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.
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:
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
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
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.
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.
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
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