Robustness of Biological and Bio-inspired Exoskeletons by Kaushik Jayaram A dissertation submitted in partial satisfaction of the requirements for the degree of Doctor of Philosophy in Integrative Biology in the Graduate Division of the University of California, Berkeley Committee in charge: Professor Robert J Full, Chair Professor Robert Dudley Professor Ronald Fearing Summer 2015 Robustness of Biological and Bio-inspired Exoskeletons Copyright 2015 by Kaushik Jayaram 1 Abstract Robustness of Biological and Bio-inspired Exoskeletons by Kaushik Jayaram Doctor of Philosophy in Integrative Biology University of California, Berkeley Professor Robert J Full, Chair The single greatest difference between biological organisms and human technologies to- day is perhaps robustness. Robustness is broadly defined as a system’s ability to maintain performance despite disturbances. Qualitatively, a complex system may be called robust if it exhibits some or all of the following properties - multi-functionality, fault tolerance, dam- age resistance, modularity and redundancy. However, even the best engineering approaches that have attempted to consider some of these aspects find themselves ’fragile’, slow and computationally intensive. On the other hand, I contend that biological systems are truly robust and capable of a plethora of complex activities such as locomotion, reproduction, respiration etc. In addition, animals constantly overcome challenges of growth and perform self-repair and learning, still a challenge for even the best engineered systems today. Using the cockroach as my model organism, I have investigated the role of exoskeletons in enabling robust high-speed locomotor behavior in cockroaches. Specifically, I have discovered that the cockroach exoskeleton (1) is effective at dealing with external loads/impulses through body reconfiguration, (2) facilitates (or enhances) rapid horizontal to vertical transitions during high-speed running, and (3) compensates for damage (loss of appendages (or its parts)) un- dergoing a limited decrement in high-speed running performance. Based on the impressive locomotion performance by cockroaches despite perturbations, internal and external to the animals, we propose that robustness is a crucial measure of the effectiveness of a system’s performance. i To my family ii Contents Contents ii List of Figures iv List of Tables vii 1 Crawling into Crevices and in Confined Spaces 1 1.1 Summary . 1 1.2 Challenges of confined locomotion . 2 1.3 Methods and Materials . 3 1.4 Crevice Traversal . 8 1.5 Confined Space Crawling . 9 1.6 Model of Frictional Legged Crawling . 11 1.7 Dynamic Compressive Forces . 15 1.8 Soft Robot with Legs . 16 2 Mechanical Mediation via Head-on Collisions 39 2.1 Summary . 39 2.2 Introducing Mechanical Mediation . 40 2.3 Methods and Materials . 41 2.4 Strategies for Transition . 44 2.5 Performance Comparison across Transition Strategies . 44 2.6 Scaling of Mechanical Properties . 45 2.7 Mechanically Mediated Transitions in a Robot . 47 2.8 Scaling of Robustness . 47 2.9 Mechanical Mediation in Robots . 49 2.10 Robustness - A Paradigm Shift . 50 3 Fault Tolerance I: Loss of Feet 63 3.1 Summary . 63 3.2 Foot structure and Function . 64 3.3 Methods and Materials . 66 iii 3.4 Running on Flat Terrain . 70 3.5 Running on Rough Terrain . 70 3.6 Running during Large Lateral Perturbations . 71 3.7 Climbing on Continuously Variable Inclined Terrain . 72 3.8 Climbing on Inclined Flat Terrain . 72 3.9 Postural Control for Fault Tolerant Performance . 73 3.10 Effectiveness of Spines as Feet . 74 3.11 Bio-inspiration and Application to Robotics . 75 4 Fault tolerance II: Loss of Legs 100 4.1 Introduction to Fault Tolerance during Locomotion . 100 4.2 Methods and Materials . 102 4.3 Cockroach Kinematics . 105 4.4 Cockroach Ground Reaction Force Patterns . 