Contact Modeling and Testing of Directional Adhesives Daniel Santos After this slide add, background on climbing robots Biomimetics Laboratory Stanford University Daniel Santos February 24, 2019

Transmission of Forces through Mechanical Interaction Contact: What and Why Transmission of Forces through Mechanical Interaction Contact Defines: Slip Limits; Pulloff Limits Guide Design Enable Control Force transmission and deformation Biomimetics Laboratory Stanford University Daniel Santos February 24, 2019

Contact Models Coulomb Friction Hertz Contact FNormal FTangential Coulomb Rigid-Body vs. Deformable Contact Point Contact vs. Area Contact Biomimetics Laboratory Stanford University Daniel Santos February 24, 2019

Analysis Stability Analysis Force Distribution Foot Orientation Stability vs. Inclination Angle Stability vs. Foot Orientation Stable Examples of what you can do with contact models Unstable Biomimetics Laboratory Stanford University Daniel Santos February 24, 2019

What is the “Right” Adhesive Model What do StickyBot Pads Do? Adhesive Models What is the “Right” Adhesive Model for Climbing? JKR = Isotropic FA = Anisotropic Examples of what you can do with contact models What do StickyBot Pads Do? Biomimetics Laboratory Stanford University Daniel Santos February 24, 2019

Experimental Contact Testing Goals: Analyze Behavior of StickyBot Pads Develop 3D Model of Directional Adhesion Method: Apply Controlled Motions to Sample Pads Measure Forces Obtain Limits Associated with Slip and Pulloff General description of setup Biomimetics Laboratory Stanford University Daniel Santos February 24, 2019

Mechanical Test Setup 3 Motor-Driven Lead Screws X/Y – 0.2” per Revolution; 1.7um per Tick Z – 0.05” per Revolution; 0.4um per Tick 6-axis Force/Torque Sensor Wall-mounted -> +/-25mN Noise 2-axis Alignment Stage X Y Z Sample Wall General description of setup Force Plate Alignment Bench Biomimetics Laboratory Stanford University Daniel Santos February 24, 2019

Electronic Test Setup F/T Computer Forces/Torques 1kHz Voltage Encoder Position PIC 500Hz General description of setup Trajectory 1kHz Biomimetics Laboratory Stanford University Daniel Santos February 24, 2019

Experimental Procedure Preload Along 45° Different Depths: 0~1000um Pulloff In Y-Z Plane between 0°-180° In X-Z Plane between 0°-180° X Y Z Z Y 45° General description of setup Biomimetics Laboratory Stanford University Daniel Santos February 24, 2019

Raw Data Preload Pulloff General description of setup Biomimetics Laboratory Stanford University Daniel Santos February 24, 2019

Determining Pulloff 165,90 150,90 150,45 General description of setup Biomimetics Laboratory Stanford University Daniel Santos February 24, 2019

Determining Pulloff Buckling? Pulloff vs. Sliding Finding Pulloff: Maximum Normal Adhesion Maximum Force in Velocity Direction Maximum Force Magnitude General description of setup Biomimetics Laboratory Stanford University Daniel Santos February 24, 2019

Data – YZ Plane 400um 600um 800um 1000um General description of setup Biomimetics Laboratory Stanford University Daniel Santos February 24, 2019

Data – YZ Plane 45° 90° 120° 135° 150° General description of setup Biomimetics Laboratory Stanford University Daniel Santos February 24, 2019

Data – XZ Plane 400um 600um 800um 1000um General description of setup Biomimetics Laboratory Stanford University Daniel Santos February 24, 2019

Data – 3D General description of setup Biomimetics Laboratory Stanford University Daniel Santos February 24, 2019

Data – 3D Show Demo General description of setup Biomimetics Laboratory Stanford University Daniel Santos February 24, 2019

Summary of Results Experimental Procedure Challenges Absolute Positioning Alignment Data Interpretation Challenges Buckling Pulloff vs. Sliding Preload INCREASES Adhesion (up to limit) Adhesion CONTROLLABLE via Tangential Angle Lateral Loads DECREASE Adhesion General description of setup Biomimetics Laboratory Stanford University Daniel Santos February 24, 2019

Future Work Continue Testing: Fill in Sparse Areas of 3D Contact Test Different Samples Understand/Explain Anomalies Model Experimental Data Linear? Incorporate Findings into Previous Work Posture, Foot-Orientation Analysis Control of Internal Forces General description of setup Biomimetics Laboratory Stanford University Daniel Santos February 24, 2019

Questions? Tidbits of Info: 5,577 Trials ~15 Hours of Continuous Operation ~4GB of Data! Biomimetics Laboratory Stanford University Daniel Santos February 24, 2019