International Journal of Advanced Robotic Systems ARTICLE Design and Construction of a Specialised Biomimetic Robot in Multiple Swimming Gaits Regular Paper Sayyed Farideddin Masoomi1*, Stefanie Gutschmidt1, Nicolas Gaume2, Thomas Guillaume2, Connor Eatwel1, XiaoQi Chen1 and Mathieu Sellier1 University of Canterbury, Christchurch, Canterbury, New Zealand The University of Technology of Belfort-Montbéliard, Belfort, Sevenans, France *Corresponding author(s) E-mail: sayyed.masoomi@gmail.com Received 10 August 2014; Accepted 21 March 2015 DOI: 10.5772/60547 © 2015 Author(s) Licensee InTech This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited Abstract Efficient cruising, manoeuvrability and noiseless perform‐ ance of fish robots have been attracting people in various scientific realms Accordingly, a number of fish robots are designed and fabricated so far However, the existing robots are only capable of one gait of locomotion This deficiency is addressed by UC-Ika with multiple gaits of locomotion including cruising and manoeuvring that are inspired from two different fishes This paper aims at presenting the design and fabrication process of UC-Ika The swimming performance of the robot is tested and compared with its previous version UC-Ika Keywords Fish Robot, UC-Ika 2, Biomimetics, Gait of Locomotion, Cruising, Manoeuvrability, Tuna, Birdwrasse Introduction Undersea operation, oceanic supervision, aquatic lifeform observation, pollution search and military detec‐ tion are just a few examples that demand development of underwater robots to replace humans [1] Since the best solutions are always inspired from nature, for develop‐ ment of an underwater robot, the nature inspiration has been also taken into account Accordingly, a number of bio-inspired robots such as fish robots have been developed so far [2, 3, 4, 5] A fish robot is defined as a fish-like aquatic vehicle which propels through undulatory or oscillatory motion of either the body or fins [6] The first fish robot, RoboTuna, was built at MIT in 1994 [7] Three years later, Vorticity Control Unmanned Undersea Vehicle (VCUUV) was developed based on RoboTuna with some improvement and more capabilities such as avoiding obstacles and having updown motion [8, 9] Afterwards, a number of institutes and universities developed their own fish robots with various capabilities such as cruising and turning by pectoral fins [10], cruising by undulating anal fins [11] and so on Nevertheless, the existing fish robots have deficiencies regarding their swimming behaviours The fish robots have been developed to have a specific gait of swimming such as cruising, accelerating and manoeuvring However, to accomplish marine tasks, underwater robots must be skilled for swimming in various gaits For instance, Int J Adv Robot Syst, 2015, 12:168 | doi: 10.5772/60547 VCUUV is a well-known tuna-mimetic robot [8] Tunamimetic robots show proficiency in cruising gait of swim‐ ming, while these kinds of robots are notorious for not being manoeuvrable among narrow areas [12] According‐ ly, tuna-mimetic robots are suitable only for navigationbased tasks such as coastal monitoring, oil and gas exploration which need long distance of swimming On the other hand, Boxybot series of robots are inspired from boxfishes and adapted for slow swimming and manoeu‐ vring gaits [10, 13] Boxybots are not sufficiently competent for cruising gait of swimming Hence, these types of robots are talented for discovery tasks such as exploring ship‐ wrecks or oil pipelines In order to address the single gaited motion of the existing fish robots, the authors have developed a multiple-gaited fish robot called UC-Ika 2.1 UC-Ika is designed for two gaits of swimming – cruising and manoeuvring2 – while it is capable of up-down motion The cruising motion of the robot must be highly efficient to save energy of swimming The remainder of this paper has four sections Section presents the design process of UC-Ika within introducing the cruising and manoeuvring gaits of motion Section discusses the fabrication step of the robot In Section 4, the swimming performance of the robot is investigated and its cruising mode is compared to UC-Ika In the last section, the paper is summarised Design The primary step of developing fish robots is the design of an optimal shape and swimming mechanism correspond‐ ing to their gait of locomotion All aquatic animals are specialised within their gait of motion These specialities root in hydrodynamic and biological aspects of their motion including swimming forces that are acting on the fishes or generated by them and also the body (and fins) shape that fishes have Accordingly, in order to have the optimal design for a two-gaited swimming robot, the specialised fishes in each swimming gait must be selected 2.1 Swimming Specialities of Tuna The investigation of the capabilities of tuna in swimming could be accomplished by studying swimming gait, swimming forces and body (and fin) shape of tunas 2.1.1 Swimming Gait The swimming gait of tuna is defined with respect to their swimming propulsors, kinematics, muscles and timebased locomotion behaviour Tuna is a thunniform fish which swim through undulation of the posterior part of its tail peduncle and caudal fin The wavelength of undulation is long and wide at the trailing edge of the caudal fin They provide thrust mainly by their stiff caudal fin.3 The angle of attack of the caudal fin changes once it reaches its maximum amplitude in order to maxi‐ mise the thrust [15] Tuna is specialised for cruising kinematics of motion which distinguishes a part of swimming that a fish has a sustain‐ able speed for more than 200 minutes without fatigue [16] In terms of muscles, tuna swims using the red or slow oxidative muscles which have low power output and are, thus, non-fatiguing The non-fatiguing nature of red muscles suits them for sustainable swimming [16] Tuna is mainly capable of periodic motion or steady motion which continues in a long period of time to navigate long distances [17] 2.1.2 Swimming Forces The dynamic behaviour of the fish robot is influenced by two main forces: hydrostatic and hydrodynamic forces Hydrostatic forces are