Parts of a Lego RCX Robot RCX / Brain A B C The red button turns the RCX on and off. The green button starts and stops programs. The grey button switches between 5 programs, indicated as 1-5 on right side the RCX s screen. Tip: Make sure you know which number your program is! A: The black ports A-C power motors and lights from batteries inside the RCX according to your program. B: The grey ports 1-3 provide data from sensors to the RCX. CHERP only uses Port 1. C: The infra-red port listens for instructions from the computer and sends them to the brain inside the RCX. Motors Wires Connect to Ports A and C with wires that go from Port A/C to the black port seen on the motor. Tip: The orientation of the wire ends on each port affects the direction the motors turn. See tip below. Provides electrical connections from ports on the RCX to components like motors and lights. Tip: Make sure the wires don t rub the robot s wheels this can slow them down! Wire Orientations Lights Tip: This orientation of wire ends and motors will result in your robot moving as expected. Connect to Port B directly or via a wire. Tip: See programming tips on light blocks.
Starter Ideas for Mobile Robot Designs There are many ways to put together a mobile LEGO robot, but starting out can be confusing for builders of all ages. Here are some ideas intended to facilitate the exploration of different designs. Note: these ideas don t necessarily all work in conjunction with each other! General Tips: Make sure all the robot s parts are connected STURDILY! Keep the IR port ( ear ) unobstructed so the robot can receive programs. Try out wheels of different sizes or other round parts, like LEGO gears. Improving Mobility: Anything (e.g. a wire or Lego piece) rubbing a wheel will significantly slow down that wheel. One way to prevent the wires from rubbing the wheels is to wrap the wires from front to back between the motors and up onto the ports (see example (a) below). Using a slider instead of a wheel on the front leg(s) of the robot allows the robot to turn smoothly. Tires in front can t pivot like on a real car and will cause a lot of friction while the robot turns. (a) Motor attachment (b) Reinforcement of motors #1 (c) Reinforcement of motors #2 (d) Reinforcement of motors (e) Wrapping wires. Tip: Attach (f) Orient the wire ends like this (#3-Can you think of others?) motor w/1 wire end connected so the robot behaves properly. to it, then wrap wire and connect on top. (g) Front leg with slider (h) Front legs with sliders (i) Different possible wheels
Building a Program with CHERP You can make the same programs with the on-screen (graphical) blocks and the wooden (tangible) blocks. Typing Control+1 (or 2 or 3) reveals the corresponding number of rows of programming instructions in the onscreen interface. This doesn t work in full-screen mode. Hit Enter / Escape to enter and exit full-screen mode. Every program must start with a BEGIN block and end with and END block: Graphical blocks will ONLY connect to a BEGIN block or to a sequence of connected blocks. Unconnected graphical blocks will appear pale and will not be downloaded to the robot. REPEATs and Ifs must be paired with their corresponding END block. The relevant action(s) go in between, like this: REPEAT and IF blocks have a grey space for a parameter additional information that says how many times the instructions will be repeated. The REPEAT parameter is optional since the default is to REPEAT FOREVER. With the tangible interface, any parameters circular barcodes must align with those of the other blocks and be visible to the camera to download the program to a robot. Keep in mind: Attach new graphical blocks to a program by dragging and dropping the new block wherever you want it. Click on any graphical block in the program to move that block and all blocks to its right. To get rid of graphical blocks from the workspace, drag them to anywhere in the rows of available blocks at the bottom of the screen. To clear all attached graphical blocks at once, click the BEGIN block and drag down. Blocks will be interpreted by the robot sequentially starting with the BEGIN block. For instance, in the IF block example above, the robot will go backwards once and then, if the light sensor detects bright light, it will shake. Once you download any program (graphical/tangible) to a robot, an editable on-screen version of it appears. The motion and sound blocks instruct the robot to do an action for half a second, then stop. The light blocks work differently. LIGHT ON turns the light on until LIGHT OFF is used. If there is no LIGHT OFF before the end of the program, the light will already be on at the start of the next program. The light blocks also make the robot do the next instruction immediately, not after half a second. It helps to think through the state of the light throughout your program. Challenge: How might you make the light blink?
If you are using the graphical blocks, skip to #2. Downloading a Program to a Robot 1. Place the tangible blocks directly facing the webcam about 18-24 inches away from it. Otherwise, the computer vision will not detect your program properly. You may be prompted to include a BEGIN block in your program. If you do have a BEGIN block and it appeared within the image shown on-screen during the attempted download, change the distance or angle between the webcam and your program and re-download the program. Tip: You can put the blocks across the table from the webcam or on the floor under the downward-pointing webcam. 18-24 inches 2. Position the IR port (the smooth black rectangle) of your RCX-based robot near the front of the LEGO USB Tower and make sure that the RCX is turned on (you will see numbers counting up on the RXC s screen). 3. Press the appropriate on-screen download button (the mouse for graphical, left; the blocks for tangible, right). The RCX will play a rising series of beeps when the download is complete. 4. Place your robot where it can safely move around (usually an open space on the floor) and press the green Run button on the RCX to run the program. IMPORTANT: If your robot won t turn on, or if it turns on but has no numbers counting up on the screen, or if your program has all the right parts but CHERP gives you this error message: Your program is missing something, it needs new firmware; get a new RCX brick from Louise / Elizabeth. ALWAYS turn off your robot while you re not downloading a program to it or running a program. It will use up its batteries very quickly if it is left on! Also Note: To download a graphical program it is NOT necessary to remove tangible blocks from in front of the webcam; likewise, to download a tangible program, it is NOT necessary to remove any graphical blocks from the screen. However, it IS a good idea to remove extraneous tangible blocks from the webcam s view when downloading a tangible program.
Working with Sensors and Sensor Parameters Robotic Parts Tip: Only one sensor can be used at a time. Make sure the sensor on your robot matches the parameter in your program! Touch Sensor Light Sensor Connect the loose wire end to Port 1. Be sure the other end of the wire is connected to the 4 pips on top of the sensor and closest to the yellow button. Tip: The sensor itself can be attached anywhere or hang loose do what works for your project. Connect the wire end to Port 1. Tip: Attach the sensor itself so that it will be directed toward the light source you intend it to measure. Tip: The light sensor only sees directly in front of it and often counts fairly bright light as dark, which can produce some surprising or inconsistent behaviors. It s best to shine a flashlight right at the sensor whenever you want it to perceive light. Programming Blocks that Use Sensor Parameters What are sensors and sensor parameters? Sensors provide information to the REPEAT and IF blocks about some condition in the robot s surroundings. A parameter provides information about how the REPEAT or IF should work, and a sensor parameter bases this information on data from a sensor rather than a given value, as is this case for number parameters. Tip: In a program, the robot checks the sensor value only when it gets to the REPEAT or IF block in the program. It does not automatically check continuously. In the following example of REPEATs with a sensor parameter, the robot will sing over and over until the light sensor indicates that it perceives darkness. The program is telling the robot to sing until dark, or, more specifically, to check if the light level perceived by the sensor, to sing if it s light, to check again, etc, etc.. The first time the sensor perceives dark when the robot checks, it will not sing, and it will end the program. In this example of Ifs and a sensor parameter, the robot check if the touch sensor is being pushed; this it will go backward if it is and forward if it is not.