Abstract This project explores algorithmic and heuristic

techniques of pathfinding by programming a Lego Mindstorms NXT Robot using the Not Exactly C(NXC) programming language. The robot itself is a three-wheeled (two powered, one support wheel) vehicle with a light and color sensor adjacent to each other attached to the front of the robot. By using a black tape track on a white background, the robot is programmed it interpret the input of its sensors to detect the track and follow it. A variety of different tracks were used to test the capabilities of the robot. Each track was designed to be more difficult to navigate than the previous track. Topics within the scope of this project include: different algorithmic and heuristic search, pathfinding, and path-following techniques; multitasking and concurrent programming; and advanced levels of complexity, such as obstruction avoidance.

Excerpt from Line Following Function:sub FollowLine(){

. . . while (true) //Follow the line forever {

. . . // set speed for motor 2 if (SensorLight < ThresholdLight && SensorColor == ThresholdColor) //if the light sensor is off the line and the color sensor is on the line // Bob has gone off the line on the right side OnFwd(OUT_B, SpeedFast); //make his right motor go fast so he can get back on line else OnFwd(OUT_B, SpeedSlow); //otherwise keep the right motor on the slow speed

if (SensorLight < ThresholdLight && SensorColor != ThresholdColor){ //if the light sensor and the color sensor are off the line in either direction Off(OUT_BC); FindLine(); //go to FindLine() so that he can get back on the line }

// set speed for motor 1 if (SensorColor != ThresholdColor && SensorLight > ThresholdLight) //if the color sensor is off the line and the light sensor is on the line //Bob has gone off the line on the left side OnFwd(OUT_C, SpeedFast); //make his left motor go fast so he can get back on line else OnFwd(OUT_C, SpeedSlow); //otherwise keep the left motor at the slow speed

Excerpt from Line Finding Function:sub FindLine(){while(SensorLight < ThresholdLight && SensorColor != ThresholdColor){ //while both the light and color sensors are off the line int degrees = 25; //the set number of degrees to turn to search for the line int i = 1; // i is the counter and the number that the degrees are multiplied // to in order to increase the number of degrees he is turning while(i <= 10){ //while the counter is less that or equal to 10 if(SensorLight < ThresholdLight && SensorColor != ThresholdColor){ //check to see that both sensors are off the line RotateMotor(OUT_B, 40, degrees*i); //if they are, rotate the motor at speed 40 for 'degrees' * i degrees SensorLight = SensorRaw(IN_1); //update sensor values SensorColor = SensorUS(S2); print(SensorLight, SensorColor); //print sensor values if(SensorLight < ThresholdLight && SensorColor != ThresholdColor){ //check to see that both sensors are off the line RotateMotor(OUT_C, -40, degrees*i); //if they are, rotate the motor at speed 40 for 'degrees' * i degrees } //Once these two if statements are complete, Bob has turned back to center //He has gone for a certain number of degrees in one direction, then //went the same number of degrees back in the other direction i = i + 1; //increase the counter so Bob can double the number of degrees he is turning //this allows us to have Bob search in a wide range in case he gets off the line by a lot } //end while }} // end FindLine()

Sources:Benedettelli, Daniele. Programming LEGO NXT Robots using NXC. 2007.Hansen, John. Not eXactly C (NXC) Programmer’s Guide. 2007.Sourceforge.net. Next Byte Codes & Not eXactly C. 2007. http://bricxcc.sourceforge.net/nbc/

Diagram: From Conception to Execution

Function Name Description

OnFwd(motor, speed); Given a specified motor and speed, this function turns the given motor at a given speed, forward.

OnRev(motor, speed); Given a specified motor and speed, this function turns the given motor at a given speed, in reverse.

RotateMotor(motor, speed and direction, degrees);

Given a specified motor, speed and direction, and number of degrees, this function turns the motor at a given speed and direction for a certain number of degrees

Off(motor); Given a specified motor, this function uses the brakes of the motor and stops the motor;

Float(motor); Given a specified motor, this function stops the motor without using the brakes.

Allison Avrich and James Padgett Advisor: Ed Harcourt