The reflectance sensors are one of the most important aspects of the AEV vehicle. The sensors work by detecting voltage changes as an object is passed over them. In this case, the aluminum tape produces a much different voltage than the plastic wheel. Each time the sensor picks up a voltage difference, it records it as one mark. Since there are two sensors and a total of four transitions from tape to plastic, there are eight marks for each rotation of the wheel. The wheel has a circumference of about 3.9 inches, meaning the ratio of marks to inches is 8 marks per 3.9 inches, or 0.4875 inches per mark. The sensors were fastened to the AEV by using two small screws. A picture of the setup is shown below.
The sensors become useful for the use of two function calls: the goToRelativePosition(n); function and the goToAbsolutePosition(n); function. Both functions are described in the Arduino function calls glossary page.