Recently, roboticists at the University of California San Diego have developed flexible feet that can help robots walk up to 40% faster on uneven terrain such as pebbles and wood chips. The work has applications for search-and-rescue missions as well as space exploration.
The feet are flexible spheres made from a latex membrane filled with coffee grounds. Structures inspired by nature such as plant roots and by man-made solutions such as piles driven into the ground to stabilize slopes are embedded in the coffee grounds.
The feet allow robots to walk faster and grip better because of a mechanism called granular jamming that allows granular media, in this case the coffee grounds, to go back and forth between behaving like a solid and behaving like a liquid. When the feet hit the ground, they firm up, conforming to the ground underneath and providing solid footing. They then unjam and loosen up when transitioning between steps. The support structures help the flexible feet remain stiff while jammed.
It’s the first time that such feet have been tested on uneven terrain, like gravel and wood chips.
The feet were installed on a commercially available hexapod robot. Researchers designed and built an on-board system that can generate negative pressure to control the jamming of the feet, as well as positive pressure to unjam the feet between each step. As a result, the feet can be actively jammed, with a vacuum pump removing air from between the coffee grounds and stiffening the foot. But the feet also can be passively jammed, when the weight of the robot pushes the air out from between the coffee grounds inside, causing them to stiffen.
Researchers tested the robot walking on flat ground, wood chips and pebbles, with and without the feet. They found that passive jamming feet perform best on flat ground but active jamming feet do better on loose rocks. The feet also helped the robot’s legs grip the ground better, increasing its speed. The improvements were particularly significant when the robot walked up sloped, uneven terrain.