Compact spherical robot rolls and propels in water with internal moving masses
Omnidirectional Amphibious Locomotion via Internal Mass Actuation
Robotics
Summary
robots that work outdoors must move across land, water, and obstacles without breaking. The authors built MARBLE, a ball-shaped robot that moves by shifting weights inside itself instead of using wheels or propellers. Its shell rolls on land and also floats with fins to glide on water, all without changing parts. This design lets it move in any direction and handle rough environments and obstacles smoothly. The authors tested it on land, water, and transitions between both to show it works well.
What this means in practice
- •For search and rescue teams: Deploy robots that can seamlessly move on land and water to navigate disaster areas with varied terrain and debris.
- •For environmental monitoring teams: Use amphibious rolling robots to gather data across wetlands and shorelines where both water and land traversal is required.
Authors
Niko Weaver, Boxi Xia, Li-Yu Lo, Yuhao Huang, Boyuan Chen
Abstract
Field robots must traverse varied terrain and obstacles while remaining robust to water, debris, vegetation, and physical contact. We present MARBLE, a fully enclosed omnidirectional amphibious rolling robot driven entirely by internal mass redistribution. Three mutually orthogonal linear sliders shift internal masses to generate body rotation, while an orientation-aware controller maps planar velocity commands into slider positions. A rigid spherical shell encloses all active mechanisms and simultaneously serves as the terrestrial contact surface, buoyant enclosure, and mounting structure for passive fins that enable water-surface propulsion. Rotation of the same shell architecture hence produces rolling on land and surface propulsion in water without mechanical reconfiguration or separate locomotion actuators. The spherical morphology further allows the robot to accommodate changes in body orientation and contact location during direct interactions with terrain and obstacles. We evaluate MARBLE through omnidirectional locomotion characterization, traversal across heterogeneous terrestrial environments, aquatic surface locomotion, land-water transitions, and deliberate obstacle interactions. These experiments demonstrate how a single enclosed mechanical architecture can combine omnidirectional mobility, cross-medium locomotion, and tolerance to environmental contact. MARBLE provides a compact design for field mobility across heterogeneous terrain, obstacles, and land-water transitions. We will open-source all software and hardware design. Our website is https://generalroboticslab.com/MARBLE