more essential for depth control, while hydrodynamic ones are used for swimming How‐ ever, to facilitate the swimming model with minimum energy dissipation, hydrodynamic forces need to be produced with respect to several factors These factors are introduced as optimal swimming factors Hydrostatic forces such as weight and buoyancy play crucial roles in the stability of fishes The weight, W , is defined as the mass multiplied by the gravitational con‐ stant, M f g On the other hand, the buoyancy, B , is defined by Archimedes’ law as the displaced mass of water multiplied by the gravitational constant, ρw V f g , where V f is the fish volume and ρw is the density of water In order to keep the position of the robot stable underwater, W and B need to be equal Additionally, the centres of mass and buoyancy must be vertically aligned, while the centre of buoyancy should be above that of the weight This assures the attitude stability of the robot As a pelagic fish, tuna has almost neutral buoyancy [18] Hydrodynamic forces such as resistive and thrust forces vary from fish to fish For a tuna-like robot, the main resistive force is associated with the pressure drag, while the main thrust force is associated with the lift force [19] Accordingly, the pressure drag and lift forces need to be decreased and increased, respectively, in order to have an efficient swimming The name of the fish robots originates from the Maori name “ika” which means fish Usually, using the term swimming gaits causes a confusion regarding the swimming behaviour of the robot In other words, claiming that a robot is single gaited, for instance, in cruising does not mean that the robot is not able to manoeuvre or accelerate But the swimming properties of the robot – explained in [14] – is optimised only for one gait of motion like cruising Hence, having a multiple gaits of locomotion delivers the idea of having swimming characteristics of different gaits In terms of UC-Ika 2, the robot has swimming characteristics of two distinct gaits of motion including cruising and manoeuvring 90% of thrust is produced by the caudal fin Int J Adv Robot Syst, 2015, 12:168 | doi: 10.5772/60547 The pressure drag is the result of the pressure gradient along the body In order to decrease this drag, the shape of the animal is a determining factor The best overall shape of swimming animals is to have streamlined bodies with the diameter of the thickest part, d , and fish length, l Streamlined bodies with d / l between 0.18 and 0.28 produce less than 10% of the minimum possible drag [18] Regarding propulsive forces, tunas use vorticity method for swimming In this method, tuna fishes generate lift forces through shedding vortices around the tips of its caudal fin [18] These vortices make two forward and lateral forces The forward force is the thrust of the fish, while the lateral forces will cancel out each other in a complete fin stroke The vortex rings behind a fish is shown in Fig (a) into account in this thesis: Strouhal number and Froude efficiency The Strouhal number is a factor that shows the structure of the vortices made through the body undulation of fishes The Strouhal number, St , is a dimensionless parameter It represents the ratio of unsteady to inertial forces and is defined as St = fh x& (1) where f is the frequency of the body undulation, h is the heave of the caudal fin and x¯˙ is the average cruising velocity of the fish If 0.25 < St < 0.4, the vortices behind the caudal fin produce maximum thrust Note that the Strouhal number is applicable for fishes whose swimming is through the liftbased methods including vorticity method [21] The Froude efficiency is another important factor to evaluate the swimming behaviour of fishes This factor relates the useful power used for propulsion to total kinetic energy of the fish which is the mean rate of transferred momentum to the wake around the fish Froude efficiency is defined by (b) h= (a) Figure Vortex rings left behind a swimming fish: (a) side view and (b) top view [20] re Vortex rings left behind a swimming fish: (a) side view and (b) top view [20] Larger vortex rings provide greater thrust forces To enlarge the vortex rings, the caudal fin and the very last part of the tail peduncle make a travelling wave; see Fig (b) The speed of the travelling wave must be greater than the A speed of the fish [17] The undulatory motion requires Uthe U caudal fin to change its orientation once it reaches its α W maximum heave ure Vortex rings left behind a swimming fish: (a) side view and (b) top view [20] λ (2) ¯˙ is the mean velocity of the fish where F¯ Cx is the thrust and x Ptotal is the total kinetic energy of the fish [22] In this paper, Ptotal is obtained through the following expression: Ptotal = FCx x& + FCy y& , (3) ¯˙ is the where F¯ Cy is the force to generate vortex wake and y mean lateral speed of the caudal fin Derivations of F¯ Cx and re Travelling wave generated by undulatory motion of fish with the overall fish swimming speed, U; the lateral speed of the caudal F¯ W; the instantaneous angle of attack of the caudal fin, α; the undulation amplitude, A; and the undulation wavelength, Cyλ [17] ors of designing an efficient swimming robot Two n criteria are taken into account in this thesis: Strouhal mber and Froude efficiency FCx x& , Ptotal are presented in [23] A tuna fish could be up to 90% efficient, where FCx is the thrust and x˙ is the mean velocity ofwhile the fish Ptotal is the total kinetic energy of theefficient fish [22] In this [24] paper, Ptotal is obtained through the following expression: a screw propeller fish robot is at most 50% Strouhal number is aAfactor that shows the structure of ˙ 2.1.3 Body and Ptotal = FCx Ux˙ + FCy y, (3) Fin Shape vortices made through the body undulationUof fishes Strouhal number, St, is a dimensionless parameter where FCy is the force to generate vortex wake and y˙ is the α It W forces and is One of the esents the ratio of unsteady to inertial mean lateral speed of the caudal fin Derivations of FCxmain sources of the swimming optimality of ned as and F are presented in [23] A tuna fish could be up to optimal shape However, the optimality of fishes is