Problem Solving with Robots

Problem Solving with Robots Scott Turner Oliver Hawkes

Acknowledgements and Introduction This project has been supported by the ICS Teaching Development Fund and also with help from Nuffield Science Bursary and SETPOINT Northamptonshire. As well as the Division of Computing and Teaching Enhancement Award, University of Northampton. Introduction This pack is aimed at supplementing taught materials on problem solving with some exercises to work through based around the Mindstorms RCX.

Sequence, Branching and Loops Let s start with three basic types of routines and these are sequences, loops and branches. Each of these makes the program behave differently when an event happens, and most programs are a combination of all of these. Sequential A sequential routine is, as its name suggests, is a sequence of commands to be completed. Put simply, it is a list of instructions that are carried out one after the other. The list below is a set of directions, and these are a sequential routine. Instruction 1 Instruction 2 Instruction 3 Once the sequence is completed the program stops. Conditional Branching Stop Go forward Turn left Go forward Turn right Etc. Conditional branching allows different commands to be carried out depending on the result of tests. It is called conditional branching because depending on different conditions, different branches of commands are followed. A condition could be birds fly or x>4, when the statement is true the condition is true. If test is true Instruction 2 or sequence 1 Instruction 1-test Instruction 4 or sequence If test is false Instruction 3 or sequence 2 Imagine you were giving directions to somewhere, but you weren t sure if one of the roads is closed. If it were open your directions would go straight on, but if it were closed you would have to re-direct them. This is a condition and the results are the branches.

Sequence, Branching and Loops Loops This is a set of commands that are followed and then repeated. The loop can be continuously looping the same instructions (for example the diagram to the right) Conditions can be added to the loop and the diagram below. The loop will only be repeated if a test has a true condition, otherwise a different set of instructions are carried out. Instruction 1 Instruction 2 Instruction 3 Instruction 1 test If test is true If test is false Instruction 2 Instruction 3 Routines often involve a combination of all sequential, branches and loops in order to make them work.

Example Let s start with an example This routines moves a robot forwards for 1 second, backward for 1 second, and then turns 90 degrees to the right. public class week2_1 public static void main(string[] args) robot2 buggy=new robot2(); buggy.forward(1000); buggy.backward(1000); buggy.spinright(1000); We are only interested in the bits in bold underlined italics. We can ignore the rest for the moment. The line buggy.forward(1000); moves the robot called buggy forward for 1000milliseconds. The line buggy.backward(1000); the buggy backwards for 1000 milliseconds The line buggy.spinright(1250); turns buggy to the right for 1000 milliseconds which for this robot ends up being a right-angle turn. Notice the order of the lines and the actions carried out: buggy.forward(1000); buggy.backward(1000); buggy.spinright(1250); 1. Do the first line first 2. Do the second line next 3. Do the third line after that

Example Here is the main part of the robot the RCX brick. The motors are drive from ports A, B, and C. The sensors are connected on ports 1,2, 3. Image taken from : http://en.wikipedia.org/ wiki/image:legomindstormsrcx.jpg In the problems unless otherwise stated the sensors will be connected on ports 1 and 2 and the motors on ports A and C. An example robot below has a left bumper sensor connected on port 1 and a right bumper sensor on port 3. The left and right motors are on ports A and C respectively.

Initial Problems Introduction Use the routine from the previous example. Replace the instructions in bold italics with instructions to do the following. You might have to experiment with times. That is good thing. Problem 1 Create a sequential routine, using the instructions provided, to make a robot trace out a square of the desk. Each side of the square will be the same length as the distance covered by the robot when it moves forward a second. Problem 2 Write routines to get the robot to trace out the following letters (approximately). It might be easier to draw these shapes out first and move the robot by hand to get a sense of how the robot would move. C Can you think of at least two ways this can be done? Z

Dancing Robot 1 Introduction Using the Framework below get the robot to do a little dance. The moves are up to you. The robot must dance in a 1m square area (as shown below). If you want some further instructions these are available in the Appendix. But be creative. Dance Floor Framework public class week2_1 public static void main(string[] args) robot2 buggy=new robot2(); //Put your dancing robot instructions here //You can have more than one instructions

