Published January 1, 2017 © GPL3+

IoT Drone - Part 1 - Motor Control

After flying a friends drone I was hooked. However, I wanted to build my own, so this is part one of my drone project - motor control.

IntermediateWork in progress16 hours5,487

Things used in this project

Hardware components

Particle Photon

ESC's and BLDC Motors

Power Distribution Board

3S Lipo Battery Pack 1300mAh

Propellers

Hand tools and fabrication machines

3D Printer (generic)

Story

Warning - This is only part one of my drone project and is not yet meant for flight. If you attempt to fly using the code below, the drone will most likely be unstable.

Background

A friend recently purchased a drone, and after flying once I was hooked. However, I figured it would be more fun to build my own.

The end goal of this project is to have a semi autonomous drone that is only connected over cellular via a Particle Electron. However, in the first few parts of the build you will noticed I used a Particle Photon. I have found that it is much easier to develop on the Photon and then deploy to the Electron (It saves on data usage).

The first step is to get motors running and build some simple controls. Below is an explanation of what I have done so far. I am far from an expert on drones, so any comments or advice would be appreciated.

What is it?

Check out the video below to see step 1 of my drone project in action. Currently I can control the motor speed, rotation direction/speed, and forward/reverse direction/speed.

Hardware

Below is a description of the hardware I used. See the components list for links to the products.

The power distribution board has an XT60 plug in for the lipo battery pack. This then distributes the power for up to 6 motors. It also has a 5vdc output which I used to power the Photon.

The electronic speed controllers (ESC's) are fairly straight forward to wire. The large red wire goes to one of the positive terminals on the power distribution board, and the large black wire goes to a negative terminal. When hooking up to the motor, the middle wire on the motor hooks up to the middle wire on the ESC. Then the two outside wires should be hooked up depending on which direction you want the motors to spin.

The brown wire connects to ground on the control board and orange hooks up to a PWM pin. On the Photon I used D0, D1, D2, and D3 as my PWM control pins. The red wire is 3.3vdc which can be used to power the controller. However, I chose to use the power supply on the distribution board.

Below is a diagram from the following link describing how to hook-up an ESC to an Arduino. http://robotic-controls.com/sites/default/files/images/esc_bb1.png

Electronic Speed Control Wiring

The ESC's I used in this project will accept 2S-4S lipo batteries. The S stands for how many cells there are. The more cells there are, the higher the voltage. Each cell has a nominal voltage of 3.7vdc. I chose to use a 3S battery pack which has a nominal voltage of 11.1vdc. I think the main advantage of higher voltage is that the wiring and electronics can be smaller due to lower amperage. I simply chose a 3S battery because I had one already, otherwise I would have went with a 4S.

Software/Firmware

Controlling the ESC's is fairly simple, however they are a little confusing for a first timer. The ESC's emit beeps to communicate settings and states. If you don't know what these beeps mean it can be frustrating.

The first time you use an ESC you need to calibrate it, which is to say you need to tell it what the maximum and minimum control signals will be. Below in the code section you will find a script you can load on the Photon (or Arduino) to calibrate the ESC's. It simply writes a maximum value of 2000 microseconds to all of the ESC's on start-up. Then you will hear a pattern of tones coming from the ESC. After a delay of 5 seconds the script will write the minimum value of 1000 microseconds to all of the ESC's, thus completing the calibration.

There are many settings you can change on the ESC however I have not had the need to change any of them yet. Changing these settings are fairly complex and requires understanding a lot of audible patterns coming from the ESC's. A program card can be used to simplify the process.

The Photon code to control the drone uses the Servo library to control the ESC's using the writeMicroseconds() command. When the Photon first boots up it needs to send the minimum control value (1000) to the ESC's. This will initialize the ESC's.

There are 5 Particle functions that can be called via the cloud. The first is "alt" which sets the speed of the motors. The next is "rot" which allows the drone to rotate. For example if the rot is set to 50, two of the motors speed up by 50 microseconds and 2 of the motors slow down by 50 microseconds, thus allowing the drone to rotate while maintaining lift. The third is "fwd" which allows the drone to fly in forward or reverse. This operates the same way as "rot", however on the "fwd" command two motors on the same side decrease speed and the other two speed up.

