LEGO MINDSTORMS - Building Robots Part 11 pdf

360 Chapter 18 • Replicating Renowned Droids You can even remove the pivoting wheel and make R2-D2 capable of standing on two legs by simply placing two aligned wheels into each leg (Figure 18.11).This way, the robot is no longer a differential drive and becomes a skid-steer drive.To use this architecture, it’s very important you keep the COG (center of gravity) as close as possible to the ground. Its vertical right should be in the middle of the sup- port base, delimited by the four touching points of the wheels in order to reduce the tendency of the robot to overturn when starting or stopping.A high reduction ratio between the motors and the wheels helps, too. www.syngress.com Figure 18.11 A Double-Wheeled Leg a b 174_LEGO_18 10/29/01 4:28 PM Page 360 Replicating Renowned Droids • Chapter 18 361 Building a Johnny Five-Style Droid Johnny Five (or Number Five) has a much less compact structure than R2-D2. Its body is slim and articulated at many points, and the whole is supported by two large tracks. Replicating this in LEGO is quite a challenging task, especially because the RCX and the motors are rather large compared to the size of the tracks avail- able in the MINDSTORMS kit.Things get better if you scale the model up, but you would need many extra parts and, above all, some larger tracks. Since we can’t have everything, we decided to be satisfied with just repro- ducing some of the main features of Johnny Five: the triangular tracks, the rear pivoting wheel, a rotating head and two (decorative only) hands (Figure 18.12). www.syngress.com Figure 18.12 Our Johnny Five-Style Droid 174_LEGO_18 10/29/01 4:28 PM Page 361 362 Chapter 18 • Replicating Renowned Droids The body of Johnny Five has been built around a chassis with a triangular section. Looking at the robot from its side, you’ll notice that three beams form a perfect right triangle with sides of length 6, 8, and 10 (Figure 18.13).The vertical 1 x 16 beam also serves as a support for the upper wheel of the tracks and the head mechanism. Since the MINDSTORMS kit includes only four track wheels, we made two more from a pair of pulleys with a bushing in the middle.The pivoting wheel is not actually necessary to support the robot, but it enhances its look. The gearing of the drive motors is rather simple: an 8t gear on the motor shaft engages a 24t gear connected to the drive axles. (Remember that you also need a 16t gear inside the track wheel to joint it to the axle.) The third motor lies on a second layer above the first two, and it’s braced by a diagonal beam with a quite unconventional slope: this triangle has a base of 2 studs, a height of 7 1/3 bricks that corresponds to 8.8 studs, and a diagonal of 9 studs.The match is not perfect, but the error is less than three parts in a thousand and gives a solid bracing to the motors without disturbing the pivoting wheel (Figure 18.14). www.syngress.com Figure 18.13 Johnny Five Side View 174_LEGO_18 10/29/01 4:28 PM Page 362 Replicating Renowned Droids • Chapter 18 363 Figure 18.15 shows the bottom of the robot.You’ll notice that we joined the front axles together to make them more solid, relying on the fact that the track wheels are free to rotate on them. On the other side, the rear track wheels have 16t gears inside.As explained in the MINDSTORMS Constructopedia, this is the way to securely join them to their axle. www.syngress.com Figure 18.14 Johnny Five Rear View 174_LEGO_18 10/29/01 4:28 PM Page 363 364 Chapter 18 • Replicating Renowned Droids The head mechanism is nearly identical to the one we designed for R2-D2: A pulley-belt system rotates a worm gear, which engages a 24t.A cam closes a touch sensor when the head is centered (Figure 18.16). We got sentimental and rebuilt for Johnny Five the same head we designed together in 1998 for one of our first MINDSTORMS projects, called S3 (see Figure 18.17). NOTE Refer to the earlier section on programming the R2-D2-style droid when programming the Johnny Five robot—the two models can be driven by the same software. www.syngress.com Figure 18.15 Johnny Five Bottom View 174_LEGO_18 10/29/01 4:29 PM Page 364 Replicating Renowned Droids • Chapter 18 365 www.syngress.com Figure 18.16 The Johnny Five Head Mechanism Figure 18.17 Close-Up of the Head 174_LEGO_18 10/29/01 4:29 PM Page 365 366 Chapter 18 • Replicating Renowned Droids Variations on the Construction In introducing this robot, we explained that if you want to make your version more similar to the one from the movie, you have to increase its scale.You will need some extra parts, but those are easy to find.The greatest problem comes from the tracks:You can’t use the ones from the MINDSTORMS kit for a larger Johnny Five, because