Zero TiltPreliminary Design Review
Frostburg State UniversityAdam 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
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Mission Overview
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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
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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.
4
Mission Overview
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)
5
Mission Overview: Theory and Concepts
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.
6
Past Research
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.
7
Mission Overview: Mission Requirements
crestock.com
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.
8
Mission Overview: Expected Results
Radial Acceleration
The max rate of spin of the rocket is 5.6Hz5.6Hz(2π)= 35.18 rad/secarad =146 m/s²=16g
Theory
Roll, αo X = 0o Y = cos(α)o Z = sin(α)
Pitch, βo X = cos(β)o Y = 0o Z = sin(β)
Yaw, γo X = cos(γ)o Y = sin(γ)o Z = 0
Theory (Cont.)
Converting to Spherical Coordinates
Theory (Cont.)
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
Expected Results
Zero Tilt ConOps
t ≈ 1.3 min Altitude: 75
km
t ≈ 15 min
Splash Down
t ≈ 1.7 min
Altitude: 95 km
-G switch triggered
-All systems on
-Initialize despin system
-Initialize zero tilt system based on magnetometer.
t = 0 min
t ≈ 4.0 min
Altitude: 95 kmApogee
t ≈ 2.8 min Altitude: ≈115 km
t ≈ 4.5 min
Altitude: 75 km
t ≈ 5.5 min
Chute Deploys
-use the position of the zero tilt plate as initial value for the gyroscope sensor.-switch to gyro input for zero tilt system.
Subsystems
Despun Platform
Zero-Tilt Data Motors Power
Gears Gimbal Micro-controller
DC motors Batteries
Materials Gears Memory Servo-Motors
Voltage Regulators
Slip Ring Gyroscope Accel-erometers
Motor Speed
Controller
Arming
Algorithms DAC
Despun Platform Subsystem
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.
Subsystem Components1. Motors
1. Drive motor2. Tilt motor3. Spin motor
2. Gears1. Drive Gear2. Main Gear
3. Gimbal 4. Platform5. Slip ring6. Center shaft7. Bearings
1. Spin bearing2. Tilt bearing
Diagram
Main gear
Drive motor
Spin motor
Tilt motor
Drive gear
Gimbal
Platform
Slip ring
Center shaft
Spin bearing
Tilt bearing
Gears
http://www.daerospace.com/MechanicalSystems/GearsDesc.php
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.
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.
Gimbal
The Gimbal will support the platform and spin with the assembly. This component will be made out of 7075 Aluminum.
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.
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
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.
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.
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
◦ 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.
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Materials (cont.)
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.
2D Design
2.6250
2.8750
2.50003.2500
0.2500
2.7500 2.0000
0.25001.0000
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
PROBABILITY
CONSEQUENCES
DP.RSK.3
DP.RSK.4
DP.RSK.1
DP.RSK.2
DP.RSK.5
Zero Tilt System
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.
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)
Zero Tilt RequirementsNumber of Requirement
Description of requirement
1 Initially we hope to be able to rotate the platform 360°. This is to ensure it remains stable through the entire flight.
2 Microprocessor should be able to pass minimum voltage requirement of 2.4V to gyroscope.
3 Microprocessor should be able to pass minimum voltage requirement of 2.4V to gyroscope.
4 Gimbal, Platform, and components shall survive the intital shock and 25g in flight acceleration.
5 The platform will be balanced to conform to center of gravity constraints,
6 The platform will be within specified design constraints. Preliminarily < 2 inches in height and 4 inches in diameter,
7 Servo motors are adequately powered and provided with correction data in appropriate time frame.
Zero Tilt System Gyroscope StudyCharacteristic L3G4200D (digital) LPR403AL (analog)Voltage Requirement 9 7
Current Requirement 9 7
Process speed 8 10Angular Rate Noise Density
7 9
Self-Test Capable 7 10Survivability( shock, g’s)
10 10
Availability 8 8Size 10 8Cost 8 10
Total (out of 100) 85 84
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)
Gyroscope Schematic
37
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.
Data Subsystem
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Data Subsystem
Accelerometer 1
Accelerometer 2
Microcontroller
Power Supply
Digital to Analog
Converter
Slip Ring
Gyroscope Microcontroller
Motor
Servo φ
Servo θ
Gyroscope Vs. Accelerometers
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• Tilt SensorGyro vs. Accel Gyroscope Accelerometer
Cost 10 10
Availability 10 10
Noise 8 2
Range 10 10
Accuracy 10 8
Power Supply 8 8
Average: 9.3 8
• 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
Gyroscope Vs. Accelerometers
42
• Spin Sensor
Gyro vs. Accel Gyroscope Accelerometer
Cost 10 10Availability 10 10
Range 0 10Accuracy 8 8
Power Supply 10 8Average: 7.6 8
• 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
Low g Accelerometer for Initializing Zero-Tilt
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• Accelerometers: ADXL203 vs. ADXL278Accelerometer ADXL203 ADXL278
Cost 10 10Availability 10 10
Range 10 10Accuracy 10 2
Power Supply 10 8Average: 10 8
• 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.
