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Re: [TowerTalk] Rotator Choice for Larger Yagi

To: towertalk@contesting.com
Subject: Re: [TowerTalk] Rotator Choice for Larger Yagi
From: "Roger (K8RI) on TT" <K8RI-on-TowerTalk@tm.net>
Date: Tue, 26 Apr 2016 23:06:52 -0400
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
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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