they’re too small and will make it look ridiculous. Staying with LEGO components you have two alternatives: the Cybermaster tracks and the modular chain link tracks (see Chapter 9), both of which are a bit hard to find.The latter represents a very flexible solution that allows you to adjust the length of the track precisely to your needs, and it’s what we used for Cinque, the larger Johnny Five-styled robot described on our site (Figure 18.18). www.syngress.com Figure 18.18 Cinque, Our Replica of Johnny Five 174_LEGO_18 10/29/01 4:29 PM Page 366 Replicating Renowned Droids • Chapter 18 367 If you’re open to nonoriginal components, you can search toy shops for cheap toy tanks: some of them feature tracks that may be adapted to LEGO and might fit your needs very well. Usually, you cannot use the standard LEGO track wheels. Instead, you have to build suitable ones combining wheels in pairs with a half or whole bushing in the middle (Figure 18.19). www.syngress.com Figure 18.19 Nonoriginal Tracks Guiding Infrared Light Cinque was not our first dual-RCX robot—we had already succeeded in co-coordinating two RCX units through IR messages. However, after fin- ishing Cinque, we realized that the two RCXs couldn’t communicate because their IR devices didn’t “see” each other. Facing the horrible scenario of starting everything over from scratch, we began looking for a solution to guide the IR light between the RCXs. IR light, though not visible to the human eye, behaves just like visible light, so what worked with visible light would have worked with the IR, too. Our first idea involved LEGO optic-fibres, the ones usually employed together with the FOS unit. We tried to position them in front Bricks & Chips… Continued 174_LEGO_18 10/29/01 4:29 PM Page 367 368 Chapter 18 • Replicating Renowned Droids Summary If you decide to reproduce one of the famous robots that populate sci-fi movies, you will face difficulties similar to what we described in Chapter 17 about making robotic animals: matching the form to the function. The process can be made a bit easier by choosing the proper scale for the model. Generally speaking, the bigger the size, the better the result, because the size of your elements become less relevant when compared to the size of the model, allowing you to make finer details. Unfortunately, sizing up is not always an option, because you must take into account your own part availability, and the size of some special components, like wheels and tracks, that limit the maximum dimension you can aspire to. On the technical side, both the droids gave you the chance to see some of the theoretical concepts of Part I put into practice. For example, the vertical shape of R2-D2 requires the thoughtful application of the ideas expressed in Chapter 5 about balancing the robot to oppose the effects of inertia.The Johnny Five model is the first robot of Part II to use the triangular structures described in Chapter 1. It is also the first one that uses tracks instead of wheels, implementing the skid- steer drive scheme described in Chapter 8.To make its tracks outline a triangular shape, we had to build a third pair of track-wheels; this is a good example of the powerful modularity of the LEGO system, which allows you to replicate the functionality of one part by using other basic elements. This chapter also introduced you to a programming challenge we haven’t discussed yet: light following. It has significant differences from line following, because you cannot rely on the constant readings that come from a black and white pad. Instead, you have to scan the environment looking for the strongest light source, and then follow that direction. For line following, we suggested a www.syngress.com of the RCX bricks, but that didn’t work. Then we experimented with a mirror, placing the robot in front of it—and found the IR messages could indeed successfully reach both the units. We were close to the solution; we simply needed a small mirror mounted on the robot. But did it really have to be a mirror, we wondered, or would something easier work? Breathing sighs of relief, we finally discovered that a simple white reflecting surface was enough to assure a reliable communication. You can see our reflector in Figure 18.18: two white tiles close to the top of the left track. 174_LEGO_18 10/29/01 4:29 PM Page 368 Replicating Renowned Droids • Chapter 18 369 calibration procedure be executed before running the robot along the line in order to evaluate the maximum and minimum values the robot should expect. In the case of light following, this kind of procedure is performed every time the robot wants to decide in which direction it should go. We invite you to visit some of the Web sites listed in Appendix A. Most of them will be of great inspiration when it comes to making your own droids. www.syngress.com 174_LEGO_18 10/29/01 4:29 PM Page 369 [...]