Subsystem Requirements - MIT OpenCourseWare ÆTT8) zTransceiver Architecture Introduction Subsystems •Actuation •Formation Control •Electronics •Comm •Requirements •Trades

5/24/2002 CDIO3 Class Project 68

Subsystem

RequirementsDetermine separation distance

Goal: sense to one-tenth the control tolerance

Determine relative attitude (direction) ofvehicle to an angular tolerance dependenton angular controllability

Goal: sense to one-tenth the control tolerance

Full field of view : 360 degrees in twodimensionsSensing presence of other vehicles to adistance compatible with test facilities

IntroductionSubsystems•Actuation•Formation Control

•Control•Metrology

•Requirements•Trades•Design•Issues•BudgetEstimates

•Electronics•Structure/Power

OperationsImplementationConclusion


Trades

Sonic and IR based systemSimilar to SPHERES metrologyExpected improvement inperformance due to 2D operationNew technology should eliminatesome accuracy of the errorsencountered by SPHERESLow refresh rate will require theuse of gyros and accelerometers







Design

A

C

B

αB

βA

sAB

t1

t3

t2







Design

1 ultrasonic omni-directionaltransmitter (Mimio)3 ultrasonic omni-directionalreceivers (cones)3 IR receivers & 2 transmitters1 rate gyro1 2-axis accelerometer







DesignIntroductionSubsystems•Actuation•Formation Control






Design

System relies only on distancereadingsUses data from all three sensorsCalculates relative attitude anddistance directly to center ofvehicle







Design

(x + x1)2 + (y + y1)

2 = d12

(x + x2)2 + (y + y2)

2 = d22

(x + x3)2 + (y + y3)

2 = d32

Y

X

d1

•Origin at center of vehicle• xi and yi are position of thesensors







DesignIntroductionSubsystems•Actuation•Formation Control






Issues

Omni-directional sonic sensorsHand made cones added to currentsensors

Effect of magnetic forcesRange and accuracyRefresh rate

Sound signal leaving the testing area

Rate gyros and accelerometers







Budget Estimates

1.090.202500Total (per vehicle)

3.270.607500Total (system)

0.180.051200Accelerometers

0.360.061200Gyros

0.250.0430IR (2+3)

0.30.0570Sonic (1+3)

Power(W)

Mass(kg)

Cost($)

PartIntroductionSubsystems•Actuation•Formation Control






Communications

Jennifer Underwood

Comm. Board

Comm. Antenna

IntroductionSubsystems•Actuation•Formation Control•Electronics

•Comm•Requirements•Trades•Design•Issues•BudgetEstimates

•Avionics•Structure/Power



Communications

“The technology employed intransmitting messages”

Architecture

HardwareSoftware

Interfacing






Subsystem

RequirementsSend information and instructions automaticallyfrom vehicle to vehicle

Control and metrology purposes

Send information and instructions on commandfrom ground to vehicle

Begin preprogrammed testsEmergency intervention procedures

Send flight health data to “ground” operatorHave no protruding antennae that might interferewith dynamics






Trades

HardwareProcessor board (chosen byavionics TT8)Transceiver

Architecture






Transceiver Metrics

EM rejection (frequency)

Bandwidth/data rateWeight

Ease of interfaceSize

CostPower consumption

Range






Transceiver Trades

Radio Frequency (RF) vs.. WirelessLAN

Avg cost of LAN > avg cost of RFLAN requires a base station ($$)Size and weight of LAN > RFLAN bandwidth, range > RFPower drain of LAN < RFBoth have capacity to reject EM (highfrequencies) and are easily interfaced

Choice: RF






RF Trades

DR1012 avail from SPHERESfor prototyping

Company inEurope

Availability

115.2 kbps115.2-882 kbpsData rate

Short-range wireless91m indoorsRange

Relatively EasyRelatively EasyEase of Interface

$35~$245Cost

Hardly any, < AC5124C-100.02 kgWeight

Development kit ready,familiar to staff, students

OEM kit, notfamiliar

Complexity

916.5 MHz2.402 –2.478GHzFrequency

0.04 W0.35 WPower

1”x1.5”2.65˝x1.65˝x0.20˝Size

RF Monolithics (DR3000-1)AC5124C-10IntroductionSubsystems•Actuation•Formation Control•Electronics

