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A novel design of an aquatic walking robot
having webbed feet
A. Saad Bin Abul Kashem; B. Hutomo Sufyan
Abstract— Inspired by the movement of duck that is able to
move on land and water utilizing its webbed feet, a novel design
of an amphibious robot has been presented in this paper. In
contrary, the orthodox design of amphibious robot which utilizes
the tracks or wheels on land and switches to the propeller to
move in water, a design that utilizes same propulsion system as
webbed feet to move on land and water is proposed. After
studying the movement of the duck underwater, a conclusion has
been drawn that it is swimming in the water by moving its
webbed feet back and forth to generate force to push its body
forward. Recreating this phenomenon of duck movement, hybrid
robot locomotion has been designed and developed which is able
to walk, swim and climb steps using the same propulsion system.
Moreover, webbed feet would be able to walk efficiently on
muddy, icy or sandy terrain due to uneven distribution of robot
weight on the feet. To be able to justify the feasibility of the
design, simulations are being carried out using SimulationXpress
of the SOLIDWORKS software.
Index Terms— amphibious robot, webbed feet, duck feet, robot
locomotion, swim, walk, climb, propulsion system
I. INTRODUCTION
Over the past decades, research and development of robot
have been growing steadily. One of the most important factors
in building a robot is the locomotion. It was mentioned by
Böttcher [1] that most of the robot locomotion is biologically
inspired which enables the robot to successfully move through
a variety of harsh environment. Silva and Machadond [2] also
mentioned that legged robot holds the advantages compared to
the traditional robot that utilizes wheels and tracks. Legged
robots are able to move through inaccessible terrain that
troubles the robot with wheels and tracks. As mentioned
above, most of the robot locomotion is biologically inspired.
There are various animals that are able to move on land and
also able to move on water. One of the animals is that is
capable of doing so is the duck. Duck is able to walk on land
and swim on water. Based on this phenomenon, it is decided
to design an amphibious robot that is able to imitate the
movement of a duck.
locomotion and it would be easier to compare and choose
which of the locomotion methods work best for the designed
amphibious robot.
A. Duck Feet
Duck is one of the animals that are able to move both on land
and water using its feet. Dai et al., [3] mentioned that ducks
can do this due to the unique feature of their feet. Their
webbed feet allow them to move on water by paddling it back
and forth. After further study on duck movement, it can be
concluded that the duck movement under water can be divided
into two phases. The first phase is the “Stroking Back” and
followed by the second phase “Forward Movement”. In the
first phase, the duck fully opens the webbed feet in order to
maximize the contact area with the water in order to create as
much force as possible to move forward. In the second phase,
the duck closes the webbed feet in order to minimize the water
resistance. By repeating these movements, the duck is able to
move on water. Figure 1 shows the “Stroking Back” phase and
Figure 2 shows the “Forward Movement” phase [3]. Based on
the study and findings in [3] Dai et al., came up with a bionic
design that imitates the duck movement. However, this design
is only able to move underwater. There are some other designs
regarding the duck feet, one of them is the prosthetic leg for a
crippled duck [4]. In this design, the main objective is to help
the crippled duck to be able to walk again since it has no
problem with swimming. Figure 2 shows the prosthetic duck
feet that are used to help the crippled duck [4].
(a)
II. LITERATURE REVIEW
Articles that involve duck feet, walking robots, swimming
robots, amphibious robots and also robot locomotion are
reviewed. The purpose of the review is to understand further
the respective topics. Articles regarding duck feet are
reviewed in order to understand how duck moves on land and
water. In addition, articles regarding walking robots,
swimming robots, amphibious robots and robot locomotion
are reviewed in order to understand different methods of robot
(b)
Figure 1 (a) Shows the stroking back phase. (b) Shows the
forward movement phase.
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Figure 2 Prosthetic feet for the crippled duck
(a)
Based on the objective of the research, a walking legged
mechanism has been applied as the locomotion for the robot.
One of the biggest problems faced by the legged robot is the
matter of its stability. It was mentioned by Böttcher that a
legged robot requires at least 4 legs in order to achieve its
stability.
