Comparing the Locomotion Dynamics of a Cockroach and a Shape Deposition Manufactured Biomimetic Robot Sean A. Bailey, Jorge G. Cham, Mark R. Cutkosky Biomimetic Robotics Lab Stanford University December 12, 2000 Robert J. Full PolyPedal Laboratory University of California at Berkeley

Intro SDM Design DynamicsConclusions Overview Introduction Shape Deposition Manufacturing Robot Design Locomotion Dynamics Conclusions

Intro SDM Design DynamicsConclusions Introduction Motivation –Small –Fast –Robust Integrated approach –Biomimetic structures –Biologically-inspired control De-mining in an unstructured environment

Intro SDM Design DynamicsConclusions Prototype Limb with Embedded Pneumatic Actuator, Sensor, Leaf Spring and Valves Leaf-spring Piston Pressure Sensor Fitting Inlet Valve Exhaust Valve Shape Deposition Manufacturing (SDM) Manufacturing

Intro SDM Design DynamicsConclusions Arbitrary geometries Embedded components No fasteners Multi-materials Tailored compliance Shape Deposition Manufacturing (SDM) Graded, multi-material 5-bar Multi-material part w/ embedded components

Biological Example Death-head cockroach Blaberus discoidalis Fast –Speeds of up to 10 body/s Rough terrain –Can easily traverse fractal terrain of obstacles 3X hip height Intro SDM Design DynamicsConclusions Blaberus discoidalis running over fractal terrain

Intro SDM Design DynamicsConclusions Biological Inspiration Control heirarchy –Passive component –Active component Full and Koditschek, 1999 Mechanical System (muscles, limbs) Environment Mechanical Feedback (Preflexes) Sensory Feedback (Reflexes) Neural System (CPG) Feedforward Motor Pattern Passive Dynamic Self-Stabilization Locomotion

Intro SDM Design DynamicsConclusions Cockroach Geometry Passive Compliant Hip Joint Effective Thrusting Force Functional Biomimesis Damped, Compliant Hip Flexure Embedded Air Piston Robot Implementation Robot Design Rotary Joint Prismatic Joint Cham et al., 2000, Clark et al., 2001

Intro SDM Design DynamicsConclusions Sprawlita Mass -.27 kg Dimensions - 16x10x9 cm Leg length cm Max. Speed - 55 cm/s 3+ body/sec Hip height obstacle traversal Legs with Compliant Flexures Actuators and wiring embedded inside structure 2.5 cm

Intro SDM Design DynamicsConclusions Movie Superficially insect-like Stable running Obstacle traversal

Whole Body Dynamics Force plate High speed video Intro SDM Design DynamicsConclusions High-speed Footage with Markers Force Plate Data Time (ms) Force (N) filtered vertical force unfiltered horizontal force Locomotion Direction Force plate High speed video markers High speed video markers

Animal Running - the SLIP model Intro SDM Design DynamicsConclusions Human TWO-Legged Cockroach Crab LeggedEIGHT- Dog LeggedFOUR- Vertical Force Body Weight Force Time Fore-aft Blickhan 1989 SIX-Legged Spring-Loaded Inverted Pendulum SLIP Cavagna et al., 1975

Time Intro SDM Design DynamicsConclusions Whole Body Ground Reaction Forces Spring-Loaded Inverted Pendulum (SLIP) Vertical Force Fore-aft Force Blaberus discoidalis Sprawlita Time (ms) Decelerate Accelerate Decelerate Accelerate Decelerate Accelerate Dragging

Individual leg forces Sprawlita drags middle and rear foot Individual legs have functions dissimilar from cockroach legs More questions –Relative contact time Intro SDM Design DynamicsConclusions ms mN ms N Front LegMiddle LegHind Leg filtered vertical force filtered horizontal force Dragging

Intro SDM Design DynamicsConclusions Sprawlita –Physically robust –Operationally robust –Open loop Comparing locomotion dynamics suggests design improvements –Foot drag - longer stroke If more SLIP-like... faster? more efficient? more robust? Summary and Conclusions

Intro SDM Design DynamicsConclusions Future Work Sprawley Davidson Leg extensions The Sprawlettes High level, not real-time sensor-based control Double piston extensionSDM linkage extension Prototype with close proximity valve and cylinder Valve Cylinder

Intro SDM Design DynamicsConclusions Acknowledgements Stanford –Center for Design Research –Dexterous Manipulation Lab –Rapid Prototyping Lab Berkeley –PolyPedal Lab Sponsors –Office of Naval Research –National Science Foundation