Auto release clip under load?

[kitebuddy]

First time poster.

Looking for a clip that will release under a load of ~250lbs.
Been looking at shear pins and torsion springs but wondering if something already exists.
It will be used between two ropes and will release automatically once load is hit. Something adjustable from 200lbs. to 300lbs.
would be ideal.

Any engineers out there have any ideas?
Thanks in advance

 

[MikeHalloran]

I can think of a few ways to do it, but it seems like a very dangerous product.
I.e., when it drops a 301 lb. illiterate idiot, you can expect to hear from said idiot's attorneys.


Mike Halloran
Pembroke Pines, FL, USA

 

[3DDave]

I've seen mechanisms like this designed for specific purposes; for example missile hold-backs to make sure sufficient thrust is generated before the missile is allowed to leave the launcher. Also safety valves with rupture disks.

Why not just get some string and make up a loop that takes about 250 pounds to break. You could get fairly repeatable results with 12 wraps (12 up, 12 back) of 10 pound test line would give 250 pounds, plus the ability to adjust it in 10 pound increments for fine tuning.

 

[gearcutter]

Over-centre latches/buckles will release under load.
Load-holding chains used in the transport industry are a good example.

 

[3DDave]

gearcutter - he's looking for something that fails under load at a specific load rating, like a mechanical fuse.

 

[MikeHalloran]

Basically any overcenter/toggle mechanism will not release because of an applied load until it undergoes significant deformation, or excessive wear at the pivot points.

"Load binders" comprising an overcenter toggle, chain, and hooks will _not_ release as a response to any given load within their capability.

They can be released by manually manipulating the toggle, which is not what the OP asked for. ... it is also best done with a long prybar or similar tool, because the stored strain energy will be converted into kinetic energy of the various parts, which can do significant damage to persons or objects in the immediate vicinity.

Similarly, if you're going to separate two connected ropes at a significant level of tension, you need to be sure that no person is close enough to be injured by whatever parts will be flying after the separation starts.


Now, as for how to do it, what comes to mind is a fairly precisely made detent, either using die springs directly, or using weaker springs set up as a sort of pilot mechanism to an _under_center toggle. It's actually a fairly difficult sophomore kinematics problem, that becomes a dangerous kinetics problem at the moment of release.

I think I read once that aircraft carrier catapults are allowed to build steam pressure behind a piston until a standardized barbell shaped holdback bar fractures under axial tension, releasing the catapult and the aircraft to move forward. I.e., the bars are consumed, one per launch.

I'd tend to prefer that frangible bar type release for its simple geometry, but you may have buy name-brand steel and machine it with unobvious precision to get predictable and repeatable results, so the consumables cost per release may be higher than you anticipate.










Mike Halloran
Pembroke Pines, FL, USA

 

[gearcutter]

Ah, OK, thanks guys.............my bad.

 

[gearcutter]

kitebuddy - A forum where the subject matter surrounds gears & pulleys really isn't the right place for your question.

The 'Mechanical engineering other topics Forum' might be more appropriate -

http://www.eng-tips.com/threadminder.cfm?pid=404

 

[kitebuddy]

For what its worth I think I came up with something.
Its used to pull fiber optic cables called a breakaway swivel.
THanks for the input!

http://www.dcddesign.com/breakaway-swivels-connectors.htm