B. Walking Robot
Another design of a walking robot is the mechanical spider. It
utilizes the Klann linkage mechanism. It was mentioned by
Lokhande and Emche [5] that legged robot utilizing Klann
mechanism is beneficial for rough and rocky areas compared
to a traditional wheeled robot. Klann mechanism does not
require complex control system. The movement is supported
by few links that are connected by pivot joints and utilizing
the rotating motion of the crank into a movement similar to
walking motion.
C. Climbing Robot
One of the famous climbing robots is the “Djedi” designed by
Richardson et al., [6]. The author has successfully designed,
constructed and developed a climbing robot. The robot called
the “Djedi” is used to explore the shafts of the queen’s
chamber within the Great Pyramid. The robot is able to climb
the steps by making use of its big wheels. However the ability
to climb the steps is limited with respect to the radius of the
wheels and furthermore, the “Djedi” is using wheels for its
locomotion. Therefore, the climbing concept of the “Djedi”
will not be suitable for the current research.
Quinn et al., [7] mentioned that Whegs™ is a robot inspired
by the insect locomotion systems. The design of the robot
enables it to move through irregular terrains and climb the
steps utilizing its wheel-legs. Another robot that is able to
move on rough terrain is the USAR Whegs™. According to
Hunt et al., [8] USAR Whegs™ is developed as an urban
search and rescue robot. It is able to climb about 15 cm
obstacles utilizing its wheel-legs. In general, the height of the
steps that Whegs™ is able to climb is depending on the size of
the wheel-legs. Whegs™ and USAR Whegs™ are shown in
Figure 3 (a) and (b) respectively [7] [8].
(b)
Figure 3(a) Whegs™ ; (b)USAR Whegs™ .
Takahashi and Shibata [9] have done an experimental study
for a biped robot that has 6 degrees of freedom and kinematics
redundancies. Based on the study conducted, they found that
the center of gravity of the robot needs to be altered in order
for it to climb the steps without falling down forward or
backward.
D. Swimming Robot
There are various types of swimming robots that have been
designed and developed previously. A bionic swimming robot
is designed by Chen et al., [10] that utilizes a balance paddle
and also two screw propellers in order to swim up and down in
the water.
A turtle-like swimming robot is also designed and developed
by Kim et al., [11]. The turtle-like robot is inspired by the
movement of a marine turtle. The robot is able to move by
recreating the soft flapping motion of the turtle. In order to
recreate the phenomenon, an actuator is developed using a
smart soft composite that is able to generate bending and
twisting motion using a simple and lightweight structure.
Sakai et al., [12] came with a design of swimming robot that is
inspired by the movement of the frog. After further study of
the frog movement, they developed a swimming robot that has
a similar musculoskeletal structure. The robot is able to swim
adaptively and the movement is mainly generated by the
hydrodynamic interaction of the water environment and the
musculoskeletal system. Calisti et al., [13] came with a design
of octopus inspired swimming robot. There are two propulsive
actions that are used in this octopus robot. The first is the
reaction forces due to the contact of its leg with the ground
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surfaces; the second is the hydrodynamic forces that arise
from the sculling motion of the legs.
E. Amphibious Robot
Li et al.,[14] come out with a design of an amphibious
spherical robot. This spherical robot makes use of water-jet
propeller and two servomotors in order to move. However,
this design is not suitable for the current research because it
utilizes two different locomotion methods instead of one.
Smaller robots are present inside the spherical robot in order
to carry out the task. Figure 4 shows the amphibious spherical
robot (Li, Guo et al. 2015).
Figure 4 Spherical Amphibious Robot
According to Zhang et al., [15] an amphibious robot should be
able to walk on the rough surface, maneuver underwater and
also pass through various transitional zones. They came up
with a design of amphibious robot the “AmphiHex-I”. This
amphibious robot utilizes the transformable fin-leg propulsion
mechanism. This design can be used in the research since it
utilizes one locomotion system. The AmphiHex is shown in
Figure 5 and Figure 6 (Zhang, Liang et al. 2013).
Figure 5 Conceptual Design for AmphiHex
(a)
(b)
Figure 6(a) AmphiHex moving on land and (b) AmphiHex
moving on water.
Based on the reviews that have been conducted, it has been
found that using the mechanism from the Klann Mechanical
Spider would be the best choice for this robot. Furthermore, a
unique feature of the duck feet will also be imitated in the
design of the amphibious robot feet in order to enable the
robot to walk, swim and climb steps. Details will be further
explained in the respective section within the research paper.
