Zero Tilt Preliminary Design Review

1. Zero TiltPreliminary Design Review Frostburg State University Adam Rexroad, Brett Dugan, Mayowa Ogundipe, Kaetie Combs, Michael Stevenson, Daniel Gares, Tyler Lemmert, Subhasis Ghosh, Jared Hughes, Sean Hughes, Andrew Huntley, Derek Val-Addo October 26, 2011

2. Mission Overview

3. Mission Overview • Mission Statement: Zero Tilt’s goal is to provide, for the first time, a stable environment throughout the flight of a Sounding Rocket via two concurrent objectives: • Tilt correction system • Despun platform system

4. Mission Overview • We plan to: • Counteract the platform spin • Orient the platform parallel to the earth’s surface at all times • Confirm the altitude reading using an accelerometer on our platform • We expect to prove that it is possible to correct spin, tilt, and determine the altitude based upon a level reference. • This could benefit any scientific experiment that requires stabilization in order to collect data.

5. Mission Overview: Theory and Concepts • The underlying theory and concepts: • negative feedback control systems • concepts of torque and centripetal force • Micro electromechanical systems (MEMS) • Electromagnetic field theory • Real-Time Systems Theory (for multi-tasking)

6. Past Research • Drexel University’s 2011 project incorporating a despun platform. The Results have not been published but the CDR offered evidence of successful trial runs at large stress. • We plan to elaborate on Drexel’s design. Modifying and improving the despun platform design in our project.

7. Mission Overview: Mission Requirements • Mission Objectives: • Counter the spin of the rocket during flight. • Keep a level surface to earth using our conceptual design. • Prove successful by comparing the acceleration data from our zero tilt platform with that from the plate. • Minimum success criteria • Our main goals as the Zero Tilt team is to receive results indicating that we achieved zero tilt and confirming the altitude. crestock.com

8. Mission Overview: Expected Results • What we expect: • Determine whether we were successful in keeping our platform level based on data analysis. (within a 10°tolerance) • Find altitude within a reasonable tolerance again based on the data we collect.

9. Theory • Radial Acceleration The max rate of spin of the rocket is 5.6Hz 5.6Hz(2π)= 35.18 rad/sec arad=146 m/s²=16g

10. Theory (Cont.) • Roll, α • X = 0 • Y = cos(α) • Z = sin(α) • Pitch, β • X = cos(β) • Y = 0 • Z = sin(β) • Yaw, γ • X = cos(γ) • Y = sin(γ) • Z = 0

11. Theory (Cont.) • Converting to Spherical Coordinates

12. Expected Results • Counter the rotation • Speeds up 8Hz • Stay within +- 5% the actual speed • Zero tilt • Keep the plate level • Stay with in +- 10% of level • General Goals • Meet all NASA requirements • Fast respond time • Reliable data collection • Reliable circuitry

13. Zero Tilt ConOps t ≈ 1.7 min Altitude: 95 km t ≈ 4.0 min Altitude: 95 km t ≈ 1.3 min Altitude: 75 km Apogee t ≈ 2.8 min Altitude: ≈115 km t ≈ 4.5 min Altitude: 75 km -use the position of the zero tilt plate as initial value for the gyroscope sensor. -switch to gyro input for zero tilt system. t ≈ 5.5 min Chute Deploys -G switch triggered -All systems on -Initialize despin system -Initialize zero tilt system based on magnetometer. t = 0 min t ≈ 15 min Splash Down

14. Subsystems

15. Despun Platform Subsystem

16. Subsystem Requirements • The platform will be able to keep the platform parallel to the Earth independently of the rockets orientation. • All electrical components must be wired to a battery source without twisting the wires. • The assembly must be contained within the size requirements.

17. Subsystem Components • Motors • Drive motor • Tilt motor • Spin motor • Gears • Drive Gear • Main Gear • Gimbal • Platform • Slip ring • Center shaft • Bearings • Spin bearing • Tilt bearing

18. Diagram Spin motor Drive gear Main gear Slip ring Drive motor Center shaft Tilt bearing Gimbal Platform Tilt motor Spin bearing

19. Gears Gear 1 is the drive motor. It will be 1” in diameter. Gear two is the main gear and will be 6.5” in diameter. This will make the gear ration 6.5:1. Both gear will be made of 7075 Aluminum machined in-house. http://www.daerospace.com/MechanicalSystems/GearsDesc.php

20. Torque • The torque required by the drive motor was calculated through the following equation. • = The calculated torque is 5.0152mNm based on G force 25 and 360 maximum rpm.

