[TowerTalk] Rotator Choice for Larger Yagi

[N2TK, Tony]

Last year I replaced the pot in a 61D so I could use a Green Heron controller. It is an easy job once you have the rotator out of the tower. Easier than changing one in a Tailtwister. Been using the 61D for 9 years turning an original SteppIR Monster without any problems. 
I did not take the top part on the rotator apart as there was no need. But no signs of water going down through it to the pot.
Two reason to replace the pot. There was a dead spot on the old pot and needed a much lower resistance pot for the Green Heron. 

The stock controller has one advantage over the Green Heron. With the stock controller you can use the preset pot for more than 360 degrees. The Green Heron is limited to 360 degrees. On the Green Heron you can use the CCW/CW switches to extend beyond 360 degrees. 
73,
N2TK, Tony

-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of Roger (K8RI) on TT
Sent: Tuesday, April 26, 2016 11:07 PM
To: towertalk at contesting.com
Subject: Re: [TowerTalk] Rotator Choice for Larger Yagi

I spent some time looking at the new PST61D and it looks as if they have addressed the issues I spoke of earlier.

The wind area is the leverage applied.  Looking at the rotator specs it lists the torque and braking loads in ft lbs.  Motor torque is 280 ft lbs and braking torque is 2100 ft lbs. Vertical load is 1,870 lb.  I'd call Array Solutions and ask them about the mount. They have fixed the water ingress for the top seal and I'd "guess" they have addressed the 4 bolt limitation between the mount and body, but could find no photos of that.  Please note the word guess is in quotes.

If they have fixed those problems, I'd go with the new PST61D without hesitation even with that price.  The old one was rated at 44 sq ft, but I see the newer, more heavily built one is rated at a more realistic 39.  There is no weakness in the internal double worm gears As far as I cam see. after looking at the old internals.
I was impressed with them when I had the old one apart.
Photos at http://www.rogerhalstead.com/Gears.htm

73

Roger (K8RI)



On 4/26/2016 Tuesday 3:13 PM, jimlux wrote:
> On 4/26/16 11:46 AM, Máximo EA1DDO_HK1H wrote:
>> PST-61D has 39sqft.
>>
>>
>
>>>
>>> The one thing that still concerns me about the Orion, however, is 
>>> that it's only rated to 35 sqft. The OB17-4 is 27 sqft, so there's 
>>> not a lot of margin there.
>>>
>
>
>
> It's not clear to me what a "square foot" rating for a rotator would 
> be.. Inertia loads would be in some sort of mass *length^2.
>
> Square foot would be for wind drag forces:  Unless you're talking 
> about the "side" (radial) load on the bearings (which depends a LOT on 
> the mast length and whether there's other bearings or mounting points.
>
> But for "turning in the wind", you'd need to know an area and a radius 
> from the axis of rotation to turn that into a torque (e.g. will it 
> overpower the brake or rip the teeth off the gears).
>
>
> Maybe they're using "square feet" as a shorthand for "size of antenna 
> and polar moment of inertia".  Square feet cross section is given for
> most antennas, polar moment is not.   Since most antennas are fairly 
> similar in construction, knowing cross sectional area (square feet) 
> probably correlates well with overall size and mass.
>
> (unless you use solid steel bar as your boom, and silver plated steel 
> bars for the elements. <grin>)
>
>
>
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-- 

73

Roger (K8RI)


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