Jumping on water is a unique locomotion mode found in semi-aquatic arthropods, such as water striders. To reproduce this feat in a surface tension-dominant jumping robot, we elucidated the hydrodynamics involved and applied them to develop a bio-inspired impulsive mechanism that maximizes momentum transfer to water. We found that water striders rotate the curved tips of their legs inward at a relatively low descending velocity with a force just below that required to break the water surface (144 millinewtons/meter). We built a 68-milligram at-scale jumping robotic insect and verified that it jumps on water with maximum momentum transfer. The results suggest an understanding of the hydrodynamic phenomena used by semi-aquatic arthropods during water jumping and prescribe a method for reproducing these capabilities in artificial systems.

Fleas have a unique catapult mechanism with a special muscle configuration. Energy is stored in an elastic material, resilin, and the extensor muscle. Force is applied by the extensor muscle to generate a torque. Energy is released as a small triggering muscle reverses the direction of the aforementioned torque. A flea can jump 150 times its body length using this elastic catapult mechanism. In this paper, a flea-inspired catapult mechanism is presented. This mechanism can be categorized as an active storage and active release elastic catapult. Owing to its unique stiffness change characteristic, a shape-memory-alloy coil spring actuator enables the mimicking of the flea's catapult mechanism. Two types of flea-inspired jumping mechanisms were developed for verifying the feasibility of applying the concept to an efficient jumping robot. The first prototype has a flea-like appearance and the second is simplified to contain just the essential components of the flea-inspired catapult mechanism. The two prototypes are 20-mm-and 30-mm-long and can jump 64 cm and 120 cm, respectively. This unique catapult mechanism can be used not only for jumping robots but also for other small-sized robots to generate fast-releasing motion.

In this paper, we propose a trajectory-adjustable integrated milli-scale jumping-crawling robot with improved ability to overcome obstacles compared to a robot that can only crawl. The robot employs a novel jumping module with enhanced energy storing-capacity and a height-adjustable active trigger. To increase the energy-storing capacity, latex rubber and knee-like joints are employed to utilize large displacement of the elastic material. The active trigger is based on a single DC motor and can release stored energy at any state, enabling the robot to control the take-off speed of jumping. The jumping module is integrated with the lightweight Dash crawler. The integrated jumping-crawling robot weighs 59.4 g and controls its moving trajectory by adjusting both its crawling speed and its jumping take-off speed.

A layer-based manufacturing method using composite microstructures is widely used for mesoscale robot fabrication. This fabrication method has enabled the development of a lightweight and robust jumping robot, but there are limitations in relation to the embedding of elastic components. In this paper, a fabrication method for embedding an elastic component at an angled position is developed, extending the capability of the composite microstructures. This method is then used to build an axial spring attached to the bistable mechanism of a jumping robot. Sheet metal is used as an elastic component, which is stamped after the layering and curing process, thereby changing the neutral position of the spring. Two linear springs are designed to be in parallel with a joint to impose bistability; thereby delivering two stable states. This bistable mechanism is triggered with a shape memory alloy (SMA) coil spring actuator. A small-scale jumping mechanism is then fabricated using this mechanism; it jumps when the snap-through of the bistable mechanism occurs. A model of the stamped sheet metal spring is built based on a pseudo rigid body model (PRBM) to estimate the spring performance, and a predictive sheet metal bending model is also built to design the die for stamping. The experimental results show that the stamped sheet metal spring stores 12.63 mJ of elastic energy, and that the mechanism can jump to a height of 175 mm with an initial takeoff velocity of 1.93 m/s.

Kangaroo rats are well known as representative hoppers in small-scale animals. Especially kangaroo rats show rapid movement when a predator approaches. If this amazing motion can be applied to small-scale robots, they will be able to traverse lands at high speed while overcoming size limitations. To take advantage of hopping locomotion, in this paper, we present a lightweight and small-scale clutch-based hopping robot called Dipo. To make this possible, a compact power amplifying actuation system has been developed using a power spring and an active clutch. The power spring is possible to take out and use the accumulated energy little by little whenever the robot starts to hop. Moreover, the power spring needs low torque to charge the elastic energy, and a only tiny space is required to install. The active clutch controls the motion of hopping legs by adjusting the timing of energy release and storage. Thanks to these design strategies, the robot weighs 45.07g, has the height of 5 cm in the stance phase, and achieves the maximum hopping height of 54.9 cm.