"We took inspiration from mythical creatures like dragons, qilins, and chimeras—composite beings that merge the traits of different animals to gain extraordinary abilities," explains Professor Liu. The team applied this idea to robotics. They observed that fish can move flexibly on land by flapping their tails against the ground, and that otariids (sea lions) can gallop at impressive speeds despite their heavy bodies by using hindlimbs for propulsion and forelimbs for support. By combining these two strategies, the team created a tripedal miniature piezoelectric robot (MPR) that excels in both speed and load capacity.
The tethered prototype is only 38 mm long and weighs 8.6 g. It has one active driving leg and two passive supporting legs with wheels. The driving leg carries four PZT elements arranged in two orthogonal groups. When excited by sinusoidal signals with a 90° phase difference, the leg produces first‑order bending vibrations in two perpendicular planes, generating an elliptical trajectory at the foot. "This single leg is responsible for both forward propulsion and turning—a design that greatly simplifies the structure while maintaining agility," says Dr. Li.
In forward motion, the robot reached a maximum speed of 313.49 mm/s (8.25 body lengths per second) —comparable to many insects in real life. For turning, it achieved an angular velocity of 11.54 rad/s and a minimum turning radius of just 12.64 mm, demonstrating exceptional maneuverability in confined spaces. "The key was tuning the leg's geometry and the tilt angle of the driving leg relative to the ground," notes Dr. Li. The team found that increasing the tilt angle and shifting weight forward improved forward speed, while a smaller tilt angle and rear‑biased weight enhanced turning performance.
What truly sets this robot apart is its ability to maintain high speed under heavy loads. Thanks to the foot‑wheel support scheme—where two passive wheels support the front while the driving leg provides thrust—the robot's speed actually increased when additional weight was applied. Under a 200‑g load (23.26 times its own weight), the tethered robot still exceeded 300 mm/s. "Adding weight improves the contact between the foot and the ground, reducing slip and allowing the piezoelectric vibration to be more efficiently converted into motion," explains Professor Liu. A performance metric λ (combining load ratio and speed) gave a value of 312.8 for the tethered robot—far higher than comparable miniature robots.
The team also built a fully untethered version by integrating a 100‑mAh battery and a compact control unit (total weight 20.9 g). Even with the added electronics, the untethered robot reached 265 mm/s under a 180‑g load (8.63 times its own weight). Its energy efficiency is remarkable: the cost of transport (CoT) is only 1.91—among the lowest reported for piezoelectric miniature robots—and it can run continuously for 70 minutes on a single charge. "Low CoT means the robot can operate for extended periods without frequent battery changes, which is critical for real‑world search and rescue or inspection missions," says Dr. Li.
To demonstrate practical potential, the team built a simulated narrow tunnel (75 mm wide with 15° turns) and guided the untethered robot through it using joystick control. The robot smoothly navigated the entire course, showcasing its ability to manoeuvre in cluttered or confined environments where larger robots cannot go. "This is exactly the kind of scenario where insect‑scale robots shine—disaster debris, pipe networks, or collapsed structures," comments Professor Liu.
The team is now working on integrating visual sensors and closed‑loop control to enable autonomous navigation. "Currently, the robot is manually controlled. Adding vision would allow it to detect obstacles and plan its own path, making it truly autonomous for practical missions," concludes Professor Liu.
By fusing two distinct biomimetic strategies into a single, simple architecture, this piezoelectric robot demonstrates that miniature machines need not sacrifice speed for strength—or vice versa. The design philosophy of "integrating multiple features from different animals" offers a fresh and powerful approach to creating the next generation of agile, capable microrobots.
Authors of the paper include Jing Li, Zhengxu Yan, Baoyi Liu, Shijing Zhang, Yu Gao, Hongwei Guo, and Yingxiang Liu.
This work was supported by the National Natural Science Foundation of China (nos. 52505010 and 52225501), in part by the Postdoctoral Fellowship Program and China Postdoctoral Science Foundation under grant number BX20250496, and in part by the China Postdoctoral Science Foundation under grant number 2024M764168.
The paper "An Insect-Scale Untethered Piezoelectric Robot with Multiple Biomimetic Features" was published in the journal Cyborg and Bionic Systems on Jul. 23, 2026, at DOI: 10.34133/cbsystems.0525.
