Copyright © April 20, 2006 Mark R. Cutkosky, Stanford University 1 RiSE Consortium Members DARPA/SPAWAR N C-8045 RiSE is funded by With additional support from the Intelligence Community Postdoctoral Fellowship Program

Copyright © April 20, 2006 Mark R. Cutkosky, Stanford University 2 Requirements for climbing with dry adhesion  Hierarchical compliance over scales from to m. Reason: obtain large contact areas and uniform loading on materials ranging from glass to bark. Consequence: need compliances at limb, toe, lamellar and setal scales; need integrated macro/micro fabrication solutions.  Anisotropic adhesion and friction Reason: control adhesive stresses and attachment/detachment. Consequence: need asymmetric, fully 3D micro structures that are difficult to fabricate with current MEMS and nanofabrication technologies  Distributed Control of Forces Reason: increase stability, prevent contact stress concentrations Consequence: need heterogeneous and anisotropic structures behind the contact surface for shear load transfer; need compliant under-actuated mechanisms and feedback for internal force control.

Copyright © April 20, 2006 Mark R. Cutkosky, Stanford University 3 Gecko hierarchical compliance Spatular shaft 2µm Spatula 200nm Setal shaft 100µm Lamella Cushions 1cm 1mm

Copyright © April 20, 2006 Mark R. Cutkosky, Stanford University 4 Stickybot hierarchical compliance 10  m Berkeley 600nm U. Dayton 1mm Multimaterial toes: 3 grades of urethane polymer with embedded fabric for shear load transfer 5 mm sandwich of pillars & membranes 3 cm anisotropic elastic features 1m1m 300  m m m m m m m

Copyright © April 20, 2006 Mark R. Cutkosky, Stanford University 5 Pressure sensitive adhesives Fat Agarose gel Soft insect cuticle PMMA Rubber Polyethylene Epoxy Aluminum Carbon nanotubes Diamond Cartilage Bone, Fiber composites tackynontacky  -keratin Young’s Modulus (Pa) polypropelene (bulk) setal array kPa polypropelene  fiber array Effective modulus of setal array Dahlquist criterion ~100 kPa for tack elastomer (bulk) elastomer  comb array larger features, more sensitivity to tip geometry increased resistance to fouling, faster dynamics length = 110  m diameter = 4.5  m Substrate backing PSA

Copyright © April 20, 2006 Mark R. Cutkosky, Stanford University 6 Anisotropic Adhesion 25 mN of Adhesion Gecko setae dragging with curvature Time (s) Force (mN) Colored: Normal force Gray: Shear force Dragging against curvature No Adhesion Time (s) Force (mN) Synthetic elastomer  -combs: optimize geometry for directional adhesion and uniform tip stress. (Stickybot movie) 100  m

Copyright © April 20, 2006 Mark R. Cutkosky, Stanford University 7 Mechanisms for active load distribution Russell: Gecko and lizard tendon routing -- consistent solutions seen across many species. Zani: Geckos and lizards that excel on rock always have claws in addition to lamellae. tendons with multiple attachment sites ensure load distribution active toes with small distal claws Key challenge: Given n adhesive patches (+ spines), how can we ensure even loading for an n-fold increase in adhesion & traction?  tuned, passive compliance for decoupling and to minimize stress concentrations at wall surface  active deployment to increase probability of establishing good attachments  route loads through tendons to prevent “premature unpeeling” lamellae load path

Copyright © April 20, 2006 Mark R. Cutkosky, Stanford University 8 Control of foot orientation and internal forces for using directional adhesion unstable stable Optimization: stability vs foot orientation for inverted clinging (optimal if all feet pull toward COM) Inverted: feet pull toward COM (  ) for max. adhesion (  ). Climbing: feet pull upward (  ) and inward (  ) for adhesion + stability Directional adhesion can be realigned to enhance perturbation rejection. Toe orientation is altered as feet change function. Observations Model predictions Contact constraint model F t > 0 (preferred direction): F t ≤ F max, F n ≥ -  F t F t ≤ 0 (non-preferred): |F t | <  F n (Coulomb), F n ≥ 0

Copyright © April 20, 2006 Mark R. Cutkosky, Stanford University 9 StickyBot: advanced platform for investigation of adhesive climbing l l Test vehicle for directional adhesives l l Selectively compliant: 4 grades of polymer, carbon fibers and fabric for directional stiffening l l Highly under-actuated: 12 servos, 38 DOF. l l Double differential toe mechanism for conforming and peeling l l Limb sensors for force control. Government purpose rights. Contract N C Contractor: Stanford University. Exp date: Nov. 30, 2008

