RoVaLL: Design and Development of a Multi-Terrain Towed Robot with Variable Lug-Length Wheels

Robotic systems play a very important role in exploration, allowing us to reach places that would otherwise be unsafe or unreachable to humans, such as volcanic areas, disaster sites or unknown areas in other planets. As the area to be explored increases, so does the time it takes for robots to explore it. One approach to reduce the required time is using multiple autonomous robots to perform distributed exploration. However, this significantly increases the associated cost and the complexity of the exploration process. To address these issues, in the past we proposed a leader-follower architecture where multiple two-wheeled passive robots capable of steering only using brakes are pulled by a leader robot. By controlling their relative angle with respect to the leader, the followers could move in arbitrary formations. The proposed follower robots used rubber tires, which allowed it to perform well in rigid ground, but poorly in soft soil. One alternative is to use lugged wheels, which increase the traction in soft soils. In this letter we propose a robot with shape-shifting wheels that allow it to steer in both rigid and soft soils. The wheels use a cam mechanism to push out and retract lugs stored on its inside. The shape of the wheel can be manipulated by controlling the driving torque exerted on the cam mechanism. Through experiments we verified that the developed mechanism allowed the follower robots to control their relative angle with respect to the leader in both rigid and soft soils.