[TowerTalk] Rotator Choice for Larger Yagi

Bob K6UJ k6uj at pacbell.net
Tue May 3 21:48:57 EDT 2016


Gene,

I agree with you 100%.
Your very last sentence should have been the first  :-)

It isn't the torque of the rotor to blame.
What needs to be done is provide isolation between the
rotor and the mast to absorb the torsional loads applied
to the mast during start/stop and also the rocking back and forth
in the wind.  Lets not blame the poor rotor.
You don't have to be a mechanical engineer to realize that there are big 
shock loads
that our antennas (and arrays) impose on the rotor gearing with 
start/stop and rocking back and
forth in the wind.   It is remarkable that they last as long as they do.

Someone here on Tower Talk in the past mentioned adapting an automotive 
drive shaft
flex disc in the mast right above the rotor.  Said he had zero rotor 
issues after installing.
As you probably already know the flex disc coupling consists of two 
mating flanges attached to a shaft with the flex disc sandwiched in 
between.  The flex disc is a synthetic rubber compound.   The automotive 
flex discs are designed to absorb the torsional shock from hard 
acceleration and deceleration.   They are well suited to our application 
and will handle our torque loads easily.  I will be installing my new 
OR2800 this summer and plan to
install an automotive flex disc coupling above the rotor.  Not that 
difficult to do and I would rather replace the rubber disc periodically 
when it shows signs of deterioration rather than repair/replace the 
rotor.  Much cheaper
too  :-)

73,
Bob
K6UJ





On 5/3/16 5:41 PM, Jim Thomson wrote:
> Date: Tue, 3 May 2016 16:47:28 -0400
> From: "john at kk9a.com" <john at kk9a.com>
> To: towertalk at contesting.com
> Subject: Re: [TowerTalk] Rotator Choice for Larger Yagi
>
> I am not even sure that torque means much. All of the rotator issues that
> I have had (broken gears, worn keyways, failed potentiometers, etc)
> occured while the station was QRT.
>
> I currently use a small and a medium prop pitch.  The small has a 9576:1
> gear ratio and the medium has a 7063:1 ratio.  It is possible that the
> small one has the same or more torque than the medium.  Which one is less
> likely to break, I would guess the medium.  I think you would be happy
> switching to prop pitch rotator and Green Heron controller.
>
> John KK9A
>
> ##  A  buddy had the monsterstepIR,  turned by an OR-2800....and it lasted
> exactly 9 days !    2 other folks  with the exact same ant / rotor combo  had
> similar results.
>
> ##  If I remember correctly, the small prop pitch had its final gear  driven in
> 3 x places,  every 120 degs, by small gears.   The OR-2800 has its  final gear
> driven by only one small gear.   By using 3 x small gears, the back lash is
> distributed over 3 gears.....and not just one.
>
> ##  Back in the late 70s, early 80s, a japanese rotor maker had a rotor out that
> used from  1-4 external, bolted on motors, every 90 degs around the perimeter
> of the motor.   You could buy it initially  with 1 motor, then add more, if you required
> more tq..and less back lash.
>
> ##  I currently have  1  OR-2800 left..and its  final small gear is chewed up / trashed.
> Back in the late 70s, early 80s,  I sold my ham-4  to a buddy, who used it to turn a
> hb 6-el 10m yagi on a 36 ft boom.  He always kept it pointed in one direction 99%
> of the time. Eventually, due to constant wind buffeting, it literally ate 1-2 teeth, completely
> gone.
>
> ## perhaps what needs to be done is to use a worm gear to drive the final gear,  that would
> eliminate the back lash, +  provide more surface area.  That and /or use a better grade of steel.
> and /or  thicker gear teeth.   Or  provide some form of isolation  between mast + rotor.
>
> Jim  VE7RF
>
>
>
>
>
>   
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