Drexel University 2010-2011 RockSat-C Critical Design Review

Drexel University Rock-Sat 1

Drexel University2010-2011 RockSat-CCritical Design Review

Joe MozloomEric MarzLinda McLaughlinSwati MainiSwapnil MengawadeAdvisor: Jin Kang, PhD


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.


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.


Team Overview

Advisor: Dr. Jin Kang, PhD.

MEM Department, Drexel University

Team Leader : Joe Mozloom

Senior, Drexel University

Subsystem Head: Despun Platform

Team MembersName 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


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


Concept of Operations


Expected Results

Workbench FlightConform to all NASA/WFF requirements as outlined in User Guide

Conform to all NASA/WFF requirements as outlined in User Guide

Counter-rotating platform effective over outer canister spin frequency range from 0.5 Hz - 10 Hz

Counter-rotating platform engaged when canister is spinning

Maximum platform spin-rate 10% of current canister spin-rate

Platform able to rotate under harsh flight conditions

Data stored in memory and accessible post test

Data stored in memory and accessible post flight


De-Scope

Initial Goal to provide a rotationally stable platform and perform experiment on our despun platform.

De-Scoped to be a feasibility study for our despun platform design.

Reasoning If despun platform failed, experiment on platform

would produce no useful results.


Off Ramps

Polycarbonate Plate -> Acrylic Plate Polycarbonate is more difficult to machine, if we are

unable to CNC a usable geared platform and pinion then Acrylic will be cut via laser cutter.

Digital to Analog Converter (DAC) Initially designed to be created out of a resistor ladder. If

precision cannot be easily obtained through this, an aftermarket DAC could be used.

Closed Loop Algorithm -> Open Loop Algorithm Can simplify algorithm to not take into account despun

platform sensor if there are difficulties.


Mechanical Design Elements


Mechanical Design


Labeled Diagram

1.2 V AAA Battery

Upper platform

Gear

Accelerometer

G-switch

Microcontroller board

1.25

2.0

1.0

5.09.3

1 Unit: Inches


Labeled Diagram

Slip ring holder

Slip ring

Motor holder

MotorDAC

4.75

2.75

Unit: Inches


Manufacturing Plan

Gear Polycarbonate CNC Milled

Pinion Polycarbonate CNC Milled

Slip Ring Holder ABS 3D Printed

Motor Mount ABS 3D Printed

Platforms (2X) Polycarbonate CNC Milled


Procurement Plan

Slip Ring (Received) Motor (Received) Polycarbonate sheets

12”x12”x 0.5” 12”x24”x0.25”

Standoffs 8-32 x ¼” x 4”

Bolts (8-32, 0-80, M3)


Current Position

All parts have been ordered Slip Ring and Motor have arrived

1st Iteration of prototyping is completed Main objective: Sizing/Fit verification

• Slip Ring Holder• Motor Mount• Gear• Pinion

2nd Iteration of prototyping has begun Altering design for better fit, wire accommodation, etc


Changes Since PDR

Slip Ring Holder and Motor Mount defined The 5x 9V batteries are replaced by 10x 1.2V

AAA batteries The components on fixed platform defined to

adjust COG


Electrical Design Elements


Electronics Schematic

Power Supply

StationaryAccelerometer Microcontroller

DespunAccelerometer Slip Ring

Digital to AnalogConverter Motor


Manufacturing /Procurement Plan

Manufactured DAC

Soldered Sensors Small electronics

• Resistors, capacitors, diodes Procured

Microcontroller purchased with integrated Control Board

Hi G and Low G Accelerometers 10 NiMH rechargeable AAA Batteries G-Switch


ATmega32 Control Board

"Mini AVR ATmega32 Board Schematic." Micro4You. Web. 1 Dec. 2010. <http://www.micro4you.com/store/mini-AVR-ATmega32-Board/prod_155.html>

Microcontroller Communications

Microcontroller and Power Connections

MicrocontrollerExternal Ports

Reset and Power LED


DAC Design 8-Bit(Subject to Off-Ramp and Improvement)

Out to Motor Control


DAC Design

8-Bit DAC Initial Design Allows for 0.148 Hz Steps (Taking into account our

motor specifications and gear ratio) 10-Bit DAC

Plan if more precision needed after initial testing Allows for 0.037 Hz Steps More difficult to control through our microcontroller’s

8-bit ports. Simple Modification from 8-bit design.