The last two functions are "idle" and "stop". These are direct commands that will either set all the motors to an "idle" speed (1100 microseconds in this case), or stop all motors.

The loop simply sets the motor speeds, factoring in the "rot" and "fwd" factors.

The html script allows the user to call the functions on the Photon and control the basic functions of the drone. At this point, my html code isn't very pretty or efficient but I'm not sure what I want to use as an interface, so it was good enough to get me going.

Html Control Interface

Test Rig/Lift Test Results

As you can see in the pictures above I 3-D printed a test rig that I could mount the motors and controls on for testing. It's not meant for flight but allowed me to test the control functions at my desk without flying away.

I also mounted it to a kitchen scale to see what the lift was for different settings. Below are the results, I stopped at 1600 microseconds because my test rig was becoming unstable. The results are fairly linear, so the performance from 1600 to 2000 microseconds could be extrapolated from the results.

Lift Test Results

Code

<html>
  <head>
      <title>IoT Drone - Part 1 - Motor Control</title>
  </head>

  <body>
      
    <P>Set Motor Speed:<br>
    <input type="range" name="degBox" id="degBoxId" min="1000" max="2000" step="50" value="1000" list="myData" onchange="speedAdjust('alt', 'args')">
    <!-- This adds the tick marks to the range but does not in Safari -->
    <datalist id="myData">
       <option value="1000">
       <option value="1100">
       <option value="1200">
       <option value="1300">
       <option value="1400">
       <option value="1500">
       <option value="1600">
       <option value="1700">
       <option value="1800">
       <option value="1900">
       <option value="2000">
    </datalist>

    <br>
    <button type="button" onclick="speedDec('alt', 'args')">-</button>
    <button type="button" onclick="speedInc('alt', 'args')">+</button>
    <button type="button" onclick="functionIdle('idle', 'args')">Motor Idle</button>
    <button type="button" onclick="functionStop('stop', 'args')">Motor Stop</button>

    <P>Set Rotation:<br>
    <input type="range" name="rotBox" id="rotBoxId" min="-100" max="100" step="10" value="0" list="myRotData" onchange="rotAdjust('rot', 'args')">
    <!-- This adds the tick marks to the range but does not in Safari -->
    <datalist id="myRotData">
       <option value="-100">
       <option value="-75">
       <option value="-50">
       <option value="-25">
       <option value="0">
       <option value="25">
       <option value="50">
       <option value="75">
       <option value="100">
    </datalist>

    <br>
    <button type="button" onclick="rotDec('rot', 'args')">-</button>
    <button type="button" onclick="rotInc('rot', 'args')">+</button>
    <button type="button" onclick="functionCenterRot('rot', 'args')">Center</button>

    <P>Set Direction:<br>
    <input type="range" name="fwdBox" id="fwdBoxId" min="-100" max="100" step="10" value="0" list="myFwdData" onchange="fwdAdjust('fwd', 'args')">
    <!-- This adds the tick marks to the range but does not in Safari -->
    <datalist id="myFwdData">
       <option value="-100">
       <option value="-75">
       <option value="-50">
       <option value="-25">
       <option value="0">
       <option value="25">
       <option value="50">
       <option value="75">
       <option value="100">
    </datalist>

    <br>
    <button type="button" onclick="fwdDec('fwd', 'args')">-</button>
    <button type="button" onclick="fwdInc('fwd', 'args')">+</button>
    <button type="button" onclick="functionCenterFwd('fwd', 'args')">Center</button>
    
    <script src="http://cdn.jsdelivr.net/sparkjs/1.0.0/spark.min.js"></script>
    <script>
      //you can use your accesstoken, or your email/passsword to log in. Uncomment accordingly below.

	var accessToken = "YOUR_ACCESS_TOKEN";
	var deviceID = "YOUR_DEVICE_ID";

	var currentValue = 1000;
	var currentRot = 0;
	var currentFwd = 0;
  
  spark.on('login', function(response) {   
    
    console.log(response);
    
  });

