IEEE Robotics & Automation Magazine - December 2022 - 80

be used to assist with maneuvering. The novel robotic system
is formed from multiple layers of actuated rings of
feathers that it uses as a means of thrust generation. All the
feathers in a single layer are actuated collectively, and
maneuverability is achieved through adaption of the body,
opposed to control of individual feathers. A mechanical
system for rapid detachment
has been integrated
into the actuated
feather rings to allow for
the detachment of individual
feathers.
Due to the complex
maneuverability is achieved
through adaption of the
body, opposed to control
of individual feathers.
interactions between the
deformable feather and
water, we utilize simulation
to perform a wide
sweep of the control
and design landscape to
identify a small range of
feather structures and
controllers that are likely
to maximize the thrust
generation. By developfeathers'
thrust generation through the codesign of the
morphology and the controller.
●
We must develop a framework for selecting the robot
structure before and after the detachment of limbs to optimize
the performance of the robot. In particular, we present
methods for the optimization of the thrust in a
particular direction and maximizing the degree of controllability
of the robot.
All the feathers in a
single layer are actuated
collectively, and
●
We must develop robotic hardware that mimics the behavior
of the feather star by considering a mechanism that
allows multiple feathers to be actuated simultaneously and
detached at will.
The following three sections present the methods developed
to address these three aspects of the problem.
ing a custom measurement setup, we validate a small subset
of these results to find the optimal feather and controller. To
understand how to design the initial configuration of the
robot and the choice of feathers to detach, we have developed
an algorithm that utilizes the state-space representation
to evaluate and determine how to change and restore
the degree of controllability.
To demonstrate the contributions of this work, we
experimentally validate the optimized robot structure
and controllers on the robot hardware. The maneuverability
of the robot is shown to alter with different configurations
of the robot's feathers, following which the
ability to detach the feathers on demand to alter the
heading and path is shown. In the remainder of this article,
we first present the methods to systematically address
this problem. The novel robotic hardware is then shown,
followed by the experimental results. We finish with a
discussion and conclusion.
Problem Statement
Using the feather star as biological inspiration, we aim to
develop a robot that utilizes feather-like structures to
swim. By providing the robot with the ability to alter, or
morph, its body, we want to show how changes in maneuverability
can be achieved through altering the body structure.
To achieve this aim, we subdivide the problem into
three key goals that all seek to explore how these bioinspired
components can be used to improve the capabilities
of robots, as follows:
●
We must explore the role of feather structures and periodic
controllers in the generation of thrust through
embodied interactions with the water and optimize the
80 * IEEE ROBOTICS & AUTOMATION MAGAZINE * DECEMBER 2022
Modeling and Optimization
of Bioinspired Feathers
To achieve the best maneuverability, we wish to optimize
the feather design parameters to maximize the thrust generated.
The thrust is generated through complex interactions
with the fluid and dependent on the geometry of the
feather and the periodic motion at its root. To begin the
optimization process, we first define the feather design
parameters. Then, we use a hydrodynamics simulation
model to explore the large design space, and we identify a
subset of parameters that produce the largest thrust.
Finally, the subset identified in simulation is further
explored through real work experiments with a custom
physical experimental setup.
Parametric Feather Design
The parameterized feather design and controller are shown
in Figure 2(a) and (b). The geometry is defined as a rectangle,
with its width w and length l as parameters. The control
motion corresponds to the angular displacement at the root
the feather. We evaluate only periodic motions to mimic
the movements of the feather star. Consequently, the signal
is fully described by the rise time
t ,rise
.
fall time t ,fall and
hold time thold We keep the amplitude constant at A = 40º
to limit the size of the design search space. The 40º value is
the maximum amplitude of the mechanical setup. Hence,
the parameters
pwlt tt
desrisefallhold
design. Polypropylene sheets of 0.4-mm thickness were
chosen as the base material for the feathers, due to their
flexibility and ease of fabrication using a carbon dioxide
laser cutter.
Hydrodynamics Modeling
In this section, we present the model of the interaction of a
single feather with the water. In particular, we first develop
a discretized model for the feather, and then we define the
forces exchanged between the structure and the fluid. We
model a single feather as a collection of discrete flexible elements,
using Simscape Multibody, where a single feather is
approximated by 10 flexible beam elements [Figure 2(a)].
Each flexible element, i, consists of two masses (a and b) of
= [, ,, ,] define the feather
IEEE Robotics & Automation Magazine - December 2022

Table of Contents for the Digital Edition of IEEE Robotics & Automation Magazine - December 2022
