Design and analysis of a transformable spherical robot for multi-mode locomotion
Sandy terrains are widely distributed on this planet and include desert, beach, and area affected by volcanic eruption where covered with ash. Currently, these environments still present a challenge for mobile robots due to their poor trafficability. One of the most essential requirements on such terrains for mobile robots is to generate enough drawbar pull with a small amount of slippage. For this purpose, protrusions or convex patterns called lugs (i.e. grousers) are attached on the wheels. However, oscillational drawbar pull generated by lugs results vibration of the robot body and therefore disturb the stability of the robot. In this paper, we aim to reduce the oscillation of the drawbar pull by proposing a novel wheeled mechanism integrated with an actively actuated lug. The drawbar pull on the sandy terrain in fabricated testbed is firstly measured on a prototype mechanism. Based on measured force, a strategy of tuning sinkage length of the active lug for generating stable drawbar pull is proposed. This method has the advantage of that it requires neither prior knowledge on terramechanic models nor physical properties of the terrain. The performance of the proposed method is finally verified by comparing the generated drawbar pull with that of a wheel with a fixed lug.