Up in the air: Modular robots assemble mid-flight

by | Aug 23, 2023

It may sound like something straight out of an anime, but TRADY is a rotor-based flying robot that can combine to boost its strength and capabilities.

As machines become increasingly sophisticated, humanity finds itself increasingly relying on robots to conduct challenging or dangerous tasks. Recent years have seen a boom in flying robots particularly.

In addition to drones used to capture imagery of landscapes from the air, which can be utilized in a multitude of fields, including cinematography, aerial robots also can be used to manipulate objects at high elevations. But, the ability to lift or carry or to perform more complex object manipulation like valve opening, for example, is a trade-off against maneuverability.

So, for example, a rotor-based flying robot that is light and compact and able to navigate tricky may not have the physical strength to manipulate heavy objects when it arrives at its destination. The ideal flying robot would with a combination of flight dexterity and lifting strength.

Aerial robots that combine and disassemble mid-air

For researchers from the University of Tokyo in Japan’s JSK Robotics Lab, “combination” is the keyword. In a paper published in the journal Advanced Intelligent Systems, the scientists describe the creation of a novel aerial robot with the ability to perform mid-air docking and undocking. This gives it the capacity to undertake complex missions that surpass the capabilities of an individual robot.

Paper co-author and JSK Robotics Lab Ph.D. student Junichiro Sugihara explained the versatility of this combining flying robot, which the team has dubbed “Tilted-Rotor-Equipped Aerial Robot With Autonomous In-Flight Assembly and Disassembly Ability” or TRADY.

“Consider, for instance, the application of aerial robots within an intricate power plant environment,” said Sugihara. “In such scenarios, a robot must navigate to specific task locations while evading collisions with both the surroundings and other robots.”

Sugihara explained that this requires a robot to possess agility and a compact body. Yet, when compared to larger robots, compact and nimble aerial robots exhibit lower force and torque capabilities, and this leads to limitations in executing their mission.

“In short, flying robots must possess both ‘smallness’ and ‘largeness’,” he added. “We can address this contradiction with a robot that can operate as a compact module while moving and subsequently assembles into a larger and more potent robot during tasks.”

Come together: How aerial robots assemble

To develop a flying robot that is more than the sum of its parts, the JSK Robotics Lab team first had to consider the mechanism by which the individual robotic units of TRADY would come together. And this mechanism had to function while the units were in mid-air and in potentially hazardous conditions. 

“We required ample rigidity in the structure, a design that facilitates straightforward undocking, and the incorporation of a device to facilitate aerial docking, even in instances of precarious flight,” Sugihara explained.

The team developed a docking system for TARDY that takes its inspiration from the aerial refuelling mechanism found in jet fighters in the form of a funnel-shaped unit on one side of the mechanism means any errors lining up the two units are compensated for. The team also developed a unique coupling system in the form of magnets that can be switched on and off.

But other challenges in aerial docking needed to be addressed by the team, including risks that don’t exist for docking robots that combine on terra-firma.

As the TRADY modules approach each other to dock, air turbulence occurs that could knock them out of docking position and could also increase the risk of the two units smashing into each other with potentially disastrous results. “In contrast to ground robots, even minor collisions can have significant consequences for aerial robots,” Sugihara warned.

To avoid this, he and the team developed a “hit and away” strategy. As the TRADY units approach each other, if either detects the risk of collision, it will immediately repeat to its safe original position. From this safe position, the TRADY system can attempt to unite again, finally merging when safe docking is ensured.

Stronger together

The team said that the merging of TRADY units delivers significant benefits to the newly created aerial robot. They said that a united TRADY demonstrated significantly boosted performance that surpassed the capability of its individual units. 

“The achievable torque has increased to over nine times that which a single module can generate, enabling tasks such as operating industrial valves in mid-air,” paper co-author and JSK Robotics Lab Moju Zhao said. 

Prior to merging, the TRADY units tilt their bodies to aid speed and maneuverability, but after unification, the resultant unit keeps its body horizontal, which is invaluable to it performing the complex manipulation of objects.

“At present, the achieved feat involves only the merging and separation of two modules,” Sugihara explained. “However, in the future, by enabling the seamless merging of numerous modules, we will be able to autonomously construct intricate structures and aerial frameworks.”

Reference: Junichiro Sugihara, Moju Zhao et al., Design, Control, and Motion Strategy of TRADY: Tilted-Rotor-Equipped Aerial Robot With Autonomous In-Flight Assembly and Disassembly Ability, Advanced Intelligent Systems (2023). DOI: 10.1002/aisy.202300191

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