•Comm•Requirements•Trades

•Design•Issues•BudgetEstimates




Transceiver Selection

Preliminary final product:DR 3000-1

Sufficient EM rejectionFamiliarityPower drain

Prototyping product:DR1012

AvailabilityFamiliarity






Architecture Trades

SequentialPass token to determine who talks and towhomHub makes calculation

SimultaneousPass token to determine who talks to everyoneAll vehicles make calculations

HybridCombination of Sequential and Simultaneous

Reliability deciding factor






Architecture Trades

SequentialVehicle 2 talks

to Hub

Token passedto Vehicle 1

Vehicle 1 talksto Hub

Hub

Vehicle 1

Command

Updates

GroundStation

1st Comm Channel

Has Token

Updates

2nd Comm Channel

Vehicle 2

Hub makes control calculationsand sends commands to Vehicle 1and Vehicle 2






Architecture Trades

SimultaneousVehicle 2 talks to

Hub and Vehicle 1

Token passed toVehicle 1

Vehicle 1 talks toHub and Vehicle 2

Hub

Vehicle 1

Command

Updates

GroundStation

1st Comm Channel

Has Token

Updates

2nd Comm Channel

Vehicle 2

Updates

Token passed to Hub

Hub talks to Vehicle 1 and Vehicle 2

Each vehicle makes control calculations






Architecture Trades

HybridVehicle 2 talks to

Hub and Vehicle 1

Token passed toVehicle 1

Vehicle 1 talks toHub and Vehicle 2

Hub

Vehicle 1

Command

Updates

GroundStation

1st Comm Channel

Has Token

Updates

2nd Comm Channel

Vehicle 2

Updates

Token passed to Hub, who talks toVehicle 1 and Vehicle 2

All vehicles make control calculations but onlyHub determines commanded control vectorsends commands to Vehicle 1 and Vehicle 2,ground listens in






Architecture Trades

SequentialRequires excess code, bandwidth (BW)Reliable from control point of view

SimultaneousEasy to implementNot reliable from control point of view

HybridReliable and versatile from control and commpoint of viewIncreased bit rate required, excess code, BW

Design Choice: Hybrid






Design

Hub

Vehicle1

GroundStation

Command

Data Flow

Command/Request/Update

Update

Update

Command/Request/Update

Vehicle2

Updates






Design

Design ConsiderationsComm channel usage

Transmission ratesData framing

Error detection/correctionChannel coding

Automatic Repeat Request (ARQ)protocols






Data Framing

Data framing is essentialWho to send info toWho sent info (Hub, Vehicle 1, Vehicle 2)Type of dataSize of data packetError checking

Ease of transmitting chunks (1 byte)

Type CheckData 1…Data nSizeFrom/To

Header Data Check

8bit 8bit 8bit 8bit ? ?

Start






Channel Usage

Cluster Comm Channel6 variables in state vector (Control)4 variables to actuators (EM, RWA)About 800 bits/cycle for controlAbout 500 bits/cycle for health updates

Ground Link Comm ChannelUndefined requirementsOn the order of 400 bits per completecycle






Transmission Rates

How frequently to measuresystems/states?

Control runs at 50 HzHealth max set at 10 Hz

Therefore, we can estimate thetransmission rate required:

800 bits/cycle * 50 cycles/sec +500 bits/cycle * 10 cycles/sec = 45kbps






Current Capabilities

TT8 to TT8 communicationCurrently connected through UARTchannel

Two byte transmissionSend and receive between twoTT8’s, one direction onlyHigh-Byte, Low-Byte

[1 1 1 1 1 1 1 1] [1 1 1 1 1 1 1 1] = 1111111111111111High Byte | Low Byte






Issues

Processor/transceiver shieldingReliability

EM resistanceError probability

Communication channel load






Budgets Estimates

0.080.24$275Total (ground station)

0.080.24$275Total (per vehicle)

0.320.96$1100Total (system)

--$70Replacements/repairs

-0.1$100Miscellaneous parts

0.040.02$35each

Transceiver

Power(W)

Mass(kg)

Cost($)

PartIntroductionSubsystems•Actuation•Formation Control•Electronics





Avionics

Avionics Board


•Comm•Avionics


•Structure/Power



Subsystem

RequirementsManage timing and resources forall subsystemsRun control loop in real-time

Inputs, calculations, outputs

Administer preprogrammed testsBe easily programmableStay within system budgets


•Comm•Avionics


•Structure/Power



Trades - Metrics

Processing speedInterfaces (I/O)Data storage (RAM/ROM)Constraint considerations

Cost

Size and massEase of use


•Comm•Avionics


•Structure/Power



Trades -

Metrics DetailsProcessor speedI/O capabilities

Digital vs.. analogSubsystem input and output needsnot necessarily the same

RAM and ROM capacityFlash memory

Power consumptionCost


•Comm•Avionics


•Structure/Power



Trades - Interfaces

The avionics team must interface with all subsystems.

