Antenna Rotor - Part 2

Antenna Rotor - Part 2 Written by Lucas Teske
on

Continuing the tracker project, I managed to make some significant progress. As Demilson (PY2UEP) had cut the original motors, I did the same. The azimuth motor was too rusted and I eventually destroyed one of the coils (which I wanted to salvage the wire), but in the end the shaft went out.

After removing the shaft, I broke the magnet with a hammer until there was any piece left. That way, the only thing that would be left there is the shaft and the hexagon magnet support.

Hexagon Magnet Support 1 Hexagon Magnet Support 2 Hexagon Magnet Support 3Motor shaft showing the hexagon support

For the elevation motor, I made a cut in a circular mark around the exit of the shaft. That way I could use the same support for coupling with the reduction gears.

"lid" of the elevation motor after cut“lid” of the elevation motor after cut Lid + Reduction GearsLid + Reduction Gears Motor PiecesMotor Pieces

For the shaft, it was nescessary to reduce its size and made a bevel so I could fit it better in a 3D Printed part. To do so, I use two plywood pieces to hold the shaft while me and my father cut it. For the bevel, we used a grinder.

Plywood and cut shaftPlywood and cut shaft Cut shaft on motor headCut shaft on motor head

With that, I could then start the 3D Drawings for the adapters.

3D Prints

After A LOT of trial and error, I managed to make good fittings between the shafts. But then I realized a problem: The space for the azimuth axis was extremelly limited, in the way that my 40 mm NEMA17 motors were too big for it.

Azimuth Adapter Azimuth AdapterAzimuth Adapter

Then I had to buy some “slim” motors to use in that place. I got a bit concerned with the final torque, but my attempts to make gears and other stuff were all failed. The motors I bought in Aliexpress (see links in the end of this post)

While the motor wasn’t arriving, I started optimizing the adapters to be the shortest as possible, saving all space I could. I use FreeCAD for being free and where I can do faster / better drawings. But don’t assume I’m a 3D Designer, because I’m not. My parts are only “functional”.

Azimuth Shaft AdapterAzimuth Shaft Adapter Azimuth SupportAzimuth Support Elevation Shaft AdapterElevation Shaft Adapter Elevation AdapterElevation Adapter Three stepper motors on a workbench with tools and wires nearby.

And the first axis to work was the elevation. To do so I used 40 mm NEMA17 motors (link in end of this post), which came with a closed-loop magnetic encoder driver. But in the end I went to use a TMC2209 to control instead the board that came in because it was easier and quieter.

After the new azimuth motors arrived, I just tried to fit everything. And it did! se ia caber. E coube!

Azimuth Azimuth Motor in place

And also working!

After everything was working, I did some tests to check what was the final resolution and reduction for both axis. To do so, I used the following code with an ESP32 to control the TMC2209 drivers, and for angle measurement I used my phone attached to the elevation base.

#include <TMCStepper.h>

#define STEP_PIN         12 // Step
#define EN_PIN           23 // Enable

#define SERIAL_PORT Serial2 // TMC2208/TMC2224 HardwareSerial port
#define DRIVER_ADDRESS 0b00 // TMC2209 Driver address according to MS1 and MS2

#define R_SENSE 0.11f 

TMC2209Stepper driver(&SERIAL_PORT, R_SENSE, DRIVER_ADDRESS);

void setup() {
  pinMode(STEP_PIN, OUTPUT);
  pinMode(EN_PIN, OUTPUT);
  digitalWrite(EN_PIN, LOW);
  
  SERIAL_PORT.begin(115200);      // HW UART drivers
  Serial.begin(115200);

  driver.begin();                 // UART: Init SW UART (if selected) with default 115200 baudrate
  driver.toff(10);                // Enables driver in software
  driver.rms_current(1000);       // Set motor RMS current
  driver.microsteps(2);           // Set microsteps to 1/16th

  driver.en_spreadCycle(false);    // Toggle spreadCycle on TMC2208/2209/2224
  driver.pwm_autoscale(true);      // Needed for stealthChop

  Serial.println("OK");
  digitalWrite(EN_PIN, HIGH);
}

bool shaft = false;

void loop() {
//  Serial.println("TURN");
  if (Serial.available() > 0) {
    int z = Serial.read();
    if (z == 'a') {
      Serial.println("Stepping 10000");
      digitalWrite(EN_PIN, LOW);
      for (uint32_t i = 10000; i>0; i--) {
        digitalWrite(STEP_PIN, HIGH);
        delayMicroseconds(350);
        digitalWrite(STEP_PIN, LOW);
        delayMicroseconds(350);
      }
      digitalWrite(EN_PIN, HIGH);
    } else if (z == 'b') {
      shaft = !shaft;
      Serial.print("Shaft direction: ");
      Serial.println(shaft);
      driver.shaft(shaft);
    }
  }
}

The results were:

The results looks promissing and, if everything goes right, will be enough for tracking satellites!

The next step is to code / assemble the required software/hardware to control it through network!

The 3D Models (Both freecad and STL) are available in Thingverse (see links section)