Esplanade Runner - Autonomous Vehicle Navigation in Small Vehicles

Contents

1 Introduction
1 System Layout
2 System Communication
3 System Specifications
3-A Proposal Specifications
3-B Specifications as Tested
4 Project Budget

2 Hardware and Sensors
1 Schematic and Wiring
2 Mounting
3 Compass Sensor
4 Acoustic Sensors
5 GPS Unit
6 Site Selection for Testing
7 Power Systems

3 MCU
1 Functionality
2 Programming and Debugging
2-A Programming
2-B Debugging
3 Issues

4 PDA
1 Introduction
2 Functionality
3 Programming and Debugging
4 Issues

5 RouteDraw Web Tool
1 Functionality
2 Programming and Debugging
3 Issues

6 Simulation Tools
1 Functionality
1-A Full System Simulation
1-B PDA Testing Simulation
2 Programming and Debugging
3 Issues

7 BasicSystem Operation
1 Site Selection
2 Route Drawing
3 Loading PDA
4 Running the Esplanade Runner
5 Issues

A Component Specification Sheets
1 Garmin eTrex PDA Specifications
2 CMPS03 Magnetic Compass Chipset
3 MMP-8 Mobile Robot Platform
4 SRF05 Ultra Sonic Ranger
5 M68DEMO908GB60 MCU Board
6 Hewlett Packard iPAQ RX1955 PDA
7 GPS TEXT Output Communication Format
8 MCU Internal Schematic

B Specification Discussion

C Future Steps
1 Route Draw Web Tool

Glossary

List of Figures

1.1 Vehicle in attack-mode

1.2 Diagram Showing the Flow of Control in the System

1.3 Diagram Describing System Communication

2.1 3D Model Used for Acoustic Sensor Placement

2.2 System Schematic

2.3 A picture of the vehicle with all the components mounted

2.4 Compass Chipset

2.5 Acoustic Sensor Chipset

2.6 Acoustic Sensor Timing Diagram

3.1 MCU Development Board

3.2 MCU USB Programmer Setup

3.3 MCU Connection Manager Settings Panel

3.4 Hyperterminal Serial Port Settings

4.1 Logging Screen showing the entries recorded for a very small course

4.2 Visual Studio 2005 Create Project Window

4.3 The Debug Menu allowing the user greater control of the PDA functionality and the system settings

5.1 Drawing a route around the baseball diamond using the WebTool

6.1 Simulation of the MCU and Vehicle Dynamics

6.2 The results of a simulation where the compass is poorly calibrated and has a large steady-state error the top graph is the vehicle path the bottom graph is a plot of the compass readings vs. time where the red is the actual orientation and the blue is the compass output

7.1 A field test being conducted in Amory Park

7.2 Parameter Screen on EspRunner application running in PDA emulation environ- ment

A.1 The Acoustic Sensor’s Beam Profile

Chapter 1

Introduction

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Figure 1.1: Vehicle in attack-mode 5

Executive Summary

The task of autonomous vehicle navigation coupled with obstacle avoidance is a notoriously difficult problem involving communication with a variety of sensors and a motor control system in real time. Our project is to create a system that will enable a mobile platform to navigate a given route, while avoiding obstacles in its path. This system consists of a portable digital assistant (PDA), a microcontroller unit (MCU), and three different sensory devices, namely, a Global Positioning System (GPS), a digital compass, and acoustic sensors. The combination of the PDA and MCU algorithmically interacting with these sensor devices creates a system that maneuvers a vehicle through a user-determined route.

1 System Layout

The concept behind this system is to utilize the information from all of the sensors to determine the answers to a few simple questions; where are we, where do we need to go and how do we get there?

We utilize a handheld GPS unit to pinpoint the vehicle’s current location (longitude, lati- tude), along with where we need to go. By using a digital compass to correctly orient ourselves in the desired direction, we repeat this procedure iteratively until we’ve successfully completed our route.

There are four main elements to this process: the web application, the PDA, the MCU and the sensory devices each playing a role to the overall function of the vehicle.

