Name: a robotic platform to study the foreflipper of the california sea lion
Uploaded: 2017-01-10T12:30:00
Description: The California sea lion (Zalophus californianus), is an agile and powerful swimmer. Unlike many successful swimmers (dolphins, tuna), they generate most ...

The authors would like to thank the George Washington University Facilitating Fund for financial support of the project. Mr. Patel is grateful the George Washington University School of Engineering and Applied Science Summer Undergraduate Program in Engineering Research and the Undergraduate Research award for financial support. Finally, we are grateful to the GWU Center for Biomemetics and Bioinspired Engineering (COBRE) for use of facilities controlled by the center.

1. Digitize a Specimen of a Sea Lion Foreflipper
<ol>
	<li>Scan a specimen of a Sea lion foreflipper.
	<ol>
		<li>Obtain a specimen of a sea lion flipper from a deceased individual (Figure 1a). 
		NOTE: In our case, they were obtained from the Smithsonian Zoological Park in Washington, D.C.</li>
		<li>Hang the foreflipper vertically from its base (where the foreflipper attaches to the animal&#39;s body). This both allows the flipper to be straight when scanned, and exposes the entire surface for scanning.</...

<ol>
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The robotic flipper apparatus will allow us to understand the hydrodynamics of the swimming California sea lion. This includes the basic thrust producing stroke (the &#39;clap&#39;), as well as non-physical variations that animal studies cannot investigate. The robotic flipper has been designed for experimental versatility, thus, step 3&#8212;where the flipper itself is made&#8212;is critical in obtaining the desired results. While this apparatus is, clearly, just a model of the living system, in situ studies of...

While scientists have investigated the basic characteristics of sea lion swimming (energetics, cost of transport, drag coefficient, linear speed and acceleration1-3, we lack information about the fluid dynamics of the system. Without this knowledge, we limit potential high-speed, high-maneuverability engineering applications to body-caudal fin (BCF) locomotion models4. By characterizing a different swimming paradigm, we hope to expand our catalog of design tools, specifically those with the potential to enable quieter, stealthier forms of swimming. Thus, we study the fundamental mechanism of sea lion swimming through direct observation of the California sea lion and laboratory investigations using a robotic sea lion foreflipper5,6 .
To do this, we will employ a commonly used technique for exploring complex biological systems: a robotic platform7. Several locomotion studies&#8212;both of walking8,9 and swimming10&#8212;have been based on either complex11 or highly simplified12 mechanical models of animals. Typically, the robotic platforms retain the essence of the model system, while allowing researchers to explore large parameter spaces13-15. While not always characterizing the entire system, much is learned through these platforms that isolate a single component of a locomotive system. For example, the fundamental functioning of unsteady propulsors, like the back-and-forth sweeping of a caudal fin during carangiform swimming, has been intensely explored through experimental investigations of pitching and/or heaving panels12,16,17,18. In this case, we can isolate certain modes of this complex motion in ways that animal based studies cannot. Those fundamental aspects of propulsion can then be used in the design of vehicles which do not need the biological complexity evolution provides.
In this paper, we present a novel platform for exploring the &#39;clap&#39; phase of the sea lion thrust-producing stroke. Only a single foreflipper&#8212;the &#39;roboflipper&#39;&#8212;is included in the platform. Its geometry is derived exactly from biological scans of a California sea lion (Zalophus californianus) specimen. The roboflipper is actuated to replicate the motion of the animals&#39; derived from previous studies1. This robotic flipper will be used to investigate the hydrodynamic performance of the swimming sea lion and to explore a wider parameter space than animal studies, particularly those of large aquatic mammals, can yield.

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			<td height="21" style="height:21px;width:247px;">Dragon Skin 20 medium</td>
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			<td height="63" style="height:63px;">PKS-PRO-E-10 System</td>
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a robotic platform to study the foreflipper of the california sea lion

The California sea lion (Zalophus californianus), is an agile and powerful swimmer. Unlike many successful swimmers (dolphins, tuna), they generate most of their thrust with their large foreflippers. This protocol describes a robotic platform designed to study the hydrodynamic performance of the swimming California sea lion (Zalophus californianus). The robot is a model of the animal&#39;s foreflipper that is actuated by motors to replicate the motion of its propulsive stroke (the &#39;clap&#39;). The kinematics of the sea lion&#39;s propulsive stroke are extracted from video data of unmarked, non-research sea lions at the Smithsonian Zoological Park (SNZ). Those data form the basis of the actuation motion of the robotic flipper presented here. The geometry of the robotic flipper is based a on high-resolution laser scan of a foreflipper of an adult female sea lion, scaled to about 60% of the full-scale flipper. The articulated model has three joints, mimicking the elbow, wrist and knuckle joint of the sea lion foreflipper. The robotic platform matches dynamics properties&#8212;Reynolds number and tip speed&#8212;of the animal when accelerating from rest. The robotic flipper can be used to determine the performance (forces and torques) and resulting flowfields.

The process described above yields a robotic model of a California sea lion foreflipper. The model can be used in two different ways. One is by actuating the flipper only at the root (Figure 6a). In this case, the driving motor sets the rotational rate of the first joint, but the resulting motion of the flipper is determined by the fluid-structure interaction between the flexible flipper and the surrounding water. Additionally, we can create robotic flipp...

A robotic platform is described that will be used to study the hydrodynamic performance&#8212;forces and flowfields&#8212;of the swimming California sea lion. The robot is a model of the animal&#39;s foreflipper that is actuated by motors to replicate the motion of its propulsive stroke (the &#39;clap&#39;).

