Mercury Tilt - This range sensor is used to detect the tilt with respect to gravity. It can tell if the robot is traveling up a steep incline and might tip. It can also be used to detect when a robot reaches a preset angle.
As a practical application, it can be used to count the number of hills a mobile robot has traveled.
IR - Infrared emitter detectors are easily implemented and can be used for collision detection, motion detection, transmitters, encoders, and color detection. IR requires testing and calibration for good results.
As a practical application, an IR sensor can be used to guide a robot along a line and avoid obstacles.
Sonar - Also called an acoustic proximity sensor, a sonar sensor gathers feedback about surroundings by emitting a sound and calculating the amount of time needed for the sound to travel back.
In practical applications it is useful in collision detection.
Capacitive - This proximity sensor uses a radio frequency (RF) oscillator, a frequency detector, and a metal plate connected to the oscillator circuit to avoid collisions with other objects. The oscillator frequency changes when a change in the capacitance is detected. Objects that conduct electricity are better sensed than object that do not.
As a practical application, this sensor can keep a mobile robot from running into humans and animals.
Encoder - Encoders can take on many forms, including slot, rotary, and linear. These sensors use relative positioning, also called dead-reckoning, and incremental counting to measure properties such as displacement, velocity, acceleration, and angle. Encoders use an optical sensor to move mechanical components. A reflector provides electric pulses allowing this sensor to measure rotation when attached to a rotating object, such as a wheel or motor.
As a practical application, encoders can determine how far a robot has traveled and how many degrees an axis has spun.