[TowerTalk] DX86 vs. HDX589
dan hearn
dhearn@ix.netcom.com
Mon, 07 Aug 2000 15:39:32 -0700
I have just finished putting new lift cables(3) on my TX472 and new
bearings in the pulleys(5). The tower is about 15-20 years old. The old
cables measure 0.195 OD and the new cables from UST are 0.250. It
appears that the new cables are much stronger than the old ones
(increased OD and larger Nicopress fittings).The old bearings appear to
have lost their internal grease seal and can be rotated only with
difficulty. They are labeled K-8 and are made by Norma and Nice. The
center bushing is 0.625 wide while the rest of the bearing is 0.500
wide. Four different bearing houses in Spokane were unable to obtain
identical replacemant bearings from the manufacturers so I had to
improvise with bushings on the ID and use slightly larger OD (required
small amount of lathe work).
Using the definition that the top section is nr. 1 and the lower
section is nr. 4, here is the way its cables work. There is a single
cable attached to the bottom of section 1 going over a pulley in the top
of section 2 and attached to the top of section 3. A similar cable is
attached to the bottom of section 2, goes over a pulley in the top of
section 3 and connects to the top of section 4.
The third cable is a multipass arrangement for mechanical advantage.
It connects to the bottom of section 3, goes over a pulley in the top of
section 4, goes down to a pulley in the bottom of section 3, around it
and up to another pulley in the top of section 4 and down to the winch.
This is the lift cable. As you pull on it, all 4 sections of the tower
extend simultaneously by the same amount. A very ingeneous system.
The load on the top cable is the top section weight plus the mast,
rotator, and antenna weight. The load on the second cable is all of this
plus the weight of the second section. The third cable actually has less
stress since it makes 4 passes. A break in any of the three cables ,
when the tower is extended, means big trouble.
I was given sets of stress calculations by the UST folks at Dallas
Hamcom convention in June. These were for the HDX 689 and HDX 5106
towers. The 5106 data table says there are single lift cables on the top
2 sections, 2 lift cables on the next 2 sections and 3 lift cables on
the lower 2 sections. I interpret this to mean that there are 2 or 3
parallel, single pass cables as noted but a single 3 pass cable between
the bottom and next higher section. Otherwise, they would have to spool
3 parallel cables on the winch drum and I doubt that they do this. Can
anyone confirm this for us? The 689 data says single lift cables on the
2 top sections, 2 lift cables on the next 2 sections, and 3 lift cables
on the bottom section.
If I understand this, You have backup cables on some of the sections
but a cable break in the top 2 sections or the winch cable is bad news.
The data for the 689 says there are single lift cables on the top 2
sections, 2 lift cables on the next 2 sections and 3 lift cables on the
2 bottom sections.
I have been told that the Triex towers have 3 lift cables at each
level. However, I suspect that the main lift cable is a single one with
multiple passes and a break is big trouble. I also do not know what the
cable arrangement is on each tower. I suspect that the smaller towers
use single lift cables between sections but would appreciate specific
information on each of their towers.
Can anyone confirm the above or add information on this topic?
73, Dan, N5AR
Al Williams wrote:
>
> I have just received a Triex LM470 motorized tower and three weeks ago I
> purchase a used (~13 years) US Tower HDX-572MDPL motorized tower ($1000,
> includes their work platform, several standoffs, mast, and a Cushcraft A4S).
>
> Both are now laying on the ground so I have been comparing them. The US
> Tower is a true level wind in that it has two jackscrews with cable guides
> driven in sync with the cable drum. One jackscrew is for playing out the
> cable and the other jackscrew is for reeling in the cable.
>
> The Triex does not have any jackscrews and so any level wind must rely on
> the tightness of the cable to cause the cable to move smoothly across the
> drum.
>
> Both towers have two cables (ends?) going simultaneously around the drum.
> One cable is being reeled in while the other cable is playing out so I
> assume both use positive pull down although I havent seen them in operation.
>
> As to two or three cables--It is difficult to follow the cables while they
> are
> telescoped so I cant comment on that. I understood Joel at First Call to
> say that there were two cables and if one broke, the other cable would keep
> the tower from collapsing. I havent been able to confirm his claim by
> inspecting the the system. However, I count ten lengths of cable traversing
> from the bottom to the top for the Triex but only six lengths for the US
> Tower. The cable in the Triex measures .196 inch whereas the
> cable in the US Tower is .248 in diameter.
