A novel interactive robotic fish exhibit has been
developed at the Dynamical Systems Laboratory
of New York University (NYU) Polytechnic School
of Engineering to address this gap [ 14]. The
exhibit features Commodore (Figure 1), a robotic
fish based on a multi-link design with a pitch and
buoyancy control system for three-dimensional
biologically-inspired swimming. An ad hoc
iDevice application with three control modes
varying in the level of robot autonomy provides
visitors with a unique experience to control the
robotic fish swimming.
BIOLOGICALLY;INSPIRED ROBOTIC FISH
Commodore is designed with inspiration from the Atlantic scup fish, Stenotomus chrysops.
The cover of the robotic fish is fabricated through
a rapid prototyping machine from solid-packing
acrylonitrile butadiene styrene plastic. Its
mechanical design includes a three degree-of-freedom motorized tail, electronics housing, and
pitch and buoyancy control systems (Figure 2).
The undulation of the tail enables the robotic fish
to swim in two dimensions, and the pitch and
buoyancy control systems allow the fish to dive
and surface. The robotic fish measures 48 cm in
length, 19 cm in height, and 10 cm in width.
The primary electronic components of
Commodore include an Arduino-based
microcontroller, a radio transceiver, and a 2200
mAh 7.4V lithium polymer battery. A battery
charge sensor, composed of a voltage divider,
is incorporated to assist with monitoring the
battery power level. Two infrared (IR) sensors,
facing 120° apart, are mounted on the front of
the robotic fish to provide navigational information when walls or
obstacles are detected.
Pitch and Buoyancy Control
The combination of the pitch and buoyancy control systems is used
to adjust the depth of the robotic fish. Specifically, the buoyancy
control system heuristically sets the robotic fish to neutral buoyancy
by adjusting the water content within a rigid volume tank.
The pitch angle is regulated by shifting a balance mass with a 2. 2
cm travel length. This mass is used to control the center of gravity
of Commodore with respect to the center of buoyancy, thus tilting
it upwards (positive pitch) or downwards (negative pitch). When
Commodore is close to neutral buoyancy, adjusting the pitch angle
while beating the tail allows rising and diving.
The buoyancy system comprises a rigid enclosure, fabricated
using rapid prototyping, which contains two separate chambers
(Figure 2). One chamber encases two motors, pumping water
between the second holding chamber and the environment through
Communication protocol between
the robotic fish and iDevice.
FIGURE 4 iDevice application screens (a) manual, (b) semi-autonomous, and (c) autonomous.