Smart Materials for Advanced Robotic Space Applications Space Engineering Research Center Texas Engineering Experiment Station, Texas A&M University Space Engineering Institute Team Members Richard Colunga Shane Davis Jimmy Espitia Tim Guenthner Brian Kuehner Chris Mahaney Lora Palacios Dr. Ron DiftlerNASA Mentor Dr. James BoydTAMU Mentor Reid ZevenbergenGraduate Mentor

Goal Design, build and test a prototype serpentine robotic arm that utilizes smart materials for actuation. Fall 2009 Semester Tasks –Perform a literature review in serpentine robotics. Research and evaluate different smart materials for use in actuation of space- based robotics. –Investigate mini/micro sensors and motor technologies that have potential uses for the prototype. –Design a prototype robotic linkage that utilizes smart materials for actuation. Include wiring diagrams and hardware considerations.

Literature Review Investigated previous work and designs of both elastic body and rigid body robotic arms. –NASA’s Tendril: Elastic deformation at tip. –Clemson University Elephant Trunk: Rigid links controlled by tendons and bias springs. OctArm: Pneumatic air muscles. Compared and contrasted smart materials based on energy density, actuation frequency, and stress vs. strain. –Shape memory alloys, Ionic Polymer Metal Composites, Piezoelectrics, Dielectric Elastomers Researched the effects of space environment on smart material’s properties and performance. –Thermal Cycling, Hard Vacuum, Atomic Oxygen, UV and Gamma Radiation

Smart Material Search –Shape Memory Alloys Only 3% conversion efficiency from electrical to mechanical work. Only able to apply force in one direction. Cyclic actuation may be slow due to cooling time –IPMCs Unpredictable voltage vs. displacement behavior. Outgassing from hard vacuum affects properties and performance of material. UV radiation causes crosslinking within polymer substrate, affecting material properties. –MSMA/Magnetostrictive Requires proximity to a permanent magnet or current run through coils to create an electromagnet. Permanent magnet proximity requires actuation device; Electromagnet requires unacceptable power consumption and possibly heating. –Piezoelectrics Solid state material with no outgassing/crosslinking. Commercially available space-rated materials. Efficiently convert electrical to mechanical power –Conventional Miniature Electric Motors Smoovy Motor: Brushless DC motor; 5mm diameter x 15mm; Designed for high RPM.

Squiggle Motor Driven by piezoelectric material. Dimensions: 1.8x1.8x6mm (2.77x 2.77mm casing). Able to exert 0.3N of force; Power-off hold of 5N. Rated at <400mW and 20-40VDC Commercially available; Hardened for space environment.

Proposed Design Can be scaled to Tendril prototype (>1cm) or to manufacture (5mm). Two hinges interface between each link. Tools and instruments can be included. Allows for bi-directional actuation per link. Utilizes linear and angular actuation provided by Squiggle motors.

Four hinges interface each link with three forces and two moments each (assuming no friction at hinges). Kinetics can be solved using N2L and E2L. Forward and Inverse Kinetic Problem –Forward: Given the orientation of each link, what is the position of the tip? –Inverse: Given the position of the tip, what are the orientations of the links? Kinetics

Kinematics Forward kinematics of a 3-2-1Euler rotation of 60°, 240° and 240° at Joint 1, 2 and 3 respectively. Given equal lengths of three rigid joints, solution to forward kinematic problem puts the position of the tip back at the origin. A code was written to calculate the position of various joints in a collection of linkages assuming each linkage consists of straight segments connected to joints that can rotate on all 3 axes.

Wiring Must be Small Constraint of 5x5mm cross section dictates the need for a small wiring harness. The size of an electrical wire depends on the applied current and length of the wire. How small can our wires be? Rigid Calculations: P = 500 mW V(source) = 40 VDC V(squiggle) = 38 VDC σ(copper) = 59.6E6 S/m L(wire) = 6 mm Wire Choice: Templfex Micro-miniature flat and wire Cable Tempflex cables are used extensively in the medical field. The outer wall coating is a Teflon alternative. AWG(Stranded)Minimum wall thickness(mils) Resistance (Ω/km) 36 to 50.5N/A Minimum wire cross-sectional area. V= Applied voltage L = Length of wire A = cross sectional area = conductivity of material

Potentially Useful Hardware Motion Sensor: MEMS 3-axis - ± 2g/± 8g Smart Digital Output “Piccolo” Accelerometer –This is a 3-axis digital accelerometer that is 3x5x0.9mm. It operates with 2.16 V to 3.6 V and the temperature range is -40°C to 85°C Position Sensor: TRACKER NSE-5310 –This position sensor is 8.5x11.5x1.61mm and can operate over -40°C to 125°C. It uses a magnet and requires 3 V to 3.6 V and is made by the same company as the Squiggle motor. Optics: Fiber Lens Scope Viewer –This lens viewer is has a 2mm diameter tube and is 1 meter long. Pressure Sensor: TouchMicro-3 v1.0 –This pressure sensor is 3mm in diameter and it uses 5 V. It can handle up to 39N of force and the operating temperature is -20°C to 100 °C.

Spring 2010 Future Work Kinematics and Dynamics –Add external forces and moments to FBD calculations. –Verify kinematic calculations with addition of translation to rotation. Prototype –Design, build, verify couple to join Squiggle to hinge. –Addition of rotational Squiggle motor to linkage design. –Fabricate and build links; Assemble links into linkage. Consider the feasibility of self-deployment.