Robots usually need power to move, and no electricity means no movement. However, engineers at the California Institute of Technology and the Zurich Federal Institute of Technology have developed robots that can propel themselves without any motor, servo system or power supply. These advanced robots move forward by paddles in the water. The switch that propels the paddle is a kind of material that can be deformed with the change of temperature.
This study blurs the boundaries between materials and robots. In an autonomous device, the material itself makes the machine work. Daraio, the first author of the paper and professor of mechanical engineering and Applied Physics in the Department of Engineering and Applied Sciences, California Institute of Technology, said, "Our example shows that we can use structural material deformation to respond to environmental cues, control and drive robots." The paper was published in the Proceedings of the National Academy of Sciences on May 15.
The new propulsion system relies on a flexible polymer material that curls when cooled and stretches when heated. The polymer is positioned to activate the switch inside the robot, which is then connected to a row of rowing oars.
The switch is made of bistable elements, which can be stabilized in two different geometric shapes. It is made of elastic strips, and when propelled by polymers, it clips from one location to another.
When the cold robot is placed in warm water, the polymer sticks out and activates the switch, resulting in sudden release of energy to move the robot forward. Polymer bars can also be "adjusted" to give specific responses at different times: that is, thicker bars will take longer to warm up, stretch and eventually activate their propellers than thinner ones. This adjustability allows teams to design robots that can rotate and move at different speeds.
The study is based on previous work by Daraio and Dennis Kochmann, professors of aerospace at California Institute of Technology. They use bistable component chains to transmit signals and build computer-like logic gates.
In the latest design version, Daraio's team and collaborators are able to connect polymer elements to switches, so that the four-propeller robot can move forward, drop a small payload, and then paddle backwards.
Osama R. Bilal, the first author of the PNAS paper and a postdoctoral scholar at California Institute of Technology, said, "By combining simple movements, we can embed programming into materials and perform a series of complex behaviors." In the future, more functionality and responsiveness can be added, such as using polymers that respond to other environmental cues, such as pH or salinity. Future versions of robots may contain chemical leaks, or smaller robots can deliver drugs, researchers say.
At present, when bistable components capture and release their energy, they must be manually reset to work again. Next, the team plans to explore ways to redesign bistable elements so that when the water temperature changes again, they can reset themselves and move on as long as the water temperature remains fluctuant.