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A Small Autonomous Fire-Fighting Robot System
Jason Plumb

Abstract

This paper describes the design and construction of a small autonomous robot for entry in the 1998 Fire Fighting Robot Competition. At the heart of the system is the 68HC12 microcontroller by Motorola. Program code to control the fire fighting robot is written in 68HC12 native assembly language. The system controls two optically isolated stepper motors for precision movement. Furthermore, the robot performs analog to digital conversion on 6 infrared sensors: 4 for wall proximity detection, one to detect floor markings, and one for candle detection. The 4 proximity sensors utilize heterodyne modulation of the IR signals to reduce the effects of ambient lighting. The extinguishing system is comprised of a large fan salvaged from a toy hovercraft, and a 3.5kHz tone decoder circuit is used to start the robot and gain bonus points.

Introduction

The annual Fire Fighting Robot Competition sponsored by Trinity College has been an exciting event for several years. Robot hobbyists and professionals of all ages from all parts of the world gather to compete and show off their creations. The goal of the event seems simple: Navigate a model house floorplan, find a lit candle, and extinguish it. As simple as this may sound, it is an intricate process to construct a device which can accomplish such a task. There are a vast number of design options and operating techniques that can be explored.

As the contest’s web page states, a primary purpose of the contest is to "provide an incentive for the robotics community to develop what will be a practical application for a real-world robot". Although the contest is merely a simulation of a real-world scenario, it requires the designers to use practical techniques to create useful designs. The competition serves as an example of what robots can do on a larger scale.

In the first year of competition, there were only a few robots that were able to successfully find and extinguish the candle reliably. The more recent events, however, have yielded a larger number of successful entries. It appears, that the designs are becoming more sound as the robotics community learns which approaches work and which fail. Because of these improvements, the event has a higher level of competition. An entry that strives to perform well must be fast and reliable. This designers of this project aim to accomplish both these tasks.

Contest Rules

Although the rules of the contest are lengthy and detailed, an overview will be given to provide a better understanding of the design approach used in this project. See the Rules Page (Appendix B) on the Trinity College web page for the full list of contest rules.

The maximum size of the robot is 12.5" x 12.5" x 12.5".
The robot must be completely autonomous and human control or intervention of any kind is not allowed.
The floorplan is a fixed layout (See Appendix A). The walls are white and the floors are black.
A white circle 12" in diameter will be placed on the floor surrounding the candle.
The bottom of the candle flame will be between 6 and 8 inches from the floor.
The candle will be placed in a room and not in a hallways.
Scoring is based on the time taken to find and extinguish the candle. Lower times are considered higher scores.
A 5% reduction in time will be given if the robot begins its trial by detecting a 3.5kHz tone.
A 10% reduction in time will be given if the robot is able to navigate back to the starting point.
A 30% reduction in time will be given if the robot does not use preprogrammed angles or distances in its calculations (ie. "dead reckoning")
A 10% reduction in time will be given if the robot is successful in finding and extinguishing the candle in 3 consecutive trials.
A 5 second penalty will be applied each time the robot touches a wall.
A 50 second penalty will be applied if the robot touches the candle.

Overview of Robot System
Figure 1 is a functional block diagram of the robot system. At the heart of the robot is the 68HC12 microcontroller from Motorolla. The microcontroller is responsible for sending signals to and receiving signals from the robot hardware. First, the 68HC12 receives input from the calibration button before each run. This allows the user to align the robot at a specific distance from the desired wall to be followed. Once this has occured, the 68HC12 waits for a logic low from the tone-decoder. Then, the controller outputs to the optoisolators to control the motor driver circuits. The controller also reads values from the IR phototransistors in order to detect walls and search for the candle.

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