An Autonomous Robot The Ideal Design Project?

This paper describes a senior design project at Trinity University from the 1997-98 academic year. Senior design at Trinity is the culmination of four years of design courses and of integration of design into undergraduate laboratories and into engineering science courses. The autonomous robot designed by four seniors (advised by two faculty) is a four wheel vehicle, powered and steered by two DC motors, controlled by an MIT “Handy Board,” with optical encoders and IR sensors as inputs. Starting from a fixed position, the robot finds its way to a given destination coordinate while avoiding randomly placed obstacles along the path. The project is an excellent teaching and learning experience due to the multiple disciplines involved: logic, electronics, control, programming and mechanics. In addition, the project provides the students with a relatively realistic professional experience involving financial and time budgeting, management, meeting of deadlines, making presentations and writing reports. Introduction Probably due to the interdisciplinary nature of the program, design has been an integral part of the undergraduate curriculum in Trinity’s Engineering Science program since its inception in the 1960s. From those early beginnings, courses in engineering design have been in the engineering science core—courses with group-oriented projects beginning with the first semester and culminating in the senior year with a full year project that builds upon the entire curriculum. The nature of the design element in the engineering science curriculum has evolved considerably in the thirty years since its inception. In the early 1990s, the Department reviewed the design components of the curriculum and redirected the emphasis on design to the entire engineering core [1] [2]. Rather than treating design as a separate component of engineering, the approach adopted by the Department tries to incorporate and integrate engineering science and design wherever possible in all courses and laboratories. Along with philosophical changes, the availability of new tools to support design (e.g. personal computers, microprocessors and simulation tools such as Spice, MATLAB® and LabView®) have changed the curriculum and the students’ ability to engage in and complete more difficult and realistic projects. The 1980s saw the first integration of computers into senior design projects and the advent of projects based on robotics and microprocessors. Besides the obvious benefits of these tools in enhancing the capabilities of students to successfully attack “real-world” problems, these technological advances also promote interdisciplinary projects. Background The design curriculum (in terms of specific courses) begins in the first year, which contains two three-hour courses that include topics in graphical analysis and communication, an introduction to the processes of engineering design, analysis techniques and two competitive design projects (i.e. groups in each semester pursue designs that meet a common set of specifications). First year projects are typically truss or bridge designs (in the first semester) and a “water balloon launcher” in the second. The second year contains two one-hour courses that address design of experiments, engineering economics, optimization and a competitive mechanics-oriented project in the second semester. The third year follow in the same (as the second year) format, addressing management of design activities, reliability, two competitive projects (electrical in the first semester and thermo/fluids [3] in the second) and initial preparation for the senior project. P ge 462.1 The fourth year consists of two three-hour courses, each dedicated to a single, small group-oriented, year-long project. Group sizes range from three to six members—groups usually are formed by following student preferences for the initial project description developed in the third year. Each group is assigned a faculty advisor and the two courses have a faculty member who oversees the entire course and who is responsible for overall coordination, presentation of specific topics and grading. As part of their execution of a design, students are expected to demonstrate the establishment of design specifications and criteria, analysis and synthesis techniques, aesthetics, safety, construction, testing and evaluation. The courses also provide some exposure to mathematical modeling, the use of chemical, mechanical and electrical analogs, optimization, ethics, robust design, life cycle analysis, reliability and other current topics in engineering design. The background that students have prior to embarking on a fourth-year project involving robotics includes physics, chemistry, six semesters of mathematics, statics and dynamics, electric networks and electronics, and controls. Most electives are taken in the third and fourth years, with many electives taught once every other year. Elective courses that are pertinent to this project are modern control systems, a second electronics course, digital logic and microprocessors. The description of the project and the robot that follows is largely derived from the student group’s final report [4]— it reflects their progress through the design process and the final decisions they made in implementing their robot. Project description and constraints The objective of this project is to design and build a microprocessor controlled land vehicle which will autonomously find its way from an initial starting position to a final destination coordinate while avoiding a set of randomly placed obstacles in its path. Up to five static obstacles could be placed at least three feet apart from each other along the robot’s path on a 30’x30’ playing field. The obstacles are opaque and they are of cubic shape. The vehicle must complete the course in less than fifteen minutes and reach its destination within three-foot radius. The robot must fit in a two-foot cubic box and must weight less than twenty pounds. The total cost for the project cannot exceed $500. To accomplish the project objectives within the above constraints, the students had to research the available types of micro-controllers, motors, obstacle avoidance sensors, navigation techniques, and the materials to use for the robot’s platform. Microcontroller The microcontroller is the most important component of this project. It monitors the inputs, performs computations, makes decisions, and drives the outputs in the manner desired by the designer. After evaluating some of the most popular microcontrollers such as the Motorola 68HC11, the Intel 8051, Microchip PICs, and the Parallax Basic Stamps, the design team decided to use Handy Board from the Media Laboratory at MIT [5]. The Handy Board uses the Motorola 68HC11 microcontroller with 2 MHZ system clock. It has the means of driving up to four separate DC motors. It contains power header inputs for 9 digital sensors and 7 analog sensors, 32k of battery-backed CMOS static RAM, 16x2 character LCD screen, internal 9.6 Volt Nicad battery with recharging circuitry, an IR input and output, and many other features. The Handy Board has an RS-232 port for easy interfacing with an IBM-PC or compatible computer. It also includes a bundled Interactive C programming language. In short, the Handy Board is ideal for robotic applications since it includes the microcontroller and all the necessary hardware to interface it with the target system. Platform, motors, and wheels: To build the platform of the autonomous vehicle, the design team decided to use model airplane wood because of its light weight, low cost, and wide availability. Model airplane wood is lighter and easier to machine than plastic, metal, or normal plywood. The base of the platform is circular with an 8-inch radius and 1⁄4 inch thickness. The circular platform was chosen in order to improve maneuverability around obstacles. Two permanent magnet DC motors are used to power the vehicle. Each motor has independent speed and direction controls, allowing the vehicle to move forward, backward, or turn in any direction. The Handy Board independently drives each DC motor. The front and the back caster wheels enable the robot to perform sharp turns around its central axis. A diagram of the robot platform with the relative positions of the wheels and motors is shown in Figure 1. P ge 462.2