Wall challenge 1 Introduction Now for something a little more challenging. Design a routine to make a robot move towards a wall, detect that the wall is there, reverse backwards and turn 90 degrees to the right. (Tip: use drawings to express your ideas) Framework Create a sequential routine, using the following: public class week2_4 public static void main(string[] args) robot2 harry=new robot2(); for(;;) //part of the routine inside the loop can go here if (harry.checkbumpers()==true) //what to do on wall detection wall goes here //further code could go here //code outside of the loop could go here This routine will keep repeating (it loops) actions. Your task to replace the lines mark in bold and starting with //, with the instructions you think should go there. This time the robot is called Harry. The line if (harry.checkbumpers()==true) checks if either both bumpers is touching if it do something. That something is the instructions in place of // what to do on wall detection wall goes here. You can have more than one instruction in place of that line.

Wall challenge 2 Introduction Now for something a little more challenging. Design a routine that makes a robot keep the wall to its right, whilst following the contour of the room. It can touch the wall. This might take some experimenting with, that is normal. Again replace the lines marked with // with your instructions. Framework Create a sequential routine, using the following: public class wall_f public static void main(string[] args) robot2 tom=new robot2(); for(;;) //instructions can go here as well if ((tom.bumper(1)==true)&&(tom.bumper(2)==true)) //put instructions in here for actions //to be carried out if both bumpers //detects a collision if ((tom.bumper(1)==false)&&(tom.bumper(2)==false)) //put instructions in here for actions //to be carried out if both bumpers //do not detect a collision if ((tom.bumper(1)==false)&&(tom.bumper(2)==true)) //put instructions in here for actions //to be carried out if right bumper only //detects a collision

Line follower Introduction Produce a line following robot routine. The robot should follow a black line. The robot is configured with two light detectors facing the floor. If a light sensor is above a black line it returns a true otherwise false. Framework Create a sequential routine, using the following: public class line_follower public static void main (String[] args) robot2 dick=new robot2(); for(;;) if ((dick.checklight(1)==true)&&(dick.checklight(2)==true)) //if both sensor are on the line what //action do you want to do? if ((dick.checklight(1)==false)&&(dick.checklight(2)==false)) //if both sensor are off the line //what action do you want to do? if ((dick.checklight(1)==true)&&(dick.checklight(2)==false)) //if left sensor is one the line and right sensor is off //what action do you want to do? if ((dick.checklight(1)==false)&&(dick.checklight(2)==true)) //if right sensor is on the line and left sensor is off //what action do you want to do?

Wall challenge 3 Introduction Produce a routine to move a robot from one corner of room to the opposite diagonal corner. The user (not necessary the designer) can be used to stop the robot to say it has reached the corner (i.e. Just turn the power off). It must be able to around objects. A real world example of this type of activity is in automatic (or autonomous) guided vehicles found in factories and warehouse. Used for delivering goods or parts. Many different technologies can be used by these robots to navigate including following magnetic tracks in the floor or laser ranging finding. Image taken from: http:// www.jervisbwebb.com/categories/agvs.aspx? cid=3 Level 1 Can you use or modify one of the routine you have developed previous to solve this problem? Is so which one and why? Level 2 Can you think of an alternative approach which could also be used to solve the problem? You can add one new feature to the room to solve this? Level 3 Can you modify the Level 1 approach developed and with the addition of a single piece of 7cm of black tape, find a way to stop it at the right place. Additional instructions are available see Appendix for more details. You can add or remove sensors as appropriate.

Maze Problem Solving with Robots Introduction Produce a routine to move a robot in a maze. The maze is made from black lines on a white background. The robot should follow these lines, either on the line or following the edge of the line. Physical Arrangement: Robot The robot has two light sensors at the front. If you wish, you can add an extra bumper that connects two bumpers together (put it on port 2) instructions to use this can be found in the Appendix. Physical Arrangement: Maze As well as the black lines on a white background, you can make one physical change to the maze. The lines are thick enough to have to the two light sensors above it at the same time. Black insulation tape can be used to make suitable lines. To be considered How does the robot know it has reached the end of the maze? What happens at T-junctions? Does the robot go left, right or straight on? What would happen if the black lines were only thick enough only one light sensor at a time to be above the line? Can a solution still be found? (a) (b) Robot following the middle of the line (a) coming up to a T junction (b) carrying on at the junction

