NUS Student 3-D Robot Carp makes waves in Singapore

(From left) Lab technologist Mr Zhang Heng Wei,
Prof Xu and Dr Ren observing the carp-like
movement of their robotic prototype

A robotic fish that swims on its own and mimics the motion of the real animal may soon be making waves in the waters in Singapore. Created by a group of engineers from NUS’ Department of Electrical and Computer Engineering, the Robot Carp is the first of its kind in Asia with autonomous 3-D motion.

This robot, basically an autonomous underwater vehicle (AUV), could lead the way to designing more efficient and smaller versions of the machines. It can be programmed to perform specific tasks, such as exploring spaces in wreckage not easily accessed by divers or traditional AUVs. Other potential applications include military operations, seabed reconnaissance, pipeline leakage detection and the laying of communication cable.

The team behind the creation comprises Professor Xu Jianxin, graduating Electrical Engineering student Fan Lupeng and Research Fellow Dr Ren Qinyuan. As part of Lupeng’s final year project, the Robot Carp won him the High Achievement Award at the Faculty’s Innovation and Research Award. It has been featured at the IEEE/RSJ International Conference on Intelligent Robots and Systems in Vilamoura last November.

Prof Xu pointed out that robot fish capable of 2-D movements are common, and these models are not able to dive into the water. “Our model is capable of 3-D movements as it can dive and float, using its fins like a real fish,” he said.

Robot Carp’s uniqueness lies in its ability to learn fish-like locomotion by observing fish swimming. It emulates biological motion patterns that require precise coordination spatially and temporally. Compared to traditional AUVs, it displays greater manoeuvrability, is quieter and consumes less energy.

Lupeng, who studied the motion of live carps to develop the robot, said the creatures were chosen because most fish swim like them. “We used a camera to capture all the possible movements of a carp and then converted the data mathematically so that we could transfer the locomotion of real carp to our robot using different actuators,” he explained.

Designing the 85-degree maximum turning angle was a big challenge, since many actuators are required to enable the robot to move in the same manner. Most robotic fish have a turning radius of only 40 to 50 degrees, said Prof Xu.

The team overcame the issue of waterproofing the fish body, the motor and the control box by using 1mm fine acrylic board for the fins and tails. Plastic foams attached to both sides of the robotic body maintain buoyancy and balance. An internal ballast system controls the diving mechanism, allowing the fish to dive sharply and to a precise depth.

The researchers have built two fish prototypes. The larger is about 1.5 m in length, weighs 10 kg and can dive to a depth of 1.8 m. The smaller version is about 60 cm long and weighs a mere 1.5 kg. As it is meant for investigation on 2-D motion control in a compact place, it can only swim at the water surface. Powered by batteries, the bigger fish can last for an hour in the water, while the smaller can swim for two hours.

The engineers plan to make the robotic fish smaller and more realistic. Other developments include adding more sensors like GPS and video camera to improve the 3-D movement, as well as conducting more difficult tests such as object detection.