TumblerBots: Tumbling Robotic sensors for Minimally-invasive Benthic Monitoring

Robotic systems show significant promise for water environmental sensing applications such as water quality monitoring, pollution mapping and biodiversity data collection. Conventional deployment methods often disrupt fragile ecosystems, preventing depiction of the undisturbed environmental condition. In response to this challenge, we propose a novel framework utilizing a lightweight tumbler system equipped with a sensing unit, deployed via a drone. This design minimizes disruption to the water habitat by maintaining a slow descent. The sensing unit is detached once on the water surface, enabling precise and non-invasive data collection from the benthic zone. The tumbler is designed to be lightweight and compact, enabling deployment via a drone. The sensing pod, which detaches from the tumbler and descends to the bottom of the water body, is equipped with temperature and pressure sensors, as well as a buoyancy system. The later, activated upon task completion, utilizes a silicon membrane inflated via a chemical reaction. The reaction generates a pressure of 70 kPa, causing the silicon membrane to expand by 30\%, which exceeds the 5.7\% volume increase required for positive buoyancy. The tumblers, made from ecofriendly materials to minimize environmental impact when lost during the mission, were tested for their gliding ratio and descent rate. They exhibit a low descent rate, in the range of 0.8 to 2.5 meters per seconds, which minimizes disturbance to the ecosystem upon water landing. Additionally, the system demonstrated robustness in moderate to strong wind conditions during outdoor tests, validating the overall framework.