... www.syngress.com 174 _LEGO_ 20 10/29/01 4:34 PM Page 391 Chapter 20 Board Games Solutions in this chapter: s Playing Tic-Tac-Toe s Playing Chess s Playing Other Board Games 391 174 _LEGO_ 20 392 10/29/01 4:34 PM Page 392 Chapter 20 • Board Games Introduction Board games are among the most challenging projects you can take on with your MINDSTORMS kit.The RCX does have the power to run software that plays Tic-Tac-Toe,... intuition, Marco Beri, the third member of our small group, came up with the idea of building a Tic-Tac-Toe machine, a robot able to play a board version of the well-known game.We immediately felt it was the right idea: Board games have been historically considered a good test for machine intelligence, so even if Tic-Tac-Toe can’t compare to Chess in complexity we thought it was the right project to present... machine used many extra LEGO parts For this reason, we decided to build a new, simplified version for use in this book.The description of our original version is still online, however; you can find the link to it in Appendix A www.syngress.com 174 _LEGO_ 20 10/29/01 4:34 PM Page 393 Board Games • Chapter 20 Building the Hardware To keep the project replicable using only parts from the MINDSTORMS kit, we gave... the sheet, we traced the Tic-Tac-Toe scheme.The centers of its squares align with the stop pegs placed along the rails (Figure 20.2) www.syngress.com 393 174 _LEGO_ 20 394 10/29/01 4:34 PM Page 394 Chapter 20 • Board Games Figure 20.2 The Tic-Tac-Toe Board This robot is designed to read the light value in the center of the squares.You can either mark the moves placing thin LEGO pieces to represent Xs...174 _LEGO_ 18 10/29/01 4:29 PM Page 370 174 _LEGO_ 19 10/29/01 4:31 PM Page 371 Chapter 19 Solving a Maze Solutions in this chapter: s Finding the Way Out s Building a Maze Runner s Building a Maze Solver 371 174 _LEGO_ 19 372 10/29/01 4:31 PM Page 372 Chapter 19 • Solving a Maze Introduction Humankind has always... theories about maze solving, which will lay the foundations for the projects that follow On the hardware side, the robots that you will come across in this chapter don’t require many more parts than what you find in your MINDSTORMS box We built the Maze Runner robot entirely from MINDSTORMS parts, while the Maze Solver robot used some additional elements unnecessary for the success of the first project... trickiest Playing Tic-Tac-Toe As we described in our introduction to the book, in October 1999 we attended the first Mindfest gathering at the Massachusetts Institute of Technology (MIT) at the Media Lab facility The Mindfest event featured many activities: lectures, workshops, a construction zone There was also a large exhibition area were the participants could show off their MINDSTORMS creations... it’s possible to use a much more compact representation using individual bits, as demonstrated by Antonio Ianiero’s YATTT (Yet Another Tic-Tac-Toe) that employs only two variables for the entire board (see Appendix A) As for the strategy, when properly played,Tic-Tac-Toe ends in a tied game in which nobody wins.The following list enumerates, in order of priority, the steps to play a perfect defensive... look at the plan of a labyrinth so you can prepare a map before actually entering it www.syngress.com 174 _LEGO_ 19 10/29/01 4:32 PM Page 389 Solving a Maze • Chapter 19 In the second approach, you proceed cell by cell, building the map while you explore the maze, as if you were inside it Recall the note-taking technique we described in the Finding The Way Out section; this is exactly what you need While... ability to find your way through a maze is considered a good test of intelligence and has been used with mice and other animals to measure their capacities Now the time has come to test your robots, too! Before building robots capable of solving a maze, you must understand what “solving a maze” means In other words, we must understand what knowledge and skills are necessary to find the way out If you ask . too. www.syngress.com Figure 18 .11 A Double-Wheeled Leg a b 174 _LEGO_ 18 10/29/01 4:28 PM Page 360 Replicating Renowned Droids • Chapter 18 361 Building a Johnny Five-Style Droid Johnny Five (or. droids. www.syngress.com 174 _LEGO_ 18 10/29/01 4:29 PM Page 369 174 _LEGO_ 18 10/29/01 4:29 PM Page 370 Solving a Maze Solutions in this chapter: ■ Finding the Way Out ■ Building a Maze Runner ■ Building a Maze. across in this chapter don’t require many more parts than what you find in your MINDSTORMS box. We built the Maze Runner robot entirely from MINDSTORMS parts, while the Maze Solver robot used some