Capability Enhancements for Autonomous Mobile Wireless

Sensor Platforms05506

Advisor: Dr. S. Jay Yang – CE

Team Members

Andrew Mullen – CE Edgar Martin – ME Khoa Nguyen – CE Darnelle Haye - ME Stephen Ortiz – CE Adam Haun - EE

Sponsor

Presentation Overview

• Project Goal– Design Objectives

• Objectives– Task Groups Formed to Accomplish Objectives

• Senior Design I Timeline• Chassis Design Process

– Concepts and Prototypes

• Electrical Design Process– Component Selection

• Communication Implementation• Senior Design II Timeline• Questions?

Project Goal

•  Develop a set of four mobile wireless sensor platforms with the ability to autonomously communicate and make decisions, independent of a base station, to create formations

Design Objectives

• Phase I– Design a cost effective and energy efficient chassis.

– Determine an appropriate sensor configuration to facilitate identification of objects and locomotion.

– Implement robust assembly code allowing the robots to move freely through their environment

• Phase II– Integrate wireless communication allowing the robots to exchange

information rapidly and effectively using the Mica2dot RF Transceivers.

– Construct an additional Three Mobile Sensor Platforms

– Develop and Code algorithms implementing formations

Task Groups

• Darnelle Haye & Edgar Martin (MEs)– Develop Chassis Design– Fabrication and Assembly of Chassis

• Stephen Ortiz & Khoa Nguyen (CEs)– Communication Interface – Wireless Software Development

• Adam Haun (EE) & Andy Mullen (CE)– Circuit-board Layout and Design– Sensor Integration– Robot Intelligence Assembly Code

Senior Design I Timeline

• First Quarter– Week 3: First Team Meetings, Performed Concept

Development and began Feasibility Analysis– Week 4: Basic chassis fabricated, performed weight test– Week 5: Completed Feasibility Analysis, Began

Implementation– Week 6: Second chassis, autonomous movement– Week 7: Improved Movement Commands to allow a more

robust and modular Interface– Week 8: Integrated Sonar Sensor– Week 9: Began Planning for Demonstration– Week 10: Debug, perform demonstration

Chassis Design Concepts

• Use a Pre-Built robotics kit or Custom Design– There are many kits to help novices design robots

• Method Of Locomotion– Different Drive Systems (Differential, Synchro, Skid-

Steer, Car-Type)

• Pivot Point Options– Castor Wheel or Ball Bearing

• Materials Selection

Feasibility Analysis Results

• Three Tier Design

• Chose to use 2 Stepper Motors– Utilizing Differential Drive

• Ball Bearings– More effective than a Castor

• Material - Acrylite FF Sheets – Lightweight , rigid, and weather-resistant thermoplastic. – Dimensionally stable, resistant to breakage, and can be

easily sawed, machined, heat-formed and cemented

Initial Concepts

-Does Not Rotate around

Center of Mass

-Inefficient Use of Space

-Awkward

-Not Enough Space for

Components

-Overly Heavy

Initial Prototypes

-Circular shape saves weight

-Makes Design more efficient

-Space for Sensors

-Location For Battery Pack

-Used for weight test

-Measured Maximum Load

-Prototype Unacceptable

For actual use

Current Chassis Design

• Ball Bearing Integrated

• Slight resize of platform levels

Mechanical Future Plans

• Integrate a more efficient ball bearing which is better suited for the mobile platform’s design

• Attach the compass chip to the chassis– Due to magnetic interference from the motors the

compass chip must be at least 6 inches from a motor– Magnetic shielding may allow the compass sensor to be

located closer to the rest of the electronics

• Examine the platform for ways to reduce weight

Electronics & Sensor Concepts

• PIC Microcontroller Selection• Motor Controller Selection• Distance Sensors

– Infrared Sensors– Ultrasonic Sensors– Which is more effective?

• Compass Sensor– Is one available which meets our needs and budget?

• Power Supply– Rechargeable battery? Size? Weight? Power?– Universal Power Supply or Multiple Power Supplies

Feasibility Analysis Results

• PIC-18F4320 Microcontroller• MC3479P & UC3770 Motor Controllers

– Both will be tested, MC3479 has a simpler interface, UC3770 may be more effective

• Front and Rear Ultrasonic Sensors– Devantech R93-SRF04 Ranger

• Integrate Compass Sensor– Devantech R117-COMPASS

• 9.6 Volt NiMh 1600 mAhr batteries– An LM317T is used to provide the 5V necessary to run the PIC,

controller logic, and sensors.– 3.3V may be added in the future to power wireless motes

Microcontroller Capability

• We used a PIC18F4320 to control the system.

