Image Acquisition and Processing of Remotely Sensed Data (ImAP RSD) Dec08-01: Inertial Measurement Unit (IMU) Team: Luis, Julian, Amar, Matt Client: Matthew Nelson - Space Systems and Controls Lab (SSCL) Advisor: Dr. Basart

Presentation Outline Background/History Requirements Specification Project Plan Design Testing/Verification on IMU system Project Evaluation

Background/History

ImAP RSD Motivation Methods of monitoring crop health over large areas are currently cost and labor intensive Airplane Manual Inspection ImAP RSD initiated by SSCL HABET program to develop an improved method of monitoring crop health Automated photography via high-altitude weather balloon Accomplished by integrating multiple subsystems including: Horizon Detection, Inertial Measurement Unit, GPS, Processing, and Camera systems

ImAP RSD Concept Sketch

ImAP System Description The ImAP RSD system will be mounted as a payload attached to a high-altitude weather balloon. The onboard sensor systems will be used to determine payload flight path and orientation This system will capture images at predetermined waypoints using flight prediction software Collected field images will be analyzed to extract image intensities and make geometric corrections The corrected images will be transferred to a plant pathology team who will interpret the images

Horizon Detection System Developed by previous team to determine pitch and roll Thermopile System Compares sky and ground temperatures to determine horizon Image System Aquires images and uses DSP to determine horizon Completed in Spring of 2008

Requirements Specification

Dec08-01 Problem Statement The ISU SSCL requires an Inertial Measurement Unit (IMU) and data logging system for the ImAP RSD project.

Block Diagram

Operating Environment The payload will operate at altitudes from 20,000 – 30,000+ feet The payload will experience temperatures ranging from -40° to 80°C

User Interface RCA power jack Serial Port 11V Serial Port RS-232 BCD to primary processor Logomatic universal data logger SD Card Post Flight Analysis

System Requirements Functional Requirements FR01: IMU shall measure balloon oscillation frequency and angular rotation rate to 1.215 degree per second. FR02: IMU shall measure linear acceleration to 0.01g for each of the three principle axes. FR03: Data logging system shall log at a 100HZ+ rate with 10 bit or greater precision. FR04: IMU shall operate over a temperature range of -25˚ C to +85˚ C Non-functional Requirements NR01: IMU shall receive power from a 11.1V nominal lithium-ion battery NR02: IMU shall function for a minimum of 2 hours using a 4 Amp-hour battery NR03: IMU may measure temperature and voltage levels during flight.

Market Survey: IMU Commercial IMUs SEN-00839 IMU with 2 degrees of freedom for $99.95 Inertia-Link-2400-SK1 IMU for $2795.00 Military grade IMUs Buying an IMU would defeat the purpose of a student project

Deliverables Project Plan √ Design Report √ Final Report Project Poster √ IRP Presentation IMU √ IMU User Manual √

Project Plan

Work Breakdown Structure: S08 Personnel Gyro and Accelerome ter Research Microcontr oller and Flash Memory Research Gyro and Accelerome ter testing Microcontr oller and Flash Memory Testing/Pro gramming Operational Manual Documenta tion, planning & organizatio n Total Hours Luis 20 10 18 30 118 Julian 35 115 Matt 25 8 15 113 Amardeep Total 75 48 70 88 80 100 461

Work Breakdown Structure: F08 Personnel IMU Circuit Board Design & Testing for Data Acquisition Gyro and Accelerometer Calibration System Integration Operational Manual Documentati on, planning & organization Total Hours Luis 30 25 20 125 Julian 50 7 35 132 Matt 15 120 Amardeep 40 10 Total 150 92 85 90 502

Resource Requirements Estimated Hours Estimated Cost ***Insert Parts list cost

Project Schedule: S08

Project Schedule: F08

Risks Unfavorable weather Power Failure Continue or cancel mission Schedule another flight

Design

Theory of Operation An accelerometer coupled with a rate gyro can efficiently be used for attitude determination purposes. Rate gyros measure angular rotation rates. By subtracting out known linear accelerations, an accelerometer can be use as a tilt measurement device. These two angles can be combined in an optimal fashion to accurately determine attitude.

