# Omnidirectional Jump of a Legged Robot Based on the Behavior Mechanism of a Jumping Spider
## 4 Results
### Forward Jump  
The simulation of the robot jumping forward is carried out to verify whether the joint angle, attitude angle, jumping height and jumping distance is consistent with motion planning or not. The simulation results are seen in Figure 10. In the forward jump, the robot's body slowly moves backwards and downwards due to a slight flexion of the hind legs and the middle legs before the acceleration phase begins. The robot begins to store energy with the CoG dropping. At the same time, the initial attitude is adjusted in preparation to jump. Then, the robot starts to accelerate by extending its legs; the effective leg length increases quickly. Eventually, the robot takes off. Figure 10b shows a sketch of the robot jumping forward. The initial height of the CoG of the robot is 180 mm, the jumping height is 100 mm, and the jumping distance is 250 mm.  
While the robot jumps forward, the legs that have contact with the ground are first flexed and then extended. Each joint of the six legs has a different rotation angle (Figure 10c). Before the acceleration phase of the forward jump, the body rotates backwards as the hind legs and the middle of the robot body slightly flex in the jumping direction. Meanwhile, the robot adjusts its attitude by moving backwards and downwards. Then, the foot impacts the ground quickly, and the robot's legs start to extend and, at 0.8 s, the robot begins to accelerate. At the same instant, the joint angle begins to quickly change (Figure 10c). At 1.0 s, the robot loses contact with the ground and takes off; due to the accumulation of velocity, the rotation of the body is reversed. At this instant, the height of the CoG is 320 mm. The robot rises to its maximum height of approximately 420 mm at 1.2 s; it then completes the task of jumping 100 mm in height (Figure 10d). After this instant, none of the joint angles change (Figure 10c).  
During the robot's forward jump, and the Coxal joint angles change by approximately 0.8 rad. The femur-patella joint angle changes by approximately 2 rad, the tibia-metatarsus joint angle changes by approximately 1.5 rad and the metatarsus-tarsus joint angle changes by approximately 1 rad. At 1.4 s, the robot lands on the ground. The robot is in the air for approximately 0.4 s, and the jumping distance is 250 mm (Figure 10d). In Figure 10e, the initial attitude angle is not 0, and the initial roll angle is 0.01 rad; the initial yaw angle is 0.025 rad; and the initial pitch angle is 0.02 rad, due to the initial pose of the robot. The roll angle changes by 0.02 rad in the jumping process, and the roll angle decreased by 0.1 rad when the robot landed. The pitch angle holds at 0.01 rad in the jumping process, and it generated a fluctuation of 0.1 rad when the robot landed. The yaw angle was almost constant until the robot landed, maintaining 0.015 rad. According to the simulation results, the robot has good stability in the forward jump process, which provides a good theoretical basis for the forward jump of the robot.  
Observing the simulation result, we find that the experimental data are consistent with our projections of the forward jump. The robot could complete the task of jumping 100 mm in height and 250 mm in distance; it maintains good stability in the flying phase.