Duke's MARBLE sealed sphere robot rolls by shifting internal weight, works on land and water
lukas_m_ziegler · x · 2026-09-30
Duke University's General Robotics Lab unveiled MARBLE, a fully sealed spherical robot that rolls on land and propels itself on water with zero external moving parts.
- Mechanism: three mass sliders on mutually orthogonal axes shift the center of mass away from the geometric center, creating a gravitational moment about the ground contact point that rolls the ball; three axes enable motion in any direction
- Control challenge: as the shell tumbles, the slider axes rotate with it, so the mapping from "go this way" to "place sliders here" keeps changing — the controller must be orientation-aware and re-solve continuously
- The shell does four jobs: ground contact surface, buoyancy, mounting for passive fins, and sealed housing for all actuation
A clever embodiment design that replaces external wheels or paddles with pure internal mechanics.
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