Author: Jacob Williamson-Rea
Photographer: Eric Sucar
Videographer: Denise Henhoeffer
In Penn’s Scalable Autonomous Robots Lab, three researchers watch from a cluster of computer monitors as small black boats navigate through water in a large indoor pool, seemingly battling against artificially produced currents. But the toy-sized, robotic ships aren’t fighting the currents; they’re actually using them to move around.
They’re part of an autonomous fleet being used by M. Ani Hsieh and a team in her lab. Their goal is to enable robots to perform useful tasks across the ocean, fueled by the power of the water’s currents, with the ability to stay in the ocean beyond the lengths of time any manned vehicle could without extensive equipment and fuel.
Hsieh, a research associate professor in the Department of Mechanical Engineering and Applied Mechanics in the School of Engineering and Applied Science, along with postdoctoral researchers Dhanushka Kularatne and Xi Yu, designs algorithms that will allow these robots to map ocean currents. Doing so could help scientists predict climate changes to stay ahead of dangerous weather events, map the potential trajectory of a chemical or oil spill, or even track the debris of a downed aircraft for a search-and-rescue team. By better understanding the current patterns, the robots will also be able to use the currents as a natural energy source to travel farther and longer—and potentially do more.
“The project really requires the robots to perform long-term and large-scale tours,” says Yu, who sees this research as a nice combination of theoretical and hands-on work. “To achieve this, we utilize the oceanic flow whenever possible.”
Getting the robots to do this, however, means Hsieh and her team need to be able to conduct experiments in a way that allows them to control the flow conditions in which the robots operate. Instead of conducting experiments in the ocean, the researchers have built a large indoor pool that can generate ocean-like currents in the lab. To test their ideas, the team uses robots—just smaller than a computer mouse—to map the currents created in the pool.
Kularatne and Yu test the robots in the Multi-Robot Coherent Structure Testbed, an ocean-simulating indoor pool that’s 15-feet long, 10-feet wide, and containing 4 feet of water and driving motors that generate artificial currents. This creates a complicated and dynamic environment to test their different strategies for mapping ocean currents and leveraging the currents for navigation.
“Ocean dynamics change based on place and time, so this is a very complex system that exhibits various spatial and temporal scales,” Hsieh says. “A single robot simply wouldn’t provide enough measurements to enable a good reconstruction of how the currents change. This is why using a swarm is truly advantageous, because we now have a number of mobile sensors that simultaneously collect measurements across a wider space and over a longer period of time. They can even adapt formations in order to focus sensing capabilities on regions of interest.”
The team uses autonomous surface vehicles, or mASVs, which measure approximately 12 centimeters in length. Each mASV is equipped with a micro-controller board, which includes the robot’s memory and processing systems, as well as an inertial measurement unit, allowing Kularatne and Yu to track and map the fleet’s movement. To enable communication with the robots, each vessel sports an XBee radio module, which sends and receives wireless messages.