Copyright © April 20, 2006 Mark R. Cutkosky, Stanford University 10 Method II: polymer fiber patches (2  m dia, 20  m long) with 100  m backing embedded in compliant (Shore 20A) substrate. + Method I: Patterned array of nano- tubes or fibers is aligned & bonded with elastic, directional  combs; connecting regions are removed. Loading Integration methods for directional multiscale contact SDM pallet (sacrificial material) Government purpose rights. Contract N C Contractor: Stanford University. Exp date: Nov. 30, 2008

Copyright © April 20, 2006 Mark R. Cutkosky, Stanford University 11 StickyBot manufacturing process [Movie: gecko_sor3.mov] Manufactured via SDM with multiple materials and embedded components

Copyright © April 20, 2006 Mark R. Cutkosky, Stanford University 12 Deposit (part) Shape Embed Deposit (support) Shape Part Embedded Component Support Shape Deposition Manufacturing

Copyright © April 20, 2006 Mark R. Cutkosky, Stanford University 13 Study biological materials, components, and their roles in locomotion. Study Shape Deposition Manufacturing (SDM) materials and components. Models of material behavior and design rules for creating SDM structures with desired properties Example: mapping from passive mechanical properties of insects to biomimetic robot structures stiff material viscoelastic material

Copyright © April 20, 2006 Mark R. Cutkosky, Stanford University 14 Fabrication sequence for leg flexures Cut pocket for casting 1st layer of hard material

Copyright © April 20, 2006 Mark R. Cutkosky, Stanford University 15 Fabrication sequence for leg flexures Cast hard material and cut pockets for flexures

Copyright © April 20, 2006 Mark R. Cutkosky, Stanford University 16 Fabrication sequence for leg flexures Cast material for soft flexures

Copyright © April 20, 2006 Mark R. Cutkosky, Stanford University 17 Fabrication sequence for leg flexures Add next support layer and machine for casting

Copyright © April 20, 2006 Mark R. Cutkosky, Stanford University 18 Fabrication sequence for leg flexures cast and machine hard material struts

Copyright © April 20, 2006 Mark R. Cutkosky, Stanford University 19 Fabrication sequence for leg flexures Cast and machine support for top layer

Copyright © April 20, 2006 Mark R. Cutkosky, Stanford University 20 Fabrication sequence for leg flexures Cast and machine top layer of hard material

Copyright © April 20, 2006 Mark R. Cutkosky, Stanford University 21 Fabrication sequence for leg flexures Cast top layer soft material for flexures

Copyright © April 20, 2006 Mark R. Cutkosky, Stanford University 22 Fabrication sequence for leg flexures Plane top surface and remove support material

Copyright © April 20, 2006 Mark R. Cutkosky, Stanford University 23 Microcombs l Sandwich the combs around a spacer l Use as a positive for a mold

Copyright © April 20, 2006 Mark R. Cutkosky, Stanford University 24 A note on Tip Geometry 1mm 100um 10um 1um 100nm Tip Contact Diameter Microcombs CNTs MicroCNC Berkeley Hairs Proposed Silicon Combs Optimal geometry is achieved when stress is uniformly distributed at pull- off, i.e. no peeling (H. Gao and H. Yao 2004) Shape Insensitive Range F optimal / F singular =1 F optimal / F singular ~1000 F optimal / F singular ~10 6

Copyright © April 20, 2006 Mark R. Cutkosky, Stanford University 25 Method II: polymer fiber patches (2  m dia, 20  m long) with 100  m backing embedded in compliant (Shore 20A) substrate. + Method I: Patterned array of nano- tubes or fibers is aligned & bonded with elastic, directional  combs; connecting regions are removed. Loading Integration methods for directional multiscale contact SDM pallet (sacrificial material)

Copyright © April 20, 2006 Mark R. Cutkosky, Stanford University 26 Mold configuration 20mm 33mm Hole diameter: in (~400um) Tip angle : 20 o * This is a mold for one toe pad. Final mold design should have more than 16 of this.

Copyright © April 20, 2006 Mark R. Cutkosky, Stanford University 27 Dimensions 20 o 1.4 mm 0.4 mm The angled surface does not need to be straight. Concave arc might be better in terms of reducing effective stiffness Angle needs to be small. ~20deg is a good number to start Lower side height (0.4mm) needs to be small to minimize clumping. But It makes the mold fragile.