Level 1 — Absolute Beginner
Engineers built a small robot. It looks and moves like a frog.
The robot is only 11 centimeters long. It is very light too.
Inside the robot are bent rods. The rods twist and then snap. This makes the robot hop.
The robot can hop on grass, sand, and wood. It can even swim in water. It moves faster than a robot with stiff legs.
- engineer
- a person who designs and builds machines or structures
- robot
- a machine that can move and do tasks
- frog
- a small animal that jumps and can live in water and on land
- rod
- a long, thin piece of material
- twist
- to turn something around and around
- snap
- to move suddenly into a new position
- hop
- to jump a short distance
- swim
- to move through water using your body
Level 2 — Elementary
A team of engineers from UCLA and the University of Michigan has built a small robot that moves like a frog. The robot is 11 centimeters long and weighs less than a quarter of a pound.
Instead of using motors to push wheels or legs, the robot uses bent elastic rods. Small motors slowly twist the rods until they suddenly snap into a different shape. That sudden snap releases a burst of energy, which pushes the robot forward in a hop, just like a frog's leg.
The researchers tested the robot on many different surfaces, including wood, cloth, leather, grass, and sand. It could even climb up a set of steps. On difficult surfaces like grass, the frog robot moved faster than a similar robot built with regular, rigid legs.
The robot can also swim, which makes it useful in more than one kind of environment. The study, published in the journal Science Advances, suggests that this snapping method could help engineers build small robots that need to move well without using much power.
- elastic
- able to stretch and then return to its original shape
- motor
- a small device that creates movement or power
- burst
- a short, sudden release of energy or activity
- surface
- the top or outside layer of something
- rigid
- stiff and not able to bend
- environment
- the natural world or conditions around something
- researcher
- a person who studies a subject carefully to learn new things
- power
- energy that makes something work
Level 3 — Intermediate
Roboticists at UCLA and the University of Michigan have demonstrated a new way to propel small robots: bending and twisting elastic rods until they suddenly snap between two stable shapes, releasing stored energy in a burst rather than relying on continuous motor power.
The resulting prototype, a frog-like robot just 11 centimeters long and weighing under 100 grams, uses low-power actuators to slowly twist a pair of helical elastic limbs at its rear. As the twist builds, the rods eventually snap into a less contorted configuration, producing a sharp, forceful push that propels the robot forward in a hopping motion reminiscent of a real frog's leap.
In testing across a range of terrains, including wood, cloth, acrylic, leather, grass, and sand, the robot proved capable of climbing a short flight of steps and, notably, outpaced a comparable robot fitted with conventional rigid legs, particularly on uneven or yielding surfaces such as grass where rigid designs tend to lose traction.
The team, co-led by mechanical engineer Khalid Jawed at UCLA and robotics researcher Xiaonan Huang at Michigan, published the work in Science Advances, framing it as a promising strategy for robots whose usefulness is constrained by strict limits on size, weight, and available power, conditions under which conventional motorized legs or wheels often struggle to deliver efficient locomotion.
- propel
- to drive or push something forward
- prototype
- an early working model built to test a design
- actuator
- a device that converts energy into physical movement
- helical
- having the shape of a spiral or coil
- configuration
- the particular arrangement or shape of the parts of something
- terrain
- a stretch of land, especially considering its physical features
- locomotion
- the ability to move from one place to another
- constrained
- limited or restricted by particular conditions
Level 4 — Advanced
A collaboration between UCLA's Structures-Computer Interaction Lab and robotics researchers at the University of Michigan has yielded a compact demonstration of bistable elastic snapping as a viable, low-power locomotion strategy, one that sidesteps the actuation bottlenecks that have long constrained small-scale, power-limited robots.
Rather than continuously driving joints or wheels, the frog-inspired prototype twists a pair of helical elastic limbs slowly, using minimal power, until accumulated strain energy exceeds a threshold and the rods snap abruptly into a less contorted configuration. That transition, occurring far faster than the actuation that precedes it, converts gradually stored elastic energy into an impulsive mechanical output, an approach that decouples the speed of the useful motion from the (comparatively slow, low-power) speed of the actuator driving it.
Empirically, the roughly 11-centimeter, sub-100-gram prototype outperformed a rigid-legged analogue across a battery of terrains, notably on compliant, irregular substrates such as grass and sand, where rigid limbs tend to dissipate energy through slippage and poor ground conformity rather than converting it efficiently into forward motion. The robot additionally demonstrated stair-climbing and swimming capability, underscoring the versatility of a single mechanical principle across markedly different locomotion regimes.
Published in Science Advances, the work situates itself within a broader research effort to decouple robotic mobility from the size, mass, and power budgets that conventional rigid actuation imposes, an especially pressing constraint for robots intended for search-and-rescue, environmental monitoring, or other applications where miniaturization and energy autonomy are non-negotiable design requirements rather than optional refinements.
- bistable
- capable of resting stably in either of two distinct states or shapes
- actuation
- the process by which a mechanism is caused to move or operate
- bottleneck
- a point of constriction that limits the rate or capacity of a process
- strain energy
- energy stored in a material as a result of being deformed
- impulsive
- occurring as a sudden, brief force or action
- compliant
- here, able to flex or yield rather than remaining perfectly stiff
- substrate
- the surface or material on which something rests or moves
- autonomy
- here, the capacity to operate independently, especially regarding power supply
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