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I'm working on a system that requires a small cord (~3ft long) to retract up into a reel and lock in place so it cannot be pulled away from the reel. Sort of like a seatbelt mechanism after it's been pulled too far or too hard.

I'm hoping to find something off the shelf that is small and lightweight (~100g) before building my own solution. I've found industrial spring reels like these, that are of the correct size and construction, but none have the locking functionality I'm looking for.

Does this mechanism sound familiar to anyone?

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    $\begingroup$ A lot of clothes-iron's have a self-winding / retracting reel for the cord built into them... $\endgroup$ – Pete W May 15 at 1:11
  • $\begingroup$ masterlock python will "lock" but doesnt have a retraction mechanism of its own $\endgroup$ – Abel May 15 at 4:58
  • $\begingroup$ The word "lanyard" in the title makes me nervous - we're talking about automatic tightening and locking in the context of something that goes around a human neck. $\endgroup$ – Daniel Hatton May 15 at 9:19
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    $\begingroup$ The seatbelt lock is centrifugal so it's velocity triggered, not distance ("too far"). $\endgroup$ – Transistor May 15 at 11:36
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    $\begingroup$ Dog leashes allow line to run, retract, then slide a button to lock the line in place. You could probably find a cheap one and include a ramp and stop with a bead (on the line), so once brought behind the stop will prevent the line from extending. $\endgroup$ – Jim Clark May 15 at 13:07
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Depending on the direction of extension/retraction you could use a mechanism for :

  • (won't extend unless you permit it) a extendable dog leash
  • (won't retract unless you permit it) a vacuum cleaner cable retracting mechanism.

dog leash

Basic parts of dog leash mechanism.

enter image description here

Figure from medium.com

Vaccum cleaner

You can see a patent like that in https://patents.google.com/patent/US5255768A/en.

This is an example part with a complete plug assembly you can buy from espares.co.uk (you can search and find something more to your specific needs).

enter image description here

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  • $\begingroup$ Seems like "by default" it works in the opposite direction than OP wants, preventing unwanted retraction, instead of unwanted extension. Might be possible to modify it by reversing the spring and the direction the cable is coiled $\endgroup$ – SF. May 15 at 11:35
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Dog leashes allow line to run, retract, then slide a button to lock the line in place. Dollar stores have inexpensive options.

This takes care of locking after full retraction: Include a ramp and stop with a bead (on the line), so during retraction once brought behind the stop-engagement this prevents the line from re-extending.

If you want a seat-belt function: You would need to include an inertial catch, like a centrifugal clutch, that when it spins at some pre-determined velocity, it catches the exterior and engages (in your case) the non-rotating housing. Add dampers so that when the "catches" engage, breakage is prevented.

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