Friday, November 6, 2015

Building my own AZ/EL Controller (Part III)

Building my own AZ/EL Controller (Part III)

This past week I've done almost all of the initial C# software requirements to control my new Application which will drive my antenna array.  This has been a mostly pleasurable experience with just a few days where I got hung up on things like running Threaded tasks in C# "WPF" but I managed to overcome that.  

Now that the software is mostly well organized I need to move on to a few more bits of hardware.  

For the "EL" (elevation) part, I needed to spec out a industrial grade 24" Jack Screw capable of push/pull @ 1000 lbs (which is way overkill for this, but I don't want something weak to break).

I also needed to determine a DC Gearmotor combination to drive the Jack Screw.  There is a LOT to consider when looking at mating up the motor and the jack screw.  I'll post my notes on that later (below).

I also then needed a set of Relays that could drive the motor as well as a Azimuth rotor which I already have.  These need to be rated well above the requirements of both the azimuth and elevation motors, as relay failures are not something I want to have happen.
In addition to Relays I wanted to find a combination of Relays, but mounted on a Controller board and ready to accept commands via USB.

For the Jack Screw I went with a Duff Norton double clevis B9250CC-24B this can move 1000 lbs on it's output shaft with only 21 lbs of torque at it's input shaft.  40 turns at the input equates to 1" of travel on the jack screw output.

I wanted this to be able to elevate my array from 0 degrees to 90 degrees in about 1 minute.  90 degrees of travel will be managed by the 24" stroke of the jack screw.  So 40 turns on the input = 1" of travel, total travel = 24" so (40 * 24) = 960 the RPM required of the DC motor to move from 0 to 90 degrees.
Finding a High Torque DC motor to a fairly exact specification I found, was not easy.  There's a lot of crap on the internet when you search for high torque dc gearmotor.  Eventually, I did find what I was searching for and decided to use MMP D33-455D-24V GP81-04.3 this can handle 21lbs of torque using 24VDC @ 14.1 Amps which is available at: This motor falls perfectly into my requirements for the Jack Screw and the NCD USB R420 Relay.

This is what I settled on for the USB/Relay Board: National Control Devices: R420PL_USB Once that arrives I'll be able to start coding around this board specifically to control my rotors.  Since I already have a rotor on the tower connected to a large antenna, I will be able to test the relay board almost as soon as it arrives in controlling my azimuth rotor.
I'll post more on this later today.  It's still early here, but I wanted to post an update to this thread.

I was sad to find that usb relay board was only good to 5 amps. :(  I love their code libraries.  But I really didn't want a two-stage relay one low power relay and then one high power relay that actually does the work.  As this adds more points of failure as well as lag time (even if only a few milliseconds) I didn't find this option acceptable so I went with something that could provide usb and the relay amp size I needed at the voltage needs I have.

Since I'm building OUTWARDS from my computer to the tower and since I have my software project well underway, the next thing to order-in is the R420 USB relay board which I've done today.