21. Gimbal • The Gimbal will support the platform and spin with the assembly. This component will be made out of 7075 Aluminum.

22. Platform • The platform will be made of polycarbonate and will hold the microprocessor. The microprocessor and components to control the tilt and The tilt motor will also be embedded in the platform. • The platform will have a hollow shaft which runs through it, this will allow the wires to be run of the board and onto the gimbal. The tilt motor will act as a bearing at one end, while the hollow shaft will be encased in a bearing on the other end as it enters into the gimbal.

23. Slip RingAeroflex CAY-1398 ELECTRICAL 1. Contacts: Gold on gold 2. Bearings: Precision ball bearings 3 Dielectric Material: High grade epoxy 4. Torque: .20 in.-oz. maximum (12 rings) 5. Speed: 1000 rpm maximum, intermittent 6. Life: 30 x 106 revs min. @ 100 rpm 7. Rotation: Bi-directional 8. Frame: Stainless steel MECHANIAL 1. No. of Rings: 12 maximum 2. Current: 1 amp maximum 3. Voltage: up to 150 volts 4. Dielectric Strength: 500 vrms, all combinations 5. Contact Resistance Variation: Less than 10 milliohms 6. Leadwire: #30 awg, teflon insulated

24. Center Shaft • The center shaft will encase the slip ring. This will not only take the force off of the slip ring, but also act as a gear for the spin motor. Teeth will be machines to the outside of the shaft to allow the gear on the spin servo to adjust the yaw of the gimbal.

25. Bearings • There are two bearings included in this design. The first is the bearing located in the gimbal which allows the platform to rotate. This will be a very small grade 5 or 7 ball bearing. • The second bearing supports the gimbal. It is a grade 5 ball bearing.

26. Materials • There were four materials considered for this project. • Aluminum • Pros - light weight • Cons – low shear strength • Steel • Pros – easy to machine • Cons – high density

27. Materials (cont.) • Titanium • Pros – very strong • Cons – high density, expensive • Polycarbonate • Pros – Very high tensile strength • Cons – not rigid After considering all of the materials chosen, Aluminum and polycarbonate were chosen as our materials. The poly carbonate was chosen for the platform material because of its light weight and strength. Aircraft grade aluminum was chosen for the gears and gimbal because it has a high strength and light weight.

28. Design Changes • In the conceptual design, thrust bearing were going to be used to keep the rotating parts stable. Due to the compact size of the rotating parts, using a ball bearing should be sufficient in stabilizing these parts. By not using the thrust bearing the friction will be kept to a minimum.

29. 2D Design

30. Risk Matrix • DP.RSK.1 • Gear teeth shear off • DP.RSK.2 • Main gear flexes until it no longer makes contact with drive gear • DP.RSK.3 • Wires snag or twist and break • DP.RSK.4 • Assembly becomes off balance and wobles • DP.RSK.5 • Two points of rotation bind

31. Zero Tilt System

32. Zero Tilt Definition • System Components: • Gimbal, “Goal Post” structure now moved to underneath the despun platform. • Servo Motors • One will make adjustments in spin so that the long side of the plate is parallel with the direction of the rocket. • One will correct the tilt relative to the earth’s surface. • Microprocessor and Gyroscope • Gyro will send data for tilt correction (spin and tilt) to the microprocessor. • Microprocessor will forward the data it receives to the two servo motors.

