Shape Memory Alloys Team: High Torque Rotary Actuator/Motor

1. Shape Memory Alloys Team: High Torque Rotary Actuator/Motor Team Members: Uri Desai Tim Guenthner J.C. Reeves Brad Taylor Tyler Thurston Gary Nickel NASA JSC Mentor Dr. Jim Boyd Faculty Mentor Reid Zevenbergen Graduate Mentor

2. Outline • Project Goal: Fall 2008 • Fundamentals of Shape Memory Alloys • Design Concepts • Heat Transfer Analysis • Comparison and Recommendations • Future Tasks: Spring 2009 • Questions

3. Project Goal: Fall 2008 • Research and understand SMAs and their applications • Research current conventions: Electric motors • Develop concepts for a Rotary Actuator/Motor driven by SMAs • Evaluate concepts • Conduct initial analysis of chosen concepts • Select a baseline design • Motivation: Design a motor that will have a higher torque per unit volume and less weight than current motors.

4. What are Shape Memory Alloys? 1 2 3 5 4 Deformed Martensite 2 • Converting thermal • energy to mechanical • work. Stress 3 4 1 Self-Accommodated Martensite Austenite 5 Temperature Mf Ms As Af

5. Applications of SMAs • Aerospace: • Airfoils, Boeing Chevrons, STARSYS • Medical • Stints, Instrumentation • Other • Eyeglasses frames, Locking mechanisms, Underwires, etc.

6. Electric Motors • Most applications for space utilize electric motors. • Electric motors are very dense and therefore there is a weight penalty • Electric motors operate better at higher speeds and lower torque: For low torque applications, a gear box must be added to the motor, which increases the weight. • Pittman motors have been used, in this case, as an example of electric motors with higher than average torque densities. • Highest torque density from Pittman motor studied: 6.83 oz in

7. Design Concept #1: Wire Rotary Actuator Bias Spring Rack and Pinion Drive Shaft SMA Wire

8. Modeling Wire Behavior: Angular Displacement Where: Δθ = angle of rotation (rad) εtrans = transition strain L = length of SMA wire Δx = change in length R = respective radii

9. Modeling Wire Behavior: Moments and Torque Where: F = respective forces R = respective radii k = spring constant FSMA = SMA recovery force Δx =change in length η = efficiency of gear train n = number of SMA wires T = torque generated

10. Modeling Wire Behavior: SMA Analysis Where: εtrans= actuation strain εelastic = elastic strain σi = recovery stress αA: coefficient of thermal expansion for austenite T -T0: change in temperature EM: Young’s Modulus for martensite EA: Young’s Modulus for austenite dSMA = diameter of SMA wire n = number of SMA wires • Typical actuation stress values: 21,755-29,000 psi • Substituting above equation into previous moment equation

11. Results • Pittman Motor: Model GM14X02 • Torque: 107 oz in • Torque Density: 6.83 oz/in2 • SMA Wire Application • 1 wire with diameter of 5mm or 10 wires with diameter of .02in (equivalent of 5mm) • Torque Density:Max: 1250 oz/in2 @ 5.5° rotationMin: 33.5 oz/in2 @ 115.5 ° rotation

12. SMA Wires

13. Design Concept #2: Torque Tube Rotary Actuator Torque Tubes Casing Drive Shaft Bevel Gears

14. Mechanism Operation Torque Tubes Bevel gear attached to drive shaft Drive Shaft Bevel gear attached to torque tube

15. Torque Tube Attachment Method Casing Torque Tubes

16. Torque Tube Analysis Where: T = applied torque J = polar moment of inertia c = radius of beam G = shear modulus L = length of beam φ = angle of twist Analyzing a shape memory alloy torque tube: Where: γ = shear strain γthermal= 0 (for isotropic material) RM = median radius of tube RM

17. Torque Analysis ηtrans=2% This data based upon: G = 152,289.625 psi RM= 0.2 in L = 2 in J = 0.0053 in4

18. Heat Transfer: Overview • Drives SMA actuation • Cp varies between 0.32 and 0.6 during actuation • Material Properties (Nitinol) • Wire Properties • Torque Tube Properties

19. Heat Transfer: Wire Cycle Time: 8 Seconds • Resistive Heating • 4 seconds to heat • Forced Air Cooling • 4 seconds to cool

20. Heat Transfer: Torque Tube Cycle Time: 18.5 Seconds • Contact Conductive Heating • 8 seconds to heat • Forced Air Cooling • 10.5 seconds to cool

21. Compare/Contrast and Future Recommendation SMA Wire Design SMA Torque Tube Design • Simple and feasible • Flexibility in altering torque versus output rotation: Gear Ratios • Less expensive to manufacture • Light weight • Modular design • Capable of extremely high torque output • Greater complexity • Difficult to implement multi-directional rotation • More expensive to manufacture Recommendation: The SMA Team recommends pursuing the SMA wire application due to its simplicity, feasibility and low cost. This design meets our objective of designing a rotary motor that has high torque per unit volume while maintaining a small weight.

22. Future Tasks: Spring 2009 • Detailed analysis of SMA wire application • Detailed design of SMA wire application • Build working prototype • Test and compare results to theoretical

23. Questions?