III. METHODOLOGY
This section would cover the details of the methodology.
A. Material Selection
The material used when constructing an amphibious robot is a
very crucial matter. The material used should be strong yet
light in weight. Furthermore, the material should be
waterproof and also resistant to corrosion as it might affect the
performance of the robot after a certain period of time. Based
on the criteria of the materials, aluminum and steel are chosen
since both meet the criteria. To decide on which material to be
used both steel and aluminium are compared and depicted in
Table 1. Based on the comparison between steel and
aluminum in the table above, aluminum is chosen as the
material to be used in constructing the body and the leg of the
robot. As for the feet of the robot, a soft material will be
needed since the duck feet need to be able to open and close
the webbed feet.
B. Mechanical Design
The most crucial part of the research will be the mechanical
design of the robot. The aim is to come up with a design as
simple as possible yet still maintaining the performance of the
robot. The mechanical design will be broken down into two
parts, the duck feet design, and the movement mechanism.
Details on each part will be further explained in their
respective section.
C. Duck Feet
The first and foremost that is needed to be done is the design
of the duck feet for the amphibious robot. The design of the
duck feet plays an important role as it is the main objective of
the research. There are several criteria in designing the duck
feet. The designed duck feet should be able to close the
webbed feet when the feet is moving forward under water and
open the webbed feet when the feet is stroking backward
under water. The designed duck feet needed to be able to open
and close the webbed feet in order to alter the contact surface
area with the water. When the feet are stroking back, the
webbed feet need to be fully open in order to maximize the
contact surface area with the water in order to maximize the
forward driving force. However when the feet are moving
forward, the webbed feet need to be closed to minimize the
contact surface area in order to minimize the reaction force
from the water resistance. Based on the criterion for the design
of the duck feet, few designs have been made using
SOLIDWORKS software.
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Table 1 Comparison between Steel and Aluminium
Steel
Aluminium
Cost
Cheaper compared to aluminum
Slightly more expensive due to the
raw material price
Strength and Malleability
Tough and resilient, might be
cracked when push to the same
limit as the aluminum
More malleable and elastic
compared to steel
Corrosion Resistance
Corrosion resistant
Need to be painted and treated to
prevent corrosion
Weight
2.5 times heavier than aluminum
Lightweight
The initial design of the duck feet is shown in Figure 7. As
shown in the Figure above, the initial design of the duck feet
has the length of 145.35 mm and width of 99.90 mm.
However in this design, instead of opening and closing the
web of the feet while moving underwater, it makes use of the
reaction force from the water resistant to bend the feet in a
flapping motion when the feet are moving forward and
backward. It is shown in Figure 8, by applying a force of 1
Newton, the edge of the feet is bent causing a displacement of
about 4.199 mm when the force is applied on the top surface
of the feet and a displacement of about 3.948 mm when the
force is applied on the bottom surface of the feet. Figure 8 is
generated through SimulationXpress Analysis from the
SOLIDWORKS software and the material used for the duck
feet in the simulation is rubber.
The initial design of the duck feet might not be the best
option for the amphibious robot since the bending moment of
the designed duck feet is depending on the force acting on the
surface of the duck feet. After encountering the problem on
the initial design of the duck feet, a new design is proposed.
The new design is able to actually open and close its webbed
feet by making use of a hinge. The web of the duck feet will
be attached to the feet using a hinge. The proposed material
used for the fabrication of the duck feet with a hinge is
aluminum.
(a)
The new designs of the duck feet utilizing a hinge have been
shown in Figure 9 and 10. Figure 9 shows the duck feet with
the hinge when it is closed while Figure 10 shows the duck
feet with the hinge when it is open.
(b)
Figure 7(a)Top view of the duck feet initial design.(b)
Isometric view of the duck feet initial design.
