Saturday, May 25, 2024

New underwater robot pioneers energy-efficient buoyancy control

A team of engineering students at Rice University has built a remotely operated underwater robot that could revolutionize buoyancy control via water-splitting fuel cells. This device offers a more power-efficient way to maintain neutral buoyancy, which is essential in underwater operations.

This robot is an example of how fuel cell-based buoyancy control devices (BCDs) can reduce operating costs for remotely operated or autonomous underwater vehicles (AUVs). The potential applications of this technology range from environmental monitoring and oceanographic research to military and industrial tasks. By providing a quieter, more energy-efficient alternative to conventional thruster-driven AUVs, the robot offers a promising solution to a long-standing problem.

Team Bay-Max, consisting of Andrew Bare, Spencer Darwall, Noah Elzner, Rafe Neathery, Ethan Peck, and Dan Zislis, have based their project on an academic paper authored by researchers from Rice and the University of Houston. The paper suggests that fuel cell-enabled depth control could potentially lead to an 85% reduction in energy consumption for AUVs in comparison to traditional DC motor-based thruster designs. Fathi Ghorbel, a professor of mechanical engineering and bioengineering at Rice, is a co-author of the study and also happens to be the team’s sponsor.

“The BayMax student team was excited to implement an innovative research idea based on electrolysis,” Ghorbel said. “The idea involves the transformation of water into hydrogen and oxygen gases to control AUVs’ buoyancy to mimic fish’ swim bladders. The research is part of a collaborative program between my lab, the lab of Professor Laura Schaefer at Rice and Professor Zheng Chen’s lab at the University of Houston.

“This collaborative research aims to develop tetherless continuum soft engines that utilize reversible proton exchange membrane fuel cells and water electrolyzers to drive volume-mass transformation. Through this design project, the BayMax team proved the efficacy of this technology in AUV interaction with the physical world.”

Ghorbel believes that this new technology has a lot of potential uses, such as in AUVs, material intelligence, assistive wearable devices, and even adaptive and reprogrammable robotic garments and fabrics. 

According to Bare, one of the most exciting things about this technology is that it’s cutting-edge and hasn’t been implemented quite like this before. Bare and his team are thrilled to be the first ones to use this technology in a device with pitch roll and extensive controls.

Andrew Bare.
Andrew Bare. Credit: Jeff Fitlow/Rice University

The use of traditional underwater robots with high energy-consuming thrusters and pumps has been a problem for a long time. However, Neathery has found a solution that is both innovative and efficient. The incorporation of reversible hydrogen fuel cells with balloons in the BCDs has allowed for minimal energy use while also enabling the robot to smoothly adjust its depth. This approach is not only cost-effective but also eco-friendly, making it an excellent alternative to the traditional methods.

“When we apply voltage to the fuel cells, we can increase the buoyancy of our device by having distilled water push through the fuel cell substrate and ionized into the two gases,” Zislis said. “When we want to conserve or regain energy and diminish the buoyancy of the device, we send the voltage in the opposite direction, which reverses the process.”

The robot generates energy through reverse electrolysis by utilizing the natural reaction between hydrogen and oxygen to form water. The device also features various sensors that gather crucial information about the system’s health and the robot’s position and orientation underwater. This data is then displayed on the dashboard, which provides real-time updates on the robot’s location, orientation, and BCDs activation state.

Elzner, who worked on the project, mentioned that the dashboard was his primary responsibility. The setup allows for real-time monitoring of the robot’s depth and orientation, among other things. The robot also features an automatic stabilizing algorithm and depth control, which can be manually overridden using a video game joystick. Darwall, who was also part of the project, had to learn new software and delve deep into control theory to make it happen.

“The team coalesced over a shared interest in vehicle engineering or robotics and a desire to deploy their skills doing something outside their comfort zone.

“Most of us knew each other from classes and/or clubs such as Rice Eclipse, the university’s rocketry club,” Zislis said. “We were inspired to work together on such an ambitious and amazing project because we knew we would have great team chemistry, which would allow us to both support and challenge one another.”

Managing system interdependencies was one of the big challenges the team faced.

“With a project like this, integration was critical,” Zislis said“Another takeaway for me is the importance of determining a clear scope for any given project. With this robot, we could have focused on a lot of different things. For instance, we could have worked on improving fuel cell efficiency or making a robotic arm. Instead, we chose to keep these other elements simple so as not to divert focus away from the main part, which is the buoyancy control device. This kind of decision-making process is not just part of good engineering, but it’s relevant with everything in life.”