Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 121BOE-BOT Lecture #3 EGR 120 – Introduction to EngineeringNavigating the BOE-BOTReference: For more complete documentation, the following items are available from www.parallax.com or www.tcc.edu/faculty/webpages/PGordy • Robotics with the BOEBOT Version 2.2• BASIC Stamp Syntax and Reference Manual Version 2.12Navigating a CourseThere are several ways to navigate a course using a robot. A variety of sensors are available to help the robot accomplish this task. Methods for navigating the a course might include:BOE-BOT Lecture #3 EGR 120 – Introduction to Engineering1) Dead reckoning - Exact path must be known ahead of time- Program tells the robot how far to travel before each turn- Errors in distances and turning angles accumulate, so best for simple, short courses.- Distances can be calculated using servos or stepper motors or infrared sensors can be used to count wheel revolutions. 2) Line following - This method requires a line to follow (some factories use lines on the floors that robots follow to deliver parts to assembly workers).- Infrared sensors (or other types) shine a beam of light on the floor and determine the line position by the amount of reflection.3) Wall following - This method requires that a wall is available for the robot to touch or sense.- One method involves using whiskers – sensors that can tell when the robot touches the wall.4) Distance sensing - This method again requires that walls are available so that the robot can sense the distance to each wall.- Range-finding sensors can be used to determine the distance to walls beside or in front of the robot.3Dead Reckoning - ExampleBOE-BOT Lecture #3 EGR 120 – Introduction to EngineeringTrack to be navigatedStartingLineFinishLineBarriers6 ft3 ftPossible path to follow• Go straight for 6 ft• Turn right 90 degrees• Go straight for 3 ft• Turn right 90 degrees• etcErrors begin to buildEach time that a distance is off or an angle for a turn is off, the robot gets further off the desired path.robot hits the wall4Line Following - ExampleBOE-BOT Lecture #3 EGR 120 – Introduction to EngineeringRounded corners are easier to followTape on trackLine on trackRobotInfrared light reflects off of the floorWheelInfrared sensor5Wall Following - ExampleBOE-BOT Lecture #3 EGR 120 – Introduction to EngineeringPath of robotPlace where left whisker hits the wallRobot naturally drives slightly to the left and then corrects right after left whisker hits the wallAreas of difficulty?RightWhiskerAdding angled barriers to corners may make navigation easier6Distance Sensing - ExampleBOE-BOT Lecture #3 EGR 120 – Introduction to EngineeringBeams from distance sensorsOne possible programming approach:- Steer more to the right if distance A < 2”- Steer more to the left if distance B < 2”- Turn right if distance C < 8”- Keep track of turns (R, R, R, L, L, L, R to complete the course)A BC7Navigating with the BOE-BOT using Dead ReckoningFirst of all, let’s be sure that it is clear what is meant by LEFT, RIGHT, FORWARD, and BACKWARD with the BOE-BOT. The Robotics Version 2.2 manual indicates that the ping-pong ball wheel is considered to be a rear wheel, so movement is defined as shown below.BOE-BOT Lecture #3 EGR 120 – Introduction to Engineering8Moving Forward with the BOE-BOTNote that in order for the BOE-BOT to move forward:• the right wheel must turn clockwise (CW)• the left wheel must turn counterclockwise (CCW)BOE-BOT Lecture #3 EGR 120 – Introduction to Engineering9Using Servo Data to control the BOE-BOTIn the last team assignment, data was gathered so that servo speed and direction could be determined as PULSOUT Duration is varied. The data might look something like the tables shown below.BOE-BOT Lecture #3 EGR 120 – Introduction to EngineeringPULSOUT Duration Servo speed and direction650 30 rpm CW660 27 rpm CW670 24 rpm CW680 21 rpm CW690 18 rpm CW700 15 rpm CW710 12 rpm CW720 9 rpm CW730 6 rpm CW740 3 rpm CW750 0 rpm (Stop)760 3 rpm CCW770 6 rpm CCW780 9 rpm CCW790 12 rpm CCW800 15 rpm CCW810 18 rpm CCW820 21 rpm CCW830 24 rpm CCW840 27 rpm CCW850 30 rpm CCWPULSOUT Duration Servo speed and direction650 30 rpm CW660 27 rpm CW670 24 rpm CW680 21 rpm CW690 18 rpm CW700 15 rpm CW710 12 rpm CW720 9 rpm CW730 6 rpm CW740 3 rpm CW750 0 rpm (Stop)760 3 rpm CCW770 6 rpm CCW780 9 rpm CCW790 12 rpm CCW800 15 rpm CCW810 18 rpm CCW820 21 rpm CCW830 24 rpm CCW840 27 rpm CCW850 30 rpm CCWLeft wheel servo Right wheel servoSince the BOE-BOT will travel forward if the left servo turns CCW and the right servo turns CCW, it will travel in a straight line using these two PULSOUT Duration values10Sample Program to move the BOE-BOT forward in a straight line (similar to the program on p. 125 in Robotics, Version 2.2)‘ Move the BOE-BOT forward in a straight lineCounter VAR WordFOR Counter = 1 TO 122 PULSOUT 13, 850 ‘Move left wheel CCW at max speed PULSOUT 12, 650 ‘Move right wheel CW at max speed PAUSE 20 ‘Pause for 20 msNEXTBOE-BOT Lecture #3 EGR 120 – Introduction to EngineeringNote that the program above assumes that the left servo is connected to P13 and the right servo is connected to P12 as shown to the right (reference: p. 100 in Robotics, Version 2.2)11BOE-BOT Lecture #3 EGR 120 – Introduction to EngineeringHow far will the BOE-BOT move? The manual (Robotics, Version 2.2) says that the program on the previous page will run each servo for about 3 seconds. Let’s see why:FOR Counter = 1 TO 122 PULSOUT 13, 850 ‘sets P13 high for 850*2 us = 1.7 ms PULSOUT 12, 650 ‘sets P12 HIGH for 650*2 us = 1.3 ms PAUSE 20 ‘pause for 20 msNEXTThe total time per loop is 1.7 + 1.3 + 20 = 23 ms plus a small amount of time for the BASIC Stamp to execute the instructions. The BASIC Stamp 2 executes 4000 instructions/second or each instruction takes about 0.25 ms. The five instructions in the loop will take about 1.25 ms, so the total time per loop is really about 24.25 ms.So the total time for the program is (24.25 ms/loop)(122 loops) = 2.96 seconds If the wheels have a diameter D = 2.5” then the circumference C = D = 7.854”If the BOE-BOT servos turn a maximum of 30 rpm, then the distance traveled in 2.96 seconds isDistance = (30 rev/min)*(1min/60 sec)*(7.854”/rev)(2.96