By this we mean physical contact between the robot and an obstacle such as a fairly massive object or a wall.

Typically, the robot has bumpers or possibly wiry 'antennae' arranged so that they are touched when the robot runs into anything. The usual response is to reverse a short distance, turn slightly to left or right, then move forward to try again. If the robot has a pair of bumpers, at front left and right, it is possible for the robot to work out which is the best direction to turn.

Side-mounted bumpers can be used for wall-following, instead of a proximity detector.

Other uses for contact detection occur when a robot is designed to sweep an area clear of light objects, or to find and pick up objects.

The fact that a robot is in contact with a sizeable object can often be inferred by monitoring its motion. If the drive motors are swtched on, but the drive wheels are not turning, it is likely that the robot is pushing against an immovable obstacle. A tachometer is used to determine if the wheels are turning or not.


Bumpers 149


Switches 306 Optical encoder 84


Avoiding obstacles 206

Line following is a special form of contact behaviour. The robot stays in contact with a line painted on the surface over which it is moving. Line following requires two simple light sensors and the programming is easy. It is one of the most reliable techniques for guiding a robot from one place to another.

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