[amsat-bb] Re: inquiry about homebrew az-el systems

Gus 8p6sm at anjo.com
Wed Feb 27 20:04:16 PST 2013

The control hardware (Arduino based or otherwise) will be the simplest 
part of any design. I recently bought all the components to make four 
'Uno' (which should be more than capable) for less than $10 each, and I 
didn't shop around.  No, the hardest part will be the actuators (IOW, 
the motors and motor control) and the sensors (IOW position detection 
and limit switches). These are also likely to be the most expensive 

In order to keep cost and complexity down, I am proposing that we DON'T 
try to replicate the G5400/5500, etc.  We don't need to swing huge 
arrays of long yagis any more, and won't need to until a HEO satellite 
appears in our sky.  So we can limit ourselves to smaller antenna 
systems like the Arrow, the Cushcraft antennas I spoke of, and similar.  
I have nothing against the K5OE antennas (they look pretty nice!) except 
they were designed for P3D, and are probably more than needed to 
reliably use the current fleet of satellites.  In any case, we have to 
decide what amount of maximum torque we want to handle, so we can go 
looking for suitable candidate motors.  We want to keep these motors as 
small as possible to keep their cost (and that of their driver 
circuitry) to a minimum.

We'll also need to work out whether we want direct drive or geared, 
brushed, brushless, stepper, etc.  And speed of rotation and so forth.

Stepper motors can produce lots of torque and their speed is 
controllable.  They usually operate in steps of less than 2 degrees.  
And since the control hardware can count steps, we probably wouldn't 
need any position-sensing hardware at all, other than simple limit 
switches.  But I'm not aware of any common source of surplus stepper 
motors.  Ordinary motors on the other hand, are available in windshield 
wipers, window winders, starting motors, etc.  But position sensing 
these will need additional hardware.

Personally, I'd like to see a system that runs entirely on 12 volts.  
This will make field day operation, emergency operation, car-park demos, 
rag-chewing while watching the windsurfing competition and bikini parade 
at the beach, etc, possible without the need for an inverter.  Base 
station use should present no problems because 12v PSUs abound in all 
shapes and sizes and current limits, and most shacks already contain at 
least one 12v PSU already.

On 02/27/2013 09:56 PM, Lizeth Norman wrote:
> Gus and the gang,
> What about K5OE's array here:
> http://rfanat.ru/s8/P3D_yagi.htm
> Still think that using:
> 8x4 aluminum tube stock
> 1" aluminum round stock
> 1 arduino
> 4 relays
> a 24 v ps
> some limit switches
> fuses, of course
> two of the appropriate value pots and maybe some gearing
> and a few gears, bearings and motors for the drivetrain,
> should give us a complete -5400 or -5500 clone.
> Norm n3ykf
> On Wed, Feb 27, 2013 at 8:30 PM, Gus <8p6sm at anjo.com> wrote:
>> Returning to this topic...
>> I'm thinking about a rotator that can handle a small system like the Arrow,
>> or the Cushcraft A270-6s or even the A270-10s.  NOT big boomers like the KLM
>> 22/40 el CP yagis!
>> So we're looking at 1½ - 2 sq. ft of windloading, and maybe 10 lbs of
>> weight.  (Including some sort of crossboom, clamps, coax and counterweights.
>> Rear mounted antennas like the Arrow will need a rear-mounted
>> counterweight.)
>> Anybody qualified to say what that adds up to in terms of TORQUE required
>> from the motors?  With a little extra thrown in for a safety margin, maybe?
>> I think a simple, low-cost, easily reproducible design is probably doable,
>> if we combine our ingenuity and expertise.
>> -- 73, de Gus 8P6SM
>> Barbados, the easternmost isle.
>> _______________________________________________
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73, de Gus 8P6SM
Barbados, the easternmost isle.

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