Soft Swimming Mechanisms

Swimming robot that uses heat to create high pressure for pulsed jets

This robot creates jets via a thermodynamic cycle. It heats a small central chamber of water which expands, increases pressure, and pushes water out of the one-way outlet valve, creating a jet for thrust. Then after sufficient water flows out, the internal pressure decreases below the ambient surrounding pressure and water flows in the one-way inlet valve. This continuous stable process happens simply with heat input, requiring no active control, no moving mechnical parts, and (in theory) no rigid parts other than the power supply. 

Ishida, M., Iida, F. & Abdulali, A. (2026, April). "Jet-propelled soft swimmer powered by a thermal oscillator". In 2026 IEEE 9th International Conference on Soft Robotics (RoboSoft) (pp. 1073-1079). IEEE. 

1 DoF linkage for underwater paddling

A paddling fin needs high drag when pushing water to create thrust but low drag when moving back to its original position. Here, I designed a linkage using a pair of cams that use a single motor to create the pushing motion (high drag during power stroke) and a twisting motion (low drag during recovery stroke). This robot uses softness in the linkage to satisfy kinematic constraints and in the fins to create additional efficiency.

Ishida, M., Abdulali, A., Hosseini, N. K., & Iida, F. (2024, April). "Exploration of fin stiffness for asymmetric thrust in a swimming robot". In 2024 IEEE 7th International Conference on Soft Robotics (RoboSoft) (pp. 946-951). IEEE. 

Jet-propelled squid robot

In this work, we created a pulsed-jet robot inspired by the squid. We showed that there is an optimal relationship between the diameter of the nozzle and the volume of the body to get the best vortex out of the body. In addition, we showed a correlation beetween nozzle angle and turning radius and that the robot can unobtrusively operate near animals.

Ongoing work includes improving the propulsion efficiency by improving the drivetrain mechanism and developing a method for steering the robot by directing the jet with a soft nozzle.

Christianson C., Cui Y., Ishida M., Bi X., Zhu Q., Pawlak G., Tolley M. T., (2020), "Cephalopod-Inspired Robot Capable of Cyclic Jet Propulsion Through Shape Change", Bioinspiration and Biomimetics, 16, 016014. 

Jet propulsion for coral reef exploration

Scientists have a great interest in exploring and mapping the inner crevices of coral reefs. These inner passages are small and winding, and it is challenged for either manual or robotic implements to squeeze through. We developed a rigid end effector that directed water jets for both propulsion and steering and was supplied with water via a long, soft, tubing tether that could squeeze through these narrow passages - like a snake robot, except that instead of undulating or slithering, it had jets coming out of the back of its head!

Since the tether led to an offboard pump and valve system, we could control it using a Bluetooth video game controller, making it great for demonstrations: 

(unpublished work led by Matt Suiter - ask me for more details!)