Problem Solving

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Problem Solving Algorithm Design for Robots

• Nawwaf Kharma

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Outline

• Programming as Problem Solving with Applied
  Algorithms
• Algorithm Design as Instruction selection,
  configuration and sequencing
• The intimate relationship between robotic
  hardware and controlling software
• Several robotic (and human) programming problems,
  with hints!
• Lessons learned and guidance issued ?

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Programming as Problem Solving

• One definition of programming is it is applied
  problem solving
• - You have a problem (e.g. need a program to
  calculate the area of the circle).
• - What inputs and outputs are needed?
• How does what is entered produce the right
  output?
• What needs to be done?

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Group Exercise

• Problem An ant is in a corner of a room at the
  ceiling. There is a bowl of sugar at the opposite
  diagonal corner of the room on the floor. The
  room is a cube with the width of the room 3m.
• In groups of 2 or 3
• Discuss different ways for solving the problem.
• Use speech, writing and drawing to explain your
  ideas.
• Can you use drawing to help you solve the
  problem?
• Come up with a preferred solution.
• Can you prove that your solution is correct?

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• stop()
• Stops both motors, then moves onto the next
  instructio if you want it stop and wait use
  halt().
• forward(time1)
• This moves the robot forward for time1
  milliseconds (ms).
• spinRight(time1)
• Moves robot in a tight circle to the right using
  both motors time1 ms.
• turnRight(time1)
• This moves the robot to the right in a looser
  circle than spinRight() using both motors time1
  ms.
• spinLeft(time1)
• This moves the robot in a tight circle to the
  left using one motor for time1 ms.
• turnLeft(time1)
• Moves robot to the left in a looser circle than
  spinLeft() using 1 motor time1 ms.
• backward(time1)
• This moves robot backward time1 ms.

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 a black
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. from
Lego
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Types of Instructions

• A. Get inputs from sensors
• B. Process inputs (and state variables)
• C. Make decisions
• D. Send outputs to effectors
• Example
• If (checkLight(1) !checkLight(2))
• turnRight(1000)

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Instructions Relate 2 Hardware

• Although
• (a) instructions are given, such as the set of
  instructions for Lego Mindstorms robots or the
  Atmega8 chip
• (b) and processing and decision making
  instructions are related to robot software
  design
• The actual number and especially meaning of the
  inputs and of the outputs are determined by robot
  hardware design you map I/O from/to the
  real-world

Distance ahead (x2)
Movement of a leg (x6)
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Instructions Relate 2 Software

• Software are programs and programs are applied
  algorithms
• Definition algorithm is an effective method for
  solving a problem using a finite sequence of
  instructions http//en.wikipedia.org/wiki/FileLa
  mpFlowchart.svg
• So, given a set of instructions, and a hardware
  design, the next thing is figuring our how to
• Configure instructions how many milliseconds?
• Sequence instructions check first then move.
• Example
• If (checkLight_x(1) AND ! checkLight_x(2))
• turnRight(2000)

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Provisional Summary

• The programmable controller of a robot determines
  your basic set of instructions
• The hardware design of a robot determines the
  number and meaning of the inputs and outputs
• These two (controller and hardware) define the
  limits of possible software solutions, where
  software applied algorithm
• So, algorithm design is really instruction
  selection, mapping, configuration and sequencing.

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Problem 1

• Create an algorithm then program, using the
  instructions provided, to make a robot trace out
  a square. Each side of the square will be the
  same length as the distance covered by the robot
  when it moves forward a second.
• A. What algorithm came to your mind? Why?
• B. What does this algorithm demand in terms of
  inputs and outputs?
• C. Is this the only solution? Which one do you
  prefer and why?
• problems 1-4 adapted from Problem Solving with
  Robots by Scott Turner

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Problem 2

• Get two identical robots to do a little dance.
  The moves are up to you. A robot will initiate
  the dance (a) when it has been moving for 5
  seconds (without incident) and (b) upon detection
  of the other robot- you may assume there are no
  other objects in the area. When a dance
  terminates, the robots should select an arbitrary
  direction to move in.
• What are the robots states of existence?
• For every state, what inputs and outputs does it
  need?
• What is the dance routine, and how does a robot
  select an arbitrary direction?
• How would the addition of 4 walls (of an empty
  room) change your approach?

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Problem 3 (human)

• Write down a detailed list of instructions for
  opening a fizzy drinks bottle.
• Your instructions must clear enough so that
  somebody could use to open the bottle based ONLY
  on your instructions. The person should not get
  wet whilstopening the bottle.
• Constraints
• It is a person opening the bottle.
• The bottle top is a screw top and is not glued
  down.
• The person has use of both hands and is strong
  enough to open the bottle under normal
  circumstances.
• The person understands simple words such as
  grip, turn, clockwise, anti-clockwise, left and
  right, on off and combinations right hand on
  bottle top.
• You do need to specify which hand is used.
• Your instruction should not be able to
  interpreted in an other way.

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Problem 4

• Produce a line following robot routine. The robot
  should follow a black line. You may configure the
  robot with any number of light sensors in any
  configuration. If a light sensor is above a black
  line it returns a true otherwise false. You
  may assume that 2 sensors can over the width of a
  black line.
• What are all the robots states of existence?
  What defines every state? How do you decide a
  change of state?
• When in a state, what routine should be executed?
• Did you include start and end states?
• How would the addition of noise (e.g.
  variable-width line) affect your design?
• Should you design for a perfect world then
• add noise or are you better off designing
• For the real world?

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Summary

• Robot Based Problem Solving is actually the
  co-design of hardware and software (i.e.
  algorithmic) solutions to real world problems
• Generally speaking, one should design a combined
  solution, which is implemented through hardware
  and software
• In many cases, hardware design restricts (and as
  such defines the scope of) algorithmic solutions
• One may approach robot control algorithms as one
  does a state machine, with
• Different states each with its own handling
  routine
• It is important, however, not to assume that your
  simplified model of the world is the real world!