Pendulum Model of HABET system The HABET balloon and payload system has been modeled as a simple, 2-D rigid pendulum. From this model we can determine angular rates, as well as the normal and tangential components of acceleration that the payload will experience.

Rate Gyro Model The equation of motion on the left can be numerically integrated to obtain rotational rates. This model is only for roll/pitch rates. These rotational rates will help us choose the appropriate rate gyro for our project. We have simulated this model on Simulink. The results follow. Fig. Model for determining roll/pitch rates.

Rate Gyro Simulink Model

Rate Gyro Simulink Results Roll/pitch rates under 75°/sec. From past data, we have determined that yaw rates typically range from 20°- 50°. FFT results suggest a sampling rate greater than 90Hz. Conclusion: Rotational rates and sampling rate obtained from math model meet functional requirements. Rate gyro used in this project, MLX90906, measures 300deg/sec, which satisfies both functional requirements and math model.

Accelerometer Model By assuming a simple pendulum, the acceleration equation reduces to the one boxed in red. This equation measures tangential and normal components of acceleration. These acceleration values will help us choose the appropriate accelerometer for our project. We have simulated this model on Simulink. The results follow.

Accelerometer Simulink Model

Accelerometer Simulink Results Greatest magnitude of acceleration expected is under 1.5g. FFT results suggest a sampling rate greater than 80Hz. Conclusion: Acceleration and sampling rate obtained from math model agree with our functional requirements. Accelerometer used in this project, MMA7260Q, measures ±2g’s, which satisfies both functional requirements and math model.

Data Storage Space and We are required to log for a maximum of 3 hours. A 1 GB SD Card will be used for data storage Using a baud rate of 19200 symbols/sec, we can log for approximately 28 hrs (maximum) at this rate

Electric schematic

Mechanical CAD of IMU Casing and PCB boards

Power Budget Device Maximum I [A] Quantity Flight Duration [hr] Amp-Hours MMA7260Q Accelerometer .0008 1 3 .0024 MLX90609 Gyroscope .02 .18 ATMega128 .019 .057 Logomatic .08 .24 LM78XX Voltage Regulator .008 .024 The power budget for the IMU components totals at .5034 Amp-Hours and will be powered by a 4.8 Amp-Hour battery leaving 4.2966 Amp-Hours for other systems.

Software Flow

Testing/Verification of IMU system

Rate Gyro Testing/Calibration EMI effects: Electromagnetic interference degrades or obstructs the performance of the circuit. Output verification using test platform: Encoder test platform  Rate gyro  angular rate We compare it by differentiate and angular rate

Accelerometer Testing/Calibration EMI Shielding: Electromagnetic interference degrades or obstructs the performance of the circuit. Tilt measurement using test platform:

Test Platform Rotations Maximum 400deg/s

Test Platform Accelerations

Accelerometer Tilt Angle Measurements

Project Evaluation

Earned Value Analysis Spring 2008 Tasks Budgeted Hours Actual Hours BCWS BCWP ACWP IMU Research 75 72 $750.00 $720.00 MCU Research 48 42 $480.00 $455.00 $420.00 Sensor Testing 70 $700.00 $684.00 Programming/SW Debugging 88 760 $880.00 $810.00 $760.00 Documentation 100 109 $1,000.00 $984.00 $1,090.00 Subtotal $3,810.00 $3,683.00 $3,740.00 Fall 200 IMU Design 150 173 $1,500.00 $1,430.00 $1,730.00 Testing/Data Acquisition 92 123 $920.00 $850.00 $1,230.00 Sensor Calibration 85 46 $460.00 System Integration 90 104 $900.00 $1,040.00 Operation Manual 60 $815.00 $820.00 $5,020.00 $4,755.00 $5,280.00 Total $8,830.00 $8,438.00 $9,020.00

Earned Value Analysis

Earned Value Analysis Schedule Variance BCWP-BCWS -$392 Behind Schedule Cost Variance BCWP-ACWP -$582 Over Budget Cost Performance Index BCWP/ACWP 0.935476718 Schedule Performance Index BCWP/BCWS 0.955605889

Conclusion/Lessons Learned We spent more hours on the project than anticipated. The system integration and debugging consumed most of our time. We tried to make the system as simple as possible. The assumptions can be wrong for the same component made by different supplier and buffers for this should be accounted. Ask for expert help sooner.

