Visit Your Local PBS Station PBS Home PBS Home Programs A-Z TV Schedules Watch Video Donate Shop PBS Search PBS
SAF Archives  search ask the scientists in the classroom cool science
scientists from previous shows
cool careers in science
ask the scientists

Photo of Michael S. Triantafyllou Michael S. Triantafyllou as seen on Natural Born Robots: Swim Like a Fish

Click on Michael's photo to read a brief bio.

q Next what kinds of materials did you use to make your robot and how is it powered? (Question sent by Dhyana)

A For the RoboPike: The robot is powered by batteries placed inside it "belly". The batteries drive three waterproofed motors, which cause it to move like a fish. The robot has two long "backbones" made of fiberglass and delrin on which "ribs" are attached, made of a fiberglass spiral. A special accordion-like skin is used which allows it to stretch without buckling.

q How did you begin to design your robot? Did you start with actual measurements of a tuna and its motions? (Question sent by Carol)

A For the RoboTuna: We bought at first a tuna from the fish market and studied all the details of its body and fins. Soon, though, the whole lab smelled of fish, so next we used a cast of a caught tuna. The external shape of the robot is an exact replica of that replica of the tuna. The inside parts of course are totally different than in the live fish.

As for the tuna motions, we had reports from fish biologists who had observed tunas for long periods of time. We used these measurements to control the tuna, but still we went to the New England Aquarium on every opportunity we had, to watch them improvise their motions live.

q I am a high school student interested in pursuing a future in robotic engineering and working on the type of projects you are. Do you have any suggestions about what I should do to get started now? (Question sent by many viewers)

A (from John Kumph, seen on this story with the robot he designed based on a pike) If you want to make robots, I recommend that you start as early as possible. Robots are a multi-disciplinary field, so they require a broad base of knowledge and skills. You'll need to know how to make things, and how things work, the transfer of energy from one domain to the other and so on. I would get robot kits and model kits from hobby stores, like Mondotronics. I would take classes at school like automotive repair, metal working, jewelry making, wood shop, and of course physics, chemistry, math, and biology... Don't wait until you're in college to start this stuff. Most robotics skills can be learned in high school.

q Scientific American Frontiers portrayed vortices originating on the body of a tuna-like fish and then being shed supposedly very efficiently by the tail. Is the body important or even required for the lunate tail motion to be efficient? If the tail were to move by magic in exactly the same way with no leading body would it still be an efficient shape for propulsion? (Question sent by Terence)

A The tail, by itself, is a very efficient propulsor and can be used for propelling boats and submarines. In fish swimming, the body is very important, because it naturally generates vortices which can be manipulated eventually by the tail to propel itself.

The contrast with a ship may give a clearer picture:

The ship hull produces small eddies which are then wasted in the wake. The propeller generates a jet to create the thrust needed to overcome the drag; this jet has also vortices especially near the edges of the jet. This results in wasted energy as both body and propeller generate independently vortices.

By contrast, a fish generates vortices in its body and then uses the tail to reposition the same vortices so as to generate the jet. In addition, it has been found that when the fish organize the vortices on their body the resistance from water (the force that retards anything that moves in water) is reduced, adding to the advantages of fish propulsion.

q When my class watched the story about the robot tuna, I was wondering how it's possible to have robots go under water. How do you keep the wires and motor "water proof"? (Question sent by Maddie)

A Water proofing is an essential and difficult task for marine robots. Specially designed submerged motors and elaborate connectors are used to insulate against sea water. In the RoboPike water proofing the off-the-shelf motors is a long process. Such difficulties make underwater exploration a slow process.

q Would the RoboTuna be able to swim efficiently in the ocean with all the currents and waves? (Question sent by students in Mr. Heavner's class)

A Fish are designed to produce with their tails large forces to overcome the forces from currents and the waves. With their flexible bodies, they are more capable at doing this than man-made submarines. The RoboTuna is designed to move like fish and is equally capable of producing with the action of its body and tail of overcoming - like live fish - the forces of the waves and the currents.


Scientific American Frontiers
Fall 1990 to Spring 2000
Sponsored by GTE Corporation,
now a part of Verizon Communications Inc.