Version 0.6.0 ROBOLAB FLL Programming 101 - ORTOPProgramming101-ROBOLABV0.6].pdf · Computer Programming 101 • Objective – Develop a basic approach to, and understanding of, programming

©2002 INSciTE1

FLL Programming 101ROBOLAB™

Sept. 25, 2002Version 0.6.0

©2002 INSciTE2

Legal Stuff• © 2002 INSciTE in agreement with, and permission from FIRST and the LEGO Group.

This document is developed by INSciTE and is not an official FLL document fromFIRST and the LEGO Group. This document may be freely copied and distributed,electronically or otherwise, in its entirety only, and only if used in conjunction withFIRST LEGO® League. Any use, reproduction, or duplication of this manual forpurposes other than directly related to FIRST LEGO League is strictly prohibitedwithout specific written permission from INSciTE.

• LEGO, ROBOLAB, and MINDSTORMS are trademarks of the LEGO Group usedhere with special permission. FIRST LEGO League is a trademark owned by FIRST(For Inspiration and Recognition of Science and Technology) and the LEGO Groupused here with special permission. INSciTE is a trademark of Innovations inScience and Technology Education.

INSciTEPO Box 41221

Plymouth, MN 55441

www.hightechkids.org

©2002 INSciTE3

Credits

This presentation was developed by Fred Rose. Theaccompanying labs were originally done in RCX Code byJoel Stone and converted to ROBOLAB by Doug Frevert. Aportion of the material is taken from “Building LEGO Robotsfor FIRST LEGO League” by Dean Hystad. Amy Harrisdefined the 10 programming steps. Eric Engstrom, JenReichow, and Ted Cochran reviewed ongoing drafts. Erictaught the first class and helped modify the contentaccordingly. Doug modified it based on his ROBOLAB classexperiences.

©2002 INSciTE4

Computer Programming 101• Objective

– Develop a basic approach to, and understanding of,programming the RCX

• Structure– Theory– Examples specific to language– Hands-on

• What this class is– Teach an approach to programming

• What this class is not– Exhaustive reference on every language command

©2002 INSciTE5

Class Agenda

• Computer basics• Programming environment• Simple commands• Subroutines• Sensors• Repetitive statements• Putting it altogether• Advanced topics

©2002 INSciTE6

Format of Each Section

• Theory• Language Specific Commands

– ROBOLAB or RCX Code

• Examples• Debugging• Frequently Encountered Situations• Tips and Tricks

©2002 INSciTE7

The Basics

©2002 INSciTE8

The Computer (Generic)

• Processor executes commands.• Memory stores program and data.• Input devices transfer information from outside world

into computer.• Output devices are vice versa.

Memory

Processor

Inputs Outputs

©2002 INSciTE9

RCX basics

Processor: Hitachi H8 8 bit microcontroller running at 5 to 20Mhz

Memory: 32K of RAM

3 Motor Outputs(A, B, C)

3 Sensor Inputs(1, 2, 3)

Select program (1-5)

Start/Stop selectedprogram

On/Off switch

View to select display

LCD Display:

Motor status, sensorvalues, programstatus

Infrared (IR)communications port

©2002 INSciTE10

Firmware on the RCXSoftware

Your PC

Firmware

Your RCX

Bytecodes{SetPower(A,C,8)}

RAM (RandomAccess Memory) ** RAM loses its datawith no power! Carefulchanging batteries!!

Your Programs

ROM (read only memory)

For FLL purposes, think of firmware as the operatingsystem (like Windows XP or Max OSX) for the RCX

Download

Firmware Setup

Processor (Hitachi)

©2002 INSciTE11

Firmware Loaded?

• Firmware must be installed onto your RCX so thatyou can program the RCX brick.

• Only required to be loaded– When the RCX is new,– Has lost it’s firmware for some reason (such as changing

batteries too slowly),– Or RCX starts behaving badly.

No firmware Firmware loaded.

