I just selected the PST71. (OB12-6 on 130MPH rated tower). It was that or a
prop pitch. Either are good (oversized in theory) choices. I don't know if its
a valid statement but the PST rotators are a bit more mainstream in my mind
whereas prop pitch is supported by a single individual (as far as I know). I
just followed my gut after I narrowed it down. Time will tell!
73!
N1KEZ de Rob
Sent from my mobile device.
Pse excuse brevity and any errorz.
> On May 3, 2016, at 11:14 AM, David Gilbert <xdavid@cis-broadband.com> wrote:
>
>
> In my opinion, and in general, turning/braking torque as a spec makes more
> sense than surface area. In theory, with normal winds, surface area of a
> perfectly balanced antenna would have little to do with with how strong a
> rotator would be required to turn it. Mass and length would be far more
> relevant.
>
> However, in my somewhat unique case, balance and mass of the antenna isn't
> all that relevant ... but rated torque of the rotator still is. I live on a
> hillside that blocks the normal flow of wind, and I get these monster
> swirlers that roar down the hillside as the wind is forced to come around the
> ridge line. I've measured them at over 100 mph on a clear day and I watched
> one literally lift my 16 year old son about two feet off the ground. When
> one of those hits my tower straight on the forces on the boom ADD UP and put
> incredible torque on the rotator. I have a PST-61D with stripped gears to
> prove it, and the total surface area of my antennas (OB16-3 and OB2-40) is
> less than 20 sq ft. The gears were stripped while in a resting state.
>
> I was going to upgrade to a PST-71D or even PST-110D, but WA7NB's litany of
> woe with two different PST-110D's (Hall effect pulse detector issues, I
> think) has me leaning more toward a prop pitch. The gears on the Smart GE
> 2500 NS Rotator by Giovannini look totally awesome but it appears to use an
> AC motor, and that would involve a permit process I'm not anxious to pursue.
>
> At the moment I'm still considering what I'm going to do.
>
> 73,
> Dave AB7E
>
>
>
>> On 5/3/2016 9:39 AM, Jerry Gardner wrote:
>> Is there a better way to determine if a rotator can handle an antenna based
>> on its size rather than just its wind area? Lots of people here have
>> recommended the M2 Orion 2800, which on paper is rated for 35 sqft, but
>> when I asked the tower installer who will be putting the antenna up whether
>> he thought the Orion could handle the OB17-4, he said that antenna will
>> tear an Orion up and strip the gears on the output shaft in short order.
>>
>> The OB17-4 has a 39' boom, 17 elements, of which the longest is 48', and
>> weighs 220 pounds. I've noticed that some rotators don't list a sqft rating
>> at all, but give turning and braking torque in Nm. Is there a way to
>> calculate how many Nm would be required to rotate an antenna and keep it in
>> place? I do have an RT-21 controller, which has slow ramp-up/ramp-down to
>> ease the load on the rotator by starting and stopping it slowly.
>>
>> The various vendors aren't much help with this as they all say their
>> rotators will handle the load, while at the same time saying their
>> competitor's product won't.
>>
>> 73, Jerry
>>
>>
>>> On Tue, Apr 26, 2016 at 12:13 PM, jimlux <jimlux@earthlink.net> 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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