The web application has three main functions. The first function is a web tool based on Google Maps that allows any user to use the satellite imagery of the earth and define a waypoint based route using only a few simple mouse clicks. The second of these functions is to translate the user defined route into a series of longitude and latitude coordinates that the PDA program will later use as the basis for its positional information. The last function is creating a file that can then can be transferred and read by the PDA as a map.

The PDA application has two main functions. The first of which is determining current location, desired location and all relative information required to connect the two. The PDA does this by requesting GPS data via the MCU. Once the PDA receives the requested data, the PDA uses the vehicle’s current position and the next waypoint in the route file that was generated by the web tool and calculates the direction between its current position and the next waypoint. The PDA sends this angle as a command to the MCU which translates that command into signals to the motors. In addition to this navigation command, the PDA also serves as the user interface for the entire system. From this UI, the user can start/stop the vehicle and set parameters pertinent to system operation (forward and rotate speed, sensor threshold, toggling obstacle avoidance, etc).

The MCU plays an important role in directly interacting with the sensors and providing real-time when they are needed such as during obstacle avoidance and turning. It is in charge of communicating, relaying and interpreting all data that passes through it. The MCU links the PDA, GPS unit, digital compass, acoustic sensors and motor control of the vehicle into a single coherent unit. Each of our components employ a distinct communication protocol and attempting to link them without a central unit to understand and standardize them would prove extremely difficult if not impossible. From the perspective of the entire system the PDA serves as the master and the MCU as the intermediary and the remaining components as the slave. When requested by the PDA, the MCU requests data from the GPS and compass and forwards it back to the PDA.

While the system is operating, the MCU functions also as an obstacle watchdog constantly pinging the acoustic sensors to determine if an obstacle exists anywhere near the body of the vehicle. If the sensors indicate there is an obstruction in its path, the MCU uses its real-time obstacle avoidance algorithm to steer clear of the object and continue along with its path once it has cleared the obstacle. The last function of the MCU is to generate signals to the motors known as pulse width modulation (PWM) that control the speeds at which the motors rotate.

The sensor units each have one primary function, and that is to acquire data indicating whether there is an obstacle in front of it. The sensors are positioned so that it is able to detect potential obstacles on the left side, right side, and in front.

The handheld GPS communicates with satellites in the sky and sends data regarding its exact location on the earth in terms of longitude and latitude coordinates. The GPS is connected to the MCU via serial- port and is constantly transmitting the coordinates of its current location. The digital compass’ provides the deviation from magnetic north. The compass is used to position the vehicle at the correct angle, in order to head in the right direction. It communicates with the MCU by means of the I2C protocol. The acoustic sensors are then used to detect if an obstacle is blocking the path of the vehicle.

2 System Communication

Communication between the different components is essential to the core of our system. Because the MCU acts as the central control unit, all components communicate via different protocols to ensure that all data do not end up on the same bus and thus risking data interference.

The GPS communicates with the MCU through a serial port connection. This data transfer is a one way (MCU does not request data from the GPS, MCU selectively ignores data bursts until the PDA requests it) in which the GPS constantly sends all information regarding current coordinates to the MCU in a string format output.

The acoustic sensors are connected to the MCU by a general purpose IO port. When information from a particular sensor is requested, a pulse is generated by the MCU, sent down the line which is translated by the sensor’s internal circuitry into an ultrasonic acoustic pulse emitted by the sensor chip. When the acoustic pulse returns (echo), the sensor chip translates the response into another pulse which is sent back to the MCU on the same IO port. By using the linearly proportional relationship of time between pulse and echo and speed of sound, the MCU can determine the distance at which an object is detected.

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Figure 1.2: Diagram Showing the Flow of Control in the System

The compass is then connected to the MCU via I2C interface. Through the I2C interface the compass sends its current heading to the MCU in byte form, where the MCU can then use this information to rotate the vehicle to the desired heading.

