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Re: [TowerTalk] HAM IV rotor / mast slipping

To: Towertalk <>
Subject: Re: [TowerTalk] HAM IV rotor / mast slipping
From: Bob K6UJ <>
Date: Thu, 5 Apr 2012 08:21:23 -0700
List-post: <">>
Looks like a good solution and easy to install !


On Apr 5, 2012, at 7:03 AM, KC2TN wrote:

> I never tried one of these but they get good reviews,
> Joe - KC2TN
> Sent from my iPad
> On Apr 4, 2012, at 10:17 PM, KA9S - Jeff <> wrote:
>> (Part - 1) I am having trouble with my rotor not holding my beam in 
>> position during wind storms. The beam wants to turn such that the boom 
>> is pointing into the wind and the elements are broadside to the wind. I 
>> have been fighting with it for a while and will make two posts. One post 
>> for each mode of failure. In this post I would like to talk about the 
>> mast slipping in the rotor bracket.
>> I have an investment in HAM IV rotors (four of them). I do not want to 
>> change to another brand/model if at all possible. My SteppIR DB-18E is 
>> installed 18 inches above the tower top plate thrust bearing. The mast 
>> goes down 10 feet into the tower to a HAM IV rotor. There is no vertical 
>> weight placed on the rotor and minimal horizontal force being placed on 
>> the rotor given the 10 ft. to 1.5 ft mechanical leverage advantage. The 
>> rotor has no problem turning the antenna and I always allow the antenna 
>> to coast to a stop before engaging the rotor "brake". I designed the 
>> system this way so that the only "work" required of the rotor would be 
>> to turn the antenna (over coming the antenna's resting momentum) and 
>> holding the antenna in position when the wind try's to turn it (the 
>> brake). The HAM IV is rated for 15 ft-sq antennas. The DB-18E is rated 
>> at 12.1 ft-sq. I used this exact same set up with a Mosley PRO-67B for 
>> decades with no issues. The Mosley is rated at 12 ft-sq wind loading. 
>> The HAM IV turns the SteppIR beam with no problem (even in the coldest 
>> weather). This set up is not holding the DB-18E in place during wind 
>> storms (30 - 50 mph gusts). The holding capability of the rotor can not 
>> stop the DB-18E from turning into the wind.
>> Here is what I have tried so far: I tried a stainless steel bolt (1/2 
>> inch) sharpened to a point that is mounted in a "nut". The nut is welded 
>> to the steel bracket that is part of the rotor to mast clamp. I would 
>> first tighten down the U-bolts and then tighten the 1/2 inch bolt such 
>> that the point would dig into the mast. This failed because the 
>> stainless steel bolt was softer than the mast and the turning mast just 
>> rounded off the point on the 1/2 inch bolt. Next I ground the end of the 
>> 1/2 inch bolt flat and drilled a 1/4 inch hole into it. Into this hole I 
>> placed the shank of a 1/4 inch drill bit that I had ground to a point. 
>> Again I tightened this new improved bolt so it would dig into the mast. 
>> This failed because the pointed 1/4 drill bit shank sheered off. My next 
>> attempt was to use strips of dry wall sanding mesh between the mast and 
>> the rotor to mast bracket (the mesh is like mosquito screen with sanding 
>> grit attached to it - there is no paper involved and it is abrasive on 
>> both sides). This arrangement held, but the "weak link" just moved to 
>> the connection between the bottom of the rotor and the rotor plate (I'll 
>> talk about this in another post). I am not happy with the sanding mesh 
>> method because I discovered while taking the rotor down that the mesh 
>> had disintegrated along the four pressure points where the mast touches 
>> the rotor bracket.
>> In general, I think the rotor bracket is a poor design. The cast 
>> aluminum portion that is part of the rotor upper bell is a V-trough with 
>> a raised cross hatch pattern. The steel outer bracket is also a 
>> V-trough. They effectively only touch the mast along four vertical 
>> pressure lines and provide very little surface area to increase friction 
>> between the bracket and the mast. They do allow for differing diameter 
>> of masts to be used which I am guessing was the primary design goal.
>> I am hesitant to pin the mast to the rotor bracket (using a bolt that 
>> travels completely through the rotor bracket and mast) as I have heard 
>> that the cast aluminum portion of the bracket that is part of the upper 
>> rotor bell housing will break under the load. Looking at the aluminum 
>> bracket, I can find no location that is very "beefy" where I would feed 
>> comfortable drilling a hole for a pinning bolt to pass through.
>> Well this is where I stand. I would appreciate some insight from those 
>> of you who have mastered this problem.
>> P.S. I don't mean to be rude, but, I am not interested in hearing how 
>> well your brand X, Y, or Z rotor works for you as I want to make my pile 
>> of HAM IV rotors work for me. It also would not be helpful to tell me 
>> that you have never had this problem with your HAM IV rotor (lucky for 
>> you). Sorry for this per-emptive gripe.
>> 73 - Jeff KA9S
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