INPUTSMetrology:

3 Ultrasonic sensors (digital)1 IR timing (digital)1 rate-gyro (analog)Possibly 2 accelerometers (analog)

CommunicationInter-vehicle data and instructions (digital)

Health Indicators (digital)


•Comm•Avionics


•Structure/Power



Trades - Interfaces

The avionics team must interface with all subsystems.

OUTPUTSCommunication

Requests and commands (digital)

Actuators3 for Y-pole magnet (analog)1 for RW (analog)

Metrology1 for ultrasonic transmitter (digital)1 for IR timing transmitter (digital, split)


•Comm•Avionics


•Structure/Power



Trades: Computer

Comparison

Low

Low

~8kB

~16 kB

4D, 1A in1D, 4A out

50 Hz

Needs

N/AN/A1.8 WattsPower

HighCustom(~$500)Cost

512 kB640 kB256kBROM

16 MB16 MB256kBRAM

N/AD parallel64 I/O

25D I/O8A, 14 time

I/O

167 MHz 1GFLOPS

50MFLOPS

16 MHz

4 MIPSSpeed

6701C40TT8FeatureIntroductionSubsystems•Actuation•Formation Control•Electronics

•Comm•Avionics


•Structure/Power



Trades: other

considerationsOther Computer ConsiderationsSize/weight satisfactory for structure?Available/Replaceable?Easy to use?Expandable?


•Comm•Avionics


•Structure/Power



Design: Hardware

Computer

A/D

D/A

RWA

Metrology

Control

EMPower

Structure

SW

SW

Physical

V in

Comm./OpsIntroductionSubsystems•Actuation•Formation Control•Electronics

•Comm•Avionics


•Structure/Power



Design: Software

Language: CCoding environment

Creating: Metroworks CodeWarriorLoading to vehicle: Motocross

ProceduresControl loop

Metrology updatesMatrix calculationsActuation commands

Test programsHealth, test data reports


•Comm•Avionics


•Structure/Power



Issues

Software is the high-risk item for theavionics subsystem.Preliminary Test Prototyping Designto find complications early.

Develop a clock-interruptBlink an LEDSignal Reproduction via PWM

Preliminary Prototype to becompleted by end of semester.


•Comm•Avionics


•Structure/Power



Budget Estimates

Mass0.028 kg per tattletale

May need two0.028 per subsystem circuit board

PowerHighest power draw: two main computersPower required: 3.6 Watts

CostPer-vehicle needs, system-wide extras$500 total allocated for TT8 repairs$6500 for circuit boards (power, comm.,controls, metrology)


•Comm•Avionics


•Structure/Power



Budget Estimates

(cont.)

?0.1131060Total(vehicle)

7000

6500

500

Cost ($US)

?0.339Total(system)

?0.113Boards

3.60.057TT8 (x2)

Power (W)Mass (kg)Part


•Comm•Avionics


•Structure/Power



Power

Amy Schonsheck

Power

IntroductionSubsystems•Actuation•Formation Control•Electronics•Structure/Power

•Power•Requirements•Trades•Design•Issues•BudgetEstimates

•Structure



Requirements

No external umbilicalsOn-board power supply

Provide sustainable power for30 minutesUse a renewable orrechargeable energy source



•Structure



Power Trades

Solar power vs.. batteriesPower requirements toodemanding for solar powerRechargeable batteries the bestoption

Choice of battery chemistry



•Structure



Battery Selection

For expected voltage and currentrequirements, viable options include:

Lithium Ion (Li-ion)Nickel Cadmium (NiCd)

Nickel Metal Hydride (NiMH)



•Structure



Battery Selection

Li-ion:High energy densityLow discharge rate (2 Amps max.)

