Project Pisces
Research
This research aim to give more insight of the fast growing area of biomimetic swimming robots. The main objective of the project is to achieve replication and optimizational efficiency of the undulating action of the tuna’s peduncle, which is essential in hovering maneuvers and cruising type swim performance, in order to influence a stationary leading edge within the bio-inspired robotic vehicle for implementation in various underwater applications.
Journal Paper 1
'The Kinematics and Dynamics of Undulatory Motion of a Tuna-Mimetic Robot"
The journal article from the International Journal of Advanced Robotic systems explores the science and creation of UC-IKA 1, which is a tuna mimetic robot created by students at the University of Canterbury in Canterbury, New Zealand. The article begins by offering the necessity of aquatic robotics in various applications and describes engineering’s tendency to mimic naturally observed occurrences due to the high rate of efficiency they possess, citing that the propulsion system for several fish can reach a maximum of ninety percent. The modeling of this specific aquatic robot to the likeness of a tuna was due to the fish’s specific swimming motion. Tuna fish belong to the thunniforms category of fish swimming modes, and all the lateral motion is constrained within the tail or peduncle, and the region connecting the tail to the main body of the fish. The undulatory motion of the peduncle allows for an efficient cruising motion which is sought after in aquatic robotics and the focus of study in the creation of the UC-IKA 1.
Patent 1
“Underwater Thrusting Apparatus With a Function of Adjusting Stiffness In Caudal Fin”
When utilizing bio-inspiration when constructing an aquatic robot, the tuna is often looked to for having possessed many qualities which are desired for the mimetic robotic forms. Possessing a caudal fin which is crescent in shape, allows the tuna to not only generate speed but also change course directionality. The challenge faced by the tuna mimetic robots is the constantly varying aquatic conditions such as flow rate. This patent maintains a solution to the afore mentioned challenge by way of implementing a caudal fin which can vary in rigidity to accommodate for environmental changes and allow the tuna mimetic to maintain stability and swim performance. The proposed rigidity controller consists of a flexible material, a polymer, to encase the fin portion of the robot for not only sealing but also flexibility purposes, and the void of the caudal to be filled with magnetorheological fluid (Magneto-Rheological fluid. Primarily a kind of oil, this smart fluid experiences an increase in apparent viscosity to the point of becoming a viscoelastic solid when subjected to a magnetic field.The control or variability aspect comes into play with a magnetic field generating coil embedded in the fluid within the tail fin. The subsequent varying of intensity of the magnetic field induces the viscosity change of the MR fluid accordingly. The use of MR fluid are largely controller based in nature, and implementation into the area of aquatic robotics maintains vast possibilities including speed control and swim performance stability.
Journal Paper 2
"An Efficient Swimming Machine"
The journal article started by giving a background of why modeling submerged free-swimming robots after their biologically-inspired marine counterparts is beneficial, as well as the applications. It turns out that the writers of this article had very similar goals as to group 29’s design project. The goal is how to make a robotic vehicle that uses propulsion created by modeling mechanisms of fish (such as the tail and fins) as efficient as possible, undertaking traditional propellers. They first found that early models underperformed when just the form and function was taken into account. They investigated the muscles in certain fish with relation to its weight and empirical speeds that they were observed at. The conclusion was that some of the fish couldn’t physically create the thrust necessary based on the motion of its tail alone. Further investigation concluded that the frequency of the tails oscillation is the critical factor, creating thrust inducing vortices that maximize efficiency. The article then takes a large interest in the Strouhal Number, and applying it to the studies air foil, and found a critical number of maximum thrust generating vortices to lie somewhere between 0.25 and 0.35. This epiphany was applied to their, at the time, inefficient models, and efficiencies were observed at values greater than 80%, when compared to common submerged vehicles with propellers at usual efficiencies of only 40%! The article then took a turn from observing thrust, to observing the natural agility that fish have, specifically on how they can instinctively switch directions on a dime. The authors focused on how these fish capture (and re-capture) kinetic energy from waves and wakes to utilize this property.
Patent 2
"Patent NO. CN106275338A"
This patent is for a twin skeg (fin) bionic robot fish, which has a similar goal as group 29’s design project. The patent focuses on a design that tries to optimize the propulsive force generated by creating a crank-slider mechanism at the tail end of the robot that creates symmetrical reciprocating motion. The goal is to reduce the noise created by traditional propellers, with many useful applications that our design team is also interested in. This patent also uses the dual skeg geometry to increase the stability of the fish, reducing lateral forces. This is a large part of our robotic fish, because there will be a camera that records data along the center axis of the body, which needs to be stable during free-swimming. This patents crank technology is not to use for the group, as we will be using servo-motors, but the geometry of the fins is important, as we will be designing a robotic fish with two-tails.
