Highly dynamic bistable soft actuators allow for varied locomotion — ScienceDaily

Highly dynamic bistable soft actuators allow for varied locomotion — ScienceDaily

Most animals can quickly switch from walking to jumping to crawling to swimming as needed without reconfiguring or making major adjustments.

Most robots can’t. But researchers at Carnegie Mellon University have created soft robots that can seamlessly transition from walking to swimming, for example, or crawling to rolling.

“We were inspired by nature to build a robot that can perform various tasks and adapt to its environment without adding actuators or complexity,” said Dinesh K. Patel, a post-doctoral fellow at Morphing Matter Lab at the School of Computer Science’s Human-Computer Interaction Institute. “Our bistable actuator is simple, stable and durable, and lays the foundation for future work in dynamic, reconfigurable soft robotics.”

The bistable actuator is made of 3D-printed soft rubber that contains a shape-memory alloy spring that responds to electrical currents by contracting, causing the actuator to bend. The team used this bistable motion to change the shape of the actuator or robot. Once the robot changes shape, it is stable until another electrical charge morphs it back into its previous configuration.

“Matching how animals move from walking to swimming to crawling to jumping is a major challenge for bio-inspired and soft robotics,” said Carmel Majidi, a professor in the Mechanical Engineering Department at CMU’s College of Engineering.

For example, one robot the team built has four curved actuators attached to the corners of a cellphone-sized body made of two bistable actuators. On the ground, the curved actuators act as legs, allowing the robot to walk. In the water, the bistable actuators change the shape of the robot, putting the curved actuators in the perfect position to act as propellers so it can swim.

“You have to have legs to walk on land, and you have to have a propeller to swim in water. Building a robot with separate systems designed for each environment adds complexity and weight,” said Xiaonan Huang, an assistant professor of robotics at the University of Michigan and Majidi’s former Ph.D. student. “We use the same system for both environments to create an efficient robot.”

The team created two more robots: one that could crawl and jump, and another inspired by caterpillars and pill bugs that could crawl and roll.

The actuators require only a hundred milliseconds of electrical charge to change their shape, and they are durable. The team had a person ride a bicycle on top of one of the actuators several times and changed the shapes of their robots hundreds of times to demonstrate durability.

In the future, robots may be used in rescue situations or to interact with marine animals or coral. The use of heat-activated springs in actuators could open up applications in environmental monitoring, haptics, and reconfigurable electronics and communications.

“There are many interesting and exciting situations where energy-efficient and versatile robots like this could be useful,” said Lining Yao, the Cooper-Siegel Assistant Professor at HCII and head of Morphing Matter Lab.

The team’s research, “Highly Dynamic Bistable Soft Actuator for Reconfigurable Multimodal Soft Robots,” is featured on the cover of the January 2023 issue of Advanced Materials Technologies. The research team included co-first authors Patel and Huang; Yao; Majidi; Yichi Luo, a mechanical engineering master’s student at CMU; and Mrunmayi Mungekar and M. Khalid Jawed, both from the Department of Mechanical and Aerospace Engineering at the University of California, Los Angeles.