# Jumping Locomotion Strategies: From Animals to Bioinspired Robots
## 2 Jumping Animals and Biomimetic Miniature Jumping Robots
### Invertebrates
#### 2.1.2 Locust Inspired Jumping Robots  
Locusts' jumping dynamics is the most investigated among jumping animals [79; 80; 48; 81; 82]. Locusts are endowed with three pairs of legs and wings. The enlarged hind legs, consisting of femur, tibiae, and tarsus [83], help these insects achieve brilliant jumping performances [79], while middle and fore legs mainly support the body weight and adjust the take-off angle and take-off direction. While middle and fore legs represent a typical walking limb, the hind legs are specialized to realize the perfect jumping and kicking in locusts [84]. The hind legs are relatively longer than middle legs and fore legs, whose femur is occupied by strong extensor muscle and relative slim flexor muscle. The extensor muscle consists of short fibers arranged in chevron blocks, while long and thin fibers make up the flexor muscle [85]. Locusts jump with catapult mechanism: through the slow contraction of the extensor muscles of hind legs, energy is stored into the fibers of the muscles themselves and into the distortions of the exoskeleton, including the two semilunar processes (SLPs) located at the end of the femur-tibiae joints. Jumping is used as the key locomotion mode in locusts to escape from predators or initiate flying phase [85]. The jump of these insects consists of three phases: initial flexion, cocontraction, and triggering [86; 87]. Normally in cocontraction phase, energy is stored in 300-600 ms. The specialized hind legs structure allows the small flexor to overcome the strong extensor in flexed position. The flexor of hind legs has a bigger mechanical advantage over extensor, increasing from 1.5:1 in 120\({}^{\circ}\) extended position to 21:1 in flexed position [85]. In contrast, this value keeps invariable, about 2:1, for middle legs. Due to the existence of a small gap between distal of tibiae and proximal of femur in hind legs, the minimum flexed angle of femur and tibiae in hind legs is almost zero, while this angle is 25\({}^{\circ}\) in middle legs, which gives locusts the ability to jump directly upright. [PERSON] et al. proposed a 7 g locust-inspired jumping robot [88], in which a micro motor and a four-stage gearbox are used to drive an eccentric cam that slowly loads the torsional spring locatedat the hip joint and then releases it fast. By means of the parallelogram legs, the energy stored into the torsional spring is transmitted to the foot to accelerate the robot's body. By manually adjusting the length of the foot and the take-off angle, the acceleration time and trajectories of the foot can be changed. The energy stored in the torsional spring can change in stepped variation via manually adjusting the fixed position of the torsional spring. In a second version, this robot can also adjust the take-off angle and velocity by manually coordinating the length of the foot and the fixed position of the torsional spring [89]. In its third and last version, it can realize landing buffering by means of an auxiliary carbon cage [90] or gliding wings [91; 92; 93], and azimuth control by means of an added motor that rotates the whole body around the carbon cage axis [94]. On the one hand, these auxiliary mechanisms improve the controllability of jumping, while, on the other hand, they sacrifice jumping height and distance because of the added weight: the latest version with fixed gliding wings can jump only 12 cm high [93]. [PERSON] et al. [95; 96; 97] developed a locust-inspired jumping robot, in which a torsional spring is located at the knee joint to mimic the important role of the semilunar process in the jumping of locusts. The femur and tibae are designed as two carbon fiber rods of equal length, and a torsional spring is located at the knee joint. By rotating a revised servo motor, the rope contracts to store elastic energy inside the torsional spring and locks the mechanism. After that, the motor rotates in the opposite direction to release the rope; this way, the locking mechanism quickly releases the hind legs to realize a powerful jump.