107 4.5 Physical Model (Robot) Running Performance . 108 4.6 Conclusion . 109 Bibliography 132 iv List of Figures 1.1 Crevice traversal setup . 19 1.2 Confined space crawling setup . 20 1.3 Static exoskeletal compression. 21 1.4 Robot schematics. 22 1.5 Performance of cockroaches traversing crevices. 23 1.6 Crevice traversal time. 24 1.7 Probability of crevice traversal. 25 1.8 Crevice crawling apparatus and experimental conditions. 26 1.9 Sprawled posture of cockroaches with performance metrics . 27 1.10 Confined space crawling performance of cockroaches. 28 1.11 Confined space frictional legged crawling characteristics . 29 1.12 Effects of varying ceiling friction on confined space crawling performance. 30 1.13 Effects of varying ground friction on confined space crawling performance. 31 1.14 Model of frictional legged crawling. 32 1.15 Performance predictions from model by varying ceiling friction. 33 1.16 Performance predictions from model by varying ground friction. 34 1.17 Testing material properties of cockroaches during compression. 35 1.18 Material properties of cockroaches during compression . 36 1.19 CRAM- Compressible Robot with Articulated Mechanisms. 37 1.20 Robot velocity at different confined heights . 38 2.1 Horizontal floor to vertical wall transition setup. 52 2.2 Head-first impact strategy . 53 2.3 Body-angled impact strategy . 54 2.4 Performance comparison of transition strategies . 55 2.5 Scaling of material properties based on analytical model . 56 2.6 Scaling of performance parameters based on analytical model . 57 2.7 Scaling of specific energy absorption . 58 2.8 Scaling of specific elastic energy storage . 59 2.9 Scaling of kinetic energy in terrestrial animals . 60 2.10 Scaling of robustness and the Haldane Limit . 61 2.11 Robustness of robots . 62 v 3.1 Force platform setup for measuring cockroach dynamics . 77 3.2 Rough terrain setup. 78 3.3 Large lateral impulse setup. 79 3.4 Curved track setup to measure climbing failure. 80 3.5 Variable incline setup. 81 3.6 Illustration of levels of tarsal manipulation . 82 3.7 Velocity on flat terrain with and without tarsi. 83 3.8 Stride frequency on flat terrain with and without tarsi. 84 3.9 Duty factor on flat terrain with and without tarsi. 85 3.10 Ground reaction force patterns on flat terrain. 86 3.11 Peak-peak magnitude ground reaction forces on flat terrain. 87 3.12 Velocity on rough terrain with and without tarsi. 88 3.13 Illustration of the effect of large lateral impulses . 89 3.14 Perturbation rejection time for large lateral impulses . 90 3.15 Orientation change upon large lateral impulses . 91 3.16 Failure angle on a high-friction curved surface. 92 3.17 Failure angle on a low-friction curved surface. 93 3.18 Velocity on inclined terrain . 94 3.19 Stride frequency on inclined terrain . 95 3.20 Stride length on inclined terrain . 96 3.21 Duty factor on inclined terrain . 97 3.22 Effectiveness of spines. 98 3.23 Postural adjustments during climbing without tarsi. 99 4.1 Cockroach leg configurations . 110 4.2 Marker system for kinematic tracking . 111 4.3 Setup for measuring cockroach kinematics . 112 4.4 Force platform setup for measuring cockroach dynamics . 113 4.5 Robots used for robustness testing . 114 4.6 Cockroach gait with 6 legs . 115 4.7 Cockroach gait with 5 legs . 116 4.8 Cockroach gait with 4 legs . 117 4.9 Cockroach gait with 3 legs . 118 4.10 Cockroach gait with 2 legs . 119 4.11 Velocity after successive leg loss . 120 4.12 Stride frequency after successive leg loss . 121 4.13 Stride length after successive leg loss . 122 4.14 Duty factor after successive leg loss . 123 4.15 Body roll after successive leg loss . 124 4.16 Body pitch after successive leg loss . 125 4.17 Body yaw after successive leg loss . 126 4.18 Vertical force after successive leg loss . 127 vi 4.19 Horizontal force after successive leg loss . ..