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Drexel University 2010-2011 RockSat-CPreliminary Design Review
Joe MozloomEric MarzLinda McLaughlinSwati MainiSwapnil MengawadeAdvisor: Jin Kang, PhD
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Mission Overview - Objective
Drexel's RockSat payload will incorporate a platform rotating opposite the spin-stabilization of the Terrier-Orion sounding rocket during ascent, resulting in a rotationally static platform from an outside reference frame.
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Mission Overview - Purpose
Experimentally determine the feasibility of a despun platform under high acceleration and turbulence, driven by a low power system.
Provide a stable platform with respect to the exterior environment to accommodate experiments requiring constant frame of reference in an ascending object.
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Mission Overview - Theory
Angular Velocity ω = dθ / dt At 5.6 Hz
ω = 35.18 rad/sec Radial Acceleration
ar = ω2 r At 35.18 rad/sec With 0.0635 meter Radius
ar = 78.62 m/s2 = 8 g
ω
ar
at
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Expected Results
WORKBENCH Meet all NASA / WFF
requirements Counter-rotating platform
effective from 0.5 Hz - 10 Hz Maximum platform spin-rate
10% of current canister spin-rate
Data is reliably collected and is usable
FLIGHT Meet all NASA / WFF
requirements Counter-rotating platform
engaged when canister is spinning
Platform able to rotate under harsh flight conditions
Data is reliably collected and is usable
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Preliminary Design
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Concept of Operations
There are several flight points which are of interest to our experiment (Seen on next slide)
Rotation measurements of despun platform during following time periods: Terrier Burnout Orion Burnout Remaining Ascent Descent
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Concept of Operations
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Subsystem Definitions
Despun Platform(DP)
Motor Systems(MS)
Data Systems(DS)
Power Systems(PS)
Slip Ring Despun Gear
DC Micro-motor Pinion
Microcontroller Memory Accelerometers Algorithms
Batteries Voltage Regulators G-Switch
Despun Platform Subsystem
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Despun Platform Definition
System Components Through-Bore Slip Ring Slip Ring Fastener
Undefined until Slip Ring is selected May be unnecessary if mounting holes can be drilled into
slip ring Despun Plate/Cog 2-axis, High-G Accelerometer
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DP - Subsystem Description
4:1 Gear Ratio between platform and motor pinion Reduces torque needed by motor
Despun gear nominal dimension of 5” (127 mm)
Gear to be CNC cut from ¼” (6.35 mm) polycarbonate Fabricated In-House
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DP - Subsystem Requirements
# Requirement
1 Platform shall be able to rotate at > 500 RPM
2 System shall be able to pass ≈ 2.2 mA from microcontroller to accelerometer
3 System shall be able to pass ≈ 5 V from microcontroller to accelerometer
4 Slip ring shall include > 5 circuits for data and power transmission
5 System shall perform throughout 25g acceleration
6 System shall allow for center standoff
7 Platform shall be < 7”
DP - Slip Ring Trade Study
Slip Ring JinpatLPT012
AeroflexCAY-1847
AeroflexCAY-1666
Max RPM 6 6 10
Max Voltage 10 10 10
Max Amperage 10 10 10
Through Bore 9 8 9
Height 7 7 7
Mass 7 9 8
Cost 10 7 2
Availability 3 9 9
Max Vertical Load 6 8 8
Torque 6 7 7
Totals 75 81 80
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DP - Selected Slip Ring
Aeroflex Airflyte CAY 1847 Max RPM: 500 Through-Bore Diameter: 3/8” =9.525 mm Length: 1.3” = 33.03 mm Stator Diameter: 1.25” = 31.75 mm # of Circuits: 18 Max Voltage: 210 V Max Current: 2A/Circuit Cost; $400
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DP - Risk Matrix
DP.RSK.1 Sensor will not function
DP.RSK.2 Teeth on gear will break due to
elevated torque levels from acceleration
DP.RSK.3 Vibrations will cause loss of contact
in Slip Ring Terminals DP.RSK.4
High Gs will cause slip ring bearings to seize
DP.RSK.5 High Load causes gear to distort,
losing contact with pinion
PROBABILITY
CONSEQUENCES
DP.RSK.3DP.RSK.5 DP.RSK.4
DP.RSK.1 DP.RSK.2
