Studying force generation and control in snakes using a sensorized robot

Snakes can combine vertical and lateral body bending to adapt to and traverse irregular 3-D terrain with obstacles much larger than their body height with little slip and instability, an ability that most snake robots still lack. Observation of snakes adapting to and traversing vertical structures on flat surfaces suggests that this ability likely relies on contact force sensing and feedback control. To begin to understand this, we created a 12-segment robot with each segment instrumented with 3 sheet contact sensors capable of measuring normal contact forces at 30 Hz. We chose to use piezo-resistive sensors considering that they are cheap, light, flexible, and can be made to desired shape to fit outside and distributed on robot body. Each segment has a soft shell to distribute force evenly on sensor by conforming to terrain. The robot traversed a large obstacle by propagating down its body a predefined vertical bending shape that conformed to the obstacle. We observed large normal contact forces on the segments in contact with front side of obstacle, resulting in net forward propulsion to overcome frictional drag. Because the sensor's piezo-resistive material displays a creep behavior when loaded, we are working on a sensor model to accurately estimate dynamic contact force.