Rob and I conducted experiments and built mathematical models of swimming fish with much help from students like Craig Blanchette, Nick Boetticher, Hayden-William Courtland, Vynette Haultaufderhyde, Wyatt Korff, Nicole Lamb, Nicole Librizzi, Matt McHenry, Karen Nipper, David Paul, William Shepherd, Eamon Twohig, and Stephanie Varga. We were able, with additional help from our collaborators Peter Czuwala, Lena Koob-Emunds, Tom Koob, and Chuck Pell, to develop theory about the importance of body stiffness in swimming fish.
The punch line: yes, you can tune a fish. Fish tune their bodies by changing stiffness. Because stiffness is proportional to the speed[187] at which a wave travels or vibrates, using muscles to stiffen the body will drive the fish’s flexural waves faster. When you make undulatory body waves, you perform the mechanical work of transferring the body’s momentum to the water, and when the body’s flexural waves move faster, you are generating more power.
When we had some evidence that real sunfish were using their muscles to alter body stiffness, ONR gave us a chance to build our first self-propelled robotic fish.[188] Matt McHenry and I were anxious to make Nektors in the image of our study species, pumpkinseed sunfish; Chuck Pell, one of the Nektor’s co-inventors, kindly agreed to share his invention and his talents. He created a mold using a dead sunfish, from which he fabricated five identically shaped sunfish-Nektors. Each sunfish model was made out of a slightly different formulation of PVC rubber, which is how Chuck varied the models’ material stiffnesses over a range that included the stiffness values we had measured in real sunfish.
With help from Vassar Professor Bob Suter, Matt and I developed a way to swim the sunfish model in a flow tank—kind of a treadmill for fish. For a given and constant frequency, each sunfish model swam upstream in the initially still flow tank. We increased the flow speed until the sunfish model could just swim in place, moving neither upstream nor downstream, balancing the drag and thrust. After doing this for all of the models and a bunch of frequencies, we found that stiffer sunfish swam faster.[189]
Recently the Navy’s biorobotic research efforts have been joined by those of another federal agency, DARPA, the Defense Advanced Research Projects Agency.[190] In addition to an ONR-like goal to improve naval technology, DARPA’s role in national defense ranges more broadly, across the services, as shown by their mission statement: “DARPA’s mission is to maintain the technological superiority of the U.S. military and prevent technological surprise from harming our national security by sponsoring revolutionary, high-payoff research bridging the gap between fundamental discoveries and their military use.”[191]
DARPA funds numerous robotics projects that use animals for inspiration. One such DARPA-funded project was led by Robert Full, professor of integrative biology and director of the Poly-Pedal Laboratory at the University of California at Berkeley. Bob, an expert in biomechanics and animal locomotion whom you may remember from Chapter 6, teamed with engineers at Boston Dynamics, Inc., the Illinois Institute of Technology, and the Robotics Institute at Carnegie Mellon University to build a six-legged robot inspired by insects. Called RiSE (Robots in Scansorial Environments), the 3.8-kilogram robot successfully scaled a three-story vertical concrete wall, untethered.[192]
RiSE is one of many successful robotics projects that DARPA has funded. In an effort to propel the development of autonomous battlefield vehicles, they created the DARPA Challenge, open to any team. In 2004 a robotic car, Stanley, the creation of Stanford and Volkswagen engineers, used its superior path planning, object detection/avoidance, and navigational skills to run the fastest time in a 138-mile course across the desert. Three years later, in the DARPA Urban Challenge, Carnegie Mellon University’s autonomous car, Boss, won the $2 million prize when it was the fastest robot to navigate a cityscape, filled with real pedestrians and human-driven cars, without violating the California driving laws. Although these well-publicized challenges featured automobiles, DARPA continues to fund research into animals and bio-inspiration.[193] Last time I checked, it looked like you could make pitches to DARPA for bio-inspired and robotics research to the officers running the following programs: “Biologically-driven Navigation (solicitation number DARPA-SN-11-07),” “Deep Sea Operations (DARPA-BAA-11-24),” and “All Source Positioning and Navigation (DARPA-BAA-11-14).”[194]
With all this potential federal funding for defense-related, bio-inspired robots in the United States, I guess it shouldn’t come as a surprise that other countries have robotic warfare programs. But I was flabbergasted, I admit, to learn just how many. According to robotics engineer Ron Arkin, professor of engineering and renowned roboticist at Georgia Technological Institute, fifty-six nations are developing robotic weapons.[195] And that forces an uncomfortable reality check: even though Arkin doesn’t discuss underwater robots in his book on robotic warfare, I too am working—at least indirectly—for the military.[196]
Growing up, I drove my mom crazy because not only did I play war incessantly with my buddies, Fritz and Karl von Valtier, but I also read about war. I read everything I could get my hands on, and I remember how impressed with myself I was when I had been through every book on war in the library of North Hills Elementary School. This was the 1970s, the middle of the Cold War with the Soviet Union, and after exhaustive scholarship, eleven-year-old John decided, to my mother’s horror, that nuclear weapons had taken all the fun out of war. The Cold War, with tanks and troops lined up just looking at each other, was boring—nothing happened. What would General Patton say, I asked? I just couldn’t see how we could be “at war” without any action.
