MagellanPreliminary Design Review

Charlie ReverteZachary Omohundro

Chris BakerChin Keong Ling

Aaron Morris12/11/2002

Operational

• Deployment and recovery through a 10” borehole• Un-tethered• Semi-autonomous• Rugged and waterproof• Drive on land and water• Traverse obstacles up to 8”• Carry mapping payload• Reasonable range• Purged and Pressurized• Expendable

Requirements

Concept Image

Mechanical

• 2 segment 4 wheeled rover

• Solid drive axles• Steering via actuated

center link• Inflatable wheels

Specifications

• Single purged and pressurized volume• Deployable sensor payload• Docking mechanism• Compact deployment configuration

Electrical

• Source: 24 volt Li-ion batteries– Target 1 KWh capacity

• Locomotion and Actuation Motors (24VDC)– Front Drive– Rear Drive– Pneumatic Pump

• Sensing– 24VDC Laser Scanner

• Computing– PC/104+ form factor– Wireless Ethernet– Hard disk drive– Includes +5 conversion/regulation for secondary sensors.

Specifications

Sensing

• Primary mapping payload– Laser rangefinder

• Purged and pressurized• Linear potentiometer to sense laser orientation

– Analog magnetic compass• Navigation sensors

– Drive motor encoder counters– Intrinsically safe steering potentiometer– 3 axis accelerometers– Tilt sensor

• Obstacle avoidance– Motor current sensors– Ultrasonic sensors

• 3 front, 3 rear, 1 overhead– Primary mapping sensor tilt scan

• Internal state sensors– Battery status– Chassis pressure monitor– Wheel pressure monitor– Thermal sensors on motors, pump and cylinders

Specifications

External Sensor LayoutMajor Subsystems

• Rear 3 sonar configuration is identical

High Level Software

• Autonomy – Preprocessed topological graph of map from Voronoi– Node waypoint selection from graph search algorithm– Cost = D(edge) * batt/D + “interesting” + D(Origin) – Waypoint following once oriented

• Track D(traveled) and battery consumption• Correct edge costs, use A* or D* to plot course to origin

– Unexpected Voids – Enter Exploration Mode• Take Unknown Crosscuts until…

– Exploration_Interest(Battery) < Battery Consumed– Dead End

• Return To LPC, Relay, Await

Specifications

NavigationSpecifications

• Navigation– Node to Node Transition

– Feature Identification: Corridor and Crosscut

– Partial Carmen Construction for Reverse

• Wall Centering and Obstacle Avoidance– Morphin algorithm

On-board / Off-board Software

• On-board– Voronoi Map and Feature ID (Bayes Classifier)– Logging: All Sensor Data – Time Stamped– Morphin– A* or D* path changes (shortest path home)– Carmen Map for reverse

• Off-board– Preprocessing– Carmen Map Software– Sensor Realization for Teleoperation GUI

Specifications

Chassis Layout

• Front Segment– 2 Identical battery packs– Drive motor and pneumatic

pump– PC/104 Stack– Sensor payload mounting

• Rear Segment– 2 Identical Battery packs– Drive motor and pneumatic

reservoir– Docking Mechanism

Major Subsystems

DrivePump

Battery Pack

Battery Pack

Air and Elec. Lines

TankDrive

Battery Pack

Battery Pack

Drive Layout

• Identical drives in both segments• Single drive shaft• O-Ring pressure seal• Bevel gear transmission• High gear ratio DC brushed motor

Major Subsystems

Steering Mechanism

• Single central steering joint• Dual pneumatic cylinder actuation• Wire/Pneumatic tubing pass-throughs• ~ +/- 30o turn angle• Intrinsically-safe potentiometer for steering

angle measurement

Major Subsystems

Chassis Pressure System• 1 Pump, 1 High pressure reservoir • 1 Valve per wheel• Solenoid valves to control pneumatic cylinders• 1 External valve/connector for initial pressurization & venting

– High pressure venting prevents mine air intake• Redundant pressure monitoring with certified pressure monitoring

system• Both segments and the mapping sensor (one pressure volume) purged

and pressurized prior to deployment• Wheels, cylinders, never directly connected to internal pressure

volume

Major Subsystems

Pump

TANK

Inflatable Wheels

• Sphere and torus shaped internal pressure volume

• Enclosed in wheel sleeve– Stability/traction– Abrasion resistance

• Central pump drives independent wheel circuits

Major Subsystems

• Wheels inflated in mine– Air supplied by base station via detachable snorkel

• Wheels are vacuum deflated for recovery– Extra air is vented to mine

Docking Mechanism

• Passive hook and catch mechanism– disengages when robot is level– engaged by driving catch into hook

