Manta rays swim through the water with a flying motion, allowing them to travel quickly with little effort, while also being quite agile. These are qualities that would likewise be desirable in an autonomous underwater vehicle, or AUV. To that end, scientists from the National University of Singapore have recently developed a manta ray-inspired swimming robot, known as MantaDroid.

Created over two years by a team led by associate professors Chew Chee Meng and Yeo Khoon Seng, MantaDroid is actually modelled after a juvenile manta ray – it measures 35 cm long by 63 cm wide (13.8 by 24.8 in), and weighs 0.7 kg (1.5 lb). The robot can "fly" underwater at a speed of 0.7 meters (2.3 ft) per second, which is twice its body length, for up to 10 hours on one charge of its batteries.

Forty different fin designs were tried, before arriving at the current fins made from flexible PVC sheets.

"Unlike other flapping-based underwater robots that replicate manta rays' flapping kinematics by using multiple motors to achieve active actuations throughout the fins, MantaDroid is powered by only one electric motor on each fin," says Chew. "We then let the passive flexibility of the fins interact naturally with the fluid dynamics of the water to propel the subsequent motions."

Along with potentially having a longer range than conventional propeller-powered AUVs, MantaDroid should also be quieter, allowing for less disruption to marine life when being used for research missions. Additionally, its flat, wide body can accommodate a range of sensors or other payloads.

Plans now call for the robot to be tested in the open ocean, to see how it handles currents. In the meantime, you can see it swimming in a pool, in the video below.

For examples of other robotic rays, check out what's been done by scientists at the University of Virginia and automation company Festo.