Software Design Elements


Software UML Diagram


Software FlowMajor Code Blocks

Fixed Platform Sensor Data Read 10 Times per second sample fixed platform sensor data and

calculate rocket rotation. Despun Platform Sensor Data Read

10 Times per second sample despun platform sensor data and calculate platform rotation.

Data Storage 10 Times per second store both Fixed Platform and Despun

Platform sensor data with timestamps. Motor Control

When either fixed platform sensor or despun platform sensor values are above threshold, adjust motor RPM through DAC.


Analysis & Prototyping

• FEA Analysis (Stress/Deformation)• Tooth Loading, Gear/Pinion• Vertical Loading, Gear/Pinion• Vertical Loading, Motor Mount

• Electronic Simulation• DAC Simulation in PSPICE

• Physical Prototyping• Gear• Pinion• Slip Ring Mount (top / bottom)• Motor Mount


Gear/Pinion Tooth FEA

10 N Horizontal Load Applied to Single Tooth Face Theoretical load

calculation = 1.26 N• Based on Moment of

Inertia of gears and elevated frictional forces in bearings at 25 G

Fixed at 2x 0-80 Set Screw Holes


Gear/Pinion Tooth FEA Results

Gear Pinion

Theoretical Load (N) 1.26 1.26

Load Applied (N) 10 10

Max Deflection (mm) .026 .012

Max Stress (MPa) 1.788 1.081

Max Stress Location Set Screw Holes Set Screw holesFilet of loaded tooth

Safety Factor 34.7 57.4


Vertical Loading FEA

Loading based on mass of component and multiply by 25G

Loading distributed across top face of component

Tested for Max Stress and Vertical Deflection


Vertical Loading FEA Results

Gear Pinion Motor Mount

Theoretical Load (N) 25 2.5 49

Load Applied (N) 50 5 100

Max Deflection (mm) 0.01 0.001 0.243

Max Deflection Location Outer Diameter Outer Diameter Top Face Inner

Diameter

Max Stress (MPa) 2.741 0.135 9.715

Max Stress Location Set Screw Holes Set Screw Holes and ID

Top face ID at mounting holes

Safety Factor of Applied Load 23.7 459.7 6.7


Prototyping Results

Slip Ring Holder (Top and Bottom) Prototyped with Fuse

Deposition Rapid Prototyping Machine

Verifies fit and sizing and integration of design

Motor Mount Prototyped with Fuse

Deposition Rapid Prototyping Machine

Verify fit and sizing and integration of design


Prototyping Results

Gear Laser Cut from .2”

Acrylic Verifies tooth design

mating with pinion Pinion

Laser Cut from .45” Acrylic

Verifies tooth design mating with gear


Center of Gravity

Center of Gravity: ( inches )X = 0.20Y = -0.88Z = 0.96


Mass BudgetComponent Mass (Kg)

Lower Platform Weight 0.268

Upper Disk 0.105

Slip Ring 0.077

Slip Ring Base 0.040

Battery Case 0.045

Battery (1×10) 0.013×10 = 0.130

Accelerometers 0.025

Microcontroller 0.050

Wiring 0.020

Bolts (1×6) 0.030×6 = 0.180

Nuts (1×6) 0.015× 6 = 0.09

Motor 0.193

Motor base 0.050

G-switch 0.015

Total 1.288

Mass (Kg)

