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** If there's a better stack exchange site for this, let me know--the mechanical engineering one is closed so I'm not sure where else is appropriate **

Do mechanical systems have fuses?

In an electrical system, like a charging circuit for example, we prevent large loads from damaging the system with fuses and circuit breakers. These will disconnect the inputs from the outputs if the load get too high.

Do mechanical systems have a similar mechanism? Something that would prevent gears or linkages from breaking when the load gets too high by disconnecting the input from the output?

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  • $\begingroup$ If you don't get a suitable answer here, you may want to try the new engineering SE site. $\endgroup$ – Paul Jan 26 '15 at 14:34
  • $\begingroup$ Something like a centrifugal clutch? $\endgroup$ – Scott Downey Jan 26 '15 at 14:44
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You are looking for a clutch. It is loaded device that 'gives' when the torque exceeds its set amount.

LEGO Clutch

Here is a LEGO clutch you can see how it works.

enter image description here

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  • $\begingroup$ Ah interesting, let me see if I understand this. When the force on the gear overcomes the friction between that rubber-looking container for the axle and those metal-looking panels, the center turns independent of the gear, which relieves the stress on the rest of the system. So, question: does the gear actually stop turning at that point? Or does it just turn a lot slower? $\endgroup$ – Robz Feb 2 '15 at 2:47
  • $\begingroup$ That depends on where the power is coming from, if it comes from the outer gear, it will continue turning. If the power is coming from the axle through the inner hole, the gear will stop. $\endgroup$ – Spiked3 Feb 2 '15 at 3:53
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I'm not a mechanical engineer, but I would imagine the analogous piece to an electrical fuse would be a piece connecting input and output that would easily break if too much pressure is exerted on it. This would be analogous to old fuses that literally burned when too much current passed them.

If you want a more modern fuse, you need a system that measures the load and detaches the input from output if too high, with the ability to connect it back again (by a human). My wife (mechatronics engineer) says you can use magnetic and force torque sensor.

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A tendon does act as a mechanical fuse, breaking up when moving parts it connects undergo unaffordable stress, overcoming its elasticity limit.

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For “Something that would prevent gears or linkages from breaking when the load gets too high”, look for shear pins and sacrificial gears, links, arms, etc. Typically a shear key, shear pin, etc is far less expensive than the components it protects.

A shear pin (ie, a transverse pin linking a gear to a shaft) typically is made of softer material (eg, plastic, aluminum, or mild steel) than the drive train parts it protects. Or it may have shear zones that are cut down to a smaller diameter than the rest of the pin.

Drive keys (eg, square keys, Woodruff keys, and less frequently Scotch keys) also are sometimes used as shear elements.

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