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1 8/22/2011 Automated Refueling for Hovering Robots Nigel Cochran, Janine Pizzimenti, Raymond Short WPI Major Qualifying Project with MIT Lincoln Laboratory.

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Presentation on theme: "1 8/22/2011 Automated Refueling for Hovering Robots Nigel Cochran, Janine Pizzimenti, Raymond Short WPI Major Qualifying Project with MIT Lincoln Laboratory."— Presentation transcript:

1 1 8/22/2011 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 2 8/22/2011 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 3 8/22/2011 Project Goals UAV to Base Communication Reliable UAV Positioning Exchange and Store Batteries Charge and Balance Lithium- Polymer Batteries Maximize In-Flight Duty Cycle Easily Adapted for other UAVs

4 4 8/22/2011 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 5 8/22/2011 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 Solution Features

6 6 8/22/2011 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) –Pololu output port to activate start button –Monitor LED Voltage to know charger’s state Lithium Polymer Battery Charging

7 7 8/22/2011 Model of Batteries Required Ideal System Prototype

8 8 8/22/2011 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 UAV Alignment Device

9 9 8/22/2011 Based on Pelican’s skid design Includes extended feet to widen base for easy battery exchange Weight added to UAV: 109g Universal UAV Skids

10 10 8/22/2011 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 Battery Transfer System

11 11 8/22/2011 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 Battery Mating and Alignment

12 12 8/22/2011 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 I/O Devices 2x 24-pin Pololu Maestro USB Controllers

13 13 8/22/2011 High-Level Program Flow

14 14 8/22/2011 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 Program Structure

15 15 8/22/2011 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 Results

16 16 8/22/2011 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 Acknowledgements

17 17 8/22/2011 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 Summary Questions?

18 18 8/22/2011 Pole LED voltage 3 times over 1 second to determine states Possible States: Charger LED Color Code LED ColorsState All orange (2.4V)Charging All green (4.7V)Charged Orange and no light (0V)Waiting: Battery connected Green and red (0.6V)Waiting: No battery connected Red and no light Error All red No light

19 19 8/22/2011 Approximate Number of Batteries Required (Worst Case) (T f + T s )n = T c + T f + T s –T f = Flight time = 15 minutes (min from specification) –T s = Service time = ~1.5 minutes –T c = Charge time = 5 Ah battery / 4.5 A charge = ~ 75 minutes –N = Number of Batteries = (T c +T f +T s )/(T f +T s ) = (91.5)/(16.5) = ~ 5 batteries With a safety factor of about 1.5, we choose 8 batteries System Battery Requirements TfTf TsTs TfTf TsTs TfTf TsTs TfTf TsTs TfTf Ts2Ts2 TcTc Ts2Ts2

20 20 8/22/2011 Estimated Analysis of Base Power – 8 Batteries Power Used (Watts) Time (minutes)

21 21 8/22/2011 UAV Communications Simulation in ROS

22 22 8/22/2011 Prior Art UMichigan (2010) : Swap/Recharge KAIST (2011) : Swap/Recharge MIT/Boeing (2011) : Swap/Manual Recharge MIT (2007) : Recharge Only 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 47.5 sec Service No Hot-swap Mechanical Arm Catching Electromagnets Battery Ring with Pusher 30-70 min Service Charge Via Contacts on Feet Sloped Landing Area w/ Recess


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