Robot Bird Achieves Flight, Underwater Swimming With Flapping Wings

Engineers have created a novel robotic bird that can perform a complete air-to-water-to-air transition, mimicking the abilities of natural diving birds. Developed by researchers at MIT and the Swiss Federal Institute of Technology Lausanne (EPFL), the 8.8-ounce robot is the first bird-scale machine to achieve this cycle using only flapping wings.

The research, published in the journal Science, addresses the significant engineering challenge of creating a small-scale device that can operate effectively in both air and water. Unlike most amphibious robots that utilize separate systems for each environment, this robotic bird relies on a single set of flapping wings for propulsion in both mediums.

Adapting to Varying Densities

The primary challenge lies in the vast difference in density between air and water. Water is approximately 800 times denser than air, creating significantly greater resistance for the robot's wings. To overcome this, the robot adjusts its flapping speed, operating at up to 11 flaps per second in the air and reducing to between 0.1 and 6 flaps per second underwater. Its flexible wings also adapt to the increased pressure, bending up to 90% and reducing the load on the motor. The robot is designed to be neutrally buoyant, conserving energy by not fighting buoyancy.

The Water Launch Challenge

Transitioning from water back to air proved to be the most complex phase. The robot achieves this in under a second, utilizing about eight to 10 wingbeats. This maneuver requires a precise combination of wing flexibility, tail placement, and launch angle. The researchers found that moderately flexible wings were optimal; rigid wings struggled in water, while excessively flexible ones reduced takeoff force. A short tail kept close to the body prevented drag, and a launch angle near 70 degrees yielded the best results.

Scientific Insights and Future Applications

The robotic bird offers a new tool for studying real diving birds, allowing researchers to isolate variables and measure performance changes. Data from the robot suggest that shorter underwater wing strokes may enhance speed, contrary to previous assumptions that they primarily reduce energy use. The robot's propulsion efficiency falls within the range associated with efficient movement in real birds.

Future applications for such technology could include environmental monitoring of waterways and coastal areas. The robot could potentially be launched from shore or a boat to fly to a location, dive to collect samples or take measurements, and then return with data. Its flapping wings offer advantages over propellers, such as reduced noise and less risk of entanglement with debris. Researchers envision missions like taking measurements near icebergs or observing marine wildlife from a safe distance.

Development and Next Steps

The prototype costs approximately $300 in materials and utilizes commercially sourced parts. The researchers have also released open CAD files, potentially enabling other institutions to replicate the design. However, the current prototype still requires human control for critical parts of its operation. Future development will focus on achieving autonomous navigation, improving saltwater resistance, and extending its range and endurance for real-world missions.