Researchers have built a 140-milligram microrobot that reuses one morphing frame for takeoff, crawling, gliding on water and controlled immersion. The separate, open-loop tests show a way to add movement modes without giving each one its own actuator, a severe mass penalty at insect scale.
The 35-millimeter machine, named Tri-RoboInsect, uses a four-wing layout around an H-shaped body frame. Shape-memory alloy artificial muscles, thin wires that contract when electrically heated, bend that frame into different configurations. The paper calls this “functional recursion”: the same structure changes its mechanical job instead of carrying a separate mechanism for every environment. The robot itself is tethered, and its stated mass excludes the external power supply, control electronics and communications.
In the air, frame deformation changes the geometry of the wing transmissions, creating unequal wing strokes for pitch, roll and yaw commands. The robot took off with its wings beating at 93 hertz, but the flight remained unstable because there was no feedback controller. On the ground, the same frame extends and contracts between feet with direction-dependent friction. On smooth paper, three open-loop trials reached 0.46 ± 0.02 body lengths per second at an 8-hertz drive frequency.
Water creates the opposite requirements: the robot needs surface tension to stay up, then must break that support to enter the water. Its kirigami footpads solve both tasks by opening patterned gaps as the H-frame bends. In calm-water tests, wing flapping drove surface gliding at up to 6.3 ± 0.4 millimeters per second across three trials. Expanding the footpads also let the robot carry an additional 242 milligrams, 1.7 times its own mass, on the surface.
For immersion, electrodes in the footpads use electrowetting, where voltage changes how readily water spreads across a surface. With the gap deformation set to 1 millimeter, 225 volts reduced the support force enough to rupture the interface and sink the robot. A 2-millimeter deformation produced more surface support and required 300 volts. During descent, asymmetric wing flapping changed pitch and roll and encouraged feet-first settling, again under a preprogrammed open-loop sequence.
The result supports structural reuse as a practical route to more functions within a milligram-scale mass budget. It does not yet establish an autonomous robot that can fly, land, crawl, cross disturbed water and dive in one mission: the demonstrations were separate, the system was tethered, calm water was used, and the thermal muscles cannot stabilize fast flight.