*Notice: I make no claim for the safety for the operations below.
Proceed at your own risk!*
I'm doing this at 4:00 AM so please excuse any typos and go for what I
meant, rather than what I said If you can figure it out..
My limited experience with tower pulleys is the ones I have used would
only increase the force a bit if they froze, but the cable would still
slide through. If they really grabbed the cable, the motor would run in
the down direction and the up cable would go slack. A jammed, caught, or
pinched pull down cable would hang in both directions, but should allow
a bit of motor run, if only for a turn or two of the motor shaft.
Limit switches can often create these problems IF they are the double
pole type that allows the motor to run in the opposite direction. IE
down off the up limit and up off the down limit.
Gear boxes, I have had a lot of experience with these, but it was many
years ago.
A frozen gearbox, or motor would result in no turning. IF, the AC motor
uses a starting capacitor, that would seem to be a starting place. As
others have said, check the gear lube for quantity and quality.
(discolored, metal filings, or a gritty feel) Any of those call for a
complete flushing of the gear box which can be difficult, in some
instances, with it bolted down. If any of the bearings, or bushings
have failed the soaking in WD40, or most and good penetrant "might" free
it up.(already suggested) Rough or frozen ball bearings need to be
replaced. Sealed bearings are very reliable, but the do fail on occasion
for various reasons. The less expensive gear boxes use bushings on the
slow moving output shaft. Some also use them on the input shaft. Some
highly rated and somewhat expensive cable winches use all bushings where
bearings are required. The rational is probably the low speed and heavy
load are better handled with Oillite or (oil-lite) bushings, or
expensive bearings.
The following is a generic approach to troubleshooting the assembly. My
apologies if this has been covered as I've read most, but not all posts
in the thread.
It would be wise to block the tower sections if it can be done safely
and *WITHOUT* climbing the tower. Never put your hands inside of a
malfunctioning, crank-up tower without first blocking the tower
sections! Use a ladder, or borrow one that will get you high enough.
Otherwise, never reach inside that tower for any reason, even
momentarily, regardless of the rationalization!
The following link is for a double worm gear rotator, but the worm gear
photos apply to most worm gear reductions. Note the sharp edge (end) of
the worm in the third photo from the top.
http://www.rogerhalstead.com/Gears.htm
Some assemblies make the following difficult.
Next step: clamp the pull cable securely without damaging it, (try to do
this without interfering with the cable drum) then disconnect the gear
box from the motor. *CAUTION* this can be*hazardous to you, the tower,
****and the antenna* if the cable clamp, block, or what ever holding
things slips. IF the motor runs then:
*
**NOTE:* You can clamp the drum, but they are often easily deformed and
it may make other steps difficult. It may be more difficult to reliably
clamp as well. Safety first!
Either remove the entire gear box (best choice), or "if possible
reconnect the gear box to the motor and disconnect the gearbox from the
cable drum. Can the shafts be turned? If not, find the instructions for
the gearbox repair.
If you are not mechanically inclined, as many are not, seek
knowledgeable help from the tower manufacturer, the gear box
manufacturer, or a well known, good, local mechanic. You are already
into the realm where a mistake can be dangerous and */ *or very
expensive, but gear boxes, whether crude, or precision and rugged can
get expensive and worm gears can be finicky about disassemble as well as
reassembly.
The worm gear "wheel" on the good ones will be contoured to fit the
radius of the worm. (Photos 1, 6, 9, and 13 in the above link) IE, the
worm sets "down" into the worm gear wheel and can not safely be removed
to the side without first raising the worm out of the wheel, or moving
the worm gear wheel. *SOME* worms can be pulled straight out along their
axis and some can't. The one in photo 3 can. Those that can, often
have a razor sharp edge at the end of the worm (Photo 3) so be careful.
To be safe resist the urge to feel the end of the worm for burrs with a
bare finger, or catching it in the palm of a hand without a leather
glove. Lots of oil, so be prepared to ruin a pair of gloves. They do
need to be clean to start.
How much applies to this problem could be all, or little, but it's a
place to start.
73 and Good Luck!
Roger (K8RI)
On 1/29/2016 Friday 4:15 PM, K7LXC--- via TowerTalk wrote:
The Hub City W300 gearbox on my US Tower 85 ft rotating mast appears
to have seized after 12 years.
Are you sure you don't have a bad bearing in a pulley (sheave)?
The UST pulleys all use sealed bearings and they have been pretty
reliable in my experience. Also the pulleys are also mostly hidden so it's not
easy to ascertain whether they're turning or not.
Cheers,
Steve K7LXC
TOWER TECH
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