IEEE Robotics & Automation Magazine - September 2019 - 37

connection that occurred on the leading edge at the gap
between each of the two neighboring fin rays was decreased
because of the action of the flexible and stretchable outer skin.
Figure 10(a) shows snapshots of the bionic fish prototype
swims in the water tank at its two amplitude positions. The
prototype obtained large flapping amplitudes, much like the
cownose ray.
The maximum linear-forward swim velocity attained by
the bionic fish was approximately 0.42 m/s, equal to 0.7 BL/s.
Figure 10(b) shows the consecutive postures of a full-cycle
pivot turn. Here, completely opposite phase differences were
applied to the two pectoral foils.
The developed bionic fish exhibited high maneuverability,
as evidenced by its tilted swim through a narrow passage. The
continuous screenshots of the water tank experiments are
shown in Figure 10(c). In the experiment, we sent target roll
angles to the bionic fish in real time, using the installed wireless serial port combined with opportune heading control.
Two sticks were set parallel to one another at a distance of
0.45 m to constitute the experimental narrow passage. As
described in the "Force Measurement" section, the thickest
part of the bionic fish at the middle body is 0.18 m, and its
wing span is 0.92 m. By means of this special posture with a
rolling angle of approximately 90°, the bionic fish prototype
can swim through narrow passages comprising widths that
are slightly less than half its wingspan.

Testing Pool

Conclusions and Ongoing Research
This article demonstrated a novel bionic fish, mimicking a
cownose ray with wide, flat pectoral foils, and discussed the
prototype theoretically and experimentally. The bionic fish
exhibits the strong swimming ability and high environmental
compatibility required for underwater applications. The robot
fish's bionic configuration makes it easy to merge into the surrounding environment, while its low flapping frequency and
flexible surface bring low hydrodynamic noise capability.
Pivot turning and roll swimming proved the robot fish's high
maneuverability. Due to its bionic mechanism and maneuverability, the bionic fish will be particularly useful in challenging
environments, e.g., shallow water near the seaboard or water
with many aquatic plants.
The structure and shape of the cownose ray were analyzed
based on biology and anatomy research results, including the
fin shape, cross sections, and skeletal characteristics. The pectoral foil movement characteristics and flexible body deformation of a free-swimming cownose ray at different swim
modes were summarized. Considering the design feasibility,
both the structures and the movements of the cownose ray
were simplified to fulfill the biomimetic development
requirements. The irregular chordwise cross sections were
regularized to series NACA airfoil shapes, and the complex
skeletons composed of cartilaginous and flexible connections
were simplified as a combination of multiple-joint fin rays

1.5 s

4.5 s

5.8 s

5.5 s

6.5 s

7.5 s

Testing Pool
(a)

Reference Point

0.6 s

1.2 s

1.8 s

2.4 s

3.6 s

4.2 s

4.8 s

7.5 s

8.5 s

9.5 s

10 s

(b)

(c)

Figure 10. The swim performance of the bionic fish. (a) A linear-forward swim, (b) a highly maneuverable turn, and (c) high
maneuverability from a rolling swim through a narrow passage.

SEPTEMBER 2019

IEEE ROBOTICS & AUTOMATION MAGAZINE

IEEE Robotics & Automation Magazine - September 2019

Table of Contents for the Digital Edition of IEEE Robotics & Automation Magazine - September 2019