>
> Hopefully, someone will explain how the cable(s) are looped that might
> provide some safety.
>
> k7puc
>
> -----Original Message-----
> From: K7LXC@aol.com <K7LXC@aol.com>
> To: dave@dbtech.net <dave@dbtech.net>; towertalk@contesting.com
> <towertalk@contesting.com>
> Date: Sunday, August 06, 2000 5:58 PM
> Subject: Re: [TowerTalk] DX86 vs. HDX589
>
> >
> >In a message dated 08/06/2000 4:37:32 PM Pacific Daylight Time,
> >dave@dbtech.net writes:
> >
> >> > What does "appears to be a bit more sturdy" mean? Both towers were
> >> >designed by the same guy - Lou Tristao - so they are slightly different
> >> >designs. The only way you could tell which one was "sturdier" is to get
> >the
> >> >engineering calculations for each tower and compare them side-by-side.
> >> Unless
> >> >you're an engineer, interpreting the calcs might be semi-useful and the
> >> >differences subtle.
> >>
> >> "Appears" to me means a three cable pull-up system and strong tubing. Of
> >> course this is information from their literature and we all know how
> much
> >> salt to take along with marketing hype.
> >>
> > Okay, you still haven't cited anything - "appears" is just as ambiguous
> >as it was before. What are the leg material, OD and wall thickness
> >differences that make it "a bit more sturdy"? Specifics only, please.
> >
> >> > I'm not sure what a 'three cable system' is. I know the US Tower
> has
> >> >positive pull-down and I'm not sure about the Tri-Ex. Nonetheless they
> >each
> >> >have to have the appropriate number of cables to run it up (and down).
> >They
> >> >probably even use the same cable schemes.
> >>
> >> I know they claim to have a positive pull down, as well as a level-wind
> for
> >> their hoist drum.
> >>
> > Please let me know what a "level-wind" is.
> >
> >> >> Regardless of which one I finally choose, the tower
> >> >> will be purchased with the raising fixture, but without the remote
> >> control.
> >> >> I see no need to spend a grand on a control box that can be easily
> >> >> constructed. I also plan to fit the tower with an extra set of limit
> >> >> switches in series with the provided ones (I want to be able to
> >operate
> >> the
> >> >> tower automatically during bad weather with some peace of mind).
> >> >
> > ERRRRR! You just validated your factory warranty!
> >
> >> > I'm not a big fan of remote controlling the raising and lowering of
> a
> >> >motorized crank-up. I know personally of several calamities that have
> >> >resulted from not being able to watch the tower as it was raised or
> >lowered.
> >>
> >> >Extra limit switches won't solve this problem.
> >>
> >> That's too bad. I won't purchase a system that I can't trust to work as
> >> advertised.
> >
> > They're advertised that they will fail during unattended raising or
> >lowering? I'll bet you a nickel that their literature stresses the
> opposite.
> >
> >> The extra limit switches are just for the extra safety margin.
> >
> > They'll protect you when the coax gets hung up or an antenna or wire
> >snags on the roof?
> >
> >> So are you saying that motorized towers fail on a too frequent basis or
> was
> >> there some issue with the respective installations?
> >
> > What I'm saying is that a crank-up is a complicated mechanical device
> and
> >should only be raised or lowered when the operator is actually observing
> it.
> >I've seen a number of failures, many caused by their owners, consisting of
> >the coax hanging up, something accidentally left in the tower causing one
> of
> >the section lifting cables to part or something else getting hung up.
> >
> > What I'm saying is that by following obvious safety procedures and the
> >instructions from the factory you will have a reliable, longterm
> >installation. The opposite is also true.
> >
> >Cheers, Steve K7LXC
> >Tower Tech
> >
> >--
> >FAQ on WWW: http://www.contesting.com/FAQ/towertalk
> >Submissions: towertalk@contesting.com
> >Administrative requests: towertalk-REQUEST@contesting.com
> >Problems: owner-towertalk@contesting.com
> >
> >
>
> --
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