©2002 INSciTE12

From: Structure and Interpretation of Computer Programs, Abelson, Sussman, and Sussman,

Computer Programs

• A model of a real or mental process.• Are intricate in detail, and

usually only partially understood.• Are rarely modeled to our satisfaction• Thus, programs continually evolve

• The computer is a harsh taskmaster, its programsmust be correct and things must be accurate in everydetail.

©2002 INSciTE13

Writing a Computer Program

• Specify the task– Inputs to be supplied– Outputs to be produced

• Devise an algorithm• Express the algorithm in a computer language

From: Introduction to Pascal, Welsh and Elder,

©2002 INSciTE14

Writing a Computer Program

• Specify the task the computer is to carry out– Move forward 5 seconds– Inputs: Time, power, direction {In an RCX some “inputs” are

set in the program}– Outputs: Motor drive

• Devise an algorithm, or sequence of steps,– Class example

• Express the algorithm as a program in a computerlanguage– Class example

©2002 INSciTE15

Running a computer program (RCX)Write program

on PC(RCX Code or

Robolab)

Downloadto theRCX

RCXexecutes

commands

Program conv.to bytecodes

(textdescription)

Bytecodesconverted toHitachi (RCX)machine code

commands

Move X to register 0011000111...

SetPower(A,3)

©2002 INSciTE16

Tips and Tricks (1)

• The RCX has 5 program slots– Slots 1 and 2 are locked. Unlocked in Administration.– Later we’ll show how to use a touch sensor to get you more

slots (virtually)

• You can also change the time delay before the RCXauto powers down.

• Shielding IR port– The IR tower has a significant range, be careful in an

environment with downloading going on– Build a shield with LEGO bricks for your RCX during the

competition

©2002 INSciTE17

Tips and Tricks (2)• Direction of connecting wires

– You can change motor direction by turning the connection tothe RCX 180º.

• Batteries– Change one at a time to reduce chance of losing program.– Rechargeable batteries work fine.– Use a power plug if you can on your RCX– Source of batteries. If you buy alkalines, buy them in bulk from

a store like BatteriesPlus or from Digikey (www.digikey.com)– Properly used, batteries should last awhile

©2002 INSciTE18

The Programming Environment

©2002 INSciTE19

Language Choices• In FLL, you have two choices for computer language

– RCX Code (also called RIS - Robotics Invention System).• Comes with the commercial version of LEGO Mindstorms

• Only runs on a PC

• Use Version 2.0 if at all possible

– ROBOLAB• Runs on MAC or PC.

• Built on a commercial engineering program called Labview.

• At the FLL level, there is no advantage to either one(we’ve been tracking this for 3 years). RCX Code iseasier to learn but ROBOLAB has more growth potential.

• For FLL at the High School level, no languagerestrictions.

©2002 INSciTE20

Settings (RCX Code)

The “RCX Settings” menu options should be set as shown.RCX IR Power Setting LowRCX Programs 1 & 2 UnlockedRCX Powerdown Time 15 minutes (5 min. to save batteries, 30 min. to lower aggravation)RCX Battery Level should be about 9 voltsRCX Firmware Version 03.01/03.09 (RoboLab 2.0) 03.01/03.28 (RoboLab 2.5)

Administrator RCX Settings

©2002 INSciTE21

The Programming Environment

Double click onInventor4

©2002 INSciTE22

Work Space

Remember to use Context Sensitive Help!

PanelWindow

DiagramWindow

Toolbox FunctionsWindow

Programgoes here

©2002 INSciTE23

Simple Commands

©2002 INSciTE24

Simple Commands

• Simple commands are basic actions– Like English statements

• Turn motor on

• Stop motor

• Reverse motor direction

• Setting parameter values– Many commands have parameters that can be set

• Motor power

• Time

©2002 INSciTE25

Simple Commands

Turn On Motor A -Forward

Turn On Motor A -Reverse

Flip Direction ofMotors

Turn On Motor B -Forward

Turn On Motor B -Forward

Wait for 4 seconds

©2002 INSciTE26

Simple Commands with Parameters

Wait for 25 Seconds Turn On Motor AForward Direction,Power Level 5

©2002 INSciTE27

Motors

• Making the motors move and do something is thepoint (the output) of your program. That’s whatmakes your creation a robot!

