SIMBI: Soft Intelligent Module for Benthic Interactions

Soft underwater grippers are well-suited for ecological sampling, providing flexibility in handling specimens of different sizes and shapes while reducing environmental impact through their compliance. Yet they are usually employed on big remotely operated vehicles, constraining their application by size, which can disturb aquatic habitats and limit their ability to access remote areas without shoreline access such as mountain and forest lakes. To support efficient underwater exploration, we designed, developed, and tested an aerially deployed underwater vehicle featuring a compact, lightweight soft gripper. This design reduces water disturbance and enables precise navigation in confined underwater environments, significantly expanding operational capabilities underwater. By analyzing the pod's volume changes, buoyancy actuation, and propulsion mechanisms, we derive a simplified dynamic model to describe the underwater motion. We developed a control framework that decouples buoyancy, thrust, and yaw to enable independent control of underwater motion. Precise buoyancy control, essential for navigating interstices without causing ecological harm, was achieved with feedback control loops taking water depth as feedback, showing a rise time of under 5 s and a 10% settling time within 30 s. Yaw control, achieved via inertial measurement unit feedback, exhibited a rise time of less than 10 s with oscillations of 10%-25% around the set values. This system enhances underwater grasping, extends mission reach and efficiency, and helps minimize environmental disruption.