Absolute Beginner's Guide to Building Robots
Project 2: Mousey the Junkbot
Some 45 years after Grey Walter's experiments with his robot tortoises (see Chapter 1, "What's in a Name?"), our robot is basically the same kind of critter, using many similar (although more modern) components. Walter's mechanical lifeforms used light sensing/avoiding as their basic behavior set. Our Mousey the Junkbot works in a similar fashion. Walter used electromagnetic relays as switches to trigger a change in the robot's behavior. We'll use a relay as well. Like his bots, ours also has a mechanical bump sensor that, when triggered, initiates a runaway sequence--in our case, making the robot back away from the direction it was heading. Our robot is not only called Mousey because its body is a computer mouse, but because its behavior is also somewhat mouse-like. The little DC motors that we'll use are very "torquey," creating a lively little critter that really scoots around on the floor. And when Mousey crashes into anything, it suddenly becomes...well...mousey, speeding off in the opposite direction for a few seconds.
The brains behind Mousey are the most ingenious part of this little robot hack. The creator of the first robot of this kind, Randy Sargent, used an audio operational amplifier (or op amp), a little 8-pin chip designed to boost signals in answering machines, speakerphones, and home intercoms, to read (and respond to) signals from light sensors. Besides the op amp, a 5V relay, two light sensors, and two motors, there's little else inside this bot (which is what allows us to fit it inside of a mouse case). The most unruly component is the 9V battery, but we managed to fit that in the case as well.
What's on the site:
IMPORTANT NOTE: All of the breadboard images from the book that show the sensitivity subcircuit, that part of the circuit is wrong. The Corrected Circuit Diagram shows the proper connections of the LED and resistor and where they hook into the IR eyes and control circuit.
Useful Project Links:
Complete instructions (free!) for building a version of Mousey, from my article in Make magazine vol. 2. (link to PDF file).
Website designed by Gareth Branwyn and Blake Maloof.
Photos by Jay Townsend/Primal Design. Illustrations by Mark Frauenfelder