• Formally called the 9 volt geared motor– Without load, motor shaft turns at about 350 rpm– With typical robots the power usage should allow 3-4 hours of

use on a set of batteries

• FLL currently allows up to 3 motors on your robot

©2002 INSciTE28

Motor Details

• Motor can be set to different power settings– 5 settings in ROBOLAB– 8 settings in RCX code– Changing power settings is usually a poor substitute for

gearing

• Turning the power setting up higher essentiallymakes the shaft turn faster

4 Studs

3.6 Studs or3 Bricks

2.8 Studs or2.33 Bricks

©2002 INSciTE29

Turning the Motor On

Turn On Motor AForwardFull Power Turn On Motor A

Forward DirectionPower Level 3

Motor direction can also be reversed by reversingthe connector on the RCX. Useful during earlystages of design.

©2002 INSciTE30

Turning the Motor Off

Turn OnMotor A -Forward, onat FullPower

Wait for 2seconds

Stop Motor A

Motors run until stopped!

©2002 INSciTE31

Lab One

Task:Move forward for 5 seconds and return

Then try: Move forward for 5 seconds, turn right 90º

©2002 INSciTE32

Problem Solving andProgramming Process

©2002 INSciTE33

Generic Problem Solving Process

• What’s the problem?• Brainstorm solutions• Evaluate solutions• Try (implement) best solution• Evaluate results

• In our current discussion, the solution is expressedas an algorithm, then converted to a computerprogram

©2002 INSciTE34From: http://whatis.techtarget.com/

What’s an Algorithm?

• The term algorithm (pronounced AL-go-rith-um) is aprocedure or formula for solving a problem. The wordderives from the name of the mathematician,Mohammed ibn-Musa Al-Khowarizmi, who was partof the royal court in Baghdad and who lived fromabout 780 to 850. Al-Khowarizmi's work is the likelysource for the word algebra as well

• A computer program can be viewed as an elaboratealgorithm. In mathematics and computer science, analgorithm usually means a small procedure thatsolves a recurrent problem

©2002 INSciTE35

An Algorithm isLike a Recipe

8 slices of bread

2 eggs

1 cup milk

1/4 cup flour

fat or butter

powdered sugar

Mix together eggs, milk and flour and pass througha strainer. Dip slices of bread into the mixtureand fry in the fat or butter on both sides in afrying pan. Before serving, sprinkle withpowdered sugar

Recipe for French Toast

How can we make this more “algorithm-like”?

Count eggs, mix eggs, for every 2 eggs add 1 cup milkand 1/4 cup flour, and pass through a strainer. Forevery 2 eggs, dip 8 slices of bread….

©2002 INSciTE36

Ways to Express Algorithms

• In the real programming world there are many waysto do this

• In the FLL world, probably the two best ways are:– Draw block diagrams– Literally act it out

• Always talk it out and test it using a team member towalk through it acting like the robot.– Keep actions at lowest possible level

• Go Forward 3 steps

• Stop

• Turn right 90º

©2002 INSciTE37

FLL Ace Programmer in 5 Steps

• Map the generic problem solving process toprogramming

• Create a map of where the robot goes and what itdoes

• Write what the program should do (your algorithm).• Code it• Test, and fix, little pieces at a time

We’ll be adding to this process as theclass progresses

©2002 INSciTE38

Example Algorithm

• Set direction and power of motors• Turn motors on and start timing• Wait 5 seconds,• Stop motors, turn right.

– Turn right by reversing right-side motor– Turn motors on for ? Seconds.