A Robotic Platform to Study the Foreflipper of the California Sea Lion

The California sea lion (Zalophus californianus), is an agile and powerful swimmer. Unlike many successful swimmers (dolphins, tuna), they generate most ...

The overall goal of this procedure is to create a robotic platform to study Sea Lion swimming. This matter can help answer key questions in biofluid dynamics, such as how Sea Lions move the water around them when they swim. The main advantage of this technique is that we can explore Sea Lion locomotion in detail while still being in a controlled laboratory setting.Though this method can provide insight into Sea Lion swimming, it can also be applied to other animal systems, such as dolphins, tuna, whales, and other fish or aquatic mammals. To begin, digitize a specimen of a Sea Lion foreflipper, or obtain it from an alternate source. Print the resulting point cloud at 68 percent of the full size, and use it to create a three-dimensional mold.Design three different pieces to mimic the bone structure of the Sea Lion foreflipper, starting with the base. In the CAD software, click on Sketch, and design the base piece so that it is proportional to the distance between the shoulder joint and the wrist of the specimen Sea Lion flipper. Add knuckles to the base by clicking on Sketch and drawing two circles at both ends of the part, then click on Boss-Extrude to extrude the desire length from the plane of the base piece.Click on the sketch of the smaller circle at the knuckles and click Cut-Extrude to make room for the shaft. To strengthen this joint, click on Fillet to smoothen the sharp joints. Next, design the middle section.Click on Sketch and draw a trapezoid with a height of 2.25 inches and bases of 1.625 and 0.85 inches. Then, click on Extrude and input the extruded length as 0.165 inches to get the basic three-dimensional shape of the middle piece. As with the base, add knuckles on both ends so that they will fit inside the volume of the foreflipper.To accomplish this, make the diameter of the extruded cut 0.125 inches. Then, click on Sketch and create a tower as a rectangle on the base of the model. Extrude the sketch by selecting it, clicking on Boss-Extrude, and setting the thickness of the tower to 0.165 inches.Finally, click on Fillet, and select the model and one edge of the extruded tower to smooth the sharp joint and strengthen where the tower and the base of the middle piece are connected. Make the length of the tip piece proportional to the distance between the knuckle joint and the tip of the longest finger bone of a Sea Lion. Do this by clicking on Sketch and sketching the desired shape on the plane.Once the geometry is designed, click on Extrude to get the basic three-dimensional shape of the tip piece. Next, form the knuckles on both ends by making an extruded cut that is equal to the diameter of the axle, which is shown here as 0.125 inches. Finally, add a tower to the base end of the piece on both sides.Once all of the pieces have been created, 3D print the base, middle, and tip pieces of the flipper. Then, reinforce the knuckles of the middle and tip piece by applying epoxy to the printed bone structures, and laying two layers of three-quarter inch long carbon threads onto the epoxy. Next, drill 05 inch diameter holes through the bottom of each tower, which will be use to thread the Kevlar string.Place all of the bone pieces on a flat table. Align the knuckles of the base and middle pieces, and insert the axle. Then, use the same technique to connect the middle and the tip piece together.Use an adhesive on each end of each axle to ensure that the axle does not move laterally. Next, cut four plastic tubes the length of the base bone piece, and two tubes the length of the middle piece. Also, cut four piece of Kevlar string, each three feet in length.Slide one string through an eight centimeter tube and then, a six centimeter tube. Slide a second string through an eight centimeter tube. Repeat the process with the remaining tubes and strings.Place the tubes on top of the bone structures and use tape to hold them in position temporarily. Using an adhesive, permanently secure the tubes onto the bone structure and then remove the tape. Next, thread the Kevlar string from the tubes through the holes drilled onto the tip and middle pieces.Make a small, secure knot once the string is through the hole. First, measure 200 milliliters of silicone and silicone medium in two different containers. Pour both these liquids into a steel bowl and then add up to ten percent paint thinner.Use a stand mixer to mix the components thoroughly for three to four minutes. If desired, add color at this step to achieve the desired visual effects. Insert a rod into the knuckles of the base part and align it with the knuckles of the flipper mold.When the pegs fit into the cavities of the mold, the bone structure should be perfectly aligned. While holding down on the two parts of the mold, secure the parts by using a clamp for added compression. Then, carefully pour the silicone mixture into the mold, until it reaches the topmost knuckles of the bone structure.Look for oozing of liquid from the bottom hole in the mold as a sign that the mixture is uniformly distributed. Once the oozing liquid is noticed, plug the hole to avoid further outflow of the liquid. Leave the liquid to cure for four hours before removing the flipper robot from the mold.Next, connect the flipper to a motor through a three-pulley system, and mount the flipper to the test system as described in the accompanying text protocol. Set the motion of the flipper by selecting the jogging function on the motor driver. Pressing the up button rotates the flipper clockwise and the down button rotates the flipper anticlockwise.Shown here on the left is a foreflipper from a female California Sea Lion, which was scanned and recreated into this robotic flipper. The digital scanned image shows a wire-frame view of the digital flipper. From this image, one can see that the flipper has an airfoil-like shape that is thicker on the leading edge and is cambered, with its upper surface more convex and its inner surface concave.Once mounted to a recirculating flume, like the one shown here, dye can be injected upstream of the flapping flipper, and the flow pattern can be imaged. Shown here are three points along the flipper cycle. In the right panel, a vortex can be seen around the tip of the flapping robotic flipper.Once mastered, this technique can be done in four and a half hours if it is performed properly. After watching this video, you should have a good understanding of how to create a robotic platform to investigate Sea Lion swimming.

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