Journal Paper 3
“The Design and Implementation of a Biomimetic Robot Fish”
The paper went over three main topics. One being the importance of robotic fish, the argument is fish have a much more efficient method of movement in water compared to modern ships and submarines. Theory on how a fish swam was also mentioned. As the tail oscillates back and forth there is a motion that possibly influences the efficiency of a fish swimming. Information like this may influence our design by implementing a tail that oscillates. Secondly the relation of joints within the tail. Equations were made to find an efficient distance between joints. Graphs also represented the wave like motion that gained amplitude through the fish as it swam. Thirdly and most importantly, the paper went over how a prototype was built. Looking at the pectoral fins, the robotic fish was able to have three degrees of motion. By positioning the fins they were able to turn left, right or move up, down and forward. This design will influence how our prototype will be constructed as the design was intuitive. The article also went over how they went about programing. Their schematics and logic rule sets will be a helpful stepping stone for our programing portion. A table depicts the size and weight of a preexisting robotic fish. This information will be helpful when choosing a size for our prototype.
Patent 3
“Mechanical Fish Robot Exploiting Vibration Modes for Locomotion”
Said patent is about the motion of an aquatic robot. Motion in the patent mimic the design of a fish where the tail is the propulsion mechanism for the system. Flippers are used to control the robot which are separate from the tails motion. Said tail has about 1/3 of the efficiency of a nominal fish performance. The tail also has a very rigid motion unlike other aquatic robots that use joins to loosen up the motion. Movement on the tail is done by a singular servo rotating what looks to be at small angles. The flippers are attached to their own servos and are limited in motion. Inspiration from this may come from how the servo moves the tail instead of a rigid motion there are possibilities of joints being added to make a more realistic motion. This may bring the efficiency of the robot up as continuing a wave like motion is supposed to increase through the tail. Placement of upper fins may influence design as they are more towards the front and can save space. Material used in tail is very rigid, more than likely a more flexible material will be used so that the tail can move in a fluid motion. Possibility of harder material used on the upper half is likely. Upper portion will not require motion so possible material from patent may influence our decision.
Journal Paper 4
"Studies of Tropical Tuna Swimming Performance in a Large Water Tunnel"
This research study gleaned the basic understanding of fish anatomy and more specifically what parts contribute to the locomotion of fish. The importance of the caudal fin and pectoral fins movements relative to their outcome such as swimming velocities (U), tail-beat frequency (TBF), stride length (l), and a propulsive wavelength (λ). When looking for a testing population, the Yellowfin Tuna (Thunnus albacares) was selected. 665 tunas were tested and were split into three separate populations dependent on their fork length (L), the length of the fish, 32cm, 42cm, 53cm. From here the results can be split into three different categories relative to the size of the tuna. First their TBF was recorded using a stopwatch for the time required for 20 tail-beats. This was done because it was necessary and simply because it was easy to examine. To confirm this, a camera was used to track their TBF, a two second clip was chosen. Video recordings were also done from a top-down view of the tuna. Five points were selected on the fish for tracking (the tip of the snout, the base of the pectoral fins, a point close to the second dorsal fin, and both the proximal base and distal tips of the caudal fin) to see their location through time and movement. From these methods, results were drawn. One trend shows that the higher the tail-beat frequency (TBF) the greater the swimming velocity the fish will reach. The data also shows that the larger the fork length (length of fish) the higher maximum speed the fish was capable at reaching. This information can then be related to stride length. From the top down video recording, what is interesting to note here is that as the fish is swimming, there is not one single point where there is no movement. The inertial forces created at the tail follow through to the tip of the snout causing the fishes head to “bob” back and forth while swimming. This is where our proposed idea comes into play where is it possible to design a robotic fish and add a second caudal fin to cancel out the inertial forces to create a no force zone and have the snout of the fish be movement free. The information in this research study can be very useful for the design and dimensions of our robotic fish.
Patent 4
" Patent NO. US20150120045A1 - Gliding Robotic Fish Navigation and Propulsion"
This patent involves the implementations of an “underwater fish glider”. Similar to the robotic fish for the proposed design project. Here this design takes more after a submarine where most of the body is fixed and there are left and right propellers to provide thrust. There is an internal pump that will adjust the buoyancy of the glider to change depth in the water. Whereas our method to vary depth will involve adjusting the angle of attack of the pectoral fins, and propulsions will be generated solely from the caudal fin and its movements. This patent has a tail fin that will flap and turn left and right to add to the propulsion and also provide a means for adjusting yaw. This method only includes one degree of freedom where the proposed two-tailed robotics fish will have two degrees of freedom. A lot can be learned from this patent being that the overall design was a success and was published. Due to the fact that there will not be a pump used for buoyancy control and will rely on the angle of the pectoral fins, the whole fish itself will be submerged with no air pockets and ideally the goal is to have it slightly heavier than neutrally buoyant that way to have a straight line projection, the pectoral fins will have to be set a small positive angle of attack. The only electronic components planned to be used will be six waterproof servo motors, an Arduino chip, bread board for controller, power source, and all necessary wires for connections.