• Stop all motors

Make robot go forward 5 seconds and then turn right 90º

©2002 INSciTE39

Conversion to a Program• Set direction of motors• Start motors• Wait 5 seconds• Set direction/power of motors• Wait ? Seconds• Stop Motors

©2002 INSciTE40

Debugging and Analysis

• Literally walk through it• Ask lots of questions

– What ifs

• Do little pieces at a time– For example, get the robot to where it needs to be first, then

work on getting it to do something

• Use pieces that you know already work– For example, you know how to turn 90°

• Feel confident in your algorithm before starting tocode it.

©2002 INSciTE41

Tricks and Tips• Don’t try to knock off too much at once

– Stick to one or two missions

• Remember to KISS (Keep It Simple)• Develop a little library of algorithms and programs

you know work with your robot.– Going straight, turning, etc.

• Keep things modular (divide task into useful pieces)– This helps a great deal when debugging

• It’s faster fixing problems at the algorithm level thancoding something and seeing what happens

• Give programs descriptive names– Mission1V2 not Amy3

©2002 INSciTE42

Frequently EncounteredSituations (FES)

• You are really not sure which solution is better– Try them both, or at least the primary element of each– Which is easiest for your team to do?

• You can’t think of all the steps needed for thealgorithm– Get out your robot, and walk through it.

©2002 INSciTE43

Subroutines and Comments

©2002 INSciTE44

Subroutines

• Many times in your programming you will want to dosimilar things– Turning 90º Left– Moving an arm to do something

• A subroutine is a small piece of a program that youcan reuse and insert in your bigger program as asingle command– Also called macros, sub vi, functions

• Subroutines are a very important aspect of a good,structured program– Allows you to create a small program fragment that works and

reuse it without thinking about its details

©2002 INSciTE45

Subroutine Use

• If you have a motion or action you can do reliably,and will use a lot, that’s a good candidate for asubroutine.

• It’s easier in an algorithm for a solving a mission tothink “Turn left here at 90º” than always repeat theset of commands you need to do that.

• Another key part of a subroutine is “Modularity”. Itallows you to isolate in one place the code forturning.– See next slide for example

©2002 INSciTE46

Modular Advantages

Start motors

Go straight10”

Turn Left 90º

Go Straight 3.5”

Turn Left 90º

Turn Left 90ºDump barrels

Algorithm - Mission 1

Subroutine

Start motors

Go straight10”

Turn Left 85º

Go Straight 3.5”

Turn Left 85º

Dump barrels85º

Algorithm Updated-Mission 1

If in the process oftesting your program,you realize it is an 85ºturn, you only have tochange your programin one place, in yoursubroutine.

©2002 INSciTE47

Subroutine Commands (local)Call Subroutine #1Define Subroutine #1

Ending Red Light for eachsubroutine definition

©2002 INSciTE48

Subroutine Names

• Useful and informative names.• Suggest using “action + to + target”, but this can be

varied. Some examples:– Fwd2Wall or ForwardToWall or Forward_To_Wall– Fwd2Line, etc.– FwdDist– TurnRight

©2002 INSciTE49

Comments

• Comments are notes in your program explaining whatand why something is being done

• Very important, as the program writer quickly forgetswhy something is done in a certain way

• In a team process like FLL, comments are especiallyimportant as more than one person will be working onthe program.

Enter commentswith the text tool

©2002 INSciTE50

Comment Use

• Add things like who made changes, how batterypower affects change, etc.

• Use color to highlight things

©2002 INSciTE51

Debugging and analysis

• Make sure your subroutine code works well beforemaking it a subroutine!

• Always check the RCX to see which program slot isselected before each download!!

• Remember: Use subroutines to hide complexity anduse comments liberally.

©2002 INSciTE52

Lab Two

Task:Make the program from Lab One into a subroutine

©2002 INSciTE53

Data Input

Sensors

©2002 INSciTE54

Sensors

• Sensors allow your robot to detect the real world.They are inputs.

• Touch– Has your robot made contact with something?

• Light– Is the surface light or dark?

• Rotation– How many times has an axle turned?