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Data Subsystem
Power Supply
StationaryAccelerometer Microcontroller
DespunAccelerometer Slip Ring
Digital to AnalogConverter Motor
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DS - Accelerometer vs. Gyroscope
Accelerometer GyroscopeRange 10 2
Resolution 5 5
Ease of Calculations 8 10
Maximum Shock 10 8
Cost 10 8
Availability 3 3
Totals 46 36
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Data Systems Definition
Microcontroller ATMEL 8-bit AVR Microcontroller Motorola M68HC12 Microcontroller
Accelerometer Analog Devices ADXL278 MEMS Accelerometer Colibrys MS8000.D MEMS Accelerometer
External Resistor Ladder for 8-bit/16-bit Digital to Analog Conversion
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DS - Software Schematic
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DS - MEM Accelerometers
ADXL103/ADXL203 Size: 5mm x 5mm x 2mm Resolution: 1mg at 60Hz Bandwidth: 0.5 Hz – 2.5 kHz Sensitivity: 960-1040 mV/g Supply Voltage: 3.0-6.0 V Supply Current: 1.1 mA 3500g Shock survival
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Accelerometers Trade Study
SpecificationSystem Requirements ADXL203
ADXL278
Size 5mm x 5mm x 2mm 5mm x 5mm x 2mm 5 mm × 5 mm × 2 mm,
Resolution > 2 mg 60 Hz 1mg at 60Hz 2 mg 60 Hz
Bandwidth 0.5 Hz – 2.5 kHz 0.5 Hz – 2.5 kHz 0.5-400Hz
Sensitivity Minimum 960-1040 mV/g 25.65-28.35mV/g
Supply Voltage 3V 3.0-6.0 V 4.75-5.25v
Supply Current 1.1-3.0mA 1.1 mA 2.9mA
Full scale range x-y ± 50g
±1.7g
±35 g/±35 g, ±50 g/ ±50 g, or ±70 g/±35 g
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DS - Accelerometers Testing
ADXL203 tested and specified at Vs = 5.0 V Radiometric output
Vs = 3.0 V output sensitivity ≈ 560 mV/g Noise density decreases as the supply voltage
increases. Vs = 3.0 V, Noise Density = 190 μg/√Hz
When ratiometricity of sensitivity is factored in with supply voltage, self test response is roughly proportional to the cube of power supply voltage. Vs = 3.0 V, Self Response ≈ 150 mV
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DS - Analog to Digital Conversion
Requirement for our electronic system: to convert signals from digital to analog forms
Analog to digital convertor (DAC)needed
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DS - Risk Matrix
DS.RSK.1 Microcontroller Power Failure
DS.RSK.2 Motor Communication Failure
DS.RSK.3 Stationary Accelerometer
Communication Failure DS.RSK.4
Despun Accelerometer Communication Failure
DS.RSK.5 Microcontroller can’t survive
launch conditions
PROBABILITY
CONSEQUENCES
DS.RSK.1 DS.RSK.2 DS.RSK.5
DS.RSK.3
DS.RSK.4
Motor Subsystem
Motor Systems Definition
Required RPM: 600 (without gearing) 2400 RPM with 1:4 gear ratio
Amperage: < 300 mA Torque: 80 mNm (without gearing)
20 mNm with 1:4 gear ratio Max Length: 3” = 7.62 cm Max Diameter: 2”= 5.08 cm Max Mass: 250g Pinion to be CNC cut from ½” (12.7 mm) polycarbonate
Fabricated In-House
MS - Motor Trade Study
Specification
SystemRequirements
Re-16Maxxon
3257 GMICROMO
3242 SCDCDC –Servo Motor
RPM 2400 RPM 7130 RPM 5700 RPM 5300 RPM
Voltage 12 Volts 12 Volts 12 Volts 12 Volts
Amperage < 300 mA 6.05 mA 258 mA 199 mA
Torque > 20 mNm 5.47 mNm 70 mNm 50 mNm
Length <762 mm 61 mm 790 mm 720 mm
Mass <250 grams 38 grams 242 grams 189 grams
Cost <300$ $283.00
Brushed/Brushless Brushed Brushed Brushless
MS - Brushed vs. BrushlessSpecification Brushed Brushless
Efficiency Medium High
Speed/Torque Moderately flat (difficulty in switching speeds at very high rpm)
Enables operation at all speeds
Electrical Noise High Low
Communication Mechanical Electronic
Maintenance High Low
Life Shorter Longer
Motor Size Larger due to commutator and heat removal Smaller
Speed Ranges Commutator limits speed Can rotate at high speeds
Drive Complexity Simple and inexpensive Complex and expensive
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MS - Selected Motor
3242 SCDC DC Servomotor from Faulhaber. Selection Criteria
This brushless motor fit all of our design criteria- electronic communication, high speed, data transfer and reception and small size.
Gearing Requirement Can be provided with the motor (3242 SCDC 012) 32A-available on request from the supplier.
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MS - Risk Matrix
PROBABILITY
CONSEQUENCES
MS.RSK.1 MS.RSK.4
MS.RSK.5 MS.RSK.3 MS.RSK.2
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.