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(a)
(a)
(b)
Figure 8 Bending caused by applied force. (a) Force applied
from the top. (b) Force applied from the bottom
(b)
In the new design of the duck feet where a hinge is used,
while moving under water, the hinge will move due to the
force exerted from the water resistant when in contact with
the surface of the web of the feet. When the leg is moving
forward, the hinge will open since the reaction force from the
water resistance is coming from the front and the hinge will
stop opening since the edge of the web will come in contact
with each other to limit the opening of the flap. When the leg
is stroking back, the hinge will close because of the reaction
force from the water resistance is coming from the back and it
will stop when the web comes in contact with the side fingers
of the duck feet. By opening and closing the web of the
designed duck feet, it changes the surface area that comes in
contact with the water. When the webbed feet are fully closed
during the stroking back movement of the leg, the contact
area with the water is maximized and the driving forward
force generated by the feet is maximized. On the other hand,
when the webbed feet are fully open during the forward
movement of the leg, the contact area is minimized and the
reaction force from the water resistance is minimized. Since
the driving force generated is greater than the reaction force
generated by the water resistance, the body will move
forward. In order to improve the performance of the feet, a
double hinge design is proposed. By using double hinge in
designing the duck feet, the opening of the webbed feet can
be increased which further reduce the contact area with the
water while moving forward. By further reducing the contact
area with the water, the drag force from the water resistance
can be minimized. Figure 11 shows the duck feet with double
hinge design.
Figure 9 Duck feet design using hinge when it is fully closed.
(a) Top View. (b) Isometric View
(a)
(b)
Figure 10 Duck feet design using hinge when it is fully open.
(a)Side View. (b) Front View.
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four-bar double-rocker linkage. The characteristic of Klann
Linkage are:
1.
2.
3.
It requires 6 links per leg.
It has 180° of crank rotation per stride
It requires 2 legs will replace a wheel.
Based on the characteristic and output motion, it has been
decided to choose Klann Linkage mechanism to be the
movement mechanism for the robot because it has some
favorable advantage with respect to the requirement of the
movement design. First of all in term of light weight, Klann
Linkage requires 2 legs in order to replace a wheel movement
(360° rotation) and each of its legs requires only 6 links.
However, Jansen Linkage requires 3 legs in order to replace a
wheel movement and each leg requires 8 links. Based on the
number of links alone, it can be seen that Klann Linkage has
the advantage of being light weight (Less number of links =
less total weight of the robot).
Figure 11 Duck feet design using double hinge (front view).
D. Movement Mechanism
Following the objective of the research to create an
amphibious robot inspired from duck, the decision is made to
design a legged robot. Selecting the appropriate movement
mechanism is very important. This movement mechanism
plays an important role to achieve the objective the project.
Therefore, some design criteria have been given to achieve its
objectives. The design criteria were:
1.
2.
3.
Stability, able to stand firm when it moves and stops.
Light Weight, the design should be light to ensure it
is able to float on water.
Climbing Steps, the movement mechanism should
allow a climbing movement (able to raise its leg to a
certain height).
There are several movement mechanisms that can be used to
achieve the criteria mentioned above. In this section, each of
these mechanisms is going to be analyzed for its advantage
and disadvantage for the robot. There are two mechanisms
that have been considered to be used in this project; Klann
Linkage mechanism and Jansen Linkage mechanism.
After discussing regarding the weight of the robot, next is to
review on the second criteria of the movement mechanism
which is climbing steps. Both Jansen Linkage mechanism and
Klann Linkage mechanism are able to climb steps. However,
based on the output motion generated by both mechanisms, it
is shown that the height of the steps differs from one another.
Referring back to Klann Linkage is able to reach a higher
position during each step compared to Jansen Linkage.
Based on the two design criteria above, the decision has been
made to use Klann Linkage as the movement mechanism for
the robot. Although Jansen Linkage is able to generate a
smoother walking motion compared to Klann Linkage, Klann
Linkage is still the better option for the movement
mechanism based on the criteria. Based on the review on
several mobile robots, the movement mechanism of the
Mechanical Spider is to be imitated [5]. The Mechanical
Spider is making use of the Klann Linkage as the movement
mechanism. It is used to simulate the gait of legged animal
and functioned as a wheel replacement. It is able to recreate a
walking motion from a simple rotating motion. The Klann
mechanism can be driven by a single motor and it does not
require any complex control system on it.
1) Jansen Linkage
Jansen Linkage [5] is a leg mechanism that is designed by the
kinetic sculptor Theo Jansen in order to simulate a smooth
walking motion. Jansen linkage is utilizing a combination of
multiple four-bar linkages. The characteristic of Jansen
Linkage are:
1.
2.
3.
It requires 8 links per leg.
It has 120° of crank rotation per stride.
It requires 3 legs to replace a wheel.
Figure 12 Klann Linkage with the traced path of motion.