• Timer– Internal sensor, keeps track of time

©2002 INSciTE55

Sensor #1: Touch

• Allows robot to detect touching or bumping intosomething

• Good for detecting robot arm movementsThe sensor is activated when the arm moves farenough to push in the touch sensor.

©2002 INSciTE56

Touch Sensor WaitFor Commands

Wait for push in(default 1 click onport 1)

Wait for let go(default port 1)

Wait for5 clickson port 2

Wait for let goon port 3

©2002 INSciTE57

Touch Sensor Fork Commands• Waiting for a touch sensor to be pushed or released

can be useful, but many times you want to dodifferent things based on the value (is it pushed in orout?)

• If touch sensor released, turn on motor A• If touch sensor pushed in, turn on motor B

Fork MergeFork

©2002 INSciTE58

Touch Sensor Loop Commands• Loop until a touch sensor is released. Useful if the

loop contains other sensor functions that must bemonitored repeatedly. For instance, a routine thatfollows a wall until the front bumper hits something.

This marks the endof the loop. Every

loop must have one.

©2002 INSciTE59

Push In, Clicks and Let Go TouchesTwo additional functions involving the Touch Sensor:• Click Counter: a counter of PushIn/LetGo cycles.• Touch and Release Counter: count changes (twice

as big as the click count).

Loops:

Forks:

Push In Let Go

Pushed?

Push InLet GoCount

ClickCount End

©2002 INSciTE60

Sensor #2: Light

• A light sensor detects reflected light from its red lightemitting diode.

• Light sensors operate in "percent" mode, anywherefrom 0 to 100 in value.– Higher the number, the brighter the light, hence the lighter the

surface the more light is reflected back

• Light sensor can be the most useful and the mostfrustrating sensor

©2002 INSciTE61

Light Sensor Readings

• Lowest reading likely 20% (in very dark room)• Highest reading likely 100% (pointing at a bright light)• Normally between 30-60%• Readings also depend on the color of the surface

– See “Building LEGO Robots for FIRST LEGO League” byHystad for extensive discussion of this

– Results vary. You should experiment with yoursurfaces/colors

• Light sensor is extremely sensitive to the distance between thesensor and the reflecting surface. Even small variations canmake the readings unusable. Try to keep the sensor close tothe surface and shielded.

©2002 INSciTE62

Light Sensor Readings

• The light sensor averages its readings over roughly acircular area. Don’t drive too fast or you will getinaccurate readings

• It is very sensitive to ambient light. Shield thesensor as much as possible and try it out under theconditions that you will compete in. Test it oncompetition day.

50%

30%40% 35%

45%

30%35% 40% 45%

50%

©2002 INSciTE63

Light Sensor WaitFor Commands

Wait for Light(greater than 45)

Wait for Brighter(increase by 10)

Also Wait for Darkand Wait for Darkercommands

©2002 INSciTE64

Fork Commands (Light)

• If light sensor greater than 45, turn motor A on in forwarddirection

• If light sensor less than or equal to 45, turn motor B on inforward direction

• The light sensor fork is very useful.

©2002 INSciTE65

Calibrate Light Sensor

• This program assumes you physically move the robotover the light and dark areas, and then use a touchsensor to trigger a reading.

• The containers Red and Blue now contain thecalibrated values of light and dark. These containerscan be used elsewhere in your program.

Position light sensor over white areaand push touch sensor to take a reading

Set container Red to this value

Position light sensor over dark area andpush touch sensor to take a reading

Set container Blue to this value

©2002 INSciTE66

Refining the Calibration for Edge Following

The example set the thresholds at the white and black.This example sets them at light and dark grey.

©2002 INSciTE67

Sensor #3: Rotation

• The rotation sensor is used to measure how far arotating axle has turned. As the axle turns, a counterin the RCX is incremented or decremented.

• Each full rotation registers as 16 counts giving thesensor a resolution of 22.5 degrees (360/16). Henceit is sometimes called the angle sensor.

