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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
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