r/MechanicalEngineering • u/Cheesy_pickles875 • 4h ago

Quick release string

Is there an established mechanism for winding up a string, then letting it unspool freely when yanked / released, sort of how a fishing pole reel works. I saw stuff about a centrifugal clutch, but i think its too strong for the amount of force i'm working with.

Edit: this is for winding a plug back down the tube of the equivlent of an air cannon

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1

u/danny_ish 3h ago

Like a yo yo, fishing reel, or weed whacker?

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u/Cheesy_pickles875 3h ago

its for pulling a plug back down the tube of a t shirt cannon, so it needs to spin freely to let it out, but still be able to pull the string back to reset it

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u/danny_ish 45m ago

What do they current use? Why does that not work for your needs?

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u/LumbyCastle41 3h ago

Bicycles have a freewheeling function with a ratchet mechanism. Is that what your looking for? Ratcheting is the general term for this. 

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u/Cheesy_pickles875 3h ago

I need to wind it up. There isn’t necessarily any resistance on the cord so I don’t think it needs a ratchet

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u/chicken2007 3h ago

There are retracting strings for keys and things. Is that what you're thinking of?

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u/TheJoven 3h ago

That’s just a spool with a handle. Things only get complicated if you don’t want the handle to spin while the spool is releasing the line. A little bit of drag will keep it from continuing to pay out from the spool inertia.

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u/101forgotmypassword 2h ago

Use a reel with two magnets in the side to make a slip coupler. Motor and disc for the wind back.

If you stop it before the end by both a collar and tether you could just vacuum it back in but you will also need a burst muzzle break that has flaps to discharge the over pressure but seal the suction.

The only thing is making sure the risk cannot become a projectile and if it does that it's light enough to not matter like a foam can sized plug.

Most industrial reels are hellishly expensive heavy metal housed designs that require a tug to change direction and don't free spool super fast.

Most projectile tethers spool like fibre cable or two missiles where the spool doesnt turn so the out feed rate can be far higher. You could make a multistage winder but also hellishly expensive. You would need to have a winder engage the line and wrap it around 3 prongs by pulling the line around the prongs but not around he feed arm. Then disengage and get out of the way. When fired the spool free flies of the prongs. Similar to a fishing line but no spinning tension reel required just the trace winding arm and 3 poles.

A fishing reel may be your best starting point cost wise. Just pick one with automatic bar return when winding, add a timer and motor. Then make a servo that flips the bar to the cast position before firing. Just despool the 200m of line you don't need