33. Zero Tilt Description • Servos • Servo 1 attached directly to shaft to resolve spin. • Servo 2 attached to side of gimbal to resolve tilt. • Zero Tilt Gear • Weight should not be a concern on the tilt platform. Therefore the torque produced in a one to one gear ratio between motor and tilt gear should be sufficient. • Fabrication • Currently have a prototype of the zero tilt platfrom made from polycarbonate. • Hoping to use the same material for tilt gear. (all manufactured in-house)

34. Zero Tilt Requirements

35. Zero Tilt System Gyroscope Study

36. Zero Tilt selected Gyro (L3G4200D) • Three selectable full scales (250/500/2000dps) • I2C/SPI digital output interface • 16 bit-rate value data output • 8-bit temperature data output • Two digital output lines (interrupt and data ready) • Integrated low- and high-pass filters with user selectable bandwidth • Ultra-stable over temperature and time • Wide supply voltage: 2.4 V to 3.6 V • Low voltage-compatible IOs (1.8 V)

37. Gyroscope Schematic

38. Zero Tilt (ZT) Risk Matrix • ZT.RSK.1 • All of the risks associated with the despun platform • ZT.RSK.2 • Servo motors will not be able to keep up initially. • ZT.RSK.3 • Vibrations will destroy gimbal arms or ZT platform • ZT.RSK.4 • High Gs will cause disrupted platform adjustment • ZT.RSK.5 • Stress on joining areas resulting in breaking.

39. Data Subsystem

40. Data Subsystem Accelerometer 2 Digital to Analog Converter Motor Accelerometer 1 Microcontroller Power Supply Servo φ Slip Ring Microcontroller Gyroscope Servo θ

41. Gyroscope Vs. Accelerometers • Tilt Sensor • The cost and availability are both 10 because they are both less then $15. • The Gyroscope filterers out Angular Rate Noise • The Gyroscope has faster and easier calculations

42. Gyroscope Vs. Accelerometers • Spin Sensor • The cost and availability are both 10 because they are both less then $15. • The max rate of spin of the rocket is 5.6 HZ. This means the accelerometer need to read up 16 G • The ADXL278 has a range of ±37g. • The gyroscope will need to be able to read up to 2016 dps

43. Low g Accelerometer for Initializing Zero-Tilt • Accelerometers: ADXL203 vs. ADXL278 • The cost and availability are both 10 because they are both less then $15. • The range is ok for the ADXL203 and the ADXL278. The ADXL has a range of ±1.7g which gives it more accurate low g readings. The ADXL278 has a range of ±37g which collects more accurate high g readings. • The power supply for the ADXL203 is between 3 and 6 volts which gives a wider range of voltage than the ADXL278 which has a voltage range of 3.5 to 6. • The ADXL203 is a better fit for initializing zero-tilt.

44. High g Accelerometer for Determining Angular Velocity • Accelerometers: ADXL203 vs. ADXL278 • The cost and availability are both 10 because they are both less then $15. • The range is better for the ADXL278 since it can collect high g readings. • Although the ADXL203 has a better accuracy, it will not be taking readings in a high g range so accuracy it N/A. The ADXL278 is not as accurate but it will meet our requirements. • The power supply for the ADXL203 is between 3 and 6 volts which gives a wider range of voltage than the ADXL278 which has a voltage range of 3.5 to 6. • The ADXL278 is a better fit for determining angular velocity.

45. Block Diagrams ADXL203 ADXL278

46. DS - Analog to Digital Conversion • Our electronic system requires a conversion from Digital to Analog signals for our motors. • A Digital to Analogconvertor (DAC) is needed

47. Data Processing • ATMEGA32-16PU-ND: we chose this chip due to its operating temperature and its compatibility with our devices and program language. • This chip is also familiar to our team, the previous model was used in our mentors Rockon project and have been extensively researched. • Having been used in the Rockon project we know that the stresses the chip undergoes will not produce an undesirable outcome.

48. DS - Risk Matrix • DS.RSK.1 • Microcontroller Power Fails • DS.RSK.2 • Motor Communication Fails • DS.RSK.3 • Stationary Accelerometer Communication Fails • DS.RSK.4 • Motor fails in measuring own speed. • DS.RSK.5 • Microcontroller can’t survive launch conditions. • DS.RSK.6 • Communication between despun and zero tilt systems fail.

49. Motor Subsystem

50. Motors The motor subsystem is divided in to two sub systems: • Motor for de-spinning the platform • Motors for adjusting the tilt of the platform and turning the gimbal