[TowerTalk] Maasdam "Powr Pull"

[Jim Lux]

On 9/23/11 4:48 PM, Rick Karlquist wrote:
> A question for you come along experts.
>
> I saw some come alongs at the Chinese tool store (you know the one)
> that claimed to pull some huge weight like 8 tons.  Assuming
> the user applies 40 lbs, this is a 400:1 mechanical advantage,
> not counting friction.  This is hard to believe.  Is this
> true of these or even the American equivalents?  Or is this
> specsmanship where it moves an 8 ton boat onto a trailer
> or something like that?
>

Rolling load might be part of it, but think of this..

Say you have a 2 foot lever arm, and the spool of cable is 2" in 
diameter.  That's 24:1 advantage, and if you had a 15:1 gear ratio 
between handle and spool, that would get you there.

I've used larger versions of this (from a different mfr) which had a 4 
foot handle or there abouts, and we had over 10,000 lb tension on the 
cable.  I was able to crank it standing in a bucket truck 50 feet in the 
air, with the device horizontal (so I wasn't using body weight).  Maybe 
50lb on the handle for 200-250 times that on the cable.

What was real exciting was that it got stuck and wouldn't release, so I 
had to dismantle part of the mechanism, with it under load.  (oh yeah, 
100 ft of 1/2 steel cable under a lot of tension.. that made me 
comfortable. a LOT of stored energy.) Turns out, though, that the device 
was actually designed for this.  The way the cams and locks work, the 
loads are carried through one path, and the "winching" is on another 
path, so you can fix the winch mechanism with no load on it.  Once 
fixed, you use the winch to take up the load, disengage the locking 
pawl, and gradually release it.   I can't remember whether it was a worm 
gear or spur gear drive, but I'm thinking spur gear, with one of those 
built in brake/slip clutch things.

(This kind of work is one reason I am glad I don't do that kind of work 
any more.  Interesting, challenging, never the same twice, but frankly, 
a bit too close to maim/death for my taste.)