The majority of animals can quickly switch between walking, jumping, crawling, and swimming if necessary without reconfiguring or making significant changes.
Most robots cannot. Yet, scientists at Carnegie Mellon University have developed soft robots that can easily switch from one motion to another, such as from walking to swimming or from crawling to rolling.
“We were inspired by nature to develop a robot that can perform different tasks and adapt to its environment without adding actuators or complexity,” said Dinesh K. Patel, a post-doctoral fellow in the Morphing Matter Lab in 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 on dynamic, reconfigurable soft robotics.”
The shape-memory alloy springs inside the 3D-printed soft rubber bistable actuator respond to electrical currents by contracting, which causes the actuator to bend. The researchers modified the actuator’s or robot’s shape using this bistable motion. Once the robot has changed shape, it stays that way until another electrical charge causes it to return to its original form.
“Matching how animals transition from walking to swimming to crawling to jumping is a grand challenge for bio-inspired and soft robotics,” said Carmel Majidi, a professor in the Mechanical Engineering Department in CMU’s College of Engineering.
For example, one robot the team created has four curved actuators attached to the corners of a cellphone-sized body made of two bistable actuators. The curved actuators serve as the robot’s legs on land, enabling it to walk. The curved actuators are in the perfect position to function as propellers so the robot can swim. In the water, the bistable actuators alter the shape of the robot.
We were inspired by nature to develop a robot that can perform different tasks and adapt to its environment without adding actuators or complexity. Our bistable actuator is simple, stable, and durable, and lays the foundation for future work on dynamic, reconfigurable soft robotics.
Dinesh K. Patel
“You need to have legs to walk on land, and you need to have a propeller to swim in the 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 other robots: one that can crawl and jump, and one inspired by caterpillars and pill bugs that can crawl and roll.
The actuators are strong and can change their shape in under 100 milliseconds of electrical charge. To demonstrate durability, the team repeatedly changed the shapes of their robots and had a person ride a bicycle over one of the actuators.
The robots may one day assist in rescue operations or communicate with coral or marine life. Environmental monitoring, haptics, and reconfigurable electronics and communication could all benefit from the use of heat-activated springs in actuators.
“There are many interesting and exciting scenarios where energy-efficient and versatile robots like this could be useful,” said Lining Yao, the Cooper-Siegel Assistant Professor in HCII and head of the Morphing Matter Lab.
The team’s research, “Highly Dynamic Bistable Soft Actuator for Reconfigurable Multimodal Soft Robots,” was 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.
