[TowerTalk] HAM IV rotor / mast slipping

KC2TN kc2tn at comcast.net
Thu Apr 5 07:03:44 PDT 2012

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 <ka9s at comcast.net> 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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