CS 102B Robot Design Tuesday, 113004

1
CS 102B Robot DesignTuesday, 11/30/04

• Todays Class
• Return Graded Project 4
• Questions for Exam 2?
• Internal robot navigation obstacle avoidance
• Depth First Search
• Hill Climbing
• Exam on Thursday 12/2 see last times slides
  for information

2
Obstacle Avoidance using Internal Navigation

• Recall
• External navigation means using external
  landmarks to know position and orientation
• Internal navigation keeps track of distances and
  turns to know position and orientation
• Obstacle Avoidance Using Internal Navigation.
  Keep track of
• Distance traveled (or time traveled)
• Last turn direction (right, left)
• Last orientation (north, south)
• When obstacle is hit (or proximity detected)
• Back up
• Turn away from obstacle
• Try to move forward again

3
Depth First Search

• General idea
• Travel forward as long as possible
• If obstacle hit, try an alternative direction
  (say right turn)
• If obstacle cleared, continue
• If obstacle not cleared, try another alternative
  (say left turn)
• If obstacle still not cleared, try last
  alternative (turn around)

4
The Program DFSNavigate.nqc

• task main()
• ClearTimer(0)
• SetSensorType (SENSOR_1, SENSOR_TYPE_TOUCH)
• SetSensorMode (SENSOR_1, SENSOR_MODE_BOOL)
• SetSensorType (SENSOR_3, SENSOR_TYPE_TOUCH)
• SetSensorMode (SENSOR_3, SENSOR_MODE_BOOL)
• start RunRobot
• start SenseObstacle
• //end main()

• task RunRobot()
• timeStart Timer(0) //initialize
• GoForward()
• int lastOp F
• until (Timer(0) TIME_PROG)

task SenseObstacle() while (true)
if (SENSOR_1 1 SENSOR_3 1)
CorrectCourse() //end if
//end SenseObstacle()
5
function CorrectCourse

• int timeNow Timer(0)
• int timeElapsed timeNow - timeStart
• Halt()
• BackUp()
• WaitTenths(TIME_BACKUP)
• Halt()
• if (timeElapsed gt DELAY) TurnRight()
• WaitTenths(TIME_RIGHT)
• lastOp R
• else if (lastOp R)
• TurnAround()
• WaitTenths(TIME_AROUND)
• lastOp L

• else if (lastOp L)
• TurnLeft()
• WaitTenths(TIME_LEFT)
• lastOp A
• else if (lastOp A)
• Halt()
• lastOp H
• PlaySound (SOUND_DOWN)
• StopAllTasks()
• //Starting regular motion again
• GoForward()
• timeStart Timer(0)

6
Hill-Climbing Obstacle Avoidance

• With the hill-climbing approach we commit
  ourselves to traveling in a single direction, and
  never turning back
• Think of a ball rolling down a hill it cant
  turn back
• North down
• East Hill slants to right
• West Hill slants to left
• NE Hill Climbing algorithm may go north or
  east, never west or south. (Could also do NW.)