Mawdeeb wrote:

J. Clarke wrote:
Mawdeeb wrote:


J. Clarke wrote:

Mawdeeb wrote:



TJH wrote:


OK, perhaps this might sound strange, but I'd like to drop a car from
a crane.

I'm thinking about doing a project for a high school senior class to
show the violence of an auto crash (educational for prom week) at
roughly 30-45mph. In order to do this, I'd hoist an auto by a crane up
say 40 - 50 feet, and then drop it to the ground. But, to do this, I
need some type of quick release mechanism, because the crane owner
isn't going to risk damaging his equipment by free-falling the cable.

I've thought about using heavy duty strap webbing with a quick release
buckles, but I'm not sure if they would support the weight. The
release has another problem - how do I do it from the ground? Ideally,
I would have some sort of remote controlled release, but wireless?
Wired? Mechanical? Cheap and easy is the challenge as well.

If any have any suggestions, I'd love to hear them.

Thanks in advance,

TJ Hanlon
SRO, Pawling Schools


I believe the device your looking for is called a Pelican Hook. The
release is manual via a second rope. Any decent rigging shop or marina
should be able to rent you one or point you a source for purchase.


Not designed to open under load.


Incorrect. The Pelican Hook was desined specifically to release a cable
or chain under load in an emergency. The trebu chet users use them to
hold the counter balance weight under tension.

http://www.ripcord.ws/triggers.html is one example.


Read that page carefully--they recommend their pelican hook for a load of
up
to 80 pounds, which one can release with a slip-knot. The discussion is
of supporting a car.


That page was offered as an example that the hooks will release under
tension. Now its just a matter of scale. Larger load, larger hook.

A short review of a google search will revel pelican hooks for chain
with capacities of 50000 lbs are commercially available. P Hooks used
with 1/2 inch steel cable start at 4000 lbs which should be sufficent
for the original posters needs.

Which alters the point how? Or perhaps the point that escapes you is that a
pelican hook, no matter how large, was not designed as a device to suddenly
release a heavy load by pulling on a lanyard. Typical use for the large
ones you mention is to restrain anchor chains on large ships and thus free
the windlass for other uses--they are not intended to release easily under
load and in fact doing so would be a disadvantage in that use. To release
the pelican hook the load on the chain is usually taken up by the windlass.

The little one works on toy trebuchets only because it is not subject to
much load. Note that even their larger model that is based on the pelican
hook concept is modified considerably to remove any overcenter retention of
the kind that is typical of a pelican hook and to provide a longer moment
arm for the lanyard, and even that is not rated for really heavy loads.

As the other posters have indicated, the real concern will be the crane
operators skill to control the rig when the load lets loose.

By the way, your manual is ready to send. Need a address to send to.

My manual? Perhaps you have me confused with someone else.


--
--John
to email, dial "usenet" and validate
(was jclarke at eye bee em dot net)