First, thanks for including the description on how the motorized version
works.
True and I agree with you. I'd certainly want what you describe for a
heavy tower, but I think that's a lot more than the typical crank-up
most hams would have. I doubt the TT population is typical though. I
believe there are a much higher % of hams with big antennas and the
towers to support them and the knowledge to know whats needed on here
than "out in the wild".
My LM470 weighs 1148# and extends to 68' while supporting 16 sq ft in
60 MPH winds which are rare around here and it does have the positive
pull down feature. Both raising and lowering cables are only 1/4 inch
(0.250"). Were I still working and had both hands and legs working I
would have installed a much larger and heavier tower. <:-( OTOH I would
have installed a big crank up instead of the 100' 45G had I known the
future. Hind sight is so much more accurate than foresight.<:-)
The TX 455 is 55' extended and although rated for larger antennas and 90
MPH winds than my LM470, it weighs considerably less. The standard
motor for raising the 455 is 1 HP.
I would add that I like the base for the TX455 a lot more than the one
on the LM470.
In prior years I'd have not hesitated to build a powered crank-up with
positive pull down for my small tower, However I spent my first 21
years on a farm, spent 26 years working in an instrument and
maintenance shop and now have my own small shop. So, yes I do have more
experience than many, maybe most.
I can also do my own calculations, but as I'm prone to making dumb math
mistakes I always have them checked. There are lots of engineers in
this area who will gladly run the numbers for me<:-)
I do have one hard rule: "When you do it yourself, have someone
knowledgeable check your work!" That's really important when safety is
involved.
I would suggest that those with little or no mechanical experience
purchase the system for the tower they have, but in many countries, that
would be cost prohibitive with shipping, import tax, Value Added Tax
(VAT) and possibly other fees, the price can easily be 70% to 100% more
than here in the US, or Canada. Adding a motor drive with positive pull
down could cost as much as the entire tower state side. BTW Once you
see one, the positive pull down feature is very simple, but you must
include ALL of the proper parts.
73
Roger (K8RI)
On 10/29/2015 8:55 AM, Jim Thomson wrote:
Date: Wed, 28 Oct 2015 22:32:50 -0400
From: "Roger (K8RI) on TT" <K8RI-on-TowerTalk@tm.net>
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Motorized Crank up
The winches used to raise and lower "most" crank up towers used by hams
are very simple arrangements. They use a "relatively small",
bi-directional 110 VAC motor to drive the take up reel through a series
of belts and pulleys as a speed reducer. I'd need to go look to see what
HP my LM470 uses, but it's less than 1 HP
The simplest uses 2 metal plates. One to mount the motor at 90 degrees
to the plate with the belt and pulley speed reduction unit. Far, far,
cheaper than a winch or worm gear reduction unit.
Most, standard AC motors run at 1700 RPM. A common cable take up drum
may be on the order of 4" in diameter. The Circumference = Pi d or 3.14
* 4 or 12.5 inches ~ 1 foot per revolution. You need to know how much
1 ft of cable raises the tower. I don't remember off hand how much that is.
Speed reduction with belts and pulleys is diameter of the larger pulley
divided by the diameter of the smaller.
I'll leave the rest to someone who is more familiar with crank ups.
73
Roger (K8RI)
## There is a reason the UST winches, like the one used on my HDX-689 cost
big bux, the entire assy weighs like 230 lbs ! 1.5 hp 1700 rpm motor, with a
I think a 2 inch od pulley on the motor shaft. Rubber belt from that pulley
goes to a
14 inch od pulley. 14 inch pulley is on the end of the hub city speed reducer.
Speed reducer has a massive built in gear redux. Other end of same gear reducer
is a 3 inch od double wide sprocket. Then the huge double wide chain that goes
to the 6 inch od sprocket on the drum.. I think the drum is apx 5 inch diam,
maybe
even 6 inch. Mine uses a positive pull down feature. The smaller .25 inch
aircraft cable is attached to dead center of the very top section, and runs
down the
inside of the tower, and terminates on one end of the big drum. Other end of
the drum
has the .3125 inch od cable that raises the tower. 4 pulley system used.
Pull down
main cable and 2nd section from bottom goes up 1 foot. On the new version of
the same
tower, they use .375 inch raising cable but only 3 pulleys.
## 1700 rpm, 1.5 hp reversible motor has loads of tq. Drives the 2 inch
pulley, with
rubber belt attached..with other end to the 14 inch pulley. That’s a 7-1
redux right there.
I forget the redux used in the big speed reducer, but it’s a bunch. then
another 2-1 redux
via the 3 inch to 6 inch sprocket with the double wide chain. I can easily
turn the 14 inch pulley
by hand, and raise / lower the tower by hand. I bought the UST optional
handcrank that bolts
to the 14 inch pulley....in case of a commercial AC power failure. You could
easily use a cordless
drill to do the same job, requires next to no torque to turn it.
## as others have noted, you don’t want to even think about using a crankup
like mine, that
weighs 5600 lbs..without positive pull down feature. As tower is being
raised, the raising cable is being
wound onto one end of the drum. Meanwhile at the other end of the big drum,
the smaller positive pull down cable
is being played out, coming OFF the drum..and running the entire length of the
tower when fully extended,
going up the inside. When lowering the tower, its just the reverse. Positive
pull down cable winds onto drum,
while main raising cable comes off the other end of drum. You also have the
main large control box on
the side of the tower, with the myriad of control relays, contactors, and a
total of two adjustable timers,
plus inputs for the two water proof limit switchs. There is also a sliding
guide that runs in a track, so the
raising cable, and positive pull down cable.... both wind perfectly, with space
between adjacent
turns, on the drum.
## If you have ever seen one up close, it’s a large assy. Mine also cane with
the heavy duty protective
industrial mesh guard over the drum...and also another one between motor and 14
inch od pulley.
## IMO, to try to build a hb version of the above would be a huge project. I
don’t really think you would
save anything. It would be a lot of fabrication work, plus the ust version is
hot dipped galvanized. Then you
have the control box to consider. I also have the 2nd box, to raise + lower
from shack, remotely. The
system also requires a 120 vac at min 20A breaker to run the entire mess. A
15A breaker will trip cuz
of the start up current, about 80% of the time. It’s a carefully thought out
system. You require an
enormous amount of torque to lift a heavy tower + mast + prop pitch + yagis.
Jim VE7RF
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73
Roger (K8RI)
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