• The PIC provides sufficient I/O ports to control the motors and interface with any of the sensors the team examined.– Nearly 40 Input/Output Bits– 4 Independent Timers– Internal USART support

• An internal clock speed of 8MHz gives the team plenty of extra processing power.

Initial Motor Controller(MC3479P)

• Pros: Low current, compact

• Cons: Weak, high heat

Current Motor Controller(UC3770AN)

• Pros: High power, low heat

• Cons: Requires two chips per motor and more complicated programming.

Sonar Sensor

• Relatively narrow Beam Pattern

• Linear Output

• Highly Accurate

• Range – 3 to 300 cm

Compass Sensor

• Adds Global Direction to Sensor Platforms

• Simplifies Algorithms

• Senses to within 0.1 Degrees

Assembly Considerations

• For the prototype, the main concern was the ability to easily change the circuit. A breadboard fills this need. However, the breadboard is unsuitable for the final robot because of its fragility and complexity.

• For the final robot, we will order a printed circuit board. This will be more compact and allow for more secure mounting.

Communication Goals

• Integrate the Mica2dot RF Transceiver with the main microcontroller.– Establish capabilities of Mica2Dot Wireless Motes.– Research Mica2 mote applications and proceed with execution on

Mica2Dot motes. – Determine how the motes are processing messages (Packet

Information)– Learn how to code NC programs to implement desired

functionality on the Mica2Dot Motes– Establish Communication between Motes, by means of a base

station controlled by PC to other motes

• Develop an interface through which communication can be effectively established.

Mica2Dot Wireless Mote

• Quarter-Sized (25mm), Wireless Platform for Smart Sensors

• Designed Specifically for Deeply Embedded Wireless Sensor Networks

• Battery-Powered• Lightweight

Mica2Dot Interface

• The Mica2Dot has 18 solderless expansion pins – 6 Analog Inputs– 6 Digital I/O Channels– UART (Universal Asynchronous Receive Transmit)

interface.

• UART transmission will be used for direct communication from the Mica2Dot to the PIC chip.

Transmission Packet Information

• Destination address (2 bytes) • Active Message handler ID (1 byte) • Group ID (1 byte) • Message length (1 byte) • Payload (up to 29 bytes):

– Source Mote ID (2 bytes)– Sample Counter (2 bytes) – Transmission Information Readings (up to 25 bytes)

Mica2Dot Code

• Written in NC (Network Channel) code. The code used to identify both switched and non-switched channel services.

• NC coding is module C based code. A module header file is needed to define the wiring used by the module as well as determine the module’s interface.

• The TinyOS operating system is Task Driven

Current Communication Progress

• Radio Communication – Set up wireless communication and packet sending

demonstrated by the red LED on a mote. One mote blinks an LED and sends packets to all other motes instructing them to blink their LED.

• Injecting and broadcasting packets sent by a Base Station – Injected packets from a PC into the sensor network by

means of Led_on and Led_off commands. Base Station mote broadcasts messages to receiving motes.

RS-232 Cable

Communication Future Plans

• Establish communication allowing a variable number of motes to send, process, and receive information without interference.

• Eliminate base station control to allow each sensor platform to remain autonomous

• Write code to visually log the information sent by the Mica2Dot motes on a computer terminal.

System Integration Challenges

• Difficult to Debug if Errors Occur– All Code done in assembly– No effective debugging tool because of sensor input

• Mica2Dot Motes– TinyOS installation and configuration is complex– UART Transmission difficult to test– CE computer virus

• Sonar Sensors– Can’t display distance easily– Difficult to manipulate received data

Senior Design II Timeline

Questions or Suggestions?

Extras

Motor Comparison

Motor Type Benefits Detractors Best For

DC motor Commonly available Too fast, needs gearbox Large robotsGreat variety High current usuallyMost powerful Harder to mount wheelsEasy to interface More expensiveA must for large robots Complex control (PWM)

Hobby servo Gearbox included Low weight capabilities Small robotsGreat variety Little speed control Legged robotsGood indoor robot speedInexpensiveGood small robot powerEasy to mountEasy to mount wheelsEasy to interfaceMedium power required

Stepper motor Precise speed control Heavy for their power Line followerGreat variety High current usually Maze solverGood indoor robot speed Bulky sizeEasy to interface Harder to mount wheelsInexpensive Low weight capability

Not very powerfulComplex controls needed

Mica2Dot Pinout

Microcontroller Pinout