fishing swimming

Novel robot fish could improve accessibility of underwater exploration

Image credit: Dreamstime

Underwater exploration could be made easier with the development of a coil-powered 'robot fish' designed by scientists at the University of Bristol.

The device was fitted with a twisted and coiled polymer (TCP) to drive it forward, a light-weight low-cost device that relies on temperature change to generate movement.

The mechanism works by contracting like muscles when heated, with the energy being converted into mechanical motion.

The robot fish uses a TCP which is warmed by Joule heating – the passage of current through an electrical conductor produces thermal energy and heats up the conductor. By minimising the distance between the TCP on one side of the robot fish and the spring on the other, this activates the fin at the rear, enabling the robot fish to reach high speeds.

The undulating flapping of its rear fin was measured at a frequency of 2Hz, two waves per second. The frequency of the electric current is the same as the frequency of tail flap. 

Lead author Tsam Lung You from Bristol’s Department of Engineering Mathematics said: “Twisted and coiled polymer actuator is a promising novel actuator, exhibiting attractive properties of light-weight, low-cost high-energy density and simple fabrication process.

“They can be made from very easily assessable materials such as a fishing line and they contract and provide linear actuation when heated up. However, because of the time needed for heat dissipation during the relaxation phase, this makes them slow.”

By optimising the structural design of the TCP-spring muscle pair, it allowed the fin at the back of the device to swing at a larger angle.

Until now, TCPs have been mostly used for applications such as wearable devices and robotic hands. This work opens up more areas of application for the technology, such as marine robots for underwater exploration and monitoring.

Tsam Lung You added: “Our robotic fish swam at the fastest actuation frequency found in a real TCP application and also the highest locomotion speed of a TCP application so far.

“This is really exciting as it opens up more opportunities of TCP application in different areas.”

The team now plan to expand the scale and develop a knifefish-inspired TCP-driven ribbon fin robot that can swim agilely in water.

In 2021, US researchers demonstrated a technique for implementing varying cruise speeds in swimming robots. Underwater vehicles are typically designed to have a single cruise speed, and they’re often inefficient at other speeds. That technology could allow underwater vehicles to travel fast through miles of ocean, then slow down to map a narrow coral reef, or speed to the site of an oil spill then throttle back to take careful measurements.

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