their Cy fh St = (1) 90% efficient, while a screw propeller fish robot is at most λ body shape is essentially determined by resistive forces, x˙ 50% efficient [24] re f is the frequency of the body undulation, h is whereas fin shapes are optimised with respect to the ure Travelling waveFigure generated by undulatory motion of fish with the overall fish swimming speed, U; the lateral speed of the caudal Travelling wave generated by undulatory motion of fish with the x˙ isofthe cruising heave of the caudalangle fin and W; the instantaneous of attack theaverage caudal fin, α; the undulation amplitude, A; and the undulation wavelength, λ [17] overall fish swimming speed, U ; the lateral speed of the caudal fin, W ; 2.1.3 Body and Fin Shape propulsive forces city of the fish If 0.25 < St < 0.4, the vortices where ismain the and is the mean velocity of the ors the of designing efficient swimming robot Two of the the instantaneous angle of attack caudal α thrust ;sources the undulation nd caudal finan produce maximum thrust Note Cx fin, One ofFthe of x˙the swimming optimality of nthe criteria are taken intoisaccount this thesis: Strouhal fish is the total kinetic of thethe fishoptimality [22] In quite this Tuna has Strouhal number applicable for whose wavelength, amplitude, Ain; and thefishes undulation [17] fishesPtotal isλtheir optimal shape.energy However, of a streamlined body shape The anterior part mber andisFroude efficiency paper, Ptotal isisobtained through the following expression: mming through the lift-based methods including body shape essentially determined byof resistive forces, its body is heavy, inflexible and often circular in cross icity method [21] is a factor that shows the structure of whereas fin shapes are respect to (3) the Strouhal number ˙ section Ptotal = Foptimised x˙ + FCy with y, While the optimised design regarding the shape of the The posterior part including the tail peduncle is Cxbody propulsive forces vortices through body important undulation factor of fishes Froude made efficiency is the another to and the caudal fin enhances the swimming performance of lighter and flexible The tail peduncle is strengthened by Strouhal number, St, is a dimensionless parameter It where FCyquite is thea force to generate and y˙ is part the uate the swimming behaviour of fishes This factor Tuna has streamlined bodyvortex shape.wake The anterior resents the ratio ofaused unsteady to inertial and is decisive es the useful power propulsion toforces total fishforrobot, there existkinetic other factors ofofinflexible designing the keels located at either sides of the peduncle Due to the mean lateral the caudal fin Derivations ofcross FCx of its body isspeed heavy, and often circular in fined gy ofasthe fish which is the mean rate of transferred Fmain presented [23] A tuna fish could be up to peduncle is wider than it is deep In addition and section The posteriorin part including the tail the peduncle Cy are an efficient swimming robot Two criteria are taken keel, tail fh mentum to the wake around St = the fish Froude efficiency (1) 90% efficient, a screw fish robot is at most is lighter andwhile flexible The propeller tail peduncle is strengthened ˙ x efined by 50% efficient [24] by the keels located at either sides of the peduncle Due ere f is the frequency of Sayyed the body undulation, h is Farideddin Masoomi, Stefanie Gutschmidt, Nicolas Gaume, Connor Eatwel, XiaoQi Chen and Mathieu Sellier: to the keel, the tail peduncle is wider Thomas than it isGuillaume, deep heave of the caudal fin Fand x˙ is the average cruising Cx x˙ Design and Construction of akeels Specialised Biomimetic Robot in Multiple Swimming Gaits In addition to Fin strengthening the tail peduncle, the 2.1.3 Body and Shape , (2) η = ocity of the fish If 0.25P < St < 0.4, the vortices total have an important role in decreasing the drag during rapid ind the caudal fin produce maximum thrust Note One ofmotion the main sources of the swimming optimality of lateral of the tail [15] t the Strouhal number is applicable for fishes whose fishes is their optimal shape However, the optimality of mming is through the lift-based methods including body shape is essentially determined by resistive forces, ticity method [21] whereas fin shapes are optimised with respect to the to strengthening the tail peduncle, the keels have an important role in decreasing the drag during rapid lateral motion of the tail [15] The main fin of tuna for swimming is its caudal fin Tuna’s caudal fin is crescent shaped with a high aspect ratio4; see Fig Its caudal fin is stiff; however, it shows a slight flexibility during powerful stroke During the stroke of the caudal fin, the centre of the caudal fin is leading and the tips are following [15] During undulation of tuna, the fluid around the fish is pushed and pulled laterally These accelerations and decelerations of the fluid result in escalation of energy dissipation and reduction of swimming efficiency Since the undulation of tuna is initiated in its tail peduncle, the joint between the caudal fin and the tail peduncle is narrow to reduce this energy dissipation In other words, the smaller surface of the tail peduncle helps tuna to move smaller volume of water laterally This saves the energy of tuna in cruising 2.1.4 The Combination of Swimming Characteristics of Tuna and Bird-Wrasse Considering the swimming gait and swimming forces as well as body and fin shape, tuna is an appropriate candi‐ date for efficient cruising However, for adding the manoeuvring gait to a tuna-mimetic robot, several design factors must be kept in mind: • Tuna has a BCF swimming mode which means that the caudal fin and the tail peduncle are engaged to the cruising gait of swimming • Tuna has vorticity method of swimming This mode does not tolerate any turbulence of water during cruising since turbulent water avoids the vortex generation and decreases the swimming power and efficiency • The body shape of tuna fishes is streamlined in order to minimise the pressure drag • Their tail peduncle has a narrow neck at its joint to caudal fin This is due to the fact that tuna needs to decrease the drag of lateral motion of their tail With