Harvey Mudd College
Computer Science 154 - Robotics
Assignment C

Lab #3 write-up
SooYoung Jung
04/02/01

Fire-fighting contest

Introduction

Because of the popularity of the annual robocup soccer competition, an effort is underway to generate large-scale interest in other robotic tasks -- in particular, marketable ones. For instance, this year's robocup will include a search-and-rescue component. In keeping with this trend, your task in this assignment is to build and program a robot that can rescue a victim from a burning house. In addition, because two lab groups will be working on this project at the same time, we will add a bit of (friendly) competition to the task, running the two robots head-to-head at the time the assignment is due. (The inspiration for this assignment is a yearly fire-fighting competition at Trinity College in Hartford, CT.)

Task specifics

At the end of this lab assignment, we will fashion a "house" in the center of the research lab (BK120) consisting of rigid walls and obstacles. The layout of the house will not be known beforehand, but teams can count on the following:

• Except at wall junctions, there will be no walls less than 24 inches apart.
• The house will be enclosed (so that the robot will not be able to wander off into the space beyond the outer walls).
• The walls and obstacles will always run horizontally or vertically (in the coordinate system of the outer walls). (Thus, they will always meet at right angles, or as close as we can devise.)
• The walls will be one foot high.

Some part of the house will be set on fire. Rather, to simulate this, a lit candle will be placed on top of a six-inch platform either against a wall, in a corner, or between two walls in the house. Thus, the height of the flame will be six inches plus whatever the height of the candle is. (Leeway will be made to raise or lower the candle if it's the "wrong" height for a particular mechanism a team has constructed.) The robot will start in one of the four corners of the house and will be aligned initially with the walls. The goal of the robot will be to seek out the candle and extinguish it. Keep in mind that this is the highest-level goal -- other goals include maintaining the robot's health and keeping it from getting stuck.

Warnings These are general cautions that you should keep in mind throughout this lab project.

• The robot should not push or ram any wall/obstacle continuously, i.e., the intent is to keep the house in its initial configuration. If a robot seems to be pushing against a wall, it will be reset.
  
  
• You may devise whatever mechanism you like to extinguish the candle, as long as no water or fluids are involved and no harm comes to the robot.
  
  
• In general, keep your robot safe! Each lab group is responsible for their Handyboard, chassis, and sensors (all told, about $500).
  
  
• Do not use any glue or epoxy on your robot (tape is OK) -- keep in mind that everything needs to be returned in its original state.

Equipment

The computational brains of the robots are MIT's handyboards, based on the 68HC11 microcontroller. Each team will have one handyboard (again, for which they are responsible) and a copy of Fred Martin's technical reference for the handyboard. In addition, each team will have at least

• Three lego motors
• Two light sensors
• One infrared sensor
• Three touch sensors

Interactive C

The programming environment available for the Handyboards is Interactive C, for which an online reference is available, as well as documentation in the Handy Board Technical Reference.

What to do...

The first thing to do is to read the handyboard technical reference. This is a must as it explains everything you will need to know about the board. It is available here in PDF format. In particular, be sure you understand how to keep the board charged. You should leave your board in trickle-charge mode when not using it. For safety, I would advise avoiding "zap" charge -- forgetting that a board is "zap" charging can fry it.

From there, the project is wide-open. Some things to consider (and references):

• There are a couple of books in the Research Lab that have some tips and advice on lego construction. In particular, lego is not as strong or stable as you might guess, and you will need to reinforce your chassis to hold the Handyboard securely. Here is a link to a PDF file named The Art of Lego Design.
  
  
• You will need to pay attention to the drive train of your robot. The lego motors are high speed and low torque, so you may want to gear them down.
  
  
• Early on (even before a chassis is built) you should try out your sensors and motors via Interactive C. That way, code development can progress in parallel.
  
  
• Either the light or IR sensors (or both) can be used to detect the candle. You might also want to use them for detecting if objects are nearby. You will certainly want to use the touch sensors for that purpose. (Bumping objects is OK, just not pushing them.) You can extend the reach of a touch sensor by resting a lever against it.
  