  // callback to be executed by each core
  var callback = function(err, data) {
    if (err) {
      console.log('An error occurred while getting core attrs:', err);
    } else {
      console.log('Core attr retrieved successfully:', data);
    }
  };
  
  function functionIdle(functionName, functionArgument){
    currentValue = 1100;
    document.getElementById("degBoxId").value = currentValue;
    spark.callFunction(deviceID, functionName, functionArgument, callback);  
  }

  function speedAdjust(functionName, functionArgument){
    currentValue = document.getElementById('degBoxId').value;
    functionArgument = currentValue;
    spark.callFunction(deviceID, functionName, functionArgument, callback);  
  }
  
  function functionStop(functionName, functionArgument){
    currentValue = 1000;
    document.getElementById("degBoxId").value = currentValue;
    spark.callFunction(deviceID, functionName, functionArgument, callback);  
  }

  function speedInc(functionName, functionArgument){
    // The function needs to be defined  in the firmware uploaded to the
    currentValue = currentValue + 50;
    functionArgument = currentValue;
    document.getElementById("degBoxId").value = currentValue;
    spark.callFunction(deviceID, functionName, functionArgument, callback);  
  }

  function speedDec(functionName, functionArgument){
    // The function needs to be defined  in the firmware uploaded to the
    currentValue = currentValue - 50;
    functionArgument = currentValue;
    document.getElementById("degBoxId").value = currentValue;
    spark.callFunction(deviceID, functionName, functionArgument, callback);  
  }

   function rotAdjust(functionName, functionArgument){
    currentRot = document.getElementById('rotBoxId').value;
    functionArgument = currentRot;
    spark.callFunction(deviceID, functionName, functionArgument, callback);  
  }

  function rotInc(functionName, functionArgument){
    // The function needs to be defined  in the firmware uploaded to the
    currentRot = currentRot + 10;
    functionArgument = currentRot;
    document.getElementById("rotBoxId").value = currentRot;
    spark.callFunction(deviceID, functionName, functionArgument, callback);  
  }

  function rotDec(functionName, functionArgument){
    // The function needs to be defined  in the firmware uploaded to the
    currentRot = currentRot - 10;
    functionArgument = currentRot;
    document.getElementById("rotBoxId").value = currentRot;
    spark.callFunction(deviceID, functionName, functionArgument, callback);  
  }

  function functionCenterRot(functionName, functionArgument){
    currentRot = 0;
    document.getElementById("rotBoxId").value = currentRot;
    spark.callFunction(deviceID, functionName, functionArgument, callback);  
  }

  function fwdAdjust(functionName, functionArgument){
    currentFwd = document.getElementById('fwdBoxId').value;
    functionArgument = currentFwd;
    spark.callFunction(deviceID, functionName, functionArgument, callback);  
  }

  function fwdInc(functionName, functionArgument){
    // The function needs to be defined  in the firmware uploaded to the
    currentFwd = currentFwd + 10;
    functionArgument = currentFwd;
    document.getElementById("fwdBoxId").value = currentFwd;
    spark.callFunction(deviceID, functionName, functionArgument, callback);  
  }

  function fwdDec(functionName, functionArgument){
    // The function needs to be defined  in the firmware uploaded to the
    currentFwd = currentFwd - 10;
    functionArgument = currentFwd;
    document.getElementById("fwdBoxId").value = currentFwd;
    spark.callFunction(deviceID, functionName, functionArgument, callback);  
  }

  function functionCenterFwd(functionName, functionArgument){
    currentFwd = 0;
    document.getElementById("fwdBoxId").value = currentFwd;
    spark.callFunction(deviceID, functionName, functionArgument, callback);  
  }
  
  // Uncomment a line below depending on your preferred log-in method.   
  //spark.login({ username: 'email@example.com', password: 'password' });  
  spark.login({ accessToken: accessToken });
  
</script>
  </body>
</html>

#define MOTOR1_PIN D0
#define MOTOR2_PIN D1
#define MOTOR3_PIN D2
#define MOTOR4_PIN D3

//Set-up Servo Controllers
Servo motor1;
Servo motor2;
Servo motor3;
Servo motor4;
  
//Define variables for each rotor speed
int alt = 1000;
int rot = 0;
int fwd = 0;

int idle = 1100;
int stop = 1000;

int spd1 = 1000;
int spd2 = 1000;
int spd3 = 1000;
int spd4 = 1000;