the same reason, tuna fishes not have any long and posteriorly extended dorsal and anal fins Among manoeuvrable fishes, bird-wrasses are selected for the second gait of swimming because of two main reasons Primarily, bird-wrasses are from labriform category of swimming mode and actuated with their small pectoral fins The nonactivated tail for manoeuvring inspired from labriforms does not interfere with the cruising motion of the robot through the tail inspired from tunas Moreover, bird-wrasses have lift-based swimming which is compati‐ ble with vorticity method of tuna swimming Using dragbased swimming like angelfish which has similarly labriform swimming mode increases the drag of motion Large span and short chord Int J Adv Robot Syst, 2015, 12:168 | doi: 10.5772/60547 2.2 Swimming Specialities of Bird-Wrasses Similar to tuna, optimal swimming of bird-wrasse is investigated through discussing the swimming gait, swimming force and their shape 2.2.1 Swimming Gait The swimming gaits of bird-wrasse are defined with respect to their swimming propulsors, kinematics, muscles and time-based locomotion behaviour Bird-wrasses are labriform fishes which swim through the oscillation of their pectoral fins Labriforms have two types of fin motion, either rowing like angelfish or flapping like bird-wrasse [15] Bird-wrasses are capable of hovering and slow swimming kinematics of motion In hovering, the fish has zero water speed with non-zero ground speed Slow swimming is different from hovering with non-zero water speed Besides these two swimming kinematics, bird-wrasses have comparable prolonged speed The fish speed greater than cruising speeds and smaller than sprinting is called prolonged speed [16] In terms of muscles, similar to the majority of MPF swimm‐ ers, the bird-wrasses employ mainly red fibres during swimming White muscles are used among MPF swimmers for adducting the fins to reduce the drag [16] From swimming kinematics of bird-wrasses, it could be understood that they could have both periodic and transient motion However, due to the flapping motion of their pectoral fins, they are more capable of periodic motion rather than transient motion 2.2.2 Swimming Forces Swimming forces are divided into two groups, resistive and propulsive forces Bird-wrasses deal with pressure drag as their main source of resistive forces This is due to the relatively high Reynolds number of bird-wrasses Fishes with high Reynolds number need to minimise the pressure drag rather than the skin friction drag The description of resistive forces are presented in [23] Regarding the propulsive forces, bird-wrasses have oscillatory flapping mode which is considered as a liftbased mechanism This mechanism consists of upstroke and downstroke; see Fig In both strokes, the vortices are made at the leading edges of the fins As shown in Fig 5, these vortices are in the shape of vortex rings and push the fish forward The surface area of the fins is not involved in the propulsion The pectoral fins of a bird-wrasse not behave similarly in the upstrokes and downstrokes The speed of upstroke is greater than downstroke Having higher speed of stroking during upstroke than that of downstroke, most of the thrust is generated during the upstroke of the fins The path of the flapping pectoral fins is shown in Fig The lift-based mechanism and generation of vortex rings are further discussed in [23] 2.2.3 Body and Fin Shapes For optimal swimming, fishes have also optimal body and fin shape However, the optimality of body shape is essentially determined by resistive forces, whereas fin shapes are optimised with respect to the propulsive forces [15] Figure Caudal fins with similar aspect ratio but different shape [18] Swimming Direction Up-Stroke Down-Stroke Bird-wrasse needs to minimise the pressure drag In order to so, bird-wrasses have a streamlined and compressed body shape The compressed shape of the body enables the fish to generate less drag and to be more flexible for turning and manoeuvring Contrary to several fishes like tuna that have a narrow neck at the posterior part of their tail peduncle, the bird-wrasses have deep tail peduncle extended by dorsal and anal fins The deep tail peduncle of bird-wrasses is used for steering of the fish Bird-wrasses swim through the lift-based mechanism of their pectoral fins [25] Accordingly, the pectoral fins of bird-wrasses need to have high aspect ratio, which means large span and short chord, since in lift-based mechanism the propulsion is made by the leading edge of the fins Enlarging the surface area of the fins decreases the thrust generation and increases the drag forces Notice that birdwrasses adduct their pectoral fins during their motion to decrease the drag forces further The caudal fin of bird-wrasses, however, has low aspect ratio since the caudal fin with the aid of the tail peduncle and dorsal and anal fins are used for steering of the fish during manoeuvring [15] Figure The flapping motion of pectoral fins of bird-wrasses 2.3 Design of UC-Ika UC-Ika is designed to be specialised for cruising and manoeuvring Taking the swimming specialities of tuna for cruising and bird-wrasse for manoeuvring as well as updown motion capability into account, UC-Ika is designed as shown in Fig Figure Vortex rings generated by pectoral fins [25] Figure The pathway of flapping pectoral fins of bird-wrasses (U is the overall swimming speed) [19] Figure The CAD design of UC-Ika Sayyed Farideddin Masoomi, Stefanie Gutschmidt, Nicolas Gaume, Thomas Guillaume, Connor Eatwel, XiaoQi Chen and Mathieu Sellier: Design and Construction of a Specialised Biomimetic Robot in Multiple Swimming Gaits The design issues of UC-Ika to combine tuna and birdwrasse are discussed in detail with respect to its shape, cruising, manoeuvring and up-down motion mechanism Fixed Point on Link C Link 2.3.1 UC-Ika Shape The robot consists of two main parts: the main body and tail The main body is designed as a rigid part and contains all stationary components such as batteries, microcontrol‐ ler and DC motors The pectoral fins and their actuation mechanism are also a part of the main body Moreover, the actuation mechanism of buoyancy control