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Automated Refueling for Hovering Robots Nigel Cochran, Janine Pizzimenti , Raymond Short

Automated Refueling for Hovering Robots Nigel Cochran, Janine Pizzimenti , Raymond Short WPI Major Qualifying Project with MIT Lincoln Laboratory Group 76 Project Presentation Day 19 April 2012. Problem Statement.

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Automated Refueling for Hovering Robots Nigel Cochran, Janine Pizzimenti , Raymond Short

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  1. Automated Refueling for Hovering Robots Nigel Cochran, Janine Pizzimenti, Raymond Short WPI Major Qualifying Project with MIT Lincoln Laboratory Group 76 Project Presentation Day 19 April 2012

  2. Problem Statement • Currently, there is an insufficient mission duration for small hovering robots compared to the down-time required to charge their batteries • An autonomous apparatus for exchanging and charging batteries quickly is needed

  3. Project Goals  *

  4. Requirements and Assumptions • Navigating: UAV navigates itself to landing zone in negligible time • Landing: X-Y disp. of ± 6”, Yaw of ± 30°, Pitch/Roll of ± 15° • Base Size: < 3’x3’x2’ and < 30 lbs (excluding batteries) • UAV Modifications: < 100 g added to UAV (excluding battery) • Battery: 5000 mAh, Discharge time 18 mins • Battery Exchange: < 3 mins, Hot swap capable • Electrical Constraints: Balance charging batteries, < 200 W, Conversion will be provided • Software Requirements: ROS communication via Ethernet/WiFi, Initiate request for landing give battery voltage • Environment: Indoors (no weather)

  5. Solution Features • Off-the-shelf charge/balancing with custom interface • Enough batteries and short service to allow missions of any length with high duty cycle • ~ 2’x2’ open landing area with active alignment • Custom battery mount and UAV skids • Can be made universal for many UAVs • Rotating battery track • ROS communication • UAV reports battery level • Base signals when UAV can land

  6. Lithium Polymer Battery Charging • Venom Easy Balance AC LiPO Charger • Small: 4.01”x2.44”x1.39” • Charge Rate: 0.1-4.5 A (Mechanical Dial) • Balances: 1 Battery, 2-4 Cells • Design Advantage: COTS • Reverse Engineering • Dial glued at 4.5A (Maximum) • Pololuoutput port to activate start button • Monitor LED Voltage to know charger’s state

  7. Model of Batteries Required Ideal System Prototype

  8. UAV Alignment Device • Aligns UAV in center of base orientated in increments of 90° • Two Servo-actuated four-bar linkages • One servo per four-bar • Required torque of 200 oz-in, using 582 oz-in servos • L-shaped arms interlock for consistent positioning

  9. Universal UAV Skids • Based on Pelican’s skid design • Includes extended feet to widen base for easy battery exchange • Weight added to UAV: 109g

  10. Battery Transfer System • Raise/Lower Batteries • Scissor lift • Same 582 oz-in servo • Move between dock and UAV • Rack/pinion & linear bearing • 582 oz-in continuous servo • Enough for 2 cars • Limit switches • Rotate between charging docks • Turntable • 219.5 oz-in Stepper motor

  11. Battery Matingand Alignment • Connects correctly to base and UAV independent of rotation • 0.2” of compliance in mechanical alignment • Pyramid guided touch latch • 2.6lb of holding force • 3D printed ABS Plastic Casing

  12. I/O Devices • Battery (8x) • Start Charge Relay: Digital-Out • Monitor LED State: Analog-In • Presence Limit Switch: Digital-In • Battery Cart • Endpoint Limit Switch (2x): Digital-In • Middle Limit Switch: Digital-In • Positioning Motor: PWM • Scissor Lift Servo : PWM • Scissor Lift Current Sense: Analog-In • Turntable • Stepper Motor Direction: Digital-Out • Stepper Motor Number of Steps: Digital-Out • Photo Interrupter (8x): Digital-In • UAV Centering • Arm Actuation Servo (2x): PWM • Arm Actuation Current Sense (2x): Analog-In • Total I/O Required: 44 2x 24-pin Pololu Maestro USB Controllers

  13. High-Level Program Flow

  14. Program Structure • BaseStation • Manages system state progression using ROS • Contents: • Callback - handle messages from UAVs • Init - initialize starting variables and ROS parameters • State - state functions for actions and state transitions • Thread - run state and listener threads • MaestroController • Manages control of peripherals (sensors, servos, etc.) • Contents: • Actions - abstracted functions called by the BaseStation • Batteries - all battery-related functions • Cart - all cart and scissor-lift related functions • Inputs - handling for gathering information from the controllers • Low_Level - abstraction for basic USB communications • Servos - general servo functions • Stepper - all stepper motor-related functions

  15. Results • Total Time: Between 4 and 5 minutes • Scissor Lift took approximately 3 of the 4 minutes • Video: • mqp complete.wmv will be shown at this time • Future Recommendations: • New battery mating systems • Lighter aluminum or plastic frame • Hot-swapability • Faster motor on scissor lift • Second cart • GUI with system states and battery life • Sensor feedback on alignment system, like limit switches • Shorter stepper motor

  16. Acknowledgements • Lincoln Lab Staff: • Brian Julian (Group 77) • Mike Boulet (Group 76) • Byron Stanley (Group 76) • Mike Stern (Group 77) • Mike Crocker (Group 72) • Group 76 Technicians • Emily Anesta and Seth Hunter • WPI Faculty: • Prof. Ken Stafford (ME/RBE), Advisor • Prof. Bill Michalson (ECE/RBE/CS), Advisor • Prof. Ted Clancy (ECE), MITLL Site Director • Joe St. Germain (RBE), Robotics Lab Manager

  17. Summary • Problem Statement & Goals • Requirements & Assumptions • Solution Features • LiPoly Battery Charging • UAV Alignment Device • Universal UAV Skids • Battery Transfer System • Battery Mating & Alignment • Controls & Communications • Program Structure Questions?

  18. Charger LED Color Code • Pole LED voltage 3 times over 1 second to determine states • Possible States:

  19. System Battery Requirements • Approximate Number of Batteries Required (Worst Case) (Tf + Ts)n = Tc + Tf + Ts • Tf = Flight time = 15 minutes (min from specification) • Ts = Service time = ~1.5 minutes • Tc = Charge time = 5 Ah battery / 4.5 A charge = ~ 75 minutes • N = Number of Batteries = (Tc+Tf+Ts)/(Tf+Ts) = (91.5)/(16.5) = ~ 5 batteries • With a safety factor of about 1.5, we choose 8 batteries

  20. Estimated Analysis of Base Power – 8 Batteries Power Used (Watts) Time (minutes)

  21. UAV Communications Simulation in ROS

  22. Prior Art • 47.5 sec Service • No Hot-swap • Mechanical Arm Catching • Electromagnets • Battery Ring with Pusher • 2 min Service • No Hot-swap • Sloped Landing Area • Servo-actuated Magnet Mating • Offset Battery Ring • 21.8 sec Service • Hot-swap • 2 Arm Catching • Rail Battery Contacts • 2 Vertical Battery Drums • 30-70 min Service • Charge Via Contacts on Feet • Sloped Landing Area w/ Recess

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