High g Accelerometer for Determining Angular Velocity
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• Accelerometers: ADXL203 vs. ADXL278Accelerometer ADXL203 ADXL278
Cost 10 10Availability 10 10
Range 0 10Accuracy N/A 8
Power Supply 10 8Average: 7.5 9.2
• 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.
Block Diagrams
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ADXL278
ADXL203
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Our electronic system requires a conversion from Digital to Analog signals for our motors.
A Digital to Analog convertor (DAC) is needed
DS - Analog to Digital Conversion
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.
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Data Processing
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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.
PROBABILITYCONSEQUENCES
DS.RSK.1
DS.RSK.2
DS.RSK.5
DS.RSK.3
DS.RSK.4
DS.RSK.6
Motor Subsystem
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
De-spinning the platform
Requirement for motor 0 (despun motor) The rocket is estimated to spin at 5.6 Hz
(336 rpm) Requirements:
Current < .4A Voltage < 30V Torque < 5.0152mNm Max. Height < 2.75in
MS – Trade Study
Specification
System Requireme
nts
2232…BX4 S
3268...BX4 SC
3268...BX4 SCDC
RPM 12,100 rpm 5,500 rpm 4,500 rpmVoltage < 30V 24V 24V 24V
Amperage <.4A .088A .215A .210ATorque < 5.0152
mNm29.4mNm 137mNm 137mNm
Height < 2.75in 1.95in 3.36in 3.36inCost n/a n/a $383.90 n/a
Brushed/Brushless
Brushless Brushless Brushless
MS – Selected Motor
3268...BX4 SC Brushless DC-Motor from Faulhaber.
Criteria Selection: possible PWM controllability. Ease of use.
Technology 4 pole brushless motorHas an integrated speed controller. Pre-configured to a continuous current. integrated feedback system.
MS – Risk Matrix MS.RSK.1
◦ Required Torque exceeds stall torque
MS.RSK.2◦ Motor-Battery
Communication Failure MS.RSK.3
◦ Motor gear head and platform may lose contact under 25G
MS.RSK.4◦ Battery unable to sustain
variable rpm requirements MS.RSK.5
◦ Motor may not respond to the micro-controller signals correctly.
Consequence
MS.RSK.5 MS.RSK.3 MS.RSK.2
MS.RSK.1 MS.RSK.4
Possibility
Adjusting the platform tilt
Requirement for motor 1 (tilt motor) We estimate no more than 20 degrees/sec. Requirements:
Current < .3A Voltage = 5-6V Torque approximately 400mNm Max. Height < 3in
MS – Trade StudySpecificatio
nSystem
Requirements
HS-5245MG AM2224-R3
Series 3056(Stepper Motor)
RPM 360 83.33 rpm 5,500 rpm 8790 rpm
Voltage 5-6V 4.8-6.0 Volts 1.4V 12V
Amperage <.3A .18A 1 A .168A
Torque 400 mNm 567mNm 22 mNm 95mNm
Height < 3in 1.54in 1.98in 2.64in
Cost n/a $70.00 n/a n/a
Control PWM Separate Encoder
Separate Motor Controller
MS – Selected Motor
HS-5245MG Digital Mini Motor from ServoCity.
Criteria Selection: High standing torque PWM controllability Ease of use.
TechnologyHas an integrated speed controller. 360 degree continuous rotation.
MS – Risk Matrix MS.RSK.1
◦ Required Torque exceeds stall torque
MS.RSK.2◦ Motor-Battery
Communication Failure MS.RSK.3
◦ Motor gear head and platform may lose contact under 25G
MS.RSK.4◦ Battery unable to sustain
variable rpm requirements MS.RSK.5
◦ Motor may not respond to the micro-controller signals correctly.
Consequence
MS.RSK.5 MS.RSK.3 MS.RSK.2
MS.RSK.1 MS.RSK.4
Possibility
Adjusting the platform turn
Requirement for motor 2 (turn motor) Requirements:
Current < .3A Voltage = 5-6V Torque approximately 400mNm Max. Height < 3in
MS – Trade Study
Specification
System Requireme
nts
HSR-1425CR
AM2224-R3
Series 3056(Stepper Motor)
RPM N/A 52 rpm 5,500 rpm
8790 rpm
Voltage 5-6V 6 Volts 1.4V 12V
Amperage <.3A .12A 1 A .168ATorque 400 mNm 330mNm 22 mNm 95mNmHeight < 3in 1.59in 1.98in 2.64inCost n/a $0.00 n/a n/a
Control PWM Separate Encoder
Separate Motor Controller
MS – Selected Motor
HSR-1425CR Robotic servomotor. Criteria Selection:
High standing torque PWM controllability Ease of use.
