When I examined the winch on my HDX-555, it seemed that the brake
mechanism applied permanent friction between the shaft and the toothed
wheel, but when the cable was being wound in the pawl allowed that
toothed wheel to turn freely. When the cable was being let out, the
spring-loaded pawl prevented the toothed wheel from turning, the
friction being sufficient to prevent free-wheeling and in fact requiring
considerable effort let the cable out and lower the tower.
AFAICS, the only way it can free-wheel is if something moves out of
alignment or if the pawl fails to engage the toothed wheel due to spring
failure or lack of lubrication of the pivot.
Without bothering to show the math here, it seemed to me that the winch
is in no way overloaded unless the whole tower is overloaded.
Although the documentation package I received from UST included nothing
about the winch, I found the information online at:
http://www.fultonperformance.com/instsht/F1851.pdf
From this I see that the KX1550 has two pawls instead of one (in
addition to having the cover over the gears). I can't imagine that this
would add much to the cost, so I am wondering why UST doesn't use this
instead or at least offer it as an option: both features would surely
make for increased safety.
73
Alan NV8A
On 03/18/07 10:57 pm Al Williams wrote:
> I have been hoping that a knowledgeable towertalkian would offer a posting
> on how brake winches work but again nobody has.
> I am not a mechanical or civil engineer and know little about winches,
> however I can make observations and these are what follows:
>
> About a year ago I was jacking up one side of my LM470 electric winch tower
> in preparation for tilting it down. When the center of gravity moved enough
> the winch handle started revolving and the tower was falling over on its
> own. The handle was moving slowly, but definitely picking up speed. I
> grabbed the handle and stopped the tower from continuing to fall.
>
> I do not know what the conditions were that allowed this to happen.
> However, I have since tilted the tower up and down several times with no
> problems but I am very careful to test that the braking mechanism is
> engaged.
>
> Actually I have two k2550 and one k1550 winch and all three were purchased
> from separate sources with months between the purchases. All three have
> what I call a "free wheeling" mode and operate similarly. When the tower is
> being tilted up and becomes near vertical the center of gravity takes over
> and the tower will fall into vertical place releasing the tension on the
> tilting cable. If the winch handle cranking is continued to take the slack
> out of the cable the tension becomes taut and the winch cannot be cranked
> tighter. Now, if the winch handle cranking is reversed (like trying to tilt
> the tower back down) but the tower center of gravity has not changed i.e. no
> effort has been made to actually tilt the tower, the handle requires a
> substantial pull to free it to turn and then become easier to turn and
> eventually the weight of the handle alone is enough to turn the winch drum.
> Remember the tower has not moved, all that has happened is that the cable
> has gone slack. (Not quite true I think-- the braking mechanism has also
> been disengaged)
>
> I make the assumption that the braking mechanism has been relaxed or even
> almost removed. The braking mechanism appears not to be engaged until the
> cable is subsequently made to become taut again by taking the slack out of
> cable and tightening firmly.
>
> When the tower is being tilted down; the braking mechanism is working
> properly and the tower comes to rest on the ground, if the winching
> continues until the cable tension is removed and the cable becomes slack,
> the braking mechanism appears to release just as I reported above. The
> winch becomes "free wheeling" but since the tower is on the ground no harm
> can result.
>
> When my near accident of the tower falling occurred, I continued cranking it
> down by keeping hold of the handle. I suspect that if I had reversed
> direction to crank the tower back up that the braking mechanism would have
> "snapped" into operation. I don't intend to experiment to confirm my
> suspicion.
>
> Joe may be correct in that "...the winches are not designed or intended to
> freewheel". However the anomaly seems to be in the design and use and not
> in my particular units. Users of Fulton k1550 and k2550 braking winches
> should be aware that these winches can get into a "free wheel" mode without
> a winch failure. It would be easy to confirm this and I hope that someone
> will and report it.
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