Before You Begin


What’s the point?


To help students understand that the behavior of a motor (e.g., which way it turns) can be controlled by switching wire connections or via a program. Instead of rewiring a device in order to change its behavior, we can use a set of instructions—a program—to do it.

To help students analyze simple motion patterns for a two wheeled vehicle such as moving forward and backward or turning and to relate these patterns to motor operations and to programming commands. For example, students will observe a turning vehicle, realizing that one motor is turning. They will then represent this observation in a computer program.


What you will need:

For Part 1:

·     M. Pathfinder for demonstration

·     2 wires, about 40 inches long, with ends stripped

·     2 alligator clips

·     1 C or 9 Volt battery

·     2 intact long connector wires




For Part 2:

For each group:

·     The Robotics Inventions System™ kit

·     A disk

·     A copy of the Technical Guide

·     A copy of M. Pathfinder building instructions

·     A building bin (optional)

·     Student activity sheet






For the class:

·     M. Pathfinder transparency # 1

Programs used Roundtrip, TurnTurn, Long, Short, and Different

Prepare Ahead:

1.       Make enough copies of the M. Pathfinder building instructions for each working group to have one.

2.       Make enough copies of the Building and Programming M. Pathfinder student activity sheets for each student to have one.

3.       Build M. Pathfinder following building directions provided with this manual. Do not attach the RCX to the base.

4.       Prepare the stripped wires as described in (See Note on Materials box below).  

5.       Download programs Roundtrip and TurnTurn onto the RCX.


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Tech Guide

Running Lego motors without the RCX




New commands  introduced in this activity:

Text Box: © The LEGO Group

Tech Guide

Tech Guide

Tech Guide

Tech Guide

Tech Guide

Tech Guide



Activity Overview

Pathfinder is a two-wheeled, two-motor vehicle without any sensors attached. It is an easy-to-build, easy-to-fall-apart vehicle. We have included building instructions since it is no longer included in the Constructopedia. We suggest using it as a vehicle (no pun intended) for introducing RCX Code.


This activity has two parts. Part 1 is designed as a transition between the Wall Hugging Mouse and programmable robots. In this part, you will demonstrate running M. Pathfinder’s base without the RCX, showing that the unit can run on batteries alone and does not have to be programmed to run. You will show students that M. Pathfinder can run with or without the RCX. When connected to batteries, it can run forward or backwards, turn right or left, all depending on wiring. You will then demonstrate how M. Pathfinder’s behavior can be controlled through a program rather than through wire switching.


In Part 2, students build the modified Pathfinder, following the M. Pathfinder building instructions. They then run it using the program in slot #1. (This program is downloaded onto the RCX when firmware is installed.) Students will notice that M. Pathfinder goes forward, but doesn’t stop by itself. In order to stop it, they must catch it and turn it off.


Next,Before You Begin (r-r) students will follow the activity sheet to help them figure out how to make M. Pathfinder move and stop on its own, using the On, Wait for, Off, and On For command blocks.


At this point students will be ready to use the newly acquired commands to write their own programs, instructing M. Pathfinder to move in a variety of ways (e.g., zigzag, go around a box). Finally, they will program M. Pathfinder to go towards a wall, hit it, and go backwards. It is important that all students solve this problem before they move on to work with touch sensors.


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