A team of engineers in Singapore have developed an aquatic robot that emulates the swimming locomotion of manta rays and is able to move quickly, while operating up to 10 hours.
The MantaDroid [watch the video], developed by researchers from the National University of Singapore (NUS) is able to swim at a speed 0.7 m – twice its body length – per second, and its long operational time means it could be used for underwater surveillance in the future.
The team took inspiration from manta rays, which are considered one of nature’s most graceful and efficient swimmers. Manta rays have a unique propulsion mechanism that enables them to cruise through turbulent seas by flapping their pectoral fins almost effortlessly. The engineers sought to understand the science behind the mechanism, and to incorporate similar mechanisms into autonomous underwater vehicles.
The research team was led by Associate Professor Chew Chee Meng from the Department of Mechanical Engineering at NUS Faculty of Engineering. The MantaDroid resembles a juvenile manta ray, and measures 35 cm in length, 63 cm in width, while weighing 0.7 kg.
The team took two years to design and optimise the MantaDroid, following an in-depth study of fluid dynamics and testing 40 different fin designs. The final iteration of the fins were made using PVC sheets. The flexible fins achieved good manoeuvrability and swimming capability when tested in the pool.
“Unlike other flapping-based underwater robots that replicate manta ray’s flapping kinematics by using multiple motors to achieve active actuations throughout the fins, MantaDroid is powered by only one electric motor on each fin. We then let the passive flexibility of the fins interact naturally with the fluid dynamics of the water to propel the subsequent motions,” explained Chew.
This is a promising alternative method to traditional propeller-based thrusters, and could potentially operate for a longer range. The MantaDroid also has a flat and wide body, just like a real manta ray, which can accommodate a range of sensors and be utilised for different purposes such as studying marine biodiversity, measuring hydrographic data and performing search operations.
The next step will see the team testing the MantaDroid in a sea environment, to investigate its swimming capability at different depths and its ability to withstand underwater current.