Week 7 Engineering Review

1. Week 7 Engineering Review Owen Accas - Dan Crossen - Rebecca Irwin - Madeline Liccione - Hao Shi

2. Detailed Block Diagram

3. Energy Flow Graph

4. Double Stance Time Propagator (RK 4)

5. Single Stance a o

6. Current Prototype v.s. Proposed System Simulation Comparison

7. Axle • 10mm diameter aluminum • Assume no tension/compression or insignificant tension/compression • Shear modulus = 26 GPa • Area = Pi*(.01m)^2=pi*10^-4 m^2 • Shear failure at ~204 million Newtons which is approximately 45.8 million lbs • This strength will more than account for the forces seen on the axle in shear

8. Braces • Worst case: 1 plate rigid, 1 side has full torque • Full torque = (40 lbs/spring)*(2 springs)*1.5 in =120 in-lbs • Bending force on each brace =(120 in-lbs)/(14 inches)/(5 braces) =1.714 lbs/brace, therefore assume 2.5 lbs with a safety factor

9. Choosing Braces • Shear Strength = 10,500 PSI • With 100 pounds, we would need a cross sectional area of .00952 in^2 or greater to avoid failure • With 2.5 lbs (calculated on previous slide), we would see no failure at all, as the pvc we are using has an area of .256 in^2 • These will ad .172 kg to entire frame, but add .0217 kg-m^2 of inertia (about 20% increase)

10. Plate Selection (Core) • The core material we intend to use is Core-Cell Foam, a boat building and repair supply • Relatively inexpensive • Very strong • Readily attainable • Thin • Low density

11. Plate Selection (Core) • Balsa wood is also a popular core material for composites applications • Deemed to be more expensive • Not as strong • Similarly thin • Higher density than Core-cell

12. Plate Selection (Composite) • SAE Boeing Carbon fiber is our selected coat • Incredibly strong, especially in tension and compression (along the weave) • Very thin • Very consistent • Aesthetically pleasing • Would be expensive (~34.99 per 50” x 30”) • We have a free connection to needed amount

13. Plate Selection (Composite) • Fiberglass was another option for our top coat • Less expensive than carbon, if we had to buy • Not quite as strong • Most fiber weaves are more random • Similar material properties, carbon is free

14. Power Consumption of Electronics • 2 Gyroscopes (L3GD20) – 3.3 V @ 7 mA = .0462 W • 1 Encoder (E5)– 5 V @ 50 mA = .25 W • Current Sensor (ACS714) – .000012 V @ 10 mA = ~negligible • Microcontroller = 0.246mW Total Power = 0.307W

15. Encoder • Requested Specs: <.5 Deg/Sec accuracy (doesn't make sense, since we will go through about 360 Deg in a second) • E5 Encoder: 1024 CpR=.35 Deg sensitivity • E5 Encoder: 292.9 RPS maximum (300KHz max count frequency)

16. Gyroscope • Requested Specs: <.1 Deg/Sec accuracy    • L3GD20: +/- 500 Deg/Sec and 400kHz sampling means resolution of .00125 deg • This is the same Gyro as is currently used in the prototype

17. Batteries • Using NiMH batteries for safety and for voltage matching (1.2V steps), as well as cost (<$3 per battery), ease of replacement, and rechargeablity.

18. Current and Voltage Sensors • No specific specs provided • Sampling rate of 500 Hz depends upon processor • Using error of 2% as spec

19. Motor (part 1) • 14.8 V @ 4.1 Amps • If this motor were on all the time, we would be looking at 61 W, and a cost of transport of approximately 3.36, way over our goal. • Therefore, we would like to estimate the CoT when our motor is only on for 1/10th of a second • CoT = .358

20. Motor (part 2) • There are certain ways to obtain our goal of .05 CoT • We looked at getting a larger motor (increased performance & weight). This decreases the amount of time the motor must be active (1/40th of a second) and increases the denominator of CoT equation. • Can rotate ¼ turn in .00625, but we are accounting for negating torque so we assume .02 seconds (max of 2500 RPMs) • CoT= (90 W*(.02 s)+.5)/(51 N*.5 m)= .9

21. Fasteners

22. Microprocessor Selection

23. Bill of Materials (1)

24. Bill of Materials (2)

25. Bill of Materials (3)

26. Questions/Concerns?