*2.1. Hexapod Walking Robot: SmartHex*

In this paper, a six-legged robot with mammalian leg structure named SmartHex is used [20]. Each leg has three joints: base joint, hip joint, and knee joint. The robot is suitable for outdoor work due to its low energy consumption and large load characteristics [21]. The robot is controlled by a backward control based on a σ-Hopf oscillator with decoupled parameters for smooth locomotion [22]. The hardware structure of the robot is shown in Figure 1. BLi, HLi, and KLi (BRi, HRi, and KRi), respectively, indicate the base joint, hip joint, and knee joint of the left (right) leg. LF, LM, and LH (RF, RM, and RH), respectively, indicate the front leg, middle leg, and hind leg of the left (right) side. Each joint consists of a high-reduction-rate gear system and a DC servo motor with an integrated encoder, which is used to detect the position of the joint angle. In order to identify the environment around the robot with a high accuracy, Microsoft's Kinect 3D vision sensor is installed on the robot chassis to collect terrain information. The Kinect's red/green/blue (RGB) camera can collect color images with a resolution of 1920 × 1080 px. A complementary metal-oxide superconductor (CMOS) sensor is responsible for receiving and transmitting infrared signals. Meanwhile, current detection modules (CuSLi and CuSRi) are installed to record the energy consumption of each leg for different gaits. The arrows in Figure 1 indicate the directions of current flow. The robot's posture is monitored by the attitude sensor (AS). The data processed by the wireless module mounted on the control panel are transmitted to the host computer to create instructions [23].

**Figure 1.** Architecture of robot: (**a**) hardware structure; (**b**) distribution of sensors. BLi, HLi, and KLi (BRi, HRi, and KRi), respectively, indicate base joint, hip joint, and knee joint of left (right) leg. LF, LM, and LH (RF, RM, and RH), respectively, indicate front leg, middle leg, and hind leg of left (right) side.
