Discussion Points

Part 1: Running Lego Motors with and without the RCX

Whole Class Activity

Before students build M. Pathfinder: Show students the base of a pre-built M. Pathfinder without the RCX. Connect one end of a long connector wire to each motor and then connect the other ends to each other, stacked on top of one another.


If you are using a stripped connector wire, connect it to the long connector wires on one end, with the stripped end free.

If you are using wires with alligator clips, connect the clips to the long connector wires (see illustration on the previous page).


Now, take one stripped wire and hold it to one end of a battery. Hold the second stripped wire to the other end of the battery. Point out that M. Pathfinder is running in one direction now. Then switch which wire is connected to which end of the battery. Have students observe that M. Pathfinder is running in the opposite direction.

Ask students what they think you should do to make the base turn in place. If needed, remind them of how the Wall Hugging Mouse moved (one motor turned on at a time).

Adding the RCX: Show students the RCX. Explain that it is a small computer that runs on batteries and can hold up to five programs. Remove the stripped wires and connect one end of a long connector wire to Port A and the other to Port C. (The other ends should remain attached to the motors.)

Hold the RCX in your hand and show students the red on/off button, the gray program button, and the green run button. Point out that when a program (1-5) is selected, a number is displayed in the display window, indicating which program is running. In addition, an icon of a running person helps you tell whether or not a program is running.

Now run the Roundtrip program and have students describe what M. Pathfinder is doing. Point out that this time you haven’t switched wiring. Then move to the TurnTurn program and run it.

Emphasize that M. Pathfinder is displaying different behavior—moving forward, backward, turning one way and then the other way—but you haven’t changed the connector wires. The motors are turned on or off by commands that are coming from a program.

Finally, attach the RCX to the base, using short connector wires, and let it run on its own. Tell students that they will build M. Pathfinder and program it in the next section (It may or may not be in the same lesson, depending on the time allocated for the activity.)

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Part 2: Building and Programming M. Pathfinder

Small Group Activity

Building M. Pathfinder: Have students work in small groups. Give each group a copy of M. Pathfinder building instructions and each student a copy of the activity sheet. As they build, talk to students in their groups, showing them the different buttons on the RCX and encouraging them to look up their function in the Technical Guide or to search the Help menu for RCX buttons and RCX display window. Make them aware of the running indicator on the display window and of how to move from one program to another. When they have finished building, if at all possible, allow students to run their vehicles in a hallway.


Tech Guide


Beyond the Basics

Students are now ready to program their RCX. Decide whether to have students follow the worksheet and refer to the Technical Guide or the Help menu on their own, or whether to introduce the IR (Infrared) tower and the download procedure to the class as a whole.

Show the class (or small groups) the IR (infrared) tower. Demonstrate how to use it to download a program onto the RCX. Point out the part of the RCX that must face the IR tower. Explain that the IR tower and the RCX must be within communication distance, just over a hand-width apart. Programs transmitted from the computer to the RCX via IR can then be run by the RCX.

Have students work on their own to solve the problem of making M. Pathfinder do things on its own—recreating a program, downloading, and running it. As they work, talk to them in small groups about the difference between downloading and saving (one goes to the RCX the other onto a disk).


Tech Guide

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