(papers under review)

We expand upon the ideas of bioinspired robotics, which often focuses on the study of a single animal in the present day, to include the axis of evolutionary time history. Instead of closely investigating a single species, our goal is create robots to study natural principles about animals (e.g., legged locomotion) that can then be used to explore how and why biological features evolved or didn't evolve in certain directions.

Some related media coverage of this project here and here; check back for more in the future! 

The walking fish proejct is funded by the Human Frontiers Science Program (HFSP) and our work is in collaboration with Valentina di Santo (Stockholm University) and Neil Shubin (University of Chicago).

Ishida M., Sandoval J. A., Lee S., Huen S., Tolley M. T. (2022) "Locomotion via active suction in a sea star-inspired soft robot", IEEE Robotics and Automation Letters/IROS, 7 (4), 10304-10311. 

Sandoval J. A.*, Ishida M.*, Jadhav S., Huen S., Tolley M. T. (2022) "Tuning the morphology of suction discs to enable directional adhesion for locomotion in wet environments", Soft Robotics, 9 (6), pp. 1083-1097.

We take inspiration from the sea star, an invertebrate that is well-suited to walking on all types of underwater terrains such as the tidepools, coral reefs, and even up the sides of aquarium tanks! Sea stars do this using soft, adhesive appendages called tube feet protruding from the bottom of their bodies. 

To enable adhesion-based locomotion for underwater robots, we developed soft, multimaterial suction discs that have asymmetric adhesion. When pulled from one direction, they have high adhesion (at the start of the step) and when pulled from the opposite direction, they have low adhesion (at the end of the step) so they can detach from the surface. This eliminates the need for an additional actuated degree-of-freedom to engage and disengage from the surface - the leg motion by itself is sufficient!

However, to get these suction discs to stick to stick to the surface, the discs have to be preloaded (pushed against the surface); unfortunately, soft actuators like tube feet aren't well suited to created these pressing forces as they tend to buckle under compression.

Ongoing work includes combining the soft suction discs with soft actuators to create similar walking motions. 

Future interests include exploring distributed control (i.e., each tube foot controlling itself with limited knowledge of the behavior of neighboring tube feet) and how to control a large array of soft fluidic actuators without using large numbers of heavy valves and pumps.

Ishida M., Drotman D., Shih B., Hermes M., Luhar M., and Tolley M. T. (2019), "Morphing structure for changing hydrodynamic characteristics of a soft underwater walking robot", IEEE Robotics and Automation Letters, 4 (4), 4163-4169. 

In this work, we augmented a soft quadrupedal robot designed for walking on land with an inflatable body to alter its hydrodynamic profile when walking underwater. Because water is denser than air, fluid forces like lift, drag, and buoyancy affect walking more significantly in water than in air, so we hypothesized that we could improve a walking robot by giving it the ability to alter its hydrodynamic profile in different flow conditions.

We showed that changing the shape of the robot's body could increase the downward lift (improves traction when the robot is walking) by over 50% while only increasing the drag (opposes walking performance) by less than 5%. We also showed that a flow sensor can be used as feedback; when walking with flow, a larger body shape is desirable to take advantage of drag, while when walking against flow, a more streamlined body shape is desirable to minimize the negative effects of drag.

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. 

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.

3D printed fluidic valve demultiplexer (with Billy Yang)

Based on microfluidics techniques like Quake valve multiplexers (using deformable membranes to pinch off flow), we made a 3D-printable valve demultiplexer to reduce the number of electromechanical valves needed to control a large number of fluidic lines.

Jet propelled coral reef explore (with Matt Suiter)

Coral reefs are filled with small passageways that are hard to map using traditional techniques. Here, we created a slender jet-propelled swimmer that could use differential jets to direct its trajectory controlled by handheld joysticks.