Simple Maze Solving Robots - Embedded Intelligent Robotics - Lecture Slides, Slides of Robotics

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Simple Maze-

Solving Robots

solving search in

real time

On line and off line search search (^) Off line Robot knows start and goal locations Robot does not know the start and goal locations Robot knows coordinates Robot knows description, can recognize when seen On line Robot knows start and goal locations Robot does not know the start and goal locations Robot knows coordinates Robot knows description, can recognize when seen Robot Has a map Creates a map

Problem Outline

• Robot is placed in a “grid” of same-sized squares
  • (Due to obscure and annoying technical limitations, the robot always starts at the “southwest” corner of the maze, facing “north”)
• Each square can be blocked on 0-4 sides (we just used note cards!)
• Maze is rectangularly bounded
• One square is a “goal” square (we indicate this by covering the floor of the goal square in white note cards )
• The robot has to get to the goal square

Using NXT you can build quickly all kind of robot

prototypes

• Uses basic “driving base” from NXT building guide, plus two light sensors (pointed downwards) and one ultrasonic distance sensor (pointed forwards)
• The light sensors are used to detect the goal square, and the distance sensor is used to detect walls

Robot Design, cont’d

Search Algorithm

• Robot does not know the map.
• Simple Depth-First Search
• Robot scans each cell for walls and constructs a DFS tree

rooted at the START cell

• As the DFS tree is constructed, it indicates which cells

have been explored and provides paths for backtracking

• The DFS halts when the GOAL cell is found

DFS Tree Example

GOAL START

DFS Tree Data Structure

• Two-Dimensional Array Cell maze[MAX_HEIGHT][MAX_WIDTH] typedef struct { bool isExplored; (= false) Direction parentDirection; (= NO_DIRECTION) WallStatus[4] wallStatus; (= {UNKNOWN}) } Cell;
• Actually implemented as parallel arrays due to RobotC limitations

Simple example of robot traversing unknown labyrinth to get to the goal

Simple example

• Example 3x3 maze GOAL

• Check for a wall – the way forward is blocked

• So we turn right

• So we go forward; the red arrow indicates that (0,0) is (1,0)’s predecessor.

• We sense a wall