‘Robocarp’ makes splash with motion breakthrough 

The lightweight, inexpensive machine relies on temperature change to prompt movement, which also limits its speed. 

Aping muscle contractions when heated, the fish converts energy into mechanical motion, the device relies on Joule heating with the progress of current through an electrical conductor produces thermal energy and heats up the conductor.

Minimising the distance between the TCP on one side of the robot fish and the spring on the other, activates the rear fin at the rear, allowing it to attain new speeds.

Lead author Tsam Lung You of Bristol’s Department of Engineering Mathematics said the paper ‘Robotic Fish driven by Twisted and Coiled Polymer Actuators at High Frequencies’ – presented to the 6th IEEE-RAS International Conference on Soft Robotics ­ indicated a new route to raising the actuation frequency of TCPs through thermomechanical design and shows the possibility of using TCPs at high frequency in aqueous environments.

“[The] twisted and coiled polymer (TCP) actuator is a promising novel actuator, exhibiting attractive properties of light weight, low-cost high energy density and simple fabrication process," he said. 

“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.”

Previously TCPs have tended to be employed for wearable devices and robotic hands, say the researchers but the latest work suggests they have applications in underwater exploration and monitoring.

Tsam 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.”

Pic: Fish model demonstrating Antagonistic muscles (Tsam Lung You)