A Light-Weight Vibrational Motor Powered Recoil Robot That Hops Rapidly Across Granular Media

Abstract

A 1 cm coin vibrational motor fixed to the center of a 4 cm square foam platform moves rapidly across granular media (poppy seeds, millet, corn meal) at a speed of up to 30 cm/s, or about 5 body lengths/s. Fast speeds are achieved with dimensionless acceleration number, similar to a Froude number, up to 50, allowing the light-weight 1.4 g mechanism to remain above the substrate, levitated and propelled by its kicks off the surface. The mechanism is low cost and moves without any external moving parts. With 2 s exposures we photograph the trajectory of the mechanism using an LED blocked except for a pin-hole and fixed to the mechanism. Trajectories can exhibit period doubling phenomena similar to a ball bouncing on a vibrating table top. A two dimensional numerical model gives similar trajectories, though a vertical drag force is required to keep the mechanism height low. We attribute the vertical drag force to aerodynamic suction from air flow below the mechanism base and through the granular substrate. Our numerical model suggests that speed is maximized when the mechanism is prevented from jumping high off the surface. In this way the mechanism resembles a galloping or jumping animal whose body remains nearly at the same height above the ground during its gait.

SurferBot: a wave-propelled aquatic vibrobot

“…Finally, in addition to those discussed previously, other small-scale vibrobots have been shown to propel along or within other media, such as along a granular bed [51] or freely immersed in a fluid [52]. At vastly larger length-scales, forced rocking motion of a canoe has also been shown to lead to self-propulsion via gravity wave effects, a technique employed in competitive 'gunwale bobbing' [53].…”

Ricochets on Asteroids II: Sensitivity of laboratory experiments of low velocity grazing impacts on substrate grain size

“…It was shown in Quillen et al (2019) that the permeability of a granular media can result in an aerodynamic force that causes a suction on a very flat object that is rising off the surface. The flow of air in the granular media could change the forces acting on the marble during the penetration and rebound phases of its trajectory.…”

SurferBot: A wave-propelled aquatic vibrobot

“…Finally, in addition to those discussed previously, other small-scale vibrobots have been shown to propel along or within other media, such as along a granular bed [47] or freely immersed in a fluid [48]. At vastly larger length-scales, forced rocking motion of a canoe has also been shown to lead to self-propulsion via gravity wave effects, a technique employed in competitive "gunwale bobbing" [49].…”