# Omnidirectional Jump of a Legged Robot Based on the Behavior Mechanism of a Jumping Spider
## 4 Results
### Sideways Jump  
The simulation experiment of the robot jumping sideways is carried out to verify whether the joint angle, attitude angle, jumping height and jumping distance are consistent with motion planning or not. Unlike the vertical jump, there is much variability in the joint kinematics and attitude with the sideways jump. At the beginning of the sideways jump, the lateral body axis began to rotate sideways in the jumping direction. The initial attitude is adjusted to prepare to jump. At the same time, the CoG drops and begins to store energy. During the acceleration phase of the sideways jump, the effective leg length of the robot extends quickly and the foot impacts the ground quickly, then the robot starts to take off. Figure 9b shows a sketch of the robot jumping sideways. The initial height of the robot is 180 mm, the jumping height is 100 mm, and the jumping distance is 250 mm. During the robot's sideways jump, the legs in contact with the ground are first flexed and then extended. Each joint of the six legs has a different rotation angle. Before the acceleration phase begins, the CoG begins to drop and store energy at 0.3 s (Figure 9d); the legs on one side of the robot's body are obviously flexed, but those on the other side remain relatively small in the jumping direction. From 0.3 s to 0.8 s, the robot body slows down and adjusts the attitude. At this instant, the femur-patella joint angle, tibia-metatarsus joint angle and metatarsus-tarsus joint angle begin to slowly change, and the cox joint angle remain constant until the jump ends (Figure 9c). Then, the foot impacts the ground quickly the robot's legs start to extend and the robot begins to accelerate at approximately 0.8 s. The joint angle begins to change quickly (Figure 9c), while the cox joint angle of the middle leg remains unchanged; this is due to the robot's structure and path planning of the sideways jump. The displacement of the robot in the jumping direction begins to change, depending on the time at which the robot is in the air. Then, the robot leaves the ground and takes off, with the height of the CoG at 320 mm in this moment. The robot rises to its maximum height of approximately 420 mm and completes the task of jumping 100 mm (Figure 9d). At 1.4 s, the robot will touch down. The robot is in the air for approximately 0.4 s, while the jumping distance is 250 mm (Figure 9d). The robot jumps to the right. From 0.8 s to 1.2 s, the femur-patella joint angle changes by approximately 2 rad, the tibia-metatarsus joint angle changes by approximately 2.5 rad and the metatarsus-tarsus joint angle changes by approximately 0.5 rad in the three left legs (Figure 9c). Concurrently, the femur-patella joint angle changes by approximately 1.5 rad, the tibia-metatarsus joint angle changes by approximately 2.5 rad and the metatarsus-tarsus joint angle changes by approximately 1.0 rad in the three right legs (Figure 9c). The attitude angle directly influences the stability of the robot when it jumps sideways in Figure 9c. The initial attitude angle of the robot depends on attitude planning. The roll angle always holds near 0.02 rad when the robot jumps, and the roll angle changes 0.1 rad until the robot has landed. The pitch angle holds at near 0.2 rad. In the process of jumping, the yaw angle of the robot always holds at 0.02 rad; it increases gradually to 0.03 rad when the robot has landed. According to the simulation results, the attitude angle of the robot is nearly invariable. Hence, the robot has good stability in the sideways jump process, which provides a good theoretical basis for the forward jump of the robot. Figure 9: (**a**) Simulation platform of the sideways jump; (**b**) sketch of robot jumping sideways; (**c**) joint angle curves of the robot leg; (**d**) trajectory of the CoG; and (**e**) attitude angle of the robot. According to the simulation results, we can see that the experimental data are consistent with what we expect from our projections for the sideways jump.