On Tue, 16 Mar 2010 19:38:35 -0700 (PDT), "
wrote:

On Mar 16, 1:56*pm, Ned Simmons wrote:
On Mon, 15 Mar 2010 09:34:07 -0500, Ned Simmons
wrote:

I'm working on a fail safe brake...

Thanks to everyone who responded. I still have to do some tweaking and
check proportions and strengths of the various components, but this
should be pretty close.

If the chain goes slack: the stack of Belleville washers (magenta)
pulls the chain rod (gray) down; as the collar on the rod (gray) falls
the arm (green) rotates CW; allowing the torsion spring to rotate the
collar (gray) CCW; the pawl (green) rotates along with the collar and
engages the slotted track (orange).

http://www.suscom-maine.net/~nsimmon...ck_100316a.jpg

--
Ned Simmons

Looks like a good solution. You might think of making the lower
portion of the threaded rod as smooth as it can be. If the chain
breaks it is likely to fly away and pull the threaded rod into a bind.
A smooth, lubricated rod would probably not bind if pulled sideways.

That one of the required tweaks -- the originals are made from alloy
threaded rod, and I just lengthened one for the layout. The new ones
will need to have only enough thread on the lower end to adjust the
chains.

--
Ned Simmons