2 studs

4 studs

2 bricksor2.4 studs

3.5 studs

1.33 bricksor1.6 studs

©2002 INSciTE68

Rotation WaitFor Commands

Wait for Rotation Absolute(count greater than 64 or 4complete rotations withoutreset). That means it doesnot reset to zero.

Wait for Rotationcounter greater than 50or 3 1/8 (50/16)rotations.

©2002 INSciTE69

Fork Command (Rotation)

• If rotation sensor greater than 64 (4 complete axlerotations), turn motor A on in forward direction

• If rotation sensor less than or equal to 64 , turn motor Bon in forward direction

©2002 INSciTE70

Using the Rotation Sensor

• Use as an odometer (how far have you gone) oras an angle sensor (where does the arm point)

• Turn motors on to go straight– Wait until eight complete rotations– {How far is eight rotations? See next slide}

• Because of momentum, a robot travels beyond therotation sensor’s stopping point. Read the sensoragain to find out where the robot stopped.

• Measure rotations: Load a program does nothing butfloat the motors and has any rotation sensor function.Run. The LCD view shows rotation value.

©2002 INSciTE71

Calculating Distance• The rotation sensor also brings in the possibility of

doing some real math!

• We’ll leave that as an exercise for the reader!• Of course, trial and error also works.• Sources of error in calculation - dirt on surface, using

a skid rather than a wheel, backlash (poor fittinggears)

Circumference

Diameter 1 Revolution

Circumference = pi x Diameter

©2002 INSciTE72

More on Rotation Sensor

• Rotation sensor can count forwards or back, up toAbsolute Value (32,767), then it rolls over to largestnegative from largest positive (or vice versa),however this is really unlikely to occur in FLL.

• Increase sensor resolution with gear reduction• Rotation sensor is quite reliable if shaft speeds are

kept in 60-1000 rpm range, some counting problemsmay occur at very high or very slow speeds.– Motors typically around 200 rpm.

©2002 INSciTE73

Debugging and Analysis

• Common sources of repeatability problems for therotation sensor– Programming: forgetting to reset the sensor before use.– Design: inadequate sensor resolution (trying to measure

something very accurately without using gear reduction)– Control: accelerating and turning too fast– Variations in the initial conditions: not putting everything in

the right place,or at least the same place, before pushing therun button.

©2002 INSciTE74

Sensor #4: Timer

• Wait until Blue Timerreaches 5 seconds– Time in tenths of a second– Blue timer must be zeroed before

it’s used– ROBOLAB has 3 timers, blue, red,

yellow

• Zero Blue Timer (reset)

©2002 INSciTE75

Tricks and Tips• Use a touch sensor to get more program slots

– If touch sensor is in, execute one fork branch– If touch sensor is out, execute the other fork branch– Do this for every program slot, and you end up with 10

program slots instead of 5.– Add a brick to robot between missions to push the touch

sensor in, to achieve this.

• Use a light sensor to achieve rotation counting– Aim light sensor at a piece of your robot that rotates and

measure color differences (for example, have two colors on apiece that rotates), and count these.

– Clockwise or Counterclockwise? Does it matter?– Touch sensors can also mimic rotation sensors.

©2002 INSciTE76

Stacking Sensor Ports

• Attaching multiple sensors to the same port• Allows you to use more than 3 sensors• Touch sensors work best for this, rotation sensors

cannot be stacked.

Out In White BlackOut 0 1 ~50 ~35In 1 1 100 100

White ~50 100 ~75 ~70Black ~35 100 ~66 ~60

Sensor 1

Sens

or 2

Stacked Sensor values Touch Light

Touch

Light

©2002 INSciTE77

Lab Three

Task:Move forward for 50 rotations, turn right 90º

orExperiment with other sensors

©2002 INSciTE78

Variables and RepetitiveCommands

Controlling looping, doing things over andover, and adding structure

©2002 INSciTE79

What’s a Variable?

• A value that you can change during your program– This value is “variable”, hence the name

• For example, the value of a light sensor may bemeasured during the program and placed in avariable called RED.

