I’ve heard of Hall effect sensors being used on robots but what are they actually used for?
Generally speaking, they’re used for detecting metal passing them, particularly steel. Could be useful for setting arm setpoints, counting teeth on a particularly large sprocket, picking up a pneumatic cylinder’s piston or linear actuator’s nut going past.
We have one available now that detects when a magnet is near. These are especially useful in detecting position and can be used to zero mechanisms like elevators or arms. The link has a user guide that provides more information but let us know if you have other questions.
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So almost like a limit switch but detecting magnets?
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Think of it as a non-contact switch.
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Yes, the most common application where you can actually touch it looks like a non-contact limit switch that senses ONLY magnets. It can easily sense through aluminum, non-magnetic stainless steel and plastic. One sweet application is putting a magnet on the piston of an air cylinder (inside the cylinder) and sensing it from the outside. Very clean!
They are commonly used to commutate brushless motors.
The magnetic encoders you see (like the CANCoder and Thrifty Encoder use a couple of analog Hall effect sensors to extract position.
Analog Hall effect sensors can do linear and angular position sensing, but can get tricky to calibrate. Plus, they will notice if you have steel bits moving near it.
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I’d take this a step further and say it’s actually part a parcel of all brushless motors. There are 3 lines running to the motor. Each line will be turned on and off in a sequence like so:
The square pattern of the halls is directly comparable to the phases of each line. Because of this you can technically have RPMRevolutions Per Minute control of any brushless motor at high speed by counting the time between each rising/falling edge. At low speeds this is less accurate. You can also get the analog strength for better accuracy
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