TechnologyHas an integrated speed controller. 360 degree continuous rotation.
MS – Risk Matrix MS.RSK.1
◦ Required Torque exceeds stall torque
MS.RSK.2◦ Motor-Battery
Communication Failure MS.RSK.3
◦ Motor gear head and platform may lose contact under 25G
MS.RSK.4◦ Battery unable to sustain
variable rpm requirements MS.RSK.5
◦ Motor may not respond to the micro-controller signals correctly.
Consequence
MS.RSK.5 MS.RSK.3 MS.RSK.2
MS.RSK.1 MS.RSK.4
Possibility
Power
Battery 9 Volt Lithium
Voltage Regulators
• 5V • 3.3V
Who are you sharing with?◦ Harting
Plan for collaboration◦ Communicated through email◦ We shall share designs and
ideas through email We are still working on the
structural interface with them but have decided upon position in the cannister. Harting will be above us below. (plate in between)
66
Sharing Logistics
grandpmr.com
Project Management Plan
67
68
Organizational ChartProject Manager
Kaetie CombsMentors
Adam RexroadBrett Dugan
Faculty AdvisorDr. Mohammed Eltayeb
Despun PlatformDaniel Gares
Tyler LemmertKaetie Combs
Zero Tilt PlatformMichael Stevenson
Daniel GaresAndrew Huntley
SensorsKaetie CombsTyler Lemmert
Andrew HuntleyMichael Stevenson
Data SystemJared HughesSean Hughes
Mayowa OgundipeDerek Val-Addo
Breakdown of Sub-Systems
69
Despun Platform
Zero Tilt Platform
Data Systems Sensors
Design:
Daniel GaresKaetie CombsTyler Lemmert
Gears:
Tyler Lemmert
Design:
Daniel GaresMike Stevenson Andrew Huntley
Everybody will be involved with programming.
Processors: Jared HughesSean Hughes
Motors:
Mayowa OgundipeVal-AddoSubhasis Ghosh
Accelerometers: Kaetie CombsTyler Lemmert
Gyroscope:
Mike StevensonAndrew Huntley
Schedule
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Tentative Schedule
• Finalize Design
• Beginning of November: Start ordering parts
• Now until end of semester: Start testing electric components, test gyroscope output, test accelerometer outputs, test servo response, make sure we are able to supply necessary power, and complete despun subsystem.
• Next semester
• End of February: Zero Tilt platform completed• For the rest of the semester we will continue testing and
correcting problems to prepare for the launch in June.
Budget
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Item Part Number
Manufacturer
Vendor
Quantity
Price (each)
Total
Dual Axis High-G Accelerometer
AD22284 Analog Devices Analog Devices
2 12 24
Dual AxisLow-GAccelerometer
AD220372 Analog Devices Analog Devices
1 10 10
Microprocessor ATMEGA32-16PU Atmel Digikey 2 8.28 14.56
Slip Ring CAY-1398 Aeroflex Aeroflex 1 As of yet unknown
~300
Gyroscope L3G4200D ST Microsystems Arrow 3 15 45
DC Despin Motor 3268BX4SC FaulHaber Micromo 1 383.90 383.90
Tilt Servo motor HS-5245MG Hitec Servocity 1 70 70
Spin Servo HSR-1425CR Hitec In house 2 In house 0
Flash Memory AT26DF161A Atmel Digi-key 2 4 8
Components still under researchRaw materials
Total Ceiling 1500
Breakdown of Sub-Systems
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Despun Platform
Zero Tilt Platform
Data Systems Sensors
Design:
Daniel GaresKaetie CombsTyler Lemmert
Gears:
Tyler Lemmert
Design:
Daniel GaresMike Stevenson Andrew Huntley
Everybody will be involved with programming.
Processors: Jared HughesSean Hughes
Motors:
Mayowa OgundipeVal-AddoSubhasis Ghosh
Accelerometers: Kaetie CombsTyler Lemmert
Gyroscope:
Mike StevensonAndrew Huntley
We hope to order 90% of the materials required and begin fabrication of the gears.
We need to solidify our power requirements as well as our electric circuitry.
We must test our materials for weight and decide if our current materials will handle the stresses of rocket flight.
We intend to finalize our budget and remain within our $1500 ceiling.
Determine how fast the rocket changes angle with respect to starting position.
73
Conclusion