My mother, who had marched against the Vietnam War, told me that if I got drafted, she’d shoot me in the foot. I’m not kidding. She said so repeatedly and passionately. During what my family called my “Spock phase,” I fought her passion with my deadpan version of Vulcan logic. I explained, without emotion, of course, that I wasn’t interested in going to war to die but rather to fight the bad guys and protect our country. When someone attacks your ship or your planet—I mean country—it was only logical to defend yourself. For some reason this line of argument failed to penetrate. I guess she was Bones to my Spock: illogical.
World War II, I told her, was my favorite war. She nearly died when I said that. How could her son—or any one for that matter—have a “favorite” war? “Well, mom,” I remember explaining, “World War II had action, on multiple fronts, with different enemies who used different strategies and tactics.” It was modern, with incredible technological developments in rocketry, aviation, and naval engineering. Best of all were the aircraft carriers and the strategic battles of the Pacific Theater! I bought books on carriers and carrier warfare. When I sat at the dinner table and explained to my older sister, Ann, that she needed to know that our pilots loved the Grumman F4F Wildcats, even though they were too slow to duel the Mitsubishi Zeroes head to head, because they had self-sealing fuel tanks and armored cockpits, I think that my mom got what I was really into: technology. Boys and their toys. She backed off—and didn’t mention shooting me in the foot again.
I forgot about World War II, and Spock, for good measure, thanks in no small part to junior high school and the rage of the hormones. Studying primate social behavior and mammalian reproductive biology became the pursuit of the neighborhood boys. On the latter subject, we found our school library to be woefully inadequate. Fortunately, both of Fritz and Karl’s parents were physicians, and the Drs. von Valtier kept their medical library at home well stocked and unlocked. We read widely and voraciously, appreciating the fact that anatomical texts were illustrated, and we thought it best not to trouble the good doctors with the knowledge of our library visits, even though I’m sure they would’ve been proud of the fact that we were inspired and independent scholars.
187
In vibratory mechanics the natural frequency of a structure is proportional to the square root of its stiffness. Other factors, like mass and damping, shouldn’t be neglected because they play huge roles in how the structure moves.
188
Details of the experiments that originally led us to this prediction can be found in the following paper: J. H. Long Jr., M. J. McHenry, and N. C. Boetticher, “Undulatory Swimming: How Traveling Waves Are Produced and Modulated in Sunfish (
189
You can read more about these early robotic fish in the following paper: M. J. McHenry, C. A. Pell, and J. H. Long Jr. “Mechanical Control of Swimming Speed: Stiffness and Axial Wave Form in an Undulatory Fish Model,”
190
For a summary of the ONR’s biorobotics program through 2005, see P. R. Bandyopadhya, “Trends in Biorobotic Autonomous Undersea Vehicles,”
192
For more on the design and performance of RiSE, see M. J. Spenko, G. C. Haynes, J. A. Saunders, M. R. Cutkosky, A. A. Rizzi, R. J. Full, and D. E. Koditschek, “Biologically Inspired Climbing with a Hexapedal Robot,”
193
For example, see DARPA CBS-ONR-ARL US Navy Marine Mammal Program, Biosonar Program Office, SPAWAR Systems Center, San Diego, CA, 2002. See also Frank E. Fish, “Review of Natural Underwater Modes of Propulsion,” DARPA, 2000. More recent projects include bio-inspired underwater sensing and autonomous underwater navigation in rivers and estuaries. For more on the workings of DARPA, I recommend Michael Belfiore,
194
I checked DARPA’s public solicitation on January 8, 2011, at www.darpa.mil/openclosedsolicitations.html.
195
As reported by John Markoff, “War Machines: Recruiting Robots for Combat,”
196
Professor Arkin’s book is timely and opens up an important discussion: Ronald C. Arkin,