79.4 Friday, Jan. 6 Robust Climbing in Cockroaches Results from Fault Tolerant Design Using Leg Spines JAYARAM, K*; MERRITT, C; FULL, R.J.; Univ. of California, Berkeley; Univ. of California, Berkeley; Univ. of California, Berkeley firstname.lastname@example.org
Previously, we found that cockroaches, Blaberus discoidalis, maintain performance on flat and rough terrain even with the loss of tarsi (or feet) by relying on large spines at the tibia-tarsus joint. Here, we examined whether tarsi-less cockroaches could maintain performance on inclined surfaces. We compared running performance (average speed) on constant inclines of 0, 30, 45, 60, 75 and 90° before and after complete tarsi ablation. Loss of tarsi did not affect performance (<5% change in mean running speed) at 0, 30 and 45° inclines. Tarsi-less animals decreased speed at 60° (-54%), 75° (-87%) and 90° (-88%) relative to the intact animals. To uniquely identify the cause of failure, we ran the animals on a curved incline track (radius = 50 cm) using two surfaces, rough (700 µm beaded) and smooth (Plexi-glas), and measured failure angle. Intact cockroaches failed at 89.6±2.6° and 58.6±7.7° on rough and smooth surfaces, respectively. After tarsal ablation, animals failed at 79.0±7.9° (rough) and 21.7±6.2° (smooth). Animals with only claws ablated (rest of the tarsi intact) showed failure at 84.4±7.72° (rough) and 56.8±4.1° (smooth). Tarsi-less animals showed negligible loss in running speeds on rough surfaces. Passive spines effectively compensated for loss of tarsi or claws except at steep inclines, but on smooth surfaces contribute minimally. Probing the structure of the tarsus by isolating the heterarchical functional regimes of the different tarsal specializations is important because most engineering solutions to climbing in robots rely on a single structure and not a hybrid, robust design.