brain says ‘Start wiggling’ and the wiggle is generated by computation down among the ganglia and not by the main brain.” Having analysed tuna locomotion, Dr Barrett’s team also had to reproduce it. “With modern materials like titanium and glass-reinforced plastic and carbon fibre, we can replicate a tuna skeleton pretty accurately, and using urethanes and silicones we can recreate the skin and tissue,” he says. “We are using linear Lorentz force actuators to replicate the muscles. Speakers for muscles “With a linear drive Lorenz force actuator you can oscillate it back and forth at very high speeds and extremely high efficiency,” he adds. “The systemwe are using is very similar to the voice coils in microphones and speakers. “The actuators are paired, twitch back and forth to create the oscillation, and are connected by springs to the next pair. We do that for the 12 or 14 ribs in the back end of the fish, and if we oscillate them all at their natural frequencies, we get very efficient drive.” To save more energy, regenerative drive electronics for the ‘speakers’ can reverse the motion with efficiencies of 98-99%, comparable to regenerative braking in an electric car. “Although we are nowhere near as sophisticated as Mother Nature, we are potentially far better than a traditional AUV in terms of efficiency, duration and speed,” he says. “I hope someday to be 20 times better, but it would be arrogant of me to say that we can achieve that in a short time frame.” Environment and aquaculture While gliders achieve great range and endurance, they are limited in speed and manoeuvrability, and fish robots are potentially far more flexible, he argues. “You could drop 100 of them along a transit route across the Atlantic and tell them all to swim due south at the same time,” he says. “That way we could do a transect of the entire ocean at once, and to capture that amount of data would revolutionise our understanding of ocean mechanics.” The same acoustic sensors that allow the robot fish to ‘see’ vortices could also serve as passive sonars, complemented by other acoustic and optical sensors on the head to home in on and identify targets, or to assess the effects of mitigations for environmental issues such as coral reef bleaching. By adding a chemical sensing ‘tongue’ a robot tuna could follow chemical gradients to trace pollutants to their sources, he says. They could also download data from arrays of sensors deployed on the seabed using a megabitclass optical datalink and raise a satcom antenna to beam it back to shore. He also sees a future for fish robots in aquaculture, monitoring the condition of salmon farmed in pens or preparing seagrass beds and, further in the future, potentially herding tuna as they grow in the open ocean and bringing the mature fish in for harvesting. Aquaculture needs a low-cost general-purpose vehicle, an equivalent of a $20,000 tractor, he says. A better world Barrett regards engineering as a powerful disruptive force with tremendous potential for good and evil. “In robotics we struggle with this on a daily basis,” he says. “So my overall philosophy is we should create things that make the world a better place, and I should be training my students to do that,” he says. “Engineering isn’t about making money or about making yourself famous; it’s about legacy and about passing on a better world.” As to his own future, he’s happy where he is. “My job is my hobby and my hobby is my job,” he says. In a few years I’ll probably become a professor emeritus and just keep doing it as long as I can. If I train a lot of young engineers to do it well, maybe they’ll keep me around!” 23 Uncrewed Systems Technology | June/July 2023 Born out on the end of Cape Cod on the east coast of the US in 1956, Dr Barrett grew up close to the water and developed passions for the ocean and building machines, inspired in part by the televised underwater adventures of pioneering French diver, naturalist, naval engineer and filmmaker Jacques Cousteau. He excelled in arts and sciences at school, and loved making things in his railway engineer grandfather’s basement workshop from an early age, along with his brothers. “I built my first robot arm in the 1970s,” he recalls. “I welded a bunch of soup cans together and put electric motors in the joints controlled by a set of switches and potentiometers, and it worked pretty well.” As a student he qualified inmechanical engineering and ocean engineering at universities including theMassachusetts Institute of Technology (MIT). That led to a career that has included senior posts with companies including iRobot andWalt Disney Imagineering, as well as posts with research institutions including the Charles Stark Draper Laboratory, MIT andOlin College, where he is nowProfessor of Mechanical Engineering and Robotics, and Principal Investigator for the Olin Intelligent Vehicle Laboratory. He is also on the boards of several robotics companies in an advisory capacity. Dr David Barrett
RkJQdWJsaXNoZXIy MjI2Mzk4