2) Klann Linkage
Klann Linkage [5] is a planar mechanism that was developed
by Joe Klann in order to simulate the gait of legged animal
and functioned as a replacement for a wheel. Klann Linkage
is an expansion of Burmester Curve which is used to develop
Figure 12 shows the Klann Linkage and the traced path of
motion when the crank starts rotating. By rotating the crank
in a clockwise direction, the other end of the leg will recreate
a motion similar to a walking motion. Each stride requires an
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180° rotation of the crank, hence, two sets of Klann Linkage
mechanism are able to replace a wheel.
For the initial design, the walking mechanism using 2 legs
with Klann Linkage has been designed. However, this design
has issues regarding stability as all legged robot have initially.
It was mentioned by Böttcher et al., [1] that to achieve static
stability, the robot needs at least 3 points that contact the
ground. To achieve walking stability, the robot needs at least
4 legs. Furthermore, this design can only move forward and
backward and is unable to change its direction because it is
only powered with one motor to move. Aside from the
stability problem and the limited movement, this design also
has a very limited body space which might not be enough to
put the other components together. Refer to Figure 13 and
Figure 14 for the initial design.
Figure 15 Right side view of 4 legs Klann Linkage
Figure 13 Front View of 2 leg Klann Linkage
Figure 16 Isometric View of 4 leg Klann Linkage
Figure 14 Isometric View of 2 leg Klann Linkage
After realizing the flaw of the initial design for the movement
mechanism of the robot, the second design is created
considering the flaw of the initial design. The second design
of the walking mechanism has 4 legs and uses 2 motors to
drive the movement. The second design also implements 4
legs instead of 2 legs to ensure the stability. Finally, space
within the body of the robot is also increased to ensure that
components can be placed on it. Refer to Figure 15 and
Figure 16 for the second design of the walking mechanism.
Based on the second design, problems regarding stability
have been solved because the robot is now having 4 legs.
Problems regarding limited movement have been solved by
installing 2 motors to generate the driving force so it can
change its direction by moving both motors in opposite
direction. Finally, the problem regarding limited space for
components has been solved by increasing the total length
and width of the robot. However with this design, another
problem arises.
The second design will have a problem with climbing the
steps because it has 4 legs all in different position making it
not feasible for climbing steps. Therefore, some changes are
made for the third design. The third design is having 4 legs
like the previous design but just has a difference in the
positioning of the 4 legs.
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Figure 17 shows the positions of all 4 legs are parallel to each
other. Although the positions of the legs are parallel to one
another, 2 motors will be used to drive the movement with 2
legs for each motor. This is to ensure that 2 legs are having
the same position at any time so it has stability during
walking and ability to climb the steps.
Figure 17 Right Side View of final design
Figure 18 shows the motions when the robot is walking and
climbing steps. All those motions can be powered by a single
motor that will rotate the connecting shaft between the two
cranks. The cranks will be positioned 180° out of phase with
each other. Using a DC motor to provide the rotation to the
connecting shaft the mechanism is able to recreate a walking
and steps climbing motion. While walking on land, the
webbed feet will be open when the legs are lifted up and close
as the feet touch the ground. There is no involvement of any
motor when opening and closing the webbed feet. The
opening and closing of the webbed feet are totally passive
motions.
Figure 18 Motion of the robot when walking and climbing
When the robot’s water sensor (attached to its body) touches
the water, it will send signal to micro controller. Micro
controller will command servo motors. The servo motors
attached to each foot will start to run and rotate the feet about
80° and repeat the same motion as when the robot was
walking or climbing steps. It will keep on moving with the
feet rotated by about 80° from the normal walking position as
long as it is in water. While moving under water, the webbed
feet will be open while the feet moves forward and will close
when the feet moves backward. The opening and closing in
the webbed feet while moving underwater is caused by the
reaction force due to water resistance. Figure 19 shows the
position of the feet when they are moving underwater. It is
stated earlier that according to Böttcher [1], the minimum
number of legs needed for a robot to be statically stable is
four. Therefore, the designed amphibious robot will have four
legs instead of two. By applying four legs into the
mechanism, total two DC motors are required. One DC motor
can actuate two legs independently. Furthermore, while using
these two DC motors to actuate the mechanism, the robot is
able to turn into different direction instead of going forward
and backward only. As it is shown in Figure 20, the final
assembly design of the amphibious robot is having four legs.
