Imagine a robot so small that it can move through tight spaces, inspect tiny objects, detect gas leaks, and even perform microscopic observations—without needing to rotate its entire body to change direction.
Researchers led by Yu Gao have developed a miniature, untethered robot designed to solve one of the biggest challenges in small-scale robotics: how to move freely in confined spaces while carrying its own power, sensors, communication and control systems.
The tiny robot uses piezoelectric actuators and a unique three-legged design to achieve what researchers describe as omnidirectional movement with an extremely small turning requirement. Its compact body measures about 3.10 cm in diameter and 2.75 cm in height, while weighing only 12.2 grams.
The technology could eventually support inspection and exploration tasks in places where conventional robots cannot easily maneuver.
The Problem With Making Robots Smaller
Miniature robots are increasingly being developed for applications such as biotechnology, environmental exploration, inspection and microscopic observation.
But making a robot smaller creates a difficult engineering problem.
A useful robot needs several components, including:
A power source
Actuators for movement
Sensors
Control electronics
Communication systems
Putting all of these components into a very small body is challenging. At the same time, a robot that can physically fit into a narrow space may still struggle to move inside it.
One important issue is the turning radius.
A robot might be small enough to enter a narrow passage but unable to turn around because there is not enough space for its body to rotate.
For robots operating inside confined environments, this can become a major limitation.
A Robot That Doesn't Need to Turn Its Body
The researchers approached the problem differently.
Instead of using one primary driving direction and rotating the robot to change course, the new robot uses three piezoelectric actuators arranged radially around its body.
Piezoelectric materials can deform or vibrate when an electrical voltage is applied. These tiny movements can be converted into mechanical motion.
In this robot, the three actuators work together to generate six driving directions around the robot.
By combining these directions, the robot can travel along different paths without continuously rotating its body.
This gives the robot a major advantage in confined environments: it can change its direction while maintaining its overall orientation.
The researchers also developed a trajectory interpolation algorithm that helps coordinate these different driving directions and create smooth omnidirectional movement.
In simple terms, the robot does not always need to point toward where it wants to go. It can move sideways, diagonally or in other directions while keeping its body orientation largely unchanged.
Zero-Radius Maneuverability
The concept becomes especially interesting when considering the robot's turning space.
Traditional wheeled or legged robots generally need some room to rotate before changing direction. The researchers developed their system to minimize this reorientation requirement, effectively bringing the required turning space close to the robot's own compact size.
This is important because in a narrow passage, every extra millimeter matters.
The robot demonstrated several movement patterns, including trajectories resembling the letters H, I and T. It also successfully navigated mazes in both directions.
Such demonstrations show how omnidirectional movement could make miniature robots more practical for confined-space inspection.
From Fast Movement to Microscopic Precision
Another notable feature is the robot's unusually broad range of motion.
The robot can operate in two different excitation modes.
In its continuous high-frequency mode, it can reach speeds of approximately 3 centimeters per second. This mode is useful when the robot needs to cover a relatively large area quickly, such as navigating a maze.
But the researchers can also switch the robot to an intermittent excitation mode.
In this mode, the robot can make extremely small movements, with a minimum demonstrated step of approximately 0.56 micrometers.
For perspective, a micrometer is one-millionth of a meter.
This means the same tiny machine can move relatively quickly when necessary and then make highly precise movements for microscopic inspection.
The researchers demonstrated potential applications involving wafer inspection and cell specimen observation, where controlled movement at very small scales can be valuable.
A Complete Robot Without a Tether
Miniaturization is not only about reducing the physical body of the robot.
The researchers also integrated multiple systems directly into the robot.
The prototype contains its:
Actuation system
Control electronics
Communication system
Power supply
Five types of onboard sensors
Because these components are carried by the robot itself, it can operate untethered, rather than relying on external wires for power or control.
The robot also demonstrated an endurance of more than 49 minutes.
One experiment used an onboard ethanol sensor for gas-leak inspection, showing how the robot could combine movement with environmental sensing.
This type of sensor integration could be important for future inspection robots that need to collect information while moving through difficult environments.
Autonomous Navigation and Robot Cooperation
The system goes beyond manually controlled movement.
The researchers developed a navigation system that can switch actuation vectors in real time and interpolate trajectories automatically.
During demonstrations, the robot followed paths including a number-shaped route and a triangular trajectory.
The researchers also explored multi-robot coordination.
In one approach, robots could share position information. This allowed a robot experiencing a sensor failure to recover its autonomous navigation capability using information from other robots.
The team demonstrated three multi-robot auto-following scenarios, suggesting that multiple miniature robots could potentially work together rather than operating independently.
This could become useful for inspection tasks where covering a larger area with several small machines is more practical than using one larger robot.
Small but Surprisingly Strong
Despite its tiny size, the robot demonstrated considerable mechanical robustness.
The prototype could carry a maximum payload of approximately 13.63 times its own body weight.
It also maintained functional movement after experiencing a 0.6-meter drop and a compressive load reported at approximately 559 times its body weight.
The researchers tested its movement on different surfaces, including glass, marble and stainless steel.
However, its movement mechanism currently works best on smooth, relatively flat surfaces.
What Are the Limitations?
The technology is promising, but it is still a research prototype.
One major limitation is that the robot currently acts mainly as a platform for carrying objects during microscopic observation. Adding active tools such as miniature grippers or suction mechanisms could greatly expand what it can do.
Power is another challenge. Because the robot is extremely small, its onboard electronics have limited boost capability and output current, which can affect movement performance.
Its vibration-based locomotion also makes rough or uneven surfaces difficult to navigate.
Finally, tiny manufacturing and installation errors can create unwanted forces that cause the robot to deviate from its planned path.
What Could Come Next?
The researchers identify several directions for future development.
More efficient piezoelectric actuator arrangements could improve speed and movement performance. Miniature grippers could allow the robot to pick up and manipulate tiny objects. Better power-management systems could increase operating time.
The control system could also be improved with velocity-smoothing algorithms and closed-loop control, allowing the robot to move more smoothly and accurately.
If these challenges can be addressed, miniature robots like this could become useful tools for micro-inspection, laboratory research, chip & spacecraft inspection, environmental sensing and other confined-space applications.
A New Approach to Miniature Robotics
The key achievement of Yu Gao and his team is not simply creating a smaller robot.
It is demonstrating how miniaturization, omnidirectional movement, precision motion and onboard intelligence can be combined in a single untethered platform.
With three radial piezoelectric actuators, the robot can move in multiple directions without repeatedly turning its body. It can travel at around 3 cm/s, yet perform steps as small as 0.56 micrometers.
That combination of speed and precision gives the tiny machine a remarkably broad operating range.
For miniature robots, the future may not depend only on making machines smaller. It may depend on making them smarter, more maneuverable and more capable within the same tiny footprint.
Reference: Gao, Y., Li, J., Zhang, S. et al. Omnidirectional motion of an untethered tripodal microrobot using radial piezoelectric actuators. Nat Commun 17, 5946 (2026). https://doi.org/10.1038/s41467-026-72449-x
Comments
Post a Comment