References Dynamics of Flight, Stability and Control; B. Etkin, L. Reid. John Wiley and Sons, 1996 Aurzkai et al. ImAP Fall 2007

Appendix

Euler angle rates: p,q,r are angular rates measured by the rate gyro in the body frame. To transform into the inertial frame, we utilize the transformation matrix, T. We run this through RK4 and produce the desired angles, and thus the payload attitude.

Acceleration on a point b with respect to CM on an arbitrary object.

Tilt Calculations Vout = Output of Accelerometer Voffset = 0g offset of Accelerometer 1g = Earths Gravity = Angle of tilt

Hardware 3 MLX90609 1-axis Gyroscope 1 ADXL330 3-axis Accelerometer 1 GB SD Card 1 Atmel Mega 128 Processor 1 Logomatic SD Data Logger Various Electrical components (resistors, capacitors, etc)

Hardware: MLX90609: Gyroscope Requirement: Measure angular rotation to 300 degrees per second for each of the three principle axes(FR:01). Operational temperature: -40°-85°C(FR:06). Reasons for choosing this part: The MLX90609 is a 1 axes gyro that includes a breakout board for evaluation purposes. Measures 300 °/s which is not excessive and will not have resolution issues, but also measures more than the required specifications. Low Price: $59.95 The selling point of this gyro is the angular rate measurement and the temperature range. Rate Gyro MLX90609 ADXRS150 IDG-300 Full Range ± 300 °/s ± 150 °/s ± 500 °/s Noise Performance 0.03 °/s/√Hz 0.05 °/s/√Hz 0.014 °/s/√Hz Sensitivity 0.006V/°/s .001 V/°/s 0.002 V/°/s Temperature Range -40°-85°C 0°-70°C Price $ 59.95 $ 69.95 $ 74.95

Hardware: ADXL330 (Accelerometer) Requirements: Measures linear acceleration to 0.01g for each of the three principle axes(FR:02). Operational temperature: -40°-85°C(FR:06). Reasons for choosing this part: Includes a breakout board which will make the evaluation process easier. Very low noise density: 280μg/√Hz rms Very good sensitivity change due to temperature: ± 0.015%/°C Non-linearity: ±0.3 Low Price: $34.95 Accelerometer ADXL330 LIS3LV02DQ MMA7260Q Full Scale ± 3.6g ± 2g ± 1.5g Sensitivity Vs Temperature .015 %/°C .025 %/°C .03 %/°C Non-Linearity ±0.3% ± 3% ± 1% Price $34.95 $43.95 $ 39.95

Hardware: Atmel Mega 128 Microprocessor Requirements: Power and weight Reasons for choosing the part: light weight price Microcontroller Atmel mega 128 Pic 18 series Throughput 16 Mhz 10Mhz Flash program memory 128 KBytes N/A On chip RAM 4 KBytes 512 – 16384 Bytes Price $100 $129

Hardware: Logomatic Serial SD Data Logger Requirements: We needed some system that had the FAT system ready to use. There is a lot of code that has to be written to be able read anything legible from the SD card Reasons for Choosing this Part: Automatically logs incoming data from the UART (saves time, and power) Comes with a lot of FAT16/32 code for free on Sparkfun.com (saves a lot more time) Has a place holder for the SD card which saves spaces An alternative was the DosOnChip ($44.95) board which also utilizes a FAT system , but it has really poor documentation and is unavailable indefinitely. Price: $59.95