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Power Subsystem
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Power System Definition
Rechargeable Battery 9 V NiMH Powerizer Batteries Amperage : 170mA Amount needed : 4 Weight:125g
Voltage Regulator ±3.3 V Linear regulator for flash memory and accelerometers ± 5.0 V Linear regulator for microcontroller
Parallel and Series connection to achieve requirements of motor and electronic devices
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PS - Power Flow
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PS - Battery Trade Study
Specification SystemRequirement
s
Energizer 175 mAh 9V
NiMH
NiMH PowerizerBatteries
Nickel-metal Hydride
Effective Voltage
16V 9V 9V 12V
Number - 4 4 2
Type Rechargeable Rechargeable Rechargeable Non -rechargeable
Amperage 300mA 175 mA per 170 mA per 2450 mA
Mass (total) 32g 125g 255g
Cost $32.0 $27.0 $ 71.90
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Critical InterfacesInterface Description Potential SolutionDespun Gear / Motor Pinion
Motor will spin Despun Platform via spur gear. Number of teeth to be determined but GR set to 4:1
Optimal number of teeth to distribute stress for PC but sill give adequate response
Despun Platform / Data System
Connected via slip ring leads. Slip ring connection may be susceptible to vibrations
Vibration test prior to launch. Slip ring connections can be adjusted to compensate for vibrations
Despun Platform / Power System
Connected via slip ring leads. Slip ring connection may be susceptible to vibrations
Vibration test prior to launch. Slip ring connections can be adjusted to compensate for vibrations
Motor / Data System Connections between motor and MC may not survive launch conditions
Validate connections method is will survive vibrations of launch with vibrations testing
Motor / Power System Connections between motor and MC may not survive launch conditions
Validate connections method is will survive vibrations of launch with vibrations testing
Data System / Power System
Connections may not survive launch conditions
Validate connections method is will survive vibrations of launch with vibrations testing
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PS - G-Switch Definition
TBD – Specified by WFF Activate/deactivate at
Wallops command Light switch form Current flow can be
inhibited by Wallops via Relay
No latch activation Able to allow Wallops to
have full control of activation/deactivation
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Shared Can Logistics
Sharing ½ can with Temple University Temple University will be measuring gamma and x-rays,
up to 100keV, through the use of a scintillator and photomultiplier-tube. They will use visible solar light as a directional z-axis reference point to characterize the high energy particles as solar or cosmic rays.
No Ports needed for experiment Drexel and Temple have been communicating regularly
thus far Close geographic proximity allows for the teams to
meet face to face and will aid in future collaboration
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Preliminary Mass Estimates
Components MassLower Platform Weight 268 grams
Upper Disk 105 grams
Slip Ring 250 grams
Battery 100 grams - 250 grams
Motor 189 grams - 242 grams
Accelerometers 25 grams
Electronic Components 100 grams
Total 1037 grams – 1240 grams
Design for 2 Kg, Leaving minimum margin of 760 grams
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Center of Gravity Estimate
The center of gravity for our Design will be confined within a 1inch cube from the center of the canister.
This will be obtained by placing the large components in such a way that their resulting moment will be within the center of gravity envelope.
Prototyping Plans
Gearing Physical prototypes of gears to verify gear ration/
teeth size Digital to Analog Converter
Created with resistor ladder and Op-Amp Motor control algorithm Slip Ring fastener
Interface stator section of slip ring to fixed platform
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BudgetItem Part Number Manufacturer Vendor Quantity Price (each) Total
Dual Axis High-G Accelerometer
AT26DF161A Analog Devices Analog Devices 2 12 24
Microcontroller ATMega32-16PU Atmel Digi-key 1 9 9
Slip Ring CAY-1666 Aeroflex 1 400 400
Pressure Sensor ASDX015A24R Atmel Digi-Key 1 25 25
DC Micro-motor 3242-SCDC MICROMO Faulhber 1 283 283
12”x24”x.25” PC Sheet
85805K43 - McMaster-Carr 1 20 20
12”x12” x 0.50” PC Sheet
8574K32 - McMaster-Carr 1 28 28
Flash Memory AT26DF161A Atmel Digi-Key 1 4 4
Battery 9 V NiMH Powerizer
Powerizer Digi-Key 4 7 28
Voltage Regulator/Misc Electronics
- - Drexel Provided
- - 0
Total 800
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Timeline
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Team Overview
Advisor: Dr. Jin Kang, PhD.
MEM Department, Drexel University
Team Leader : Joe Mozloom
Senior, Drexel University
Subsystem Head: Despun Platform
Team Members
Name Eric Marz Linda McLaughlin Swati Maini Swapnil Mengawade
Year and Major
Senior, Electrical and Computer Engineering
Senior, Electrical and Computer Engineering
Senior, Mechanical Engineering and Mechanics
Senior, Mechanical Engineering and Mechanics
Subsystem Head
Micro-controller, Storage and G-switch
Sensors, DAC and Power Systems
Motor System and Organization
Modeling, System level requirements and Compliance to User guide
Future Work
Finalize design for slip ring holder Choose number of teeth/ tooth design for
gearing system Determine interfacing between motor and
fixed platform Continue to become comfortable with
Solidworks