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Limit switches are used to detect when some mechanism has hit some form of limit. For instance, a limit switch would be used to detect when an elevator is at its lower limit or when an arm is at its maximum angle. To design for controllability, every mechanism that has a limit should have a limit switch on it. Ideally, there should be at least one limit switch and a Quadrature Encoder.

Most limit switches are mechanical, using the physical movement of a switch to short an electrical circuit which is then detected by the robot controller. One kind is the Snap Action Switch

Other limit switches use the Hall Effect, which allows the detection of a strength of a nearby magnetic field. These consist of two components. First is the magnetic, which typically sits on the moving mechanism. The second is the Hall Effect Sensor, which will stay on the static part of the mechanism. Internally, the Hall Effect Limit Switch will convert the analog Hall Effect into a digital output that behaves similarly to a mechanical limit switch.