Frog-Inspired Robot Uses Twisting Elastic Rods to Jump, Swim and Navigate Obstacles

Frogs have inspired a new type of small robot that can jump, swim and move across difficult surfaces using a powerful “snap” generated by twisted elastic rods.

Researchers investigated how twisting a bent elastic rod can create rapid snapping motions that help small robots move without relying on large motors or continuous high power. The study was published on September 18 in Science Advances.

The mechanism could improve robots designed to operate with limited power or navigate rough terrain, cluttered environments and underwater settings.

A palm-sized robot inspired by frogs

The researchers built a prototype to demonstrate the technology. The palm-sized robot weighs just 3.4 ounces, roughly the same as a deck of playing cards. It can move at about three body lengths per second and launch itself forward in a short jump.

The final prototype has a frog-like shape, with a pair of elastic snap rods positioned at the rear of its body. The rods store energy as they bend and twist, then release that energy suddenly to propel the robot.

How the robot’s snap movement works

As a flexible rod bends and its ends rotate, it can reach a point where its shape changes and releases built-up tension. That change does not always happen in the same way. Some combinations of bending and twisting cause the rod to change shape gradually, while others make it snap rapidly from one shape to another.

The rapid change releases energy in a short burst, producing a strong push that moves the robot. The researchers used computer modeling and robotic-arm experiments to repeatedly deform the rod and identify the most effective configuration.

They ultimately selected a helix, similar to a coiled spring, because it could release a large amount of stored energy into the robot’s movement.

Small motors can produce powerful movements

The team connected the snap rods to a rotating motor. The motor twists the bent rods until they reach the point of snapping, then untwists and twists them again to repeat the motion.

“The bigger opportunity is to have robotic mechanics do some of the work that would otherwise require larger motors or more complex controls,” said Xiaonan (Sean) Huang, an assistant professor of robotics at the University of Michigan and a co-lead author of the study.

“By programming when the elastic structure stores and rapidly releases energy, we can give small robots powerful, repeatable motions without requiring continuous high power from the motors,” Huang explained in a statement.

The approach could eventually help robots navigate cluttered terrain, overcome obstacles, change direction quickly and operate on both land and water.

Robot tested on wood, glass, sand and grass

The researchers tested the frog-like robot on a wide range of surfaces. These included hard materials such as wood and glass, as well as soft and slippery surfaces covered with materials such as leather.

Outdoor tests showed that the robot could move across sand and grass. The researchers also noted that it could travel up and down stairs. With a paddle attached, the robot was able to swim.

Using just one snap rod, the team also made the robot rotate and navigate a small obstacle course with a remote control.

Elastic snap rods could scale to tiny robots

The design principles are based on the shape of the rod and the way its ends move. That means the same rules could be applied at different sizes and scales, according to Khalid Jawed, the study’s co-first author.

“This opens a promising avenue for small robots just a few millimeters in size that can transform small motor movements into powerful explosive movements,” Jawed said.

The researchers say the frog-inspired propulsion system could provide a way for future miniature robots to achieve powerful, repeatable movements while using relatively simple mechanical designs.

Source: Tong, D., Wang, J., Chen, Z., Borum, A., Huang, W., Huang, X. and Jawed, M. K. (2026). “Geometrically controlled instability path selection in elastic helices enables fast and efficient locomotion by robots.” Science Advances, 12(38), eaeh2779. Read the study.