There is a hole cut on the bottom of the robot body to allow
the inner two legs move freely without coming into contact
when the leg moves.
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be the core of the robot. It is responsible for all the active
movement that is produced by the robot. In order to be able to
build the amphibious robot designed in the research, several
components are needed. The components needed are
Microcontroller, DC Motor, Servo Motor, Motor Driver,
Water Sensor, and Ultrasonic Sensor.
Figure 19 Position of the feet when it is moving under water
(a)
(b)
Figure 20 Final assembly design of the robot. (a) Diametric
view. (b) Top view.
IV. ELECTRICAL COMPONENTS
In this section, the electrical design of the amphibious robot
will be discussed. The electrical design can be considered to
a)
Micro Controller
The microcontroller can be considered to be the head or brain
of the robot. It is used to control the output based on the
information from the input. The output from the
microcontroller in this research will be the actuation of the
motors. The input comes from the information received
through the sensors that are attached to the robot. The
microcontroller that is proposed to be used is Arduino UNO
Rev3 [16].
b)
DC Motor
DC motor is used to drive the crank to generate the rotational
motion which later is converted into a walking motion with
the help of the Klann mechanism. The DC motor is the
primary actuator in the robot, the DC motors keep on running
whenever the robot is walking, swimming and climbing steps.
Based on the motion analysis done in the SOLIDWORKS
model, the minimum torque required by the DC motors to
drive the robot is obtained. In the SOLIDWORKS model, the
material has been set to aluminum. Refer to Figure 21 for the
torque exerted by the DC motor. The maximum torque shown
in the graph is 251 N.mm, therefore, it is found that the DC
motor needs to have a torque of at least 251N.mm.
c)
Servo Motor
There are four servo motors in the design which will be
attached to each foot of the robot. The servo motors will start
running and turning the feet from walking form into
swimming form when the robot comes in contact with water
or entering the water. Since the servo is attached to the feet
and the feet will be submerged under water the servo motors
used should be water proof. Four servo motors will be
attached to the feet of the robot. Servo motors to be used is
the HS-646WP. The specification of the servo motors is
shown in Table 2 [17].
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Figure 21 Motor Torque against time graph when the speed of the motor is constant at 40 RPM
Table 2 Specifications of HS-646WP waterproof servo motor
Motor Type:
3 Pole
Bearing Type:
Dual Ball Bearing
Speed (6.0V/7.4V):
0.20 / 0.17
Torque oz./in. (6.0V/7.4V):
133 / 161
Torque kg./cm. (6.0V/7.4V):
9.6 / 11.6
Size in Inches:
1.65 x 0.83 x 1.57
Size in Millimeters:
41.8 x 21.0 x 40.0
Weight ounces:
2.12
Weight grams:
60.0
d)
Motor Driver
The motor driver used is L298. It is a very common motor
driver. The purpose of using motor driver is to increase the
current supplied from the microcontroller to the DC motors.
Some DC motors require higher current which the
microcontroller is unable to supply. Figure 22[18] shows the
pin-out connection of L298 motor driver.
f)
Ultrasonic Sensor
The ultrasonic sensor will act as the eyes of the robot. While
the robot is in swimming mode and moving towards the land,
it has to know when to change the feet position from
swimming mode into walking mode. The ultrasonic sensor
will be attached to the front body of the robot pointing
downward in order to sense the distance between the body
and the ground while the robot is in swimming mode. A
threshold distance would be set for the ultrasonic sensor
considering the height of the legs in swimming mode. If the
swimming mode is still on when the feet touch the ground,
the legs may break. Once the sensor detects the distance
between the body of the duck and the ground is less than the
threshold that has been set, the servo motors will start to
change the position of the feet from swimming mode to
walking mode. While the robot is in walking mode, the
ultrasonic sensor is turned off. An ultrasonic sensor or a
camera may also be connected in the front of the duck to
detect the presence of obstacles in the robot path. This can be
considered in the future development of the design.
V. PROGRAM FLOW
Figure 22 Pin out for L298 motor driver
e)
Water Sensor
The water sensor is used to detect the presence of water when
the robot is moving. When the presence of water is sensed,
the sensor sends a signal to the microcontroller. The
microcontroller will then send a signal to the servos to start
running. Then, servo motors alter the position of the duck feet
from walking form to swimming form.
