Common or uncommon sensors used in FRC

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Garage door sensors are the IR beams used to detect if something (like a child) is in the way of your garage door as it descends. The sensor is actually a pair of devices: an IR emitter and an IR receiver. The receiver sends a different signal when it can and cannot see the emitter beam. We have used them for a variety of purposes. Taking Rebound Rumble as an example, we had a garage door sensor mounted low in the robot. When we started picking up a ball it would block the beam and the sensor would signal that something (a ball) was blocking its beam. When the ball cleared the beam and the receiver could again see the emitter the robot knew to turn off the conveyor. A similar set up at the top was used to "count" balls going to the shooter. Together these two garage door sensors let us move balls efficiently inside the robot and count the balls we picked up and shot.