system is located inside the main body The tail includes a flexible tail peduncle and a rigid caudal fin Inside the tail peduncle, the undulation actuation mechanism is located D Link E θ1 XO Motor O θ2 Caudal Fin h θ3 B YO A Link Figure The link mechanism of the tail peduncle DC Motor Link The body shape of UC-Ika is inspired from both afore‐ mentioned fishes Those parts of the main body that are necessary for optimal cruising are mimicking tuna, while the rest are inspired from bird-wrasse UC-Ika has a streamlined body shape with deep and compressed body shape scaled from tuna and bird-wrasse The body shape of tunas has been described in the previous section A C B D Link F E Link Caudal Fin Figure 10 The CAD design of tail mechanism of UC-Ika This mechanism is capable of mimicking the optimised undulatory swimming of tunas Moreover, since tunas change their caudal fin orientation at the end of each stroke, a flexible joint between the caudal fin and the tail peduncle is designed The angular motion of the caudal fin is depicted in Fig 11 θ4 [deg] The tail part including the tail peduncle and caudal fin is used for cruising mode inspired from a tuna Accordingly, the tail peduncle has a narrow neck at its connection to the caudal fin The caudal fin is stiff with a high aspect ratio The pectoral fins resemble the bird-wrasse fins with a different scale The fins have five ribs with a flexible material surrendering the ribs to guarantee the flexibility of the fins; see Fig Similar to the body shape and dimensions, the aspect ratios of the caudal fin and the pectoral fins are scaled from the real tuna and bird-wrasse, respectively θ4 G F t [s] Figure The CAD design of pectoral fins of UC-Ika The cruising mechanism of UC-Ika is introduced in [23] and shown in Fig However, the tail mechanism is optimised using PSO algorithm described in [14] This mechanism is actuated by a DC motor which is located inside the main body The rest of the mechanism including three links is inside the flexible tail peduncle The motor directly actuates link 1, but the other links are passively actuated through geometrical constraints shown in Fig 10 Int J Adv Robot Syst, 2015, 12:168 | doi: 10.5772/60547 Figure 11 The angular motion of the caudal fin 2.3.2 Manoeuvring Mechanism The pectoral fin actuation is actuated with two independent separate DC motors Each DC motor is connected to a cam and slider mechanism which is connected to the link rod The mechanism in Fig 13 is consisted of a DC • • ••as •• shown •• motor, a cylinder and a gear system that converts the rotational motion of the motor into translational motion of the piston in the cylinder The buoyancy control system also makes benefit of two mechanical switches that turn off the motor when the cylinder is filled with or drained from water This mechanism is designed only to enable the robot to have cruising and manoeuvring underwater at a • •• • specified depth Sliding part moved by cam Rubber lid & Support (Fixed to the main body) • ••• •• •••• • ••••• • Figure 14 The pectoral fin of UC-Ika Piston Cylinder 3.3 Fabrication of the Actuation Mechanisms Rotating cam actuated by motor The actuation mechanisms of both robots and pectoral fins of the first robot are fabricated with commonly known fabrication machines The materials used in the actuation Limit Switch mechanisms are steel and aluminium DC Motor (a) Left fin mechanism 3.3.1 Cruising Actuation Mechanism Pectoral Fin DC Motors Slider Axle Pectoral Fin Rubber Lid & Support Connection Axle Slider Cam • •• • •• (b) Whole mechanism Figure The CAD design of pectoral fin actuation system of UC-Ika Figure12.12 The CAD design of pectoral fin actuation system2 of UC-Ika One of the ribs of each pectoral fin is connected to the link rod; see Fig 12 Piston mechanism converts Cylinder This the rotational motion of the motor into flapping motion of the fins with different upstroke and downstroke speeds, similar to bird-wrasse flapping motion shown in Fig Limit Switch The design parameters of the robot is presented in Table 2.3.3 Up-Down Motion Mechanism DC Motor Static depth control through playing with the buoyancy Figure 13 The CAD design of buoyancy control system of UC-Ika and the weight of the robot is targeted for up-down motion Indeed, a mechanism similar to ballast control system of Fabrication is of designed the pectoral fins ofthe UC-Ika slightly submarines to change weight2ofisthe robot different since its ribs (shown in Fig 14) are rigid and through filling and draining its container with water In PDMS is around it Accordingly, a mould including the other words, the balance of hydrostatic forces is employed ribs is made with FDM method, and then the silicone is in the system to raise and lower the robot When the syringe poured into the mould which covers the ribs When the accordingly, is filled is with water, the its M f and, silicone solidified, ribs are detached fromWtheincrease, mould ρwinside V f g , Bthe while , is silicone constant.Note Then thethe robot sinks the and left that main rib isOn made from aluminium and is not attached to the mould other hand, draining the water decreases W in comparison with B and the robot float The tail ofofboth robots has similar kinematic Figure 13 mechanism The CAD design buoyancy control system of UC-Ika principles; however, the tail mechanism of UC-Ika is optimised The first tail mechanism shown in Fig 15 is Fabrication made up of both steel and aluminium, while the second tail mechanism is mainly from aluminium to decrease its The final step of developing biomimetic swimming robots weight and, thus, its mass moment of inertia.6 The caudal is the In from this step, several issues are to be fin of fabrication UC-Ika isstep made plywood that is filed and dealt with Primarily, the fish-mimicking robots have polished to have a streamlined shape intricate shapes to meet the optimal performance of fishes This shape cannot be simply made by the conventional • • •• • •• •tools machining Besides, the swimming robots have rigid and flexible parts The latter must be flexible enough to not demand addition‐ al motor torque during bending Simultaneously, the flexible part has to be stiff enough