  

The Contest

On the day the assignment is due (or the day after), each team will need to schedule a time to demonstrate their robot's search-and-rescue performance. There will be at least three trials for each robot on its own.

The first trial will involve a setup like the one below. This maze will be available for testing at least a week before the end of the project. The robot is indicated by the green rectangle (positioned upper left, facing toward the wall at the bottom of the diagram), and the candle is represented by the yellow circle (in the middle on the right).

The second trial will involve a similar set up, in that the maze and robot starting position will be identical, but the candle will be in an unknown location in the maze.

The third trial will involve an unknown maze (though not substantially different from the one depicted above) and unknown positions for the candle and robot.

Finally, if it seems feasible with the robot designs that the teams have created, there will be a head-to-head run with both robots located in an unknown (but symmetric) environment at equal distance from the candle.

1. Does the robot drive without getting stuck or endangering itself?
2. Can the robot find the candle and indicate that it knows that fact?
3. Can the robot extinguish the candle?
4. How quickly can it do so?

Write-up

In your write up, be sure to include at least a paragraph on each of the following items:

• An inroduction explaining how you intended to approach the problem.
  
  
• A description of your design and any special characteristics of your robot. Use pictures to help your description. There will be a digital camera available in the lab.
  
  
• A description of your control program and its organization. Also, add a link to your code.
  
  
• Problems you encountered and how you dealt with them.
  
  
• An evaluation of your system. (If you have pictures, again, you should include them as further explanation.)
  
  
• (Optional, but appreciated) Any comments about how this lab assignment could be improved.

Problem Approach and description of program

Since there were not much sensors (I tried to limit the sensors and motors as the project described) and smarter stuff that I can use in this project, I decided to use an algorithm as simple as possible.

The algorithm goes like follow:

The robot will wonder the maze until it finds the candle.  If the bump senses while wondering, it will avoid against to the wall or obstacle and wonder again.

When the IR sensor detect the flame, the robot will make left-right align, and move closer to the candle and make left-right align again to the flame and extinguish the flame.

Source code: sy.c

Extinguisher in action : ~~~.mpg

Characteristics of my robot and some pictures

Before the spring break, I tried to build the body, but it was my first time use lego, so it was not really easy to figure out which is for which.  So I built over spring break and it took some times to figure out the function of lego parts.  The robot was composed with following:

• Three lego motors
  - Left and right wheel are powered by these two motors and the other one is used for fan.
   
• Two light sensors
  - They were used to align to the flame, but not at the final.  They are located at the left and right side of the fan.
     This two light sensors couldn't really detect the flame so I covered with lego block so it can detect some of reflection from the candle.  However, they are very dependable to the size of flame and candle.
   
• One infrared sensor
  - This detects the flame and located at the center of the fan.
   
• Three touch sensors
  - Two of them are located at the front and the other is at the back to sense the wall.  The motor were geared down to 3:1 so it can go fast but not really high power but they are fine for this project.
   
• Bunch of lego blocks
   

    Pictures

Problems and solutions

The most problem for this project was aligning the robot to the flame.

The first approach was using two light sensors to make the robot left-right align to the candle.  However, the light sensors were not good to detect the candle location so I gave up with them and changed whole alignment function.

The second approach was using IR sensor to align to the flame and it worked much better than light sensors.  The robot will turn left and right and store the value of previous IR sensor (before making turn) and current one (after turing).  These two values were compared and used to make the robot align to the flame.

Final evaluation of my robot

The robot detects the candle well and the speed is pretty fast.  Moreover, the alignment was very accurate.
However, it was not smart enough to detect candle faster.  It just wonders the maze until it randomly detects the candle.   I firstly thought that I will put one IR sensor on left so I could use wall following algorithm or maybe other algorithms.  But I felt that the IR sensor isn't too good to detect the wall and because of the fault of motor (different power of motors for same input), I just decided to make the robot wonders with a lot of luck until it finds the candle.