Fracture-based grasping: dynamic impact enables predictable robotic anchoring to freshwater ice

Gripping to smooth and wavy substrates, such as naturally occurring ice, presents a challenge for climbing robots in the field. Existing ice anchoring solutions require either substantial initial surface compression force (drilling; at least 50 Newtons) or require large energy expenditure (thermal picks; almost 1000 Joules). We present an anchoring mechanism capable of attaching to ice with lower initial surface compression force and lower energy consumption compared to drill-based or melt-based methods. The system leverages surface fracture caused by dynamic impacts with axes - inspired by mountaineers - to create indentations for grasping. A model describes the indentation depth, recoil energy, and surface compression force required for anchoring success, each as a function of impact energy. An integrated dual-ax gripper system successfully generates usable indents with as low as 8.3 Newtons of initial surface compression force and 8 Joules of combined mechanical potential energy on -14^∘ C freshwater ice - a result consistent with first-principle model predictions. The gripper then successfully holds its own weight on steep glacier slopes in the field. These results indicate fracture-based grasping approaches are promising for climbing systems on ice. This concept can also apply to other surfaces such as wood, rock, and packed soil.