to stand the pressure of water column • • • • • ••• •• • •• • •• • •• • •• Moreover, similar to the other underwater robots, the fish Figure The tail mechanismissues of UC-Ika robots 15 have waterproofing which is more challeng‐ ing since the electronics and actuation mechanisms inside the body of the robot need to be accessible 3.3.2 Manoeuvring Actuation Mechanism The last issue returns to the underwater communication The actuation mechanism of pectoral fins of UC-Ika 2, problem underwater robot cannot be remotely control‐ shown inAn Fig 16, is fabricated using steel Instead led without an antenna that is coming out of the aquatic of aluminium, steel is employed in order to increase environment, whereas the antenna affects the hydrody‐ the weight of the robot and also decrease the friction namic two behaviour of the when surfaces of robot steel underwater are in contact with each other during motion In fabrication of actuation system, The microswitch aforementioned issues are addressed in the fabrication one is employed for synchronisation of the of both UC-Ika flapping motion of the pectoral fins together since the pectoral fins use two separate motors 3.1 Fused Deposition Modelling 3.3.3 Buoyancy Control System In order to build the intricate shapes, a rapid prototyping For fabrication buoyancy control system of UC-Ika 2, ais method calledofFused Deposition Modelling (FDM) syringe a cylinder of holding water is employed where applied.as FDM is a 3D printing technology directly using the CAD model Then the design is fabricated layer by layer The tail mechanism with high mass moment of inertia increases the using two different melted the base and swinging motion of the robot which ismaterials not ideal foras an efficient cruising Sayyed Farideddin Masoomi, Stefanie Gutschmidt, Nicolas Gaume, Thomas Guillaume, Connor Eatwel, XiaoQi Chen and Mathieu Sellier: www.intechopen.com Design and Construction of a Specialised Biomimetic Robot in Multiple Swimming Gaits Int J Adv Robotic Sy, 2013, Vol No, No:2013 Tail Mechanism Distance between point M and O Posterior part of link ¯ = 0.180 m OC Posterior part of link ¯ = 0.069 m CF Anterior part of caudal fin ¯ = 0.030 m FG Anterior part of link ¯ = 0.030 m AO Distance between point M and B ¯ = 0.089 m OB Length of link ¯ = 0.228 m DE Anterior part of link ¯ = 0.026 m EC General Caudal Fin DC Motor ¯ = 0.077 m MO Mass M = 7.426 kg Mass moment of inertia I = 0.667 kgm2 Vertical semi-axis a = 0.100 m Horizontal semi-axis b = 0.075 m Tip to point M length L = 0.273 m Projected area along X Sx = 0.021m2 Projected area along Y Sy = 0.126m2 Mass M c = 0.120kg Mass moment of inertia I c = 0.001kgm2 Span S = 0.372 m Chord CC = 0.024m Spring constant k = 12.191 Nm / rad Amplitude A = π / 18 rad Frequency f = 1.5 Hz Table Constant parameters of UC-Ika after optimisation support materials The base material, Acrylnitril-ButadienStyrol-Copolymerisat (ABS), is in fact the actual material of the fabrication After 3D printing, the support material is resolved and removed from the part in a 70°C hot alkaline bath [26] solidified, the ribs are detached from the mould and left inside the silicone Note that the main rib is made from aluminium and is not attached to the mould FDM method is employed for fabrication of complicated rigid parts including the outer surface of the main bodies of UC-Ika 2.5 3.2 Fabrication of Flexible Part In order to build the flexible parts, polydimethylsiloxane (PDMS) silicone Sylgard 184 is selected This silicone is durable, tensile and resistant against water and most solvents [27] The silicone is made up of two components including base and curing agent These two components need to be combined and poured into a mould The solidifying of the tail takes approximately 72 hours This method of fabrication is applied for fabrication of the tail peduncle of both robots Fabrication of the pectoral fins of UC-Ika is slightly different since its ribs (shown in Fig 14) are rigid and PDMS is around it Accordingly, a mould including the ribs is made with FDM method, and then the silicone is poured into the mould which covers the ribs When the silicone is Figure 14 The pectoral fin of UC-Ika 3.3 Fabrication of the Actuation Mechanisms The actuation mechanisms of both robots and pectoral fins of the first robot are fabricated with commonly known fabrication machines The materials used in the actuation mechanisms are steel and aluminium The moulds for the flexible parts, explained in Sec 3.2, of both robots are also built with FDM method Int J Adv Robot Syst, 2015, 12:168 | doi: 10.5772/60547 3.3.1 Cruising Actuation Mechanism The tail mechanism of both robots has similar kinematic principles; however, the tail mechanism of UC-Ika is optimised The first tail mechanism shown in Fig 15 is made up of both steel and aluminium, while the second tail mechanism is mainly from aluminium to decrease its weight and, thus, its mass moment of inertia.6 The caudal fin of UC-Ika is made from plywood that is filed and polished to have a streamlined shape its shaft is actuated by a DC motor The mechanism of buoyancy control system converts the rotational motion of the motor to translational motion of the shaft of syringe To ensure that the cylinder is filled with or drained from water, two limit switches are used in the path of the piston of the cylinder Figure 16 illustrates the buoyancy control system Figure 17 The buoyancy control system of UC-Ika Figure 15 The tail mechanism of UC-Ika 3.3.2 Manoeuvring Actuation Mechanism The actuation mechanism of pectoral fins of UC-Ika 2, shown in Fig 16, is fabricated using steel Instead of aluminium, steel is employed in order to increase the weight of the robot and also decrease the friction when two surfaces of steel are in contact with each other during motion In fabrication of actuation system, one microswitch is employed for synchronisation of the flapping motion of the pectoral fins together since the pectoral fins use two separate motors 3.4 Waterproofing Besides tight connections of the caudal fin and the tail peduncle and also the tail peduncle and the main body with a pretension in the tail peduncle, the body is coated with