Sound travels faster and farther underwater because it’s denser than air, and that can make it harder for researchers trying to study marine life who get an early heads up to go into hiding. But a new underwater robot could move stealthily through the waves using a propulsion system that doesn’t rely on a propeller or any visible moving parts.
Getting around underwater isn’t particularly hard, we’ve had functional submarines for hundreds of years, believe it or not. But most rely on moving propulsion systems that are noisy underwater and require a lot of power to keep them running. The well-funded US Navy solved that problem with nuclear-powered submarines, but not everyone has access to that level of technology.
Researchers designing marine robots for undersea exploration have instead focused on using submersible vehicles called underwater gliders that propel themselves forward through buoyancy by repeatedly rising and sinking. They can run for months at a time on a single charge, covering thousands of miles in the process, but they’re slow and not very manoeuvrable, which limits their practicality. Mechanical engineers at Indiana’s Purdue University have developed an updated design for an underwater glider that solves those limitations while still autonomously operating for months at a time, as detailed in a recently published paper.
The researchers have named their submersible ROUGHIE, which is short for Research-Oriented Underwater Glider for Hands-on Investigative Engineering: an acronym as impressive as the vehicle itself. There are no moving parts visible on the outside of the vehicle, but inside the sealed four-foot-long tube are ballast tanks that can be filled with water or air to cause ROUGHIE to float to the surface or dive below the waves.
A tail-mounted wing transforms the craft’s up and down motions into forward momentum, but to provide even finer control of ROUGHIE’s pitch underwater its heavy rechargeable battery inside is mounted on a sliding mechanism that can shift that weight forward or back.
The steering has always been a challenge for underwater gliders, often requiring a turning radius of over 9 metres which makes them problematic for use in shallower areas where natural formations and debris simply don’t afford enough space to turn around unobstructed. A robot designed for exploration that’s easily trapped isn’t very useful.
That problem was solved with ROUGHIE by mounting all of its internal components on a single rail that can rotate inside the vehicle. As everything inside rotates and shifts its weight it causes the entire submersible to roll making it easy to steer. In testing inside one of Purdue University’s pools, ROUGHIE had a turning radius of around 3 metres making it better equipped at getting itself out of tight spots.
The submersible’s design might not be ideal for ferrying human passengers: that constant up and down motion seems like a reliable way for nausea to quickly set in. But it makes ROUGHIE a much better tool for collecting data when equipped with sensors that could measure water temperatures, detect algae blooms, and even magnetometers that could locate shipwrecks or underwater munitions posing a safety threat. Its ability to stealthily move through the water could also make the submersible an invaluable tool for studying underwater creatures that don’t necessarily want to be seen or studied.