• Think of a variable as a container containing thevalue of something.– In ROBOLAB, variables are called containers

• Useful in subroutines to pass in parameters– For example go straight N seconds where N is a variable.

©2002 INSciTE80

Defining a Container

• On the Functions pallet, thecontainer menu has manychoices. All of these fill acontainer with a value.

• There are 21 containers.3 are predefined containers:Red, Blue, and Yellow. Use amodifier to identify the rest(numbers 3-20).

©2002 INSciTE81

Use of a Container

• Instead of “hardcoding” 50 (above),fill a container with “50”, then get the container (below).

• Once set, containers hold their values (unless thefirmware fails.) Fill in Program #1, get in Program #2.

Set the redcontainer to 50.

Get the value ofthe red container.

©2002 INSciTE82

Structures

• In creating an algorithm, many times you want to dosomething like “As long as the light sensor reads adark value, keep going straight”.

• Structures (or repetitive commands, loops, controlstatements, while commands) are used for thispurpose

• These commands allow the repetition of somecommand, or group of commands, until somecondition is met.

• There are always multiple ways to do these, thissection will cover some examples.

©2002 INSciTE83

Structures

• Split Task– Make 2 parallel program tasks

• Subroutines– Declare, then call a local subroutine

• Forks– Either this way, or that

(If, then, else)

• Jumps– Jump to another spot in program

(GoTo)

• Loops– Repeat until something happens

(While Do or For Next)

©2002 INSciTE84

Split Task

• Make two tasks• Start motors A and B• Wait for 2 sec, or until touch sensor on port 1 is

pushed in, whichever comes first, then stop motor B.

Create a new task to runsimultaneously

©2002 INSciTE85

Jumps

• Jumps can form infinite loops.• Multiple jumps (like red above) are allowed, but only one “Land”.• ROBOLAB has a variety of jump colors/numbers to allow

multiple jumps in your program• Jumps are a simple control structure.• Warning: Multiple jumps are difficult to debug.

Jump from hereto “Land” here

Music never plays!

Useless, but not harmful

©2002 INSciTE86

Loops

• Loops are a powerful and useful control structure– In other programming languages:

For … Next Do loop n timesWhile … Do Repeat until some test is false

• There are loops for every sensor to allow you tocontinually do a command or sequence of commandsuntil a sensor condition changes– Extremely useful for navigation, moving an arm, etc.

• If your algorithm says something like: “While thesensor reads x, keep doing this”, then this is a placefor a loop.

©2002 INSciTE87

Loops Palette

• Play music while thetouch sensor isreleased.

• Additional commandscan be put in the loop.

©2002 INSciTE88

Simple Loop

• Convert this setof commands

• to somethingsimpler usingloops

©2002 INSciTE89

More Complex Use of StructuresFollow lines (based on light sensor thresholds pg 65).

IF over edge to white, THEN turn left until over edge to dark.

This results in a zig-zag motion along the line edge.

ELSE (not over edge to white) IF over edge to dark, THEN

turn right until over edge to white, ELSE go straight.

©2002 INSciTE90

Comparing Algorithms

• Compare the previous line follower to this one:

• Better– Simpler. Doesn’t assume motors are running.

• Worse– Motors only run one at a time.

©2002 INSciTE91

Comparing Sensor Commands

You can generally make your algorithm fit the commandyou want to use.

• Loop– Execute something until an event

• WaitFor– Wait for an event, then execute something

• Forks– Make a choice based on a sensor value at a given point in time.– Be careful to make sure you will be watching for the event at the

right time

©2002 INSciTE92

Tricks and Tips

• Never wait for a sensor to be an exact value, alwaysgreater than or less than– You could miss the event due to sampling rate– For example, wait until rotation greater than 64 not equal to 64.

©2002 INSciTE93

Lab Four

Task:Move exactly one lap around an oval.