Dancing Robot 2 Introduction Using the Framework from dancing robot below get the two robots to dance. The moves are up to you. But this time if the two robots touch they must react to each other. For example if the touch they might reverse away a short distance. The robot must dance in a 1m square area (as shown below). If you want some further instructions these are available in the Appendix. But be creative. Dance Floor

Follow the leader Introduction Now for something a little more challenging. Some robots are programmed to follow the actions of a Leader robot, in order to make them copy each other. The picture on the right shows a long train of small robots, which are all following the same commands as the robot at the front of the line. The movements that the robots need to do varies from level to level, with the ultimate goal being to get a robot that can go forwards, backwards, left and right (not tight turns) and stop. You can use light sensors (as below), bumper sensors, or a combination of sensors. These can be move as you see appropriate. This task has three levels, with increasing difficulty. It is possible to write a routine that will work for all three. A long chain of robots following one another (www.csail.mit.edu/events) Hints and warnings You have solved a similar problem earlier. You might need to change the light levels in the room (or if you feeling more confident about programming within the robot2 class). It might be worth adding a bit of white card on the back of the robots to help improve the reflectance. You are going to need to write at least two routine one for the front robot (Leader robot) and another for the followers.

Follow the leader Task Levels: Level 1: Build and program a robot that can follow a leader robot as it go forwards in a straight line by at least 20cm and stops when the leader robot does so. Level 2: Build and program a robot that can follow a leader robot as it go forwards in a straight line by at least 10cm, makes turn a left, moves forward a further 5cm and stops when the leader robot does so. Level 3: Build and program a robot that can follow a leader robot as it go forwards in a straight line by at least 10cm, makes turn a left followed by a right turn, moves forward a further 5cm and stops when the leader robot does so. Robots carrying out the level 1 task

Bomb disposal Many robots are used to defuse bombs when it is too hazardous for humans to be sent in. Using the Mindstorm Robots move the bomb into a containment area (without making any sudden movements that would set the bomb off) and get the robot back behind the safety line. If the detonator is triggered then the task is failed. In these challenging tasks it is expect that you may rearrange the sensors. In this case the bomb can be a drinks can. Levels 3,4 and 5 require a wall to be built around the area. This can be done by using very thick books or boxes. Bomb Disposal Robot (www.army-technology.com) Level 1: Build and program a robot that can take a bomb that starts just in front of the robot into a containment area, which is marked with a black line, and move the robot back behind the safety line. Level 2: Build and program a robot that can detect whether there is a bomb in the area or not, and if detected move it into the containment area. If not, stay behind the safety line. If the bomb is present then it will still be in front of the robot. Level 3: Build and program a robot that can take a bomb that is in a know location (measurements shown in diagram) and move it to the containment area, which is marked with a black line. When this is done, move the robot back behind the safety line. Level 4: Build and program a robot that can take a bomb that is in a known location (measurements shown in diagram) and move it to the containment area that the robot must find. When it has found the containment area, it must move to a safe distance (touching at least one wall). Level 5: Build and program a robot that can find a bomb regardless of where it is located and move it into the containment area, which is marked with a black line, and move the robot back to a safe distance, which is when the robot is touching one of the walls. Task Extension: In addition to Level 5 program to robot to look for additional items before it returns behind the safety line.

Bomb disposal: Level 1 Level 1 Build and program a robot that can take a bomb that starts just in front of the robot into a containment area, which is marked with a black line, and move the robot back behind the safety line. Bomb CONTAINMENT AREA Move the bomb in a straight line and use the sensors to stop the robot when the bomb is in the containment area. Move the robot back to the beginning. Framework public class bomb_1 public static void main(string[] args) robot2 robot=new robot2(); for(;;) if (robot.checklight(1)==false) //to be carried out if no line is //detected if (robot.checklight(1)==true) //to be carried out when a line is //detected for the first time while(robot.checklight(1)==false) //to be carried out when a line is //not detected after the first line //has been if (robot.checklight(1)==true) //to be carried out when a line is //detected for a second time