The PDA is connected to the MCU through the MCU’s second serial port. This connection is a bi-directional communication in which the PDA and MCU can send information back and forth. The MCU takes the GPS data string that it receives and forwards this information to the PDA. Once the PDA calculates the angle that the vehicle should rotate, it then sends this angle back to the MCU through the serial port connection with instructions to rotate the vehicle until the desired heading is reached.

The MCU’s PWM module is responsible for regulating the signals sent to the motors are responsible for vehicle motion. Based on the MCU’s instructions of how fast and which direction the vehicles motors should rotate, the MCU will send a duty cycle pulse of 1.0 - 2.0 milliseconds, 1.0ms being the maximum reverse speed, 2.0ms being the maximum forward speed, and 1.5ms being the dead zone.

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Figure 1.3: Diagram Describing System Communication

3 System Specifications

In out initial proposal we produced a number of specifications for the operation of our vehicle and system based on simulations, research, and manufacturer specifications.

3-A Proposal Specifications

Vehicle and onboard computers Specifications

- Operational Specs
– Minimum operating speed is 1 foot/second
– Climbs 10% grades
– Operates anywhere with GPS coverage
– Operates for at least 1 hour without recharging
– Operates on 12V battery pack
– Operates on concrete or short grass surfaces
– Adapts route to avoid objects greater than 20cm× 20cm× 20cm
– Withstands impact of up to 1 foot/second without loss of performance
– Will navigate the predefined route within a 20 foot radius
- Modular Design (components can be removed and added)
– Sensor Units
– GPS supporting UART & NMEA

3-B Specifications as Tested

- Vehicle is within 5-10 feet of desired route, in the absence of obstacles, given a GPS fix of 3 or more satellites
- Vehicle travels at 2.5 feet/second and the speed can be adjusted from 0.7 feet/second to 3.7 feet/second
- Vehicle can climb 20% grade
- Vehicle operates for approximately 40 minutes depending on conditions
- Vehicle is easily capable of navigating concrete, grass, dirt paths, and bumpy fields. Per- formance however as the terrain quality decreases.
- Withstands impact of up to 3 feet/second into solid object (testing on tree) without loss of performance
- Vehicle avoids obstacles with at least a 15cm× 15cm cross section to the vehicle sensors
- Vehicle communicates with GPS using TEXT standard developed by Garmin and available in all of their products

The discrepancies and changes made between these two specifications are discussed in detail in Appendix B (Page 59).

4 Project Budget

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Chapter 2

Hardw are and Sensors

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Figure 2.1: 3D Model Used for Acoustic Sensor Placement

The hardware and sensors are a crucial area of the project since this is how all everything is physically connected together and the communication methods between components. Much of our time was spent this semester in determining and documenting how many of these standards worked because the available material was not adequate.

1 Schematic and Wiring

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Figure 2.2: System Schematic

2 Mounting

The way in which we mounted all the hardware on vehicle was important in the design process because nothing could be drilled or permanently attached to the car. Everything connected to the actual vehicle must be temporary. Because the vehicle is built on two separate planks that move up and down individually, we could not mount all the components on one plane and rest it on the entire surface. To overcome this challenge, we created a system that is raised above one side of the vehicle so that it will not interfere with the up and down motion of the two planks. A cork plate is used to support the PDA, the GPS, the MCU, and the compass. To attach all the components we use double sided velco tape. Velcro is the ideal mounting material because it is strong and will support the weight of the components, yet it is temporary and does not destroy

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Figure 2.3: A picture of the vehicle with all the components mounted

the vehicle. All the components are therefore attached to the cork plate via the velco tape. This enables the user to detach all the components at will and reattach them with ease. The sensors are connected to metal L shaped brackets using electrical tape which are strategically placed to maximize the visibility of obstacles. Two sensors attached to brackets are velcro’d to the vehicle in front, and two are placed on the sides of the vehicle (one on each side). The plastic plate is raised 4 inches from the car to clear the sensor brackets as well as the vehicles bidirectional up and down motion of the two sides. To raise the plate, there is a wooden bridge type support system that is attached to one side of the vehicle by Velcro, also allowing the user to detach it at will.

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