A detent is a mechanical or magnetic means to resist or arrest the rotation of a wheel, axle, or spindle. Such a device can be anything ranging from a simple metal pin to a machine. The term is also used for the method involved.
Magnetic detents are most often used to divide a shaft rotation into discrete increments. Magnetic detents are inherent in some types of electric motors, most often stepper motors.
The vertical angle of the sides of the notches that face the direction that rotation is desired is generally acute (45 degrees or less), so that as the wheel rotates in that direction, the end of the lever is easily lifted or pushed out and over the top of a notch. Following this, the lever drops into the next notch and the next et cetera as the wheel or shaft continues to spin.
The angle of the backside of the notch is severe (usually 90 degrees or greater to the end of the lever) so that the lever cannot be pushed up or out of the notch if wheel attempts to turn in the opposite direction. The lever is jammed between the back of the notch and its pivot point, stopping movement in that direction against any force that the materials used can withstand. The wheel has little resistance moving in the direction desired, other than that required to lift or push the lever over the next notch.
To resist movement (or when creating incremental steps), methods are employed which include a spring-loaded ball bearing that locates in small incremental depressions, or a piece of spring steel that snaps into position on flat surfaces or shallow notches milled into the shaft or wheel.
Stepper motors rely on magnetic detents to retain step location when winding power is removed. They are well suited to be used in printers and cnc devices (numerical control).
A well-known example of a detent can be seen on the popular game show "Wheel Of Fortune", which employs rubber flippers to help disambiguate on which wedge the wheel has stopped after being spun by a contestant. Other common examples include:
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