UC Berkeley's Mole Crab Robot Can Burrow Deep to Collect Environmental Data
EMBUR can self-burrow vertically using a novel leg design that emulates how Pacific mole crabs bury themselves in beach sand.
Engineers from UC Berkeley have taken inspiration from nature to develop a mole crab robot that can burrow vertically underneath sediment to help evaluate soil at agriculture sites, marine environments and rocks at construction sites. Known as EMBUR (EMerita BUrrowing Robot), the robot uses a novel leg design to achieve downward motion that emulates how Pacific mole crabs bury themselves in beach sand. While that may sound easy, it’s difficult to move downward through sediments such as sand and soil, as the deeper the robot digs, the harder it is to push the material out of the excavation hole.
To overcome those obstacles, the team designed EMBUR’s legs to have an anisotropic force response, meaning they experience a much greater force in one direction than another. The robot’s soft fabric legs expand for large forces during the power stroke but fold and retract during the return stroke. “There have been some recent advances in creating anisotropic legs for granular media, but this is the first time they have been implemented successfully on a free-burrowing robot,” explains Laura Treers, Ph.D. student in mechanical engineering.
To design the robot, the researchers observed the burrowing capabilities of Pacific mole crabs in a lab setting and noted the crab’s five leg pairs could be split into two groups, which sweep in opposite directions from one another. They also noticed a pattern of insertion, sweeping, and retraction, with the latter appearing to reduce drag on the return stroke. With those incites, the team was able to create a robotic implementation, then used physics models to estimate the forces on those legs.
The modeling technique they used is known as RFT (Resistive Force Theory), which allowed them to design the robot with the necessary geometries and behavior needed to burrow beneath different soils successfully. While the EMBUR robot could burrow under sand in a lab setting, it still needs revisions to tackle real-world environments.