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

A 1-cm coin vibrational motor fixed to the center of a 4-cm square foam platform moves rapidly across granular media 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 across granular media without any external moving parts. With 2-s exposure, we photograph the trajectory of the mechanism with an LED fixed to the mechanism. Trajectories can exhibit period doubling phenomena similar to a ball bouncing on a vibrating table top. A two-dimensional robophysics model is developed to predict mechanism trajectories. We find that a vertical drag force is required in the model to match the height above the surface reached by the mechanism. We attribute the vertical drag force to suction from air flow below the mechanism base and through the granular substrate. Our numerical model suggests that horizontal 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. Our mechanism and model illustrate that speed and efficiency of light-weight hoppers on granular media can be affected by aerodynamics and substrate permeability.

The Effect of Place of Residence on Physical Fitness and Adherence to Mediterranean Diet in 3–5-Year-Old Girls and Boys: Urban vs. Rural

The aim of the present study was to examine the effect of place of residence on physical fitness and adherence to Mediterranean Diet (AMD) in 3–5-year-old children, i.e., whether those who live in urban areas differ than those in rural and whether any difference varied by age. Participants were 363 preschoolers (age 3–5 years old), who performed a series of anthropometric, physical fitness tests and measured their nutritional habits through a 16-item Mediterranean Diet (KIDMED) questionnaire. The main findings of the present study were that (a) boys had better performance in ball bouncing, Medicine Ball Throw Test (MBTT), 25 m sprint, Standing Broad Jump (SBJ), crawling, and shuttle run test (SRT) than girls, and the magnitude of these differences was small; (b) preschoolers in urban residence were taller than those in rural and had better performance in SRT; (c) older preschoolers had larger anthropometric characteristics and better performance than younger preschoolers; (d) the magnitude of the effect of age was larger than the effect of residence; and (e) good AMD was more prevalent in boys than in girls and in 3-year-old participants than in their older peers, but was not related to place of residence. Therefore, these findings identified the need to develop exercise and nutrition intervention programs in preschoolers considering sex, age, and place of residence.