THE lEgo® mindsTorms® nxT® idEa book
Contents
1. Sn Clear Action Blocks gt File ET x 1 Y 8 Smile 02 Display Block Smile 03 Lamp Block Motor Block 1 Use the pull down menu to choose whether you want to display an image some text or nz gt your own drawing or whether you just want to reset the display ho Motor Block 2 an MEL y 2 To erase the contents of the NXT s screen check the Clear checkbox v Figure 2 2 The Help HTML screen with the index and the page describing the Display block work area sometimes called the programming sheet because you can have multiple sheets open and hidden behind each other like sheets of paper and so on But as far as elements of the actual NXT G programs the Ed 1S y manual doesnt go into great detail E Get J There are three basic elements used to build le programs in NXT G sequence beams blocks and structures and wires Okay that s four but blocks and structures are really very closely related Figure 2 3 Logic wire shows each of these elements 1 Sequence beam J Switch structure Figure 2 3 A simple program that shows sequence beams blocks wires and a Switch structure THE GRAMMAR OF NXT G 11 12 sequence beams Sequence beams are the white studless beams that link blocks together onscreen The order of blocks along the sequence beam controls the order in which they execute The first block connected to the start symbol executes first then usually when the first blo2. of the bridge Both wheels will then turn the same amount giving a preciseness to the downward movements that is necessary to get a good scan Y 251 SCANBOT AN IMAGE SCANNING ROBOT
3. the NXT was released was always impressed when someone made a robotic scanner Since scanners are used in everyday life and require very precise measurements to function properly they re some of my favorite robots But since the RCX in the RIS set had very limited display capabilities designers of LEGO scanners had to come up with a way to display the scanner s picture on a computer monitor instead of on the robot itself When the NXT came out with enhanced display capabilities immediately saw a great opportunity to build a simple robotic scanner After a few tries succeeded with ScanBot a robot that can scan black and white pictures and display them right on the NXT s LCD This chapter will show you how to build and program your own ScanBot see Figure 15 1 using only one basic MINDSTORMS NXT kit Light Sensor carriage Figure 15 1 ScanBot 250 building ScanBot ScanBot has a simple design and is quite easy to build It works by moving a Light Sensor across every part of an image to be scanned taking hundreds of measurements as it goes It compares each measurement with a variable threshold and determines whether to represent the tiny area from which the measurement was taken with a black or white dot on the NXT s LCD A unique and fun aspect of ScanBot s design is that the entire robot moves over the image to be scanned instead of feeding the image through the robot or moving the Light Sensor over the image within the rob
4. MS 20NXT engine EditorVis Help 20Content Full 20Help Q Google hi m Apple 94 Amazon eBay Yahoo News 1297 v BelvillePatr 2007mod jpg Contents index Search Display Block General Topics Help and Support Calibrate Sensors Use this block to display an image write some text or draw a shape on the NXT s display screen By positioning several Display blocks in a row you can create more complex drawings by adding Data Wires additional images text and shapes with each new Display block Data Wires Broken If you want to erase the contents of the screen before beginning check the Clear checkbox Download to Multiple NXTs If you would like to return to the default LEGO MINDSTORMS icon select Reset in the pull down menu Files and Memory on the NXT The screen measures 100 pixels wide by 64 pixels high Profiles Sequence Beam Starting Point Updating the NXT s Firmware Common Blocks 1 This icon shows whether the block is set to display an image some text or a drawing or Display Block whether it will just reset the display to the default icon non Block 2 You can change values dynamically by connecting data wires to this block s data hub See the Data Hub section below for more information Move Block Record Play Block Raro ay 2 ce Configuring the Display Block Sound Block Switch Block Display Fr Action Image G E IE Position 4 2 Wait Block El Display
5. THE LEGO MINDSTORMS NXT IDEA BOOK design invent and build martijn boogaarts jonathan a daudelin brian l davis jim kelly david levy lou morris fay rhodes rick rhodes matthias paul scholz christopher r smith and rob torok Excerpts from Chapter 2 The Grammar of NXT G pages 9 13 and Chapter 15 ScanBot An Image Scanning Robot pages 249 251 the grammar of NXT G The first problem most people have with the LEGO NXT MINDSTORMS kit is the studless architecture Where did all the studs go How can you connect the pieces firmly in the ways you want to With a little bit of help from the building instructions and some experimenting you can cross that hurdle only to immediately face another one How do you program your creation What are all these funny icons snapped to a beam on the screen and how do they work is NXT G a toy programming language For some people used to a text based language NXT G just looks well weird Instead of a series of ordered instructions it looks as if we have a bunch of brightly colored blocks lined up along the midline of the screen Even more confusing few text clues onscreen hint at what these various blocks are trying to do or how they work together As a result a lot of folks are likely to throw their hands up in frustra tion decrying the fact that LEGO and National Instruments NI created a toy language Well to a point they re correct NXT G is indeed a computer langua
