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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