February 23, 2024


When designing a fish-like underwater robot, you need a form of propulsion that is energy-efficient and moderately fast. A new tail-flapping system might fit the bill, paving the way for more widespread use of such robots.

A team of scientists at the University of Bristol, led by PhD student Tsam Lung You, has integrated the experimental setup into a robotic fish. It uses a modified mechanism called twist and coil polymer (TCP).

In short, TCP takes the form of a coiled wire, not unlike the handset cord of a landline telephone. When the thread is heated, it coils tighter, contracting like a muscle. When the heat is removed, the thread relaxes again, returning to the default length.

One limitation of such devices is that they cannot generate repetitive motions very quickly, as they take at least a second or so to contract again. Robot fish solves this problem.

Overview of the robot TCP spring propulsion system
Overview of the robot TCP spring propulsion system

Zhan Longyou

It combines conductive yarn TCP and conventional steel coil springs, which are placed side by side along the length of the robot. They are attached to opposite sides of the tail slap mechanism at the rear end of the robot, and are connected to each other by linkages at the front end.

When current is applied to the TCP, it heats up and contracts, pulling the tail to one side and Tension coil spring. When the current stops and the TCP relaxes, the stretched spring contracts, pulling the tail to the other side. When the tail finishes moving to that side, the TCP is ready to retract and pull it back again.

different parts of the system
different parts of the system

Zhan Longyou

In tank tests, the robot was able to swim at a tail-flapping speed of two waves per second. Scientists are now integrating the technology into a more agile robotic knifefish that has an auger-like fin that runs along its base.

“Our robotic fish swims at the fastest driving frequency in a real TCP application, and the highest locomotion speed in a TCP application to date,” You said. “This is really exciting because it opens up many more opportunities for TCP applications in different fields.”

A Paper The research was presented at the 6th IEEE-RAS International Conference on Soft Robotics in Singapore earlier this month. The robot in action can be seen in the video below.

(embed) https://www.youtube.com/watch?v=5DGKq4bdf7A (/embed)

TCP Propelled Robot Fish

source: University of Bristol