanical devices can be regarded as computational processors, as long as they execute certain mathematical operations. This was the inspiration to create a mechanism, or mechanical computational processor, to complement the electronic processors.