Mass Allowance 2

Theoretical Mass 1.288

Mass Margin 0.722


Power Budget

Sub System Voltage (V) Current (A) Operating Time (min) Ampere Hour

Motor 12.0 4.0 10 0.65

High G Accel. 3.0 - 6.0 1.1m 10 0.0011

Low G Accel. 4.75 - 5.25 2.9m 10 0.0029

Microcontroller 2.7 - 5.5 2.2m 10 0.0022

Total 0.6562


Testing Plan

System Testing

Mechanical Testing

Electrical Testing Sensor Testing

Data Testing


System Level TestingSystem Requirement Physical Test Success CriteriaConform to all NASA/WFF requirements as outlined in User Guide

Measure Mass & Volume

Counter-rotating platform effective over outer canister spin frequency range from 0.5 Hz - 10 Hz

Spin final assembly at different spin ratesOutside measurement compared to stored data.

Despun Platform able to operate

Maximum platform spin-rate 10% of current canister spin-rate

Spin final assembly at different spin ratesOutside measurement compared to stored data.

Measure despun platform acceleration has max 10% of current canister acceleration

Experiment Should be able to survive launch conditions

Vibration Test at 2x flight conditions (50G)

System operational after test


Mechanical Testing

All components will be individually measured for mass Masses will be summed to verify compliance

Vibration Testing at 2x Flight Conditions (50 G) Each Subsystem tested Final Assembly tested

Motor Mount to have vertical loading destructive testing to verify flight readiness


Electrical Testing Battery Testing

Battery will be tested using the battery voltage method with a digital D.C. Voltmeter

Battery is fully charged before testing

Percent Charge Voltage [12V]

100% 12.7

75% 12.4

50% 12.2

25% 12.0

Discharged 11.9


Sensor Testing ST pin test : the typical

change in output should be 750mV(750mg) ST pin test allows to verify if the

accelerometer is functional ST pin should never be exposed

to a voltage Vs+0.3 V If Vs=3V is used, the output

sensitivity is 560mV Vs= 4.75 V to 5.25 V, sensitivity

is 186 mV/g to 215 mV/g.


Sensor Testing Self Test response in g: However if Vs≠5V, self test response

in volts is roughly proportional to the cube of the supply voltage.

Thus, at Vs=3V, self test response will be approximately equivalent to

150mV(270mg) Supply current decreases as the

voltage supply decreases. Typical consumption at VDD=3V is 450uA.

2VsH

ctekkVsH ,2


DAC Testing

Differential non-Linearity Test(DNL) DNL is generally more critical when outputting small signals

To test the linearity of a DAC, we will generate the digital stimulus and capture the analog response.

DAC is swept from 000…0 to 111...1 DNL will show up as a change between each successive digital error output

Comparison between PSPICE simulations with real simulations will make improvements on DAC


Risks


DP - Risk Walkdown 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

Walkdown FEA Analysis verifies distortion due to

vertical loading will be minimal

PROBABILITY

CONSEQUENCES

DP.RSK.3DP.RSK.5

DP.RSK.1DP.RSK.2 DP.RSK.2

DP.RSK.4DP.RSK.5


MS - Risk Walkdown

PROBABILITY

CONSEQUENCES

MS.RSK.4 MS.RSK.2

MS.RSK.1MS.RSK.3 MS.RSK.1

MS.RSK.4 MS.RSK.2MS.RSK.3

MS.RSK.1 Motor-Battery

Communication Failure MS.RSK.2

Motor gear head and platform may lose contact under 25G

MS.RSK.3 Battery unable to sustain

variable rpm requirements MS.RSK.4

Motor may not respond to the micro-controller signals correctly.