epoxy resin to avoid passing of water through the body over time as it is slightly porous Moreover, the caudal fin in UC-Ika which is made from plywood is coated with polyurethane to ensure its water resistance without degrading its flexibility 3.5 Communication To solve the communication problem underwater, a microcontroller is employed For UC-Ika 1, an open-loop controller is designed and coded into an Arduino Uno microcontroller to control 12V DC gear head motor of the fish This controller could communicate with any Bluetooth device like computers and smartphones using a Bluetooth connector In UC-Ika 2, the microcontroller controls four 12V DC motors and three limit switches The codes of both microcontrollers are available upon request 3.6 Assembly Figure 16 The pectoral fin actuation mechanism of UC-Ika 3.3.3 Buoyancy Control System For fabrication of buoyancy control system of UC-Ika 2, a syringe as a cylinder of holding water is employed where Besides the actuation mechanisms and electronic parts including batteries, microcontroller, motor shields and Bluetooth device, several pieces of lead and steel as well as lead shots are provided to compensate the difference between the buoyancy and the weight of the robots calculated during the design The difference is worse in UCIka where 2.42 kg is needed to have a neutral buoyant robot UC-Ika & after complete assembly are shown in Fig 18 The tail mechanism with high mass moment of inertia increases the swinging motion of the robot which is not ideal for an efficient cruising Sayyed Farideddin Masoomi, Stefanie Gutschmidt, Nicolas Gaume, Thomas Guillaume, Connor Eatwel, XiaoQi Chen and Mathieu Sellier: Design and Construction of a Specialised Biomimetic Robot in Multiple Swimming Gaits 2.5 1.5 X˙ [m/s] X [m] 0.5 Figure 18 UC-Ika after assembly 10 12 t [s] Swimming Performance (a) Real translational motion of UC-Ika along X Axis Figu X [m] In order to analyse the swimming performance of UC-Ika 2, it is tested in a 5×15m2 pool A motion analysis software is also employed to make the graphs of motion in order to compare with the simulation results UC-Ika is able to cruise and turn In cruising mode, only the tail peduncle and the caudal fin are undulating, while the pectoral fins are stationary The graph, shown in Fig 19(a), reveals that the robot is swimming linearly in time with a slope of 0.246 which is the average cruising speed of UC-Ika 2.8 This curve matches the simulation results done for the robot The simulation is explained in [14] Regarding cruising speed of the robot, it must be men‐ tioned that the speed analysis of the robot shows that it has periodic motion (see Fig 20) similar to results obtained from simulation Similar to UC-Ika 1, the swimming parameters of UC-Ika are obtained, given in Table The computation of the swimming forces is explained in [29] t [s] (b) Simulated translational motion of UC-Ika along X Axis Value Undulation frequency f = 1.5 Hz Heave h = 0.04m Mean forward velocity x¯˙ = 0.25m / s Mean lateral velocity y¯˙ = 0.04 m / s Mean thrust F¯ Cx = 0.25N Mean lateral force F¯ Cy = 0.17N Table Swimming parameters of UC-Ika Through these results, Froude efficiency and Strouhal number of the robot are calculated UC-Ika has an Figure 19 Speed Speed ofof thethe fish fish robotrobot along xalong -axis x-axis Figure 19 efficiency of 89%parameters and Strouhalofnumber Table Swimming UC-Ika of 0.37 These values Figu fin a show of efficiency and Strouhal number confirm the optimal Parameter Value swimming performance of the robot in cruising Undulation frequency f = 1.5 HZ The cruising motion of UC-Ika is also compared with its h = 0.04 m Heave previous version, UC-Ika 1, which is introduced in [29] and Mean forward x˙ =constant 0.25 m/s shown in Fig.21 Despite velocity UC-Ika 2, the parameters of UC-Ika lateral are notvelocity optimised.y˙ Accordingly, Mean = 0.04 m/s Froude efficiency and Strouhal number of UC-Ika are far better Mean thrust F = 0.25 N than those of UC-Ika The efficiencyCxand Strouhal number Mean force FCy respectively = 0.17 N of UC-Ika arelateral equal to 78% and 0.72, Angle [deg] Parameter -2 -4 10 The cruising motion of UC-Ika is also compared with its previous version, UC-Ika 1, which is introduced in Simulation of cruising mode is thoroughly described in [28] [29] and shown in Fig.21 Despite UC-Ika 2, the constant In order to measure the cruising speed of the robot, the displacement of the centre of mass ofof theUC-Ika robot, or the of buoyancy, is computed parameters centre are not optimised Accordingly, Froude efficiency and Strouhal number of UC-Ika are far Int J Adv Robot Syst, 2015, 12:168 | doi: 10.5772/60547 better than those of UC-Ika The efficiency and Strouhal number of UC-Ika are equal to 78% and 0.72, respectively Besides cruising, UC-Ika is also able to turn by its -6 Figu with The teste UC- t [s] (b) Simulated translational motion of UC-Ika along X Axis Figure 21 UC-Ika Figure 19 Speed of the fish robot along x-axis Table Swimming parameters of UC-Ika fin are stationary The motion analysis of the pectoral fins shows the path of the fin in flapping; see Fig 22 Parameter Value 0.4 0.4 Undulation frequency f = 1.5 HZ h = 0.04 m Mean forward velocity x˙ = 0.25 m/s 0.30.3 Mean lateral velocity y˙ = 0.04 m/s FCx = 0.25 N Mean lateral force 0.2 FCy = 0.17 N X˙ [m/s] X˙ [m/s] Mean thrust 10 12 12 along X Axis X Axis 0.2 X [m] x able FigureFigure 20 Periodic speed of UC-Ika -axis 20 Periodic speed of along x-axis Besides cruising, UC-Ika UC-Ika is2 along also to turn by its flapping pectoral fins similar to the flapping fins of Figure 20 Periodic speed of UC-Ika along x-axis bird-wrasses (see Fig 6), while its tail peduncle and caudal 10 Int J Adv Robotic Sy, 2013, Vol No, No:2013 Figure 21 UC-Ika xis m 0.25 N 0.17 N m/s Figure 21 UC-Ika Figure 21 UC-Ika fin are60 stationary The motion analysis of the pectoral fins Besides cruising, UC-Ika is also able to turn by its flapping shows the path of the fin in flapping; see Fig 22 pectoral40fins similar to the flapping fins of bird-wrasses (see 20 Fig 6), while its tail peduncle and caudal fin are Angle provided by thestationary right 60 pectoral fin The motion