//Tuning Parameters
int MAX_ROT = 1; //This is a multiplier for the rotation variable
int MAX_FWD = 1; //This is a multiplier for the forward variable

void setup() {
  
  //Begin serial communication for diagnostics
  Serial.begin(9600);
  
  // Set-up Spark functions for altitude, rotation, and forward velocity
  Spark.function("alt",setAlt);  //Set altitude (throttle) 1000 to 2000 microsecond range
  Spark.function("rot",setRot);  //Set rotation
  Spark.function("fwd",setFwd);  //Set forward speed
  
  Spark.function("idle",setIdle);  //Set motors to idle speed
  Spark.function("stop",setStop);  //Turn all motors off

  //Attach pins to servo controllers
  motor1.attach(MOTOR1_PIN);
  motor2.attach(MOTOR2_PIN);
  motor3.attach(MOTOR3_PIN);
  motor4.attach(MOTOR4_PIN);
  
  //Write initial value to servos for start-up calibration of the motor controllers
  motor1.writeMicroseconds(spd1);
  motor2.writeMicroseconds(spd2);
  motor3.writeMicroseconds(spd3);
  motor4.writeMicroseconds(spd4);

  delay(2000);

}

void loop() {  
    //Set the speed of each motor, including factors for rotation and direction
    spd1 = alt + rot + fwd;
    spd2 = alt - rot + fwd;
    spd3 = alt + rot - fwd;
    spd4 = alt - rot - fwd;
    
    //Write the speed of each motor to the servos
    motor1.writeMicroseconds(spd1);
    motor2.writeMicroseconds(spd2);
    motor3.writeMicroseconds(spd3);
    motor4.writeMicroseconds(spd4);

delay(500);
}

int setAlt(String command) {

    alt = command.toInt();
    Serial.println(alt);

    return 1;
    
}

int setRot(String command) {

    rot = command.toInt();
    rot = rot * MAX_ROT;

    return 1;
    
}

int setFwd(String command) {

    fwd = command.toInt();
    fwd = fwd * MAX_FWD;

    return 1;
    
}

int setIdle(String command) {

    alt = idle;
    rot = 0;
    fwd = 0;

    return 1;
    
}

int setStop(String command) {

    alt = stop;
    rot = 0;
    fwd = 0;

    return 1;
    
}

#define MOTOR1_PIN D0 //Front Left Motor
#define MOTOR2_PIN D1 //Front Right Motor
#define MOTOR3_PIN D2 //Rear Left Motor
#define MOTOR4_PIN D3 //Rear Right Motor

//Set-up Servo Controllers
Servo motor1;
Servo motor2;
Servo motor3;
Servo motor4;

void setup() {
  
  //Begin serial communication for diagnostics
  Serial.begin(9600);

  //Attach pins to servo controllers
  motor1.attach(MOTOR1_PIN);
  motor2.attach(MOTOR2_PIN);
  motor3.attach(MOTOR3_PIN);
  motor4.attach(MOTOR4_PIN);
  
  //Write initial value to servos for start-up calibration of the motor controllers
  motor1.writeMicroseconds(2000);
  motor2.writeMicroseconds(2000);
  motor3.writeMicroseconds(2000);
  motor4.writeMicroseconds(2000);

  delay(5000);

  motor1.writeMicroseconds(1000);
  motor2.writeMicroseconds(1000);
  motor3.writeMicroseconds(1000);
  motor4.writeMicroseconds(1000);
}

void loop() {  
    
}

Credits

Courtney Achen

4 projects • 28 followers

Electro-Mechanical Engineer

IoT Drone - Part 1 - Motor Control

Things used in this project

Hardware components

Hand tools and fabrication machines

Story

Background

What is it?

Hardware

Software/Firmware

Test Rig/Lift Test Results

Schematics

Arduino ESC Wiring

Code

HTML Control Code

Photon Code

Photon ESC Calibration Code

Credits

Courtney Achen

Comments

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IoT Drone - Part 1 - Motor Control

IoT Drone - Part 1 - Motor Control

Things used in this project

Hardware components

Hand tools and fabrication machines

Story

Background

What is it?

Hardware

Software/Firmware

Test Rig/Lift Test Results

Schematics

Arduino ESC Wiring

Code

HTML Control Code

Photon Code

Photon ESC Calibration Code

Credits

Courtney Achen

Comments

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