6. anguage right in the product For example open up the Help window and click Starting Point in the General Topics section in the left pane This not only tells you that the odd little symbol at the start of your program has a name but lets you know that by selecting it it opens up a comments text box in the configuration pane You can document anything you like about your program here your name when you wrote it special hardware it needs your grocery list and so on There are many more little gems like this in the documenta tion but you have to actually read the documentation to find them If sound like your fourth grade teacher there s a reason teachers know that a student usually has to actively process something to learn it not just have it available and unread How many times have you heard the words Did you read the instructions Well in support of beleaguered spouses everywhere have to repeat them Read the instructions now that you know where they are the basics starting out First let s lay out some terminology not because terminology is fun but because it s useful to have a common language in which to talk and think about such things The hard copy user s manual that comes with NXT does a great job of describing the programming environment including things like the configuration panel or configuration pane the 900 LEGO MINDSTORMSO NXT Help and Support file Applications LEGO 20MINDSTOR
7. ay to sample a graphical programming language Now I ll be the first to admit that there s no way to explain the entire NXT G language in a single chapter There s just too much to talk about There are 28 stock blocks and a lot more can be added and each block can have as many as 8 different sections in its con figuration pane as well as multiple configuration panes and so on In fact an entire book could be written about programming in NXT G Instead I m going to try to explain some of the quirks and tricks that you can use to do much more in NXT G I ll assume that you have programmed at least some in NXT G but need a little boost to understand some of the oddities about the language or how to use some specific blocks But this really begs the question of how you get this basic competency where s the guidebook The first step most people take in learning NXT G is to work through at least some of the programming examples in the Acad emy content those detailed build and program instructions that are initially available along the right hand side of the main window Figure 2 1 shows the Academy area Home Robo Center Vehicles Quickstart al Machines 4 Animals Humanoids Figure 2 1 The Academy area as it appears when the program starts While these instructions will walk you through building a program step by step they don t offer much at all in the way of detailed explanations So how can
8. by NXT G and not incorporated into your finished program Now to branch a sequence beam and link in this first block of a parallel sequence hover the arrow cursor over the existing sequence beam at the point you want it to branch and press and hold the SHIFT key You can now click and drag out a new branch of the sequence beam to the start of your orphan block and that s it you ve started a new parallel sequence Any blocks you drop behind this newly connected block will obediently join the rank and file of the second sequence You can branch a new sequence from anywhere the start symbol midway along a sequence beam or even within a Loop or Switch although that s a bit trickier Fig ure 2 5 shows a sample three pane sequence Figure 2 5 A three pane sequence of creating a parallel sequence beam MULTITASKING NO SUCH THING AS A FREE LUNCH Dont think that running two sequences in parallel makes things twice as fast Just like you the NXT cant really do multiple tasks at once there s only one primary processor trying to execute your code Behind the scenes it rapidly switches between all the currently executing sequences It first executes a little bit of code from this sequence it then skips down and executes a little bit of code from the next parallel sequence and so on In effect running two sequences in parallel means that each sequence is running significantly slower than if the processor were running only one There are s
9. ck is completely finished the next block along that sequence beam executes then the third one and so on Sequence beams are just a visual way to represent the program flow not unlike the arrows in a flowchart as you can see in Figure 2 4 pa Play a sound Yes Is it equal to 0 Get a No C Figure 2 4 A simple flowchart for the program shown in Figure 2 3 branching and sequences Like a flowchart these execution sequences can branch but they branch in two very different ways The first is when a choice has to be made Should the execution follow this path or that one In a text language this is done with something like an if then or a switch case command while in NXT G the Switch block takes over this role more on that in a second And NXT G offers another very different very powerful way to make the execution proceed You could have it go down two dif ferent branches simultaneously This is parallel programming using two or more parallel sequences to accomplish two things at once In NXT G parallel programming is as natural as breathing Once you have laid down one sequence or even a portion of that sequence you can start asecond sequence by dropping a block somewhere below it not connected to the existing sequence beam CHAPTER 2 actually it could be below it above it or anywhere else as long as it doesn t link up to the sequence beam Such an orphan block is normally ignored
10. ge designed to explicitly run on a toy after all that is what the NXT is and what LEGO produces So any language that ships with the NXT should be easily used by the target audience which is kids not a bunch of folks with years or decades of experience programming in high and low level text based languages But don t let that fool you into thinking that NXT G is just a toy or that it can t be used to write real programs True some things have been limited or hidden to make the environment a little easier for a first time user to navigate and true there are some things that are missing but there is a lot of power under the hood in NXT G The trick is that in order to use it you have to approach it as a new language and learn its intricacies and strengths as well as its weaknesses NXT G is no more a crippled toy than the graphical user interface GUI on your PC at work is a toy humans can use pictures to com municate a lot of information rapidly and graphical languages and interfaces take advantage of this NXT G was developed on top of and owes a lot to a highly regarded professional development language called LabVIEW Far from being a toy LabVIEW is used in complex data acquisition and control systems all over the world serving as a flexible and powerful tool for scientists and engineers Since a full LabVIEW environment retails for hundreds to thousands of dollars you can consider NXT G a wonderful and inexpensive w
