[TowerTalk] Motorized Crank Up Towers

[knormoyle at surfnetusa.com]

I agree. I don't have any motors. 3 towers all with hand winches.
(3 different hand winches by the way. Hey I also have a side mounted lj-155 on one HG-70HD above 
the 2nd section, but I'll not take the risk here to describe it...)


That's why I was wondering why people seemed to imply user error on motor related cablefailures. 

I'm thinking cable failures in the field still goes back to cable corrosion mostly. While there 
is pulley jumping and cable damage, I'm still thinking weakness due to corrosion is the big 
issue. And lubing is about corrosion protection...not cable protection (due to our low cycling, 
as Steve pointed out).

I've been trying to read about as many crankup cable failures as I can find.

It goes to the question of "why lube". I think cleaning the cable is as important as the actual 
lube?

Was just reading up on winches used on 4x4s, jeeps etc to understand stall loads vs max working 
load.

Apparently, they size the winch for something over working load to account for initial inertia 
etc,
but those winches appear to have a stall load that's not more than 30-50% greater than the max 
working load???

So assuming winches for towers are sized for a max load of 1500-2500 lbs, then I would think the 
stall load would be no more than 3700 lbs or so? or what do people think?

I would also think the motor input current would go way up and trip a breaker once you start 
getting past the max working load. (are there breakers?)

So if that's true, are people saying they've seen motors deliver 3700 lbs or so and break a 1/4" 
wire? Or was their cable damage? Or was the cable weak to start with.

Or was it a dynamic effect...i.e. a sudden stop while the tower was moving (the tower moves 
slow, so I wouldn't think that would be a big deal)

Here's a magazine review on 10,000 lb winches. You can see they did separate cable fail tests, 
and then winch stall tests with an oversized cable..to see the stall load for these winches 
relative to spec.


So this idea that it's "normal" to have to worry about motors breaking cables on crankups: it's 
not, right? Something else is wrong if your motor can break your cable.

-kevin
ad6z


------- Original Message -------
>From    : Bill Aycock[mailto:billaycock at centurytel.net]
Sent    : 5/20/2010 4:15:35 PM
To      : knormoyle at surfnetusa.com; towertalk at contesting.com
Cc      : 
Subject : RE: Re: [TowerTalk] Motorized Crank Up Towers

 Kevin--
I think you have it backwards. The cable should be sized to do its job, with 
appropriate safety factors, and the motor limited to less than the danger 
level. Bigger is NOT better, if it can damage things.
Bill-W4BSG

----- Original Message ----- 



>
> maybe someone can answer this for me.
> I've been thinking, that based on everything said, that cable corrosion is 
> the main issue to worry about.
>
> Steve's example of motor-driven failures got me wondering about the max 
> force a typical motor setup can put on a cable.
> Obviously there's gearing.
>
> The system has to be designed minimally for the tower weight, friction, 
> and an unknown amount of antenna/mast/rotator/cable
> load. I suppose there's static friction to overcome from a stationary 
> position also, so that's more.
>
> I'm wondering how much force the motor can put on the cable without 
> stalling. Is it 2-3x the maximum force needed?
>
> If so, does that mean the cable broke at 2-3x working load?
>
> Or did the motor put 10x the working load on the cable without stalling?
>
> I'm wondering if the real issue was cable weakness, even if it was the 
> motor pulling on it. I would think the numbers work
> out so that the cable should be able to tolerate the max force from the 
> winch possible (even if tower is stalled). (assuming
> a new cable, not degraded by corrosion?)
>
> Don't know though. Thoughts?
>
> -kevin
> ad6z
>
>
>
>