My work on Paul Birkmeyers CLASH robot has been published in IROS 2011.
During the development of CLASH, I assisted by testing the engagement properties of the feet on loose cloth substrates using a custom built 2 axis force displacement apparatus. Testing revealed that the foot-ankle linkage allowed for spines on the feet to engage with a strong tensile force, yet allow for easy retraction through a variety of angles.
From Paul Birkmeyers abstract: CLASH is a 10cm, 15g robot capable of climbing vertical loose-cloth surfaces at 15 cm per second. The robot has a single actuator driving its six legs which are equipped with novel passive foot mechanisms to facilitate smooth engagement and disengagement of spines. These foot mechanisms are designed to be used on penetrable surfaces and offer improved tensile normal force generation during stance and reduced normal pull-off forces during retraction. CLASH is the first known robot to climb loose vertical cloth and is able to climb surfaces when surface rigidity is not guaranteed.