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.

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 components.

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 [email protected] 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. _______________________________________________ Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb

I particularly like the idea of using bicycle gears/chain for gearing. Whatever we come up with, I'd prefer if the bulk of it was available locally, wherever you live. There are no Home Depots in my country, but there are lots of bicycles. Perhaps we can use the frame of the bicycle to provide materials for the main structural component too! So, one old bicycle could provide gears, bearings, structural components, and more perhaps? :-)

I'm fine with the Arduino as a platform for the software.

The multi-turn pot would obviously work, but I'm a little dubious about it. They aren't that easy to source, and would have to be connected to the rotating shafts somehow that there would be very little backlash and no creep/slippage. I'd thought of the sensors from a couple old optical mice, mounted right over the shaft, and detecting rotation directly, but after a bit of googling, I'm not sure we can easily pull off movement info. Then I thought about a hall-effect switch mounted near one of the (bicycle?) gear wheels, detecting the passage of each tooth. An optical sensor, looking through your bicycle chain, detecting the passage of each link? Or a simple micro-switch, being bumped to produce a pulse for each link in the chain? But how would you determine direction of motion?

Perhaps a design that can accommodate either a voltage variable position sensor, OR a pulse train, making it easier to build the machine with whatever parts are available?

I'm chucking out a lot of silly ideas in the hope that someone can use them as the starting point, and come up with something practical.

On 02/28/2013 12:49 AM, Lizeth Norman wrote:

Gus, I like your thinking. Simply put we need to make feedback position sensor with associated motor/motor control stuff.

The motor rpm's and gear ratio are functions of the number of degrees per unit of time, as you say.

One simple solution that I was going to try was a reversible dc gear motor being polarity switched by a dpdt relay, and a three turn pot for position sensing. The pot is 16$US. Per copy. Need two as well as the associated hardware. Scaling the dac on the uP is a nit.

Then again, since we can fiddle with the values in software, so our inputs can be anything (from a hardware standpoint) of reasonable accuracy.

Just thinking, why use gears and gear motors?? Why not a dc motor, bicycle chain and sprockets? The HD bearings for the shaft are $6.95 as I recall, a piece.

Still set on using stock sizes/materials if I can. This would give me a start modelling this stuff with CAD and make it easier to source.

A note regarding your comment on the Arduino. It really does not matter what we use in terms of antenna rotators at this point. I think that if we coherently model the design process, someone in cost reduced circumstances could reproduce whatever we decide with far more basic tools than available to us. The key is that there is a microcontroller with tons of IO attached to a serial port...

Or then again, CO7WT is bit banging the parallel port. Now that's the way to go.

blah, blah, blah,

Norm n3ykf

This is what I was getting at when I made my earlier post about about the old Gemini OR-360 TV rotators. The gear train is driven by a "540" sized DC motor. I can tell you from experience that one of these rotors will rotate a mini sized beam on HF. I do it everyday. So if we are driving a smaller array, we might be able to eliminate some or all of the gearing involved and go with one of the smaller motors. I can't recall the issue but it seems to me I saw an article in QST where someone was driving a small little beam on top of a tripod with a small little motor. I still think a position pot is a better option for pointing over a stepper motor though. Michael, W4HIJ On 2/27/2013 8:30 PM, Gus 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. _______________________________________________ Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb

On 02/28/2013 11:24 PM, Lizeth Norman wrote:

A stepper still needs some sort of position feedback..

Not really.

Steppers rotate a predictable amount with each step. To calibrate, the software only needs to count steps from one limit switch to the other. Then, by keeping track of step count (+/-), it will always know exactly how far round the turn it is. It can store last position in NV RAM or EEPROM, so as to avoid the need to recalibrate on every startup.

Unfortunately, I can't think of a common source for surplus steppers of useful size. And driving them is slightly more complicated than firing a relay to a DC motor.

OK, why do we have to use A multi-turn pot? Why not just an ordinary linear pot?

-- 73, de Gus 8P6SM Barbados, the easternmost isle.

On 03/01/2013 02:17 AM, Lizeth Norman wrote:

Three turn pots are necessary unless we want to limit rotation to 360 degrees. Easy enough to in satpc32. Also, not all pots rotate 360. Some only 320, some less. The more expensive pots have much greater possible feature set.

Unless we want lightning fast antenna rotation, we're going to need some sort of gearbox with virtually any motor we're likely to find. We could gear the drive to a simpler pot as well.

Tom, I must congratulate you on a nicely written Arduino application. As you demonstrate, it's not critical what hardware gets used. The feedback/hysteresis loop in the program is nicely documented. It begs to be used.

Your design is much like mine. I was going to use tube stock rather than build it. The bearings are remarkably cheep, though. I found them for $$7bux.

From a simplicity point of view, building it from bicycle parts is as

common as you can get.

Have fun, Norm