In this section, program flow of the robot will be shown and
explained. The program flow acts as the sequence of actions
that the robot takes. The robot will take these actions
depending on the condition met. As shown in Figure 23, once
the robot is turned on, the water sensor will detect the
presence of water. If water is not present, the robot will
initiate the walking mode. When in walking mode, the robot
will check the position of the feet. If it is in walking position,
the DC motors will start running. If the feet position is not in
walking position, the servo motors will start to turn the feet
into the walking position then the DC motors will start
running. The same process happens while the robot is in
swimming mode. It will check the position of the feet and
correct the feet into swimming position before the DC motors
start running. The process is then repeated until the robot is
turned off.
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Figure 23 Flow Diagram of the robot
(a)
(b)
Figure 24 Linear displacement of the leg. (a) X-axis direction. (b) Y-axis direction.
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VI. RESULTS AND DISCUSSIONS
In this section, the results obtained from the walking,
climbing and swimming are discussed.
For the future works, it is strongly recommended to create an
actual prototype of the robot. After the creation of the
prototype, an application can be implemented into the robot.
A blue tooth module can be implemented into the robot so
that it can be controlled manually using smartphones.
A. Walking and Climbing
In the walking mode of the robot as shown in Figure 24, it is
found that the feet have a linear displacement with respect to
X-axis which is 24.7 cm. This shows that every step that the
robot took will move the robot forward by about 24.7 cm.
The feet also have a displacement with respect to Y-axis of
148 mm. This shows that the feet are able to be lifted up to
about 14.8 cm. Based on the simulation done by
SOLIDWORKS, it can be safely assumed that the robot is
able to climb steps that are 10 cm in height since the
maximum limit of the linear displacement in Y-axis is 14.8
cm. Two motors have been used to drive the movement with
2 legs for each motor. This is to ensure that 2 legs are having
the same position at any time so it has its stability during
walking and able to climb the steps.
Moreover, webbed feet would enable it to walk efficiently on
muddy, icy or sandy terrain because the weight of the whole
body of the duck would be uneven in the different areas of the
webbed feet. While walking, the weight of the robot will be
less on the flap as it is not solid. Hence, the whole feet would
not be covered by mud or ice or sand which would help the
locomotion of the robot on this terrain efficiently.
VIII. CONCLUSION
In conclusion, the designed duck feet are able to meet its
criteria. They are capable of imitating the movement of real
duck feet. The designed duck feet are able to open and close
the webbed feet by utilizing a hinge mechanism and the water
resistance when it was moving under water. While walking
on land, the webbed feet are open when the legs are lifted up
and close as the feet touches the ground. The opening and
closing of the webbed feet are purely passive motion without
the help of any motor. The amphibious robot is designed to be
able to walk, swim and climb steps using the feet that are
inspired from the duck. Based on the results shown in Figure
19, the robot is able to walk and cover a distance by about 25
cm (247 mm) in a single step. The Figures also show the
maximum height that the feet can go is up to 15 cm (148
mm). Although the prototype of the designed amphibious
robot has yet to be built to test the performance of the design,
the designed duck feet met most of the objectives of the
research.
4.
1.
B. Swimming
Based on the design implemented, the duck should be able to
move forward when it is on water. The duck feet are designed
in a way that the hinge will open when the force from the
water resistance hit it from the front allowing less contact
with the duck feet. Furthermore, when the feet are striking
backward, the hinge will be closed due to the normal force
exerted by the water being kicked. When the hinge is fully
closed, the contact area is maximized hence the driving
forward force is maximized.
2.
3.
4.
5.
VII. RECOMMENDATION & FUTURE WORK
First of all, it is recommended to use a DC motor having
torque more than 251N.mm to ensure enough force is
generated. By using a higher torque DC motor, it ensures the
linkage will be able to move since the calculated force needed
and the actual force needed might differ due to the friction
force on each link.
As for the duck feet, a larger size is recommended. By having
larger duck feet, the surface area is enlarged with increased
contact area with the water to generate more driving force and
also contact area with the ground is increased, which
consequently enhances the stability of the robot.
6.
7.
8.
9.
The microcontroller used can also be changed into the one
with more I/O pins. By having more I/O pins, there will be
more functionalities that can be implemented into the
amphibious robot.
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