Major Subsystems

Docking MechanismMajor Subsystems

Docking MechanismMajor Subsystems

Docking MechanismMajor Subsystems

Base Station

• Purged and pressurized– For deployment in gas filled mines

• Video– Low light panospheric camera– Downward facing camera

• Assists docking maneuvers– Light

• LED rings around camera lenses• Tether to surface

– Winch cable (pass through to robot)– Ethernet (fiber)– 2 video cables– Snorkel (pass through to robot)– Base station power

• Borehole anchoring mechanism– Can anchor on sides of borehole like Ferret for stability during docking

• Compass– Gives orientation of base station to assist docking

• Wireless Ethernet• Detachable Snorkel

Major Subsystems

Power ConfigurationMajor Subsystems

Rear Segment

Batt 1

Front Segment

Batt 2RearDrive Front

Drive

CPU

Laser

+5 Regulated

Air Pump

Batt 4

Batt 3

AdditionalSensors

Status and Control Electronics

• Battery health monitor– One in each segment

• Locomotion and actuation control– Front/Rear drive

• RS-485 motor controller– Steering

• Direct CPU control• Plain motor amplifier

– Pneumatic pump• Pneumatic manifold control

– Relay amplifier

Specifications

Status and Control ElectronicsMajor Subsystems

Rear Segment Front Segment

SteeringControl

Valves

Pot

Rear DrvController

Amp

PIDRS-485

Rear BatteryMonitor

Current

Voltage

A/D

Front DrvController

Amp

PIDRS-485Front Battery

Monitor

Current

Voltage

A/D

CPUDigital Out

PneumaticControl

Valves

Pump

Sensor LayoutMajor Subsystems

Rear-LeftWheel

Pressure

Rear-RightWheel

Pressure

RearSegmentPressure

Inertial Sensing

A/D

A/D

3-axisaccel

Gravimetric Sensing

2-axistilt

A/D

A/D

Front-LeftWheel

Pressure

FrontSegmentPressure

A/D

DIO

Electromagnetic Sensing

AnalogCompass

A/D

Front-RightWheel

Pressure

A/D

LaserRS-422

CPU

I/O Card

Serial

3 + 1UltrasonicSensors

RS-485

Current &Thermal Sensing

Current &Thermal Sensing

A/DA/D

3UltrasonicSensors

RS-485

SteeringAnglePot

Rear Segment Front Segment

DriveEncoder

DriveEncoder

RS-485

DIO

Laser Angle Pot

A/D

Battery Voltage &

Current

Battery Voltage &

Current

A/D

RS-485

Primary Sensor Deployment

• Primary mapping sensor deployed pneumatically– Dual redundant pneumatic actuators– Deployment device also serves as tilt module

Major Subsystems

Performance Goals

• > 1 kWh battery life– Li-ion 142 Wh/kg, 357 Wh/L 7 kg, 2.8 L

• < 70 lbs final mass• > 1 mph top speed• < 200 W average power consumption

– 2.5 mile maximum straight line travel– 2 mile maximum safe straight line travel– .5 mile radius maximum circular traverse

• > 50 deployments MTBF• < $20K• < 2 Person field team

Operations

Deployment

• Drill Borehole• Deploy Ferret to examine mine conditions• Power on computer and systems• Purge and pressurize cylinders and laser• Lower robot and base station• Inflate front wheels when front segment clears ceiling• Deploy primary mapping sensor• Lower front wheels onto floor and drive forward• Inflate rear wheels• Disengage docking mechanism and detach snorkel• Begin mine exploration

Operations

Recovery

• Teleoperate robot to engage docking mechanism

• Raise base station and robot• Deflate wheels in mid air• Stow primary mapping sensor• Raise robot• Retrieve data for post processing• Inspect robot and recharge air and power

Operations

Failure ScenariosOperations

Failure Mode

EffectFailure Mode Consequence Response

Wheel puncture/Loss of drive actuator

Loss of mobility in that direction

Deflate axle, use body as a reaction/steering tail

Slow pressure loss Robot becoming unsafe, or wheel is deflating

Open reservoir to maintain pressure level

Rapid loss of main pressure Robot unsafe Full systems shutdown

Computer Lockup Robot shuts down Reboot w/ watchdog

Navigation Sensor Failure Robot effectively blind Attempt immediate return to base with sonar and internal map

Proximity Sensor Failure Robot likely to hit obstacles Attempt immediate return to base with navigation sensor and internal map

Loss of steering actuator Reduced mobility Only actuate remaining functional steering piston

Violation of room and pillar assumption

Wall centering is no longer valid

Follow a single wall to continue mapping