Search

The soldier crab appears in great numbers and feeds while wandering during daytime low tide. When they see an approaching object, they screw themselves into the sand. The mechanism of formation of mass wandering has not been clarified. In this study, to investigate if the soldier crabs use visual images of neighbors as a stimulus for wandering, dummy crabs were presented to crabs. In the experiments, one, two, four, or eight dummies were placed in a circle on a sand arena. Each crab was placed in the center of the arena and observed whether it burrowed into the sand or wandered. The proportions of wandering individuals in each experimental treatment were compared with the expected value. Significantly more crabs were wanderers when only two and four dummies were present. This result suggests that soldier crabs chose burrowing or wandering depending on visual image of the distribution of the neighbors.

Lunar rovers are required to traverse rough terrains such as those found in craters and cliffs, which are scientifically important location for exploration.

The rovers, which some researchers and agencies are developing, have many functions to sense a lot of information from peculiar environments like the lunar surface for localization, path planning and so on. On rough terrain, without artificial ground maintenance, like the lunar surface, the rovers avoid obstacles by using sensors, which they have. However, if the rovers traverse loose soil, like the planetary surface, there exists the sinking behavior. This sinkage is caused by the weight of the rover. At present the rover sensors are unable to sense it. Actually, Mars Exploration Rover (MER, NASA/JPL), during its exploration on Mars, was disabled because of this. If MER could have known the subsidence of each wheel in time, MER may have avoided this catastrophic condition. We therefore propose to have the grouser mechanism, which can detect sinkage of the wheels of rovers, installed on the wheels of rovers. The grouser mechanism is needed to traverse loose soil like lunar surface and mars surface. When the wheel rotates on loose soil, the resistance force from the loose soil is given to the grouser. However, initially, for the wheel contacts on the surface of loose soil, the resistance from the loose soil is small. We will develop the grouser mechanism with a function that can detect the whole range of the effective resistance force from loose soil including this small resistance force. This study moreover carries out experiments with various loads and verifies the effectiveness of the proposed mechanism, using pictures, of contact with the loose soil surface.