Drone Control with an Analog Joystick

Prep Work

Instructions

1. Rebuild your circuit as shown in the diagram below (click for a bigger version of the breadboard layout or circuit diagram). Note that the circuit diagram and code are for the PING ultrasonic distance sensor. If you have an HC-SR04 ultrasonic sensor instead, you should follow the instructions in our HC-SR04 ultrasonic distance sensor tutorial to modify your circuit and code.

   1. Remove the potentiometer completely.
   2. You will need to move the button up on the breadboard to make room for the joystick.
   3. Connect the joystick's pins, as follows:
      1. L/R+ and U/D+ to 5V (breadboard positive bus)
      2. L/R to Arduino analog input A1
      3. U/D to Arduino analog input A0
      4. GND to breadboard ground bus

   

   
2. Download drone_altitude_joystick.ino and upload it to your Arduino.

   What happens when you run the code and push the joystick up and down?

   Does anything happen if you push the joystick left to right?

3. Try changing the scale variable in the code. This variable controls how quickly the analog voltage from the joystick changes the drone's target height. The smaller the number, the faster the drone will move.

   What happens when you change this number? Can you find a value that feels "just right" for controlling the drone with the joystick?

   
   

1. Rebuild your circuit as shown in the diagram below (click for a bigger version of the breadboard layout or circuit diagram).

   1. Remove all four push buttons from the breadboard.
   2. Connect the joystick's pins, as follows:
      1. L/R+ and U/D+ to 5V (breadboard left positive bus in the diagram below—the right bus is used for 6 V from the battery pack. Do not connect the two!).
      2. L/R to Arduino analog input A1.
      3. U/D to Arduino analog input A0.
      4. GND to breadboard ground bus.

   

   
2. Download drone_steering_joystick.ino and upload it to your Arduino.

   What happens when you run the code and press the joystick up and down or side to side?

   Does anything happen if you move the joystick in a circle?

3. There are several variables in the code that you can experiment with changing, but you need to be careful (explained in more detail in the next step). You will not break your drone, but you might see some strange or unexpected behavior depending on the values you enter for these variables.

   1. defaultSpeed sets the default speed for each motor when the joystick is in the neutral position.
   2. speedChange sets the maximum possible speed change for each motor.
   3. a is a multiplier that converts the analog joystick voltage to a speed change for each motor.
4. Why do you need to be careful when changing these values? Because of something called overflow. The Arduino controls the motors' speed using a pulse-width modulation (PWM) signal via the analogWrite() function. For the Arduino UNO, analogWrite() only accepts values between 0 and 255. If you try to enter a value of 256, it will overflow and wrap back around to zero. Conversely, if you try to enter a value of -1, it will wrap back around to 255. This is why you need to be careful when changing the defaultSpeed, speedChange, and a variables. Depending on the values you enter, the code may calculate motor speed values (e.g. the variable motor1speed) that are outside the allowed 0–255 range. This will result in strange drone behavior, such as a motor spinning very slowly when you expect it to spin very fast, causing your drone to tilt in the wrong direction. You could get around this problem by adding IF statements to make sure the motor speeds stay within the allowed range, such as:

   if(motor1speed>255){motor1speed=255;}
   if(motor1speed<0){motor1speed=0;}

Cleanup