Bomb disposal: Level 2 Level 2 Build and program a robot that can detect whether there is a bomb in the area or not, and if detected move it into the containment area. If not, stay behind the safety line. If the bomb is present then it will still be in front of the robot. Bomb CONTAINMENT AREA Detect whether there is an object in front of the robot and if so move the bomb in a straight line. Use the sensors to stop the robot when the bomb is in the containment area. Move the robot back to the beginning. Framework public class bomb_2 public static void main(string[] args) robot2 robot=new robot2(); for(;;) if (robot.checklight(1)==false) //to be carried out if no line is //detected if (robot.checklight(1)==true) //to be carried out when a line is //detected for the first time while(robot.checklight(1)==false) //to be carried out when a line is //not detected after the first line //has been if (robot.checklight(1)==true) //to be carried out when a line is //detected for a second time if ((robot.checklight(2)==true)) //to be carried out when no bomb //is detected

Bomb disposal: Level 3 Level 3 Build and program a robot that can take a bomb that is in a known location (measurements shown in diagram) and move it to the containment area, which is marked with a black line. When this is done, move the robot back behind the safety line. 20cm Bomb CONTAINMENT AREA Move the robot over to the bomb and collect it. Move the bomb into the containment area and move the robot back to behind the safety line. 30cm Framework public class bomb_3 public static void main(string[] args) robot2 robot=new robot2(); //that are going outside the main //loop for(;;) if ((robot.checklight(1)==false)) //to be carried out if no line is //detected if ((robot.checklight(1)==true)) //to be carried when a line is //detected while((robot.checklight(1)==false)) //to be carried out when a line is //not detected after the first line //has been if ((robot.checklight(1)==true)) //to be carried out when a line is //detected for a second time

Bomb disposal: Levels 4 and 5 Level 4 Build and program a robot that can take a bomb that is in a known location (measurements shown in diagram) and move it to the containment area that the robot must find. When it has found the containment area, it must move to a safe distance (at least 40cm away from the bomb). 20cm Containment area located in Move the robot over to the bomb and collect it. Use the sensors to find the containment area and move the robot back to a safe distance. 30cm Bomb Framework for this is given on the next page. Level 5 Build and program a robot that can find a bomb regardless of where it is located and move it into the containment area, which is marked with a black line, and move the robot back to a safe distance, which is when the robot is touching one of the walls. Bomb location: Unknown Bomb located in this area CONTAINMENT AREA Use the robot to locate the bomb and move it into the containment area. Move the robot back behind the safety line.

Bomb disposal: Level 4 public class bomb_4 public static void main(string[] args) robot2 robot=new robot2(); //that are going outside the main //loop for(;;) if (robot.checklight(2)==false) //to be carried out if no line is //detected if (robot.bumper(1)==true) //to be carried out if a wall is //detected. if (robot.checklight(2)==true) //to be carried out when a line has //been detected

Appendix A Instructions Please note that time1 in these instruction is a whole number, so for example 300.5 is not allowed but 301 is. stop(); This stops both motors, but then moves onto the next instruction if you want it stop and wait use halt(). forward(time1); This moves the robot forward for time1 milliseconds (1/1000 th of second) spinright(time1); This moves the robot in a tight circle to the right using both motors time1 milliseconds (1/1000 th of second) turnright(time1); This moves the robot in a looser circle than spinright() to the right using both motors time1 milliseconds (1/1000 th of second) spinleft(time1); This moves the robot in a tight circle to the left using one motor for time1 milliseconds (1/1000 th of second) turnleft(time1); This moves the robot in a looser circle than spinleft() to the left using one motor for time1 milliseconds (1/1000 th of second) backward(time1); This moves the robot backward time1 milliseconds (1/1000 th of second) bumpit(int time1) Using both touch sensors on ports 1 and 3 : If either touch sensor is true then move the robot backwards. bumper(x) Using a touch sensor on port x: Returns true if contact is made.

checkbumpers() Using both touch sensors on ports 1 and 3 : If either touch sensor makes contact then true is returned else false is. checklight(x) Uses a light sensor on port x: Returns true if the sensor is above the line halt() Stops the robot until the view button is pressed change_direction(a,b,c) A sets the duration, B power to left motor and C power to the right motor checklight_x(x) which produces true value for light levels measured to be between 33 and 42 by the light sensor on port X. measurelight(x) Returns the light level as an integer for a particular sensor port X.