analysis of the pectoral fins shows the path of Angle provided by the left 0.53 0.73 0.93 1.13 1.33 pectoral fin t [s] the fin40in flapping; see Fig 22 -20 Angle [deg] 25 m/s Z04 m/s fin are stationary The motion analysis of the pectoral fins shows the path of the fin in flapping; see Fig 22 Angle provided by simulation 20 Angle provided by the right The turning motion of the robot in both directions is also -40 Angle [deg] 04 m pectoral fin m/s so compared with tested.0In order to0.93 turn1.13 left, 1.33 the right pectoral fin of UC-Ika Angle provided by the left -60 0.53 0.73 is introduced in N pectoral fin t [s] ka 2, the constant2 flaps-20while its left pectoral fin is stationary and vice versa Angle provided by simulation N Accordingly,The test sed Figure 22 The path of pectoral finsleft in comparison shows thatflapping the robot isthe able to turn with a speed with the simulation result of UC-Ika are far -40 of 2.47deg/s (at the beginning of the motion) and turn right ompared with ency and Strouhal with a speed of 5.24 deg/s In other words, in swimming to -60 The turning motion of the robot in both directions is also in dintroduced 0.72, respectively tested In order to turn left, the right for pectoral finwith of its the robot needs to go forward 2.36m , the constant the left, le to turn by its UC-Ika while its leftofpectoral fin is fins stationary and Accordingly, Figure 22.2 flaps The flapping path the the pectoral in comparison pectoral fin in order to have lateral motion 0.967m flapping fins ofright vice The test shows that the robot is able to turn left with theversa simulation result C-Ika are far duncle and caudalin 9s.with Similarly, in swimming to the right, the robot a speed of 2.47 deg/s (at the beginning of the motion)needs and Strouhal 2, respectively Angle provided by the right pectoral fin 0.53 0.73 -20 0.93 t [s] 1.13 1.33 Angle provided by the left pectoral fin Angle provided by simulation -60 Figure 22 The flapping path of the pectoral fins in comparison with the Figure 22.result The flapping path of the pectoral fins in comparison simulation with the simulation result Summary The turning motion of the robot in both directions is also tested In order to turn left, the right pectoral fin of The existing fish robots are only capable of one gait of UC-Ika flaps while its left pectoral fin is stationary and motion In The othertest words, thethat fish the robots areisoptimised in one vice versa shows robot able to turn left type of motion like cruising or manoeuvring This limits the with a speed of 2.47 deg/s (at the beginning of the motion) performance of the robots To address this problem, UCIka with multiple gaits of locomotion including cruising www.intechopen.com and manoeuvring is fabricated In the design process of UC-Ika 2, the optimal swimming characteristics of two fishes – tuna for cruising and birdwrasse for manoeuvring – are mimicked The robot in cruising mode swims by means of its tail peduncle and caudal fin In manoeuvring mode, the tail part of the robot is stationary and its pectoral fins flap a along X Axis HZ 20 -40 The cruising motion of UC-Ika is also compared with its previous0.1version, UC-Ika 1, which is introduced in 0.1 [29] and shown in Fig.21 Despite UC-Ika 2, the constant parameters of UC-Ika are not optimised Accordingly, Froude efficiency and Strouhal number of UC-Ika are far 0.5 1.5 2.5 better than 0those of UC-Ika 1.1 The efficiency and Strouhal X [m] 0.5 equal 1to 78% 1.5 2.5 number of UC-Ika are and 0.72,2respectively ong X Axis 40 Angle [deg] Heave 60 to go 0.97 of m the with its left pectoral fin inisorder Theforward turning for motion robot in both directions also to have the lateral motion 0.59m in 6s difference between tested In order to turn left, theThe right pectoral fin www.intechopen.com of o turn by its flaps while its left left pectoral fin is directions stationary and theUC-Ika speed of turning towards and right is due pping fins of vicedifferent versa The test shows that the robot is ablefins to turn left in to the thickness of the left and right caused cle and caudal with a speed of 2.47 deg/s (at the beginning of the motion) the fabrication process The thickness of fins determines their flexibility which plays an essential role in their thrust www.intechopen.com generation.9 Using FDM method, the intricate shape of rigid parts of the robot is fabricated The flexible part is also made with PDMS materials The actuation mechanism is also made using conventional machining tools For waterproofing the robot, it is painted with epoxy resin Regarding communi‐ cation, the robot uses a microcontroller that has a Bluetooth connector to connect to any Bluetooth device like comput‐ ers and smartphones The experimental analysis shows that the robot with Froude efficiency of 89% and Strouhal number of 0.37 is an optimal swimmer in cruising mode In comparison with the previous robot, UC-Ika 1, the robot shows improved cruising performance Besides, the robot is also capable of manoeuvring similar to bird-wrasses The robot turns left with a speed of 2.47 deg/s and turns right with a speed of 5.24deg/s The difference in the speed of turning is due to the fabrication inaccuracies of actuation mechanism of pectoral fins References [1] J Yu, M Tan, S Wang, and E Chen Development of a biomimetic robotic fish and its control algo‐ rithm IEEE Transactions on Systems, Man, and Cybernetics, Part B: Cybernetics, 34(4):1798–1810, Aug 2004 This speed is obtained when the caudal fin and the tail peduncle not have any inclination and are parallel to the axis of the main body Otherwise, if the tail steers the motion, the speed of turning goes up Sayyed Farideddin Masoomi, Stefanie Gutschmidt, Nicolas Gaume, Thomas Guillaume, Connor Eatwel, XiaoQi Chen and Mathieu Sellier: Design and Construction of a Specialised Biomimetic Robot in Multiple Swimming Gaits 11 [2] L.D Paulson Biomimetic robots Computer, 37(9): 48–53, 2004 [3] J Ayers, J.L Davis, and A Rudolph Neurotechnolo‐ gy for biomimetic robots The MIT Press, Cambridge, Cambridge, Massachusetts, USA, 2002 [4] Y Bar-Cohen and C.L Breazeal Biologically inspired 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