IEEE Robotics & Automation Magazine - December 2022 - 79

feather and theoretical framework, we demonstrate, on a
robotic setup, how the detachment of feathers can be used
to change the motion path while maintaining the same lowlevel
controller.
Overview
The feather star is a marine crinoid, an invertebrate with multiple
soft " feathery " arms that enable swimming and maneuvering
to avoid prey and feeding on drifting microorganisms
[1]. These animals show many fascinating properties, including
their deformable feather-like structure and cyclically actuated
muscles. One of their properties, which is believed to be
unique to echinoderms, is mutable collagenous tissue [2].
This enables them to drastically alter their body structure
within a timescale of seconds, under direct control of the
nervous system. In the case of feather stars, they use this tissue
to detach their feathered arms. It is believed that this
mechanism is used to distract prey and also change feather
stars' dynamics to assist with evading predators [3]. This
demonstrated ability to drastically alter the body morphology
and passive properties to alter maneuverability is of keen
interest to the robotics community. It provides inspiration for
the development of robots that can utilize or change their
body structure to aid their end goal or, indeed, their survival
[4]. Thus, the goal of this work is to develop a feather starinspired
robot that uses an artificial equivalent of this
" mutable tissue " to change its body structure. Furthermore,
we present a theoretical model to
investigate how the detachment of
the arms affects the control and
maneuverability of the design.
Within the domain of underwater
bioinspired robots, there have been a
number of notable examples where
limbs (similar to the feathers on the
feather star) and their controllers have
been optimized to maximize the generated
thrust [6]. This includes an
octopus-inspired robot [7] and a star
fish robot [8]. While these examples
consider the optimization of the
design of the structure to maximize
thrust or behavioral range, there are
limited examples of underwater
robots that show considerable changes
in body structure to aid control.
Developing and designing robots that
can utilize change in the passive properties
or morphology is a key quest for
embodied intelligence researchers.
The role of morphology-driven control
has been previously formalized [9]
and shown to aid in achieving stability
in legged underwater vehicles [10]
and shaping the behavioral landscape
of complex systems [11].
This previous work has highlighted the potential for
morphology-driven control, which could be particularly
beneficial in aquatic environments where fluid-structure
interactions can be complex and challenging to control
and exploit. To explore
these capabilities, we
must first create robots or
structures that show significant
variation in their
physical structure or passive
properties. To date,
this has mostly been
demonstrated through
stiffness change in robotic
systems [12] or modular
reconfigurable robotic
systems [13]. Using these
new capabilities, we must
then optimize for the
morphology for optimal
thrust generation [14], [15] and address how we should
design the global structure before and after body changes to
achieve morphology-driven control.
By developing a feather star-inspired robot with detachable
feathers, we introduce a new approach to achieving
significant morphological transformation in a swimming
robot, which we then use to explore how body adaption can
The feather star is a
marine crinoid, an
invertebrate with multiple
soft " feathery " arms that
enable swimming and
maneuvering to avoid prey.
(a)
(b)
Rings of Independent
Actuation
Detachable
Feathers
(c)
Figure 1. The (a, c) developed feather star robot with multiple actuated rings and
(b)detachable feathers and its biological inspiration [5].
DECEMBER 2022 * IEEE ROBOTICS & AUTOMATION MAGAZINE *
79
IEEE Robotics & Automation Magazine - December 2022

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