ETH Zurich develops a collision-resistant flexible quadcopter drone, FlexiQuad

Researchers at ETH Zurich have developed a flexible quadcopter drone called FlexiQuad, designed to maintain flight capability even after collisions. Unlike traditional drones that rely on rigid frames, this new design features a deformable structure that can absorb impacts by changing shape. Despite its flexible body, FlexiQuad can maintain stable flight, achieve high speeds, and execute agile maneuvers. This design could ultimately support applications such as infrastructure inspections, rescue operations, and environmental monitoring in confined and challenging environments.

FlexiQuad is a flexible quadcopter drone capable of withstanding collisions while maintaining flight capability. Unlike traditional rigid quadcopters, this drone features a deformable annular structure that can absorb impact forces. This design allows FlexiQuad to temporarily change shape upon colliding with obstacles, reducing the impact on its frame and onboard components. Despite its flexible structure, the drone can reach speeds of 49 mph (approximately 80 km/h), with acceleration levels comparable to traditional rigid drones.

Design Principles of the Flexible Structure

According to ETH Zurich, the main innovation of this drone lies in its frame, which combines flexibility with structural rigidity. Its annular body lacks a central fuselage, with four rotors, a battery, and a flight control module distributed across the frame. This layout allows the structure to deform laterally when encountering obstacles while maintaining rigidity in the vertical direction.

Researchers drew inspiration from birds and insects, whose wings can bend in certain directions while maintaining relative rigidity in others. Utilizing this principle, FlexiQuad can absorb collision energy without hindering the force transmission necessary for effective rotor operation. In collision tests, researchers flew the drone into obstacles at speeds of up to approximately 15.5 mph (about 25 km/h), with its frame temporarily deforming upon impact, reducing the forces acting on the structure and allowing it to continue flying. Researchers noted that the test speeds were primarily limited by the space required to accelerate the drone.

Applications and Potential

According to Girardi, FlexiQuad can achieve linear and angular acceleration levels comparable to rigid drones. The flexible structure can also be used for grasping and transporting objects. During demonstrations, the drone picked up, transported, and placed a soft first aid kit, and lifted a load exceeding its own weight. This design supports operations in narrow or cluttered environments, including inspecting ship ballast tanks, conducting search and rescue missions in collapsed buildings, and performing environmental measurements in dense forests. Its ability to withstand physical contact also aids in navigating obstacles that could disrupt missions.

Another proposed application is to install a net in the hollow part of the frame to capture uncontrolled drones. This deformable design allows heavy drones to pass through narrow gaps, carry additional sensors, and extend flight time. FlexiQuad features a modular design aimed at simplifying transport and assembly. The material cost of its frame is less than 15 Swiss francs, with potential for further cost reductions. The frame can also open and fold into a compact shape suitable for fitting into a medium-sized suitcase. Quick-release fasteners and insertable batteries ultimately enable operators to rapidly assemble the drone on-site.

However, autonomous navigation remains a technical challenge. Vibrations in the flexible frame after a collision may blur camera images and interfere with navigation. Researchers are using reinforcement learning to teach the drone to stabilize itself using onboard motion sensors after a collision, then resume autonomous flight. They are also investigating whether measuring frame deformation and vibrations can provide additional information to facilitate flight control.

Item	Specifications
Maximum Flight Speed	49 mph (approximately 80 km/h)
Test Flight Speed	15.5 mph (approximately 25 km/h)

Technological Innovations and Application Prospects of FlexiQuad

The design of FlexiQuad breaks through the limitations of traditional rigid drone frames, using a deformable structure to absorb impacts. This not only enhances its survivability in collision situations but also expands its range of applications. The drone's flexibility allows it to operate effectively in confined or challenging environments, making it suitable for tasks such as rescue and environmental monitoring. Additionally, its modular design and low-cost materials provide advantages in transport and assembly, with potential for significant impact across multiple industries in the future.