NiCd:Adequate discharge rateLow efficiency at high current draws

NiMH: Final choiceHigh energy densityFast discharge rateEfficient even at high current draw



•Structure



Power Design

Subsystem power estimates:

60-7012 (min.)EM: Electromagnet

1328?RWA: Reaction Wheel

~ 90 W (max)TOTAL:

0.19-12Comm/Ops: (shares Tattletale)

0.0663Metrology: Transmitters/Receivers

0.3612-18Metrology: Gyros

0.188-30Metrology: Accelerometers

2 (each)9-12 (each)Avionics: Tattletale (x 2?)

Power (W)Voltage (V)Subsystem



•Structure



Power Design

Total current draw: 7 Amps (current design)Operation time: 30 minutes (min.)Total energy: 3.5 AhCandidate battery: Panasonic HHR200SCP

Voltage - 1.2 VCapacity - 1.9 AhWeight – 42 gDimensions: 23 mm diameter, 34 mm height



•Structure



Power Design

Candidate battery architecture:1 “Pack” = 15 batteries x 1.2 V (wiredin series)

18 V1.9 Ah

2 Packs wired in parallel18 V3.8 AhSufficient voltage, current for the system



•Structure



Power Design

Voltage Regulators used tostep down voltages

9-12 V : Tattletale processors5 V : Transmitters/ReceiversGyros, accelerometers may have built-involtage regulators

Switchmode amplifier usedto control current throughelectromagnet

Commercially available



•Structure



Power Flowchart

15 x 1.2 V

Gyro,

Accel.

RW

5V

Regulator

Trans. /

Receivers

9-12V

Regulator

Tattletales

SwitchmodeAmplifier

EM

15 x 1.2 V



•Structure



Issues

NiMH batteries have strictcharge/discharge limits

Overcharging decreases performance

Rapid discharge produces heat

Safety precautionsAvoid excessive heatAvoid contact with water



•Structure



Issues

Possible greater power requirementsCurrent design allows 7 ampsEM may require up to 10 amps

May require more batteriesPossibly switch to next higher batterymodel (much higher mass)

Charging takes ~ 1.2 hoursTwo or three complete battery setsneeded (per vehicle) higher cost



•Structure



Budget Estimates

Mass:30 batteries

42 g eachTotal battery weight: 1.26 kg

Additional components: ~ 50 g(regulators, amplifier)



•Structure



Budget Estimates

Cost:Switchmode amp: ~$65

Voltage regulators: ~ $60Batteries: $400 - $500

Power:Supply 100% of EMFFORCEpower needs



•Structure



Structure

Structure


•Power•Structure

•Requirements•GeometricalOverview•Trades•Design•BudgetEstimates



Structure

RequirementsVehicle Casing:

Provide physical interfacing capabilityPrevent damage in case of collisionThermal considerations due to magnetheating

Magnetic Shielding:Protect electronics hardware frommagnetic interference

Air Carriage:Provide adequate cushion height forvehicle mass






Geometric Overview

Lid

Body encasing

Base

Air Carriage






Geometric OverviewIntroductionSubsystems•Actuation•Formation Control•Electronics•Structure/Power





Geometric OverviewIntroductionSubsystems•Actuation•Formation Control•Electronics•Structure/Power





Shielding

Sample kit includes various materialsof different properties.Determine functional material at leastmass.Conduct tests using electronics/electromagnets, andtest shielding material.






Air Carriage: Trades

Fabricate vs.. Off-the-ShelfCost, Efficiency

Tanks vs.. CompressorsCost, Power, Mass

Infinite(?) air supply






Air Carriage: Design

Objective: For a given weightaccurately predict and obtain amaximum air cushion thicknessDesign variables

Supply pressure

Puck radiusSupply orifice






Linear radial pressure distributionfor single, central orifice

Possible compressible effectsnear aperture

Air Carriage: Model

Assumptions

p

passp R

rPPPrP )()( −−=






Thin film:h << Rp

very low Reynolds Number

Similarities to Couette andPoiseuielle flows: parabolicvelocity distribution

∝= 2

2

Repa

ppa

a

a

R

hURcU

µρ

µρ

Air Carriage:

Lubrication TheoryIntroductionSubsystems•Actuation•Formation Control•Electronics•Structure/Power





Air Carriage: Next

Steps…Lubrication flow solver

Pressure gradientFlow VelocityLoadCushion thickness

Assess compressible behaviorAssess puck designs





Documents

Subsystem Requirements - MIT OpenCourseWare ÆTT8) zTransceiver Architecture Introduction Subsystems •Actuation •Formation Control •Electronics •Comm •Requirements •Trades