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always have a longer process than the other, and the bot will tend to turn. Rig your motors so that the normal — S1 closed — turn is to the left, which for Harvey is towards a wall. (Harvey is a liberal, left-leaning wallbanger. If you prefer a conservative, right-leaning wallbanger, just reverse the switch!)

When the feeler on S1 hits a wall, the switch opens and

PARTS LIST — For the Series

R2 is associated with the opposite half of the Bicore, causing that half to be on longer. This results in a turn to the right, away from the wall.

Once Harvey has turned away enough for the feeler to lose contact with the wall, S1 will close and Harvey will head back toward the wall. If you don't get this behavior, swap your motor and switch leads around until everything works right.

We'll leave the mechanics to you. You can use the gearmotors from TimerBot (as explained the September, 2004 issue of SERVO) or turn up new ones if you don't want to sabotage your existing robot. In our prototype, the SPDT switch was salvaged from an old computer mouse with a length of springy brass strip epoxied to the switch tab. Be creative!

In the photo of our prototype of Harvey, you'll notice little sockets soldered to the switch pins and to parts of the "free-formed" circuit. This is so various resistors could be tried "on the fly" to change how much the bot would turn. The switch is fastened to the motor cases with double-sided foam tape. Be prepared to do some experimenting to find the best angle and length of feeler to get the best results.

One use for Harvey's pattern of movement is maze solving. A popular method for solving a maze is the left-hand rule. Keeping your left hand on the wall and following it around will eventually get you out.

This only works for mazes that have all of the walls connected together, though, but it is a good strategy nonetheless.

So, the next time you find yourself stuck in a labyrinth with friends, family, or a Minotaur, think of SERVO Magazine.

Quickly build a Harvey Wallbanger, follow him out to safety, and be the hero. SV

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