Gravity is what comes into play when your tower doesn't have positive pull
down, which is very dangerous, especially when attempting to let the tower
down at night when you can't watch the tension in the cables and the wind is
blowing. Positive pull down pulls the tower down when you are lowering the
tower(slackening the cables that were used to pull the tower up).
Bob W6TR
----- Original Message -----
From: "FISCHER,GREG" <ab7r@cablespeed.com>
To: <frohro@wwc.edu>; "towertalk" <towertalk@contesting.com>
Sent: Thursday, April 05, 2007 11:51 AM
Subject: Re: [TowerTalk] Photos of a Crank Up Positive Pull Down mechanism?
>
> I've also wondered about the positive pull down. I have
> an old Hygain manual for their electric winch (I don't
> have the electric winch though) and it shows how to run
> the positive pull down cable.
>
> If I recall correctly, the cable runs from the bottom of
> the 3rd section down to a pully at the bottom of the
> second section up to the top of the second section. This
> is repeated with another cable from the bottom of the 4th
> section to a pulley at the bottom of the 3rd section and
> up to the top of the 3rd section.
>
> How does this create "positive pulldown" when it is still
> gravity that brings the sections down when lowering with
> the winch? Is it the weight of that 2nd section that is
> being used to help pull down the lighter 3rd and 4th
> sections?
>
> Tnx
> 73
> Greg
> AB7R
>
>
>
>
> On Thu, 05 Apr 2007 07:45:18 -0700
> Rob Frohne <frohro@wwc.edu> wrote:
>> Hi,
>>
>> I have two Tri-EX THD series towers and have had trouble
>>with them
>> jamming when partially erected. I am thinking of
>>putting a cable from
>> the top section to a pulley on the bottom section so
>>that I could pull
>> down if necessary if it gets jammed again. I have read
>>of a thing
>> called a "positive pull down" on some crank up towers,
>>and would like to
>> see some photos of it before I do my thing, in case I'm
>>missing
>> something, and they have a better way of doing it than I
>>am envisioning.
>> Does anyone have any photos of a "positive pull down"
>>mechanism?
>>
>> Thanks & 73,
>>
>> Rob, KL7NA
>> --
>> Rob Frohne, Ph.D., P.E.
>> E.F. Cross School of Engineering
>> Walla Walla College
>> 100 SW 4th Street
>> College Place, WA 99324
>> (509) 527-2075
>> http://www.wwc.edu/~frohro/
>>
>> _______________________________________________
>>
>>
>>
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>
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>
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>
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