(Black 2cm line on white paper)

©2002 INSciTE94

Advanced TopicsEvents

Debugging ToolsAdditional Resources

©2002 INSciTE95

Events

A programming style used to handle situations whereany one, of many things, can happen. It is mostuseful when more than two sensors are beingwatched at the same time.

An event is:• The moment something happens.• It’s also the setup. Knowing what to watch, when,

and where.• And it’s what to do after the event happened.

©2002 INSciTE96

Events (the logic)

• Coding an Event– The setup: declare the sensor to watch, the port, the threshold

that triggers the event.– Start watching– Event Landing

• All events land in the same place. (ROBOLAB)

• Determine which event triggered and react.

• May continue on or restart event watching.

• Events could be recoded– Events could be coded as infinite loops containing sensor

forks and jumps that land outside the infinite loop.

©2002 INSciTE97

Events Using Forks

Here is an example that watches 3 sensors using forks.

©2002 INSciTE98

Events

ROBOLAB 2.5 introduced event functions.

©2002 INSciTE99

Events (Hysteresis)

Hysteresis – a lagging between the time a force has aneffect and the time it makes a change.The word was created to describe the process inmagnetic regions (like magnetic tape) that allowsthem to be changed, but then resist change.Not related to the word “hysterical”, but often thoughtof as the behavior of sensors near their thresholdvalue.

In robotics, a resistance to change factor added tosensor values so they don’t behave “hysterically”.

©2002 INSciTE100

Debugging Tools

• Music– ROBOLAB has several functions that play notes on the RCX.

• Use them to identify sections of code.

• Identify the end of the task, subprogram, or program.

– It helps to make the notes quick. A good ear can hear thedifference between C, E, and G, otherwise use two notes.

• LCD– ROBOLAB 2.5 introduced a function

to write to the RCX’s LCD panel.

• RCX Interrogator– From your PC (or MAC), use the interrogator to view the values

of containers and sensors.

©2002 INSciTE101

Additional Resources

• Internet:– www.hightechkids.org/fll/coaching (this presentation)– www.lugnet.org– www.crynwr.com/lego-robotics/ (firmware decoded)– www.ni.com (LabVIEW™)

©2002 INSciTE102

Putting it All Together

How to Become an FLL Ace Programmer in10 Easy Steps

©2002 INSciTE103

FLL Ace Programmer in 10 Steps1. Create a map of where the robot goes and what it

does. These are your Requirements.2. Use the Requirements to further examine the

problem– What tasks can go in the same program?– Any actions we do in multiple places? (good candidates for

subroutines)– Will using variables help?

3. Write out your algorithm4. Think about how it could fail. How can you recover?

– For example, the robot hits a wall it shouldn’t have. What canyou do to allow it to recover?

©2002 INSciTE104

5. How are you going to test and debug it?– Perhaps use a series of beeps in the program to tell you where

the program is.

6. Have a system for versions.– Put comments at the beginning of the program– Always save a working version in a file with a name that

makes sense (like date, etc.).

7. Write the code using above information

FLL Ace Programmer in 10 Steps

©2002 INSciTE105

7. Write the code using above information– Code little parts and test them– Name subroutines and files with descriptive names

(Right_90_Deg_turn is better than Rturn)– Think about how readable the code is. This makes it less

confusing.– Use a lot of comments

FLL Ace Programmer in 10 Steps

©2002 INSciTE106

8. Fix bugs in a stepwise manner– Fix the bug, test it, then test other things related to it to make

sure they weren’t broken by your fix.– 80% of the bugs come from 20% of the code.

9. Don’t be afraid to scrap everything and start over ifthings are getting complex and fragile.

10. If coding/testing/bug fixing is driving you insane, gohave an ice cream cone! Take a break, have a friendlook at your code, come back another day.

FLL Ace Programmer in 10 Steps

©2002 INSciTE107

Summary

• Remember the problem solving process• Remember to create the algorithm before writing your

code• Use subroutines to keep things cleaner• Be careful in using sensor commands.• Use comments liberally• Program and test little pieces at a time• Have fun!!