1. Strain Sensing at High Altitude Annual Arizona Space Grant Consortium ASCEND! 2010-2011 Andy Gee Pima Community College Mentor: Mike Sampogna Pima Community College April 9 th, 2011 1

2. Overview Goal: To measure strain forces during balloon flights using strain gauges within a Wheatstone Bridge http://www.opamp-electronics.com/tutorials/bridge_circuits_1_08_10.htmhttp://www.omega.com/Pressure/images/SGD_LINEAR1-AXIS_l.jpg 2 Wheatstone Bridge Circuit Strain Gauge

3. How does it work? Strain gauges replace resistors within the Wheatstone Bridge As stress is placed upon the strain gauge, the other gauge compensates for temperature change 3

4. Hardware and Design Components 1 Axis-Linear Strain Gauges, nominal 120 Ω resistance Nylon Material Wheatstone Bridge circuit Instrumentation amplifier 120 Ω resistors Potentiometers Strain Gauge Nylon Rod Amplified Wheatstone Bridge with potentiometers Temperature Compensation Sample 4

5. Solid Mechanics and Rod Design Observe data from previous flights Understand material properties before designing the rod Include calculation of, axial tension, bending, and shear stress Determine the dimensions of the rod 5

6. Dimensions of Nylon Rod Total Length: 203 mm Large Diameter: 30 mm Inner Length: 122 mm Small Diameter: 11.7 mm 6

7. Launch PCC Flight 7, ANSR – 60 Launch date: March 26 th 2011 Launch site: Gila Bend Landing site: Florence Maximum Altitude: ~78,000 ft PCC Flight 7 Launch SitePCC Flight 7 Launch Profile 7

8. Results Strain force data was successfully recorded Bridges were not completely balanced Data had to be normalized Strain Gauge 1 readings before normalization Strain 1 readings after normalization 8 0 minutes = Time equipment was turned on 0 = 34 minutes after the equipment was turned on

9. Results 9

10. Preliminary Analysis 10 EventStrain Gauge 1Strain Gauge 2Average Strain Gauge Tension Ground000 Launch310 N (69.7 lbs) 481 N (108.1 lbs) 495.5 N (99.9 lbs) Steady Ascent171.5 N (38.6 lbs) 210.4 N (47.3 lbs) 191.0 N (42.9 lbs) Burst621.8 N (139.8 lbs) 1074.3N (241.5 lbs) 848.0 N (190.7 lbs)

11. Preliminary Analysis 11 0 = 34 minutes after the equipment was turned on The Steady Ascent is an average force calculated over the 10 minute period after the launch point The 10 minute period mark was chosen to provide ample acceleration time for the balloon Ensures that both strain gauges have recorded acceleration shortly after launch

12. Evaluation of Data 12

13. Evaluation of Data 13

14. Conclusions Proven concept through trial and error Built a payload that was able to measure tension on the rod Designed a rod that is able to withstand flight Analysis is still currently being done More room for improvement Fantastic research and learning experience 14

15. Thank You! I would like to thank the following: Michael Sampogna Dr. Denise Meeks Pima Community College ASCEND! Team NASA Arizona Space Grant Consortium Jack Crabtree and ANSR 15