LEGO Robots 101

#include <rcx.h>                // include file for LEGO robots

int main()
{
   playSound(UP_SCALE);         // play simple scale
   MotorAOnFwd();               // turn motor A on in forward direction
   MotorCOnRev();               // turn motor C on in reverse
   return 0;
}

1. Insert the control tower's USB plug into the computer. If you get a message about having "insufficient privileges to install devices", try plugging the tower into a different port. If none of the ports work, talk to your instructor.

2. In HiC, select Options from the Edit menu. Click on the "Lego RCX" tab and set "NQC Path:" to

           H:\Apps-EMS\HiC\nqc.exe
   

   This allows HiC to use "NQC" - aka "Not Quite C" - to download your program to the brick.

3. Turn on the RCX brick by clicking on the red On/Off button. You should see a bunch of 0's, a standing person, and a number between 1 and 5. If you do not see the 0's - that is, if you see a picture such as shown to the right - contact your instructor to have the firmware reset on your system. (If you're adventurous, you can simply start up a DOS prompt and execute "H:\Apps-EMS\HiC\rcxfirm.bat".)

4. Aim the front panel of the robot at the tower with a few inches between the two (as shown to the right). The picture is a thumbnail - click on it to make it larger.

5. Make sure the unit is turned on - it turns itself off after a few minutes of inactivity - and click on . During the download, you should see dots flashing across the top of the RCX display. When the program is downloaded the robot will play a quick tune and you should see "No errors! Downloading Program:....complete" at the bottom of the HiC window. If you get a message about "no firmware", you need to reload the firmware as described above. For other error messages, contact your instructor.

6. Put the robot near the center of the table and click the green Run button on the RCX unit. The robot should play a quick tune and start spinning around. Since there's nothing to make the motors stop, it will keep spinning until you turn it off (by pressing the red button).

   Warning! Be careful that the robot does not fall off the table. It should survive the fall onto the carpet, but all of the pieces will fall off and you'll have to reconstruct the robot before continuing.

7. Next we will extend the program so that the robot reacts to the world. There should be a small light sensor (see right) attached to the robot on input port 3. Change your main to use the following to spin the robot right or left depending on how much light is reaching the sensor.

      int level;
      readLightSensor(3, level);
      if ( level > 40 )
      {
         // bright light, spin right
         MotorAOnRev();
         MotorCOnFwd();
      }
      else
      {
         // dark, spin left
         MotorAOnFwd();
         MotorCOnRev();
      }
      wait(500);   // turn for 5 seconds
      MotorAOff(); // stop
      MotorCOff();
   

   When you press the run button, if there's a decent amount of light in the room then the robot should spin to the right. Next, cover the light sensor with something like a mouse pad (or anything black - your hand will probably not work) and run the program again. This time the robot should spin the other direction. Note the sensor has to be covered before you press the run button; the program reads the light sensor just once and so later changes are ignored.

   If you're having troubles getting the robot to spin both directions, press the View button on the RCX unit until there's a little "^" below the light sensor port. The display will show the current level; you can use this information to adjust what level controls whether the robot spins right or left. The number read by the sensor is between 0 and 100 with 0 being very dark and 100 being very light. The above program uses 40 simply because that's been found to work well in the lab; you might need a larger value if your room lighting is brighter and a smaller value if it's darker.

   Further robot commands are documented in the next section. You might want to skim through the list to get an idea of what commands are available.

8. Once you have run through the demo, click on to create a new program and work on the lab problem. Please turn the robot off when it's not in use to conserve the batteries.

Robot Commands

  if ( lightSensorLevel(1) > 50 )
     MotorAOnFwd();