11. has only one default state when dropped from the palette but that s not much help if you want to repeat a block that is set with something other than the default state To repeat an existing block you can clone it If you ALT drag an existing block oPTION drag on the Mac the environment makes a clone of the block you selected copying every setting from its configuration pane into the new one and even imitating the data plugs that are currently displayed This is another wonderful feature inherited from NXT G s parent language LabVIEW and it s great that the developers left such things in to help the advanced user loop and switch structures The Loop and Switch structures function almost like composite blocks or blocks that contain other blocks When they are first placed they do nothing because there is nothing inside them to do you must drop blocks into them to set up their sequences Notice that the block icons give you hints about how the configurations are set up For instance a Move block set to unlimited displays a little infin ity symbol in its lower right corner telling you how it is configured without your having to view the configuration pane Another great example is the mini Venn diagram on the Logic block which changes to represent the sort of logical operation that it is configured to perform in this case a logical AND THE GRAMMAR OF NXT G 13 15 ScanBot an image scanning robot Before
12. ot ScanBot has four main components which are labeled in Figure 15 1 In the middle of ScanBot two long beam constructions form the bridge which supports the Light Sensor carriage a motor ized carriage that holds a Light Sensor and travels back and forth y mv w x A x 3 A z LCS Tr x La x 5 A N x Oa hod m Hr a x CHAPTER 15 x x a x N vu x across the bridge to scan successive lines of the image Each end of the bridge is supported by a wheel one under the NXT module and one which isn t visible in Figure 15 1 under the motor module The two wheels are connected by a drive shaft which the motor module rotates to move the entire ScanBot across the image To scan the Light Sensor carriage travels over the bridge scanning one line of the image Then the motor module moves ScanBot down a tiny bit and the Light Sensor carriage travels across the bridge again scan ning another line of the image right below the previous line This process is repeated many times until as much of the image that can fit on the LCD has been scanned First build the motor module which moves ScanBot down the image being scanned The motor module includes the wheel beneath it and part of the drive shaft that extends toward the other side of the bridge This will later be connected to the wheel which sits under the NXT module on the other side
13. till times when these parallel sequences are handy for instance watching a sensor for something to change while at the same time calculating some math or moving the robot but it doesnt mean your NXT is working twice as fast blocks and structures Blocks and structures are the real workhorses of NXT G They are specialized chunks of code that do something specific such as play a sound control a motor get the current reading from a sensor and so on Almost any time you place a block or a structure you need to set up its various limits and conditions from the configuration panel such as what port a sensor is connected to how long to run a motor and so on and there can be a lot of things to configure blocks Of the two blocks are the simplest they re just one square icons that accomplish something specific Program execution usually halts while a block is executing that is the next block on the sequence doesn t start doing its thing until the previous upstream block has completely finished But that s not always the case Some blocks can start actions and then let the sequence continue executing even while these actions are still taking place A good example of such a block is the Sound block which enables you to check or uncheck the box next to the words Wait for completion CONFIGURATION HINTS cloning blocks Re editing the configuration panel every time you drop a new block gets old fast Every block
14. you learn the language Where did LEGO put the programming guide help is built in LEGO put the programming guide right into the programming envi ronment Just hover don t click the mouse pointer over any block CHAPTER 2 or structure on the programming sheet and a brief explanatory note will pop up in the Help pane in the lower right corner of the window Actually there are two useful panes down there Clicking the upper question mark tab brings the Help pane forward while clicking the lower magnifying glass tab brings the navigation pane forward More about that later These brief notes are helpful but the real secret is what s under them If you click the More Help link NXT G obediently opens a full detailed linked web page of information about almost every aspect of the block including what each input or output plug does what the limits on certain parameters are how it can be used and in some cases how it shouldn t be used and so on help index You can also open this detailed help from the NXT G menus by selecting Contents and Index from under the Help menu in the menu bar The index that opens along the left side of your screen is valuable see Figure 2 2 It not only contains the help files for every NXT G block but it also starts with some important overview subjects such as sequence beams and data wires for example In short LEGO and NI have included a wonderful detailed block by block description of the l
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