DS - Risk Walkdown DS.RSK.1

Microcontroller Power Failure DS.RSK.2

Despun Accelerometer Communication Failure

DS.RSK.3 Microcontroller can’t survive launch

conditions

Walk-Down Microcontroller with previous

launch experience selected to limit DS.RSK.5

Secure housing for slip ring designed to protect data transmission

PROBABILITY

CONSEQUENCES

DS.RSK.1 DS.RSK.3 DS.RSK.3

DS.RSK.2 DS.RSK.2


New Risks

PROBABILITY

CONSEQUENCES

New.RSK.1

New.RSK.3 New.RSK.2

New.RSK.1 Bolts become loose during

launch New.RSK.2

Components come in contact with the vibrating canister wall

New.RSK.3 Motor or Sensor

communication Failure with Microcontroller

Walk-Down Caps could be used on bolts Minimizing placement of

components near canister wall Using hard Soldering for

connections


User Guide Compliance

G-Switch will be used for system activation No ports will be required No plans for high voltage

Mass (Kg)

Mass of Experiment 1.288

Mass of Canister 3.134

Total 4.422

Payload Mass Requirement 6.35


Shared Can Logistics

Sharing ½ can with Temple University Drexel on bottom half, Temple on top half

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.

Both experiments to be separated via two individual platforms (top and bottom)

Recovery and AnalysisWallops Island Flight facility

Weekely Teleconference 9Weekly Teleconference 8 (LRR)

Launch Readiness Review (LRR) TeleconferenceWeekly Teleconference 7

Second Full Mission Simulation Test Report DueWeekly Teleconference 6Weekly Teleconference 5Weekly Teleconference 4

Fit Check with TempleWeekly Teleconference 2Weekly Teleconference 3

Mission Simulation and TestingAsembly Vibration TestingWeekly Teleconference 1

Final Installment DueAssembly Spni Testing

Payload Subsystem Integration and Testing Report TeleconferencePayload Subsystem Integration and Testing Report Due

Online Progress Report 4 DueSubsystem Assembly

Individual Subsystem Testing Report TeleconIndividual Subsystem Testing Reports Due

Online Progress Report 3 DueDestructive Testing of Motor Mount

Vibration Testing of SubsystemsRockSat Payload Canisters Sent to Customers

Machining of Mechanical ComponentsBuild Dac

CAM Coding Development and TestingFlight Selections

Subsystem ConstructionMicrocontroller Programing

Critical Design Review (CDR) Due3D Printing Prototyping

Online Progress Report 2 DueGear Prototyping

Receive PartsOrder Parts

Preliminary Design Review (PDR) TeleconferenceSource Parts

Iterative Design Process

9/15/2010

10/15/2010

11/14/2010

12/14/2010

1/13/2011

2/12/2011

3/14/2011

4/13/2011

5/13/2011

6/12/2011

Start Date

Completed

Remaining


BudgetItem Part Number Manufacturer Vendor Quantity Unit Price ($) Total ($)

Dual Axis Accelerometer AT26DF161A Analog Devices Analog Devices 2 12 24

Integrated Board/ ATMega32 Microcontroller MINWST7N47 Atmel micro4you.com 1 28 28

Slip Ring CAY-1847 Aeroflex Aeroflex 1 400 400

G-Switch ASDX015A24R Atmel Digi-Key 1 25 25

DC Micro-motor 3242-SCDC Faulhber Micromo 1 345 345

12"x12"x0.50" PC Sheet 8574K32 - McMaster-Carr 1 28 28

12"24"x0.25” PC Sheet 8574K43 - McMaster-Carr 2 20 20

Flash Memory AT26DF161A Atmel Digi-Key 1 4 4

AAA NiMH Rechargeable Battery 16546 Accupower onlybatteries.com 12 3.25 39

2" Standoffs 92745A369 McMaster-Carr McMaster-Carr 8 1.12 8.96

1/8" Standoffs 91780A191 McMaster-Carr McMaster-Carr 4 0.029 0.116

Various Bolts 10

Totals 932.076

Conclusion

Issues Unsure if re-chargeable batteries can be used Holder materials ABS or metal- steel, aluminum Temple may not be using center standoff

(Drexel will include center standoff)Plan of action Currently prototyping parts On receiving shipments, assembly of parts to

be ready for testing.

Drexel University 2010-2011 RockSat-C Critical Design Review

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