The slip clutch is a special type of gear. It has 24 teeth, just like a spur gear, but it has one major difference. The difference is if the slip clutch gets stuck, the axle can continue to rotate.

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Look at this example. The output wheel is connected to the motor through a slip clutch. If the output wheel stops rotating, the motor can continue to turn and not stall. Stalling a motor is bad for the motor and could damage it. You should use a slip clutch in situations where the output axle might get stuck. The slip clutch is similar to belts and pulleys by not allowing the motor to stall, but it can transmit more force because it has teeth like a gear.

See also: Gears, Belts and Pulleys