DIY Mini Drone: Arduino™ Altitude Control

Prep Work

1. Follow the instructions in the DIY Mini Drone activity to build your drone.
2. If you do not know how to use a breadboard, refer to our Breadboard Tutorial before you continue.
3. If you have never used an Arduino before, refer to our How to Use an Arduino guide.

Instructions

1. After following the instructions in the DIY Mini Drone activity, your drone should look like this.
   
   
   
2. Glue a second vertical piece of straw to the middle of your drone's frame, opposite the first piece.
   
   
   
3. Cut out a small circle of paper, about 7 cm in diameter. Poke holes in it for the straws, and slide it onto the underside of your drone. This will provide a larger, flat surface for the sound waves from the ultrasonic sensor to bounce off of.
   
   
   
4. Build a support for your drone with two dowels spaced apart so they fit through both straws. It is important to make sure the dowels are parallel or your drone will get stuck. Make sure the drone slides smoothly up and down the dowels. Optional: place a piece of soft foam at the base of the dowels. This will provide some padding if your drone falls.

   1. Alternatively, you can use two strings. Tape the strings to a shelf or the edge of a table, and let them hang down. Thread the drone onto the strings, and then make sure the strings are pulled taut (for example, by taping heavy weights to the ends, or by having a helper hold them).

   
5. Orient the breadboard so it is facing you with the writing upright. Then connect all of the following, as shown in the breadboard diagram (click for a bigger version of the diagram). If you know how to read a circuit schematic, you can use that instead. 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. Arduino 5V pin to breadboard positive bus.
   2. Arduino GND pin to breadboard ground bus.
   3. Breadboard left positive bus to breadboard right positive bus.
   4. Breadboard left ground bus to breadboard right ground bus.
   5. PING sensor GND pin to breadboard ground bus (use male-female jumper wires to connect to the PING sensor pins).
   6. PING sensor 5V pin to breadboard positive bus.
   7. PING sensor SIG pin to Arduino digital pin 7.
   8. MOSFET in holes F8, F9, and F10, with the large metal tab facing to the left.
   9. Hole J8 to ground bus.
   10. Hole G10 to Arduino digital pin 10.
   11. Potentiometer in holes F16, F17, F18.
   12. Hole J16 to positive bus.
   13. Hole J17 to Arduino analog input A0.
   14. Hole J18 to ground bus.
   15. Push button straddling the middle gap of the breadboard, with pins in holes E23, E25, F23, and F25.
   16. Hole A23 to Arduino digital pin 3.
   17. 10 kΩ resistor from hole J23 to positive bus.
   18. Hole J25 to ground bus.
   19. Drone positive wire to J1. The drone's wires are too flexible to push into the breadboard on their own. Twist or crimp them to a short piece of jumper wire to make the connection.
   20. Drone negative wire to J9.
   21. 4xAA battery pack negative (black) wire to ground bus.
   22. 4xAA battery pack positive (red) wire to F1. Important: Do not connect the battery pack's positive wire to the breadboard's positive bus! This will create a short circuit between the Arduino's 5 V power and the battery pack's 6 V power.

   

   
6. Upload the code to your Arduino.

   1. Download drone_altitude_control_code.ino to your computer. If you have some computer programming experience, you can look through the code and read the comments to understand how it works.
   2. Temporarily disconnect one of the drone's wires from the breadboard. This will prevent the drone from accidentally taking off when you power up your Arduino (this can happen depending on the last program that ran on the Arduino).
   3. Connect the Arduino to your computer with the USB cable.
   4. Open drone_altitude_control_code.ino in the Arduino IDE.
   5. Press the "Upload" button to send the code to your Arduino.
7. Test your drone.

   1. Make sure the drone is threaded onto the guide poles.
   2. Place the ultrasonic sensor directly under the drone, facing up.
   3. Re-connect the drone's wire to the breadboard.
   4. Press the push button once to make the drone lift off.
   5. Adjust the potentiometer to change the drone's height.
   6. Gently tap the drone up or down with your finger or a pencil (watch out for the propellers!). What happens?
   7. Press the push button again to make the drone land. You can re-press the button to make it lift off again.

   What happens if you change the value of the variable K, re-upload your Arduino code, and test again?

   
8. Troubleshooting:

   1. If your drone's motors do not spin at all, double-check all of your breadboard wiring. A single misplaced wire can prevent the entire circuit from working.
   2. To confirm that your drone is working, temporarily connect its two wires directly to the two wires from the 4xAA battery pack.
   3. Make sure all your wires are connected to the correct Arduino pins. The code does not "know" which pins you have plugged the wires into. You need to plug wires into the pins that are used in the code.
   4. If your drone flies but behaves erratically, try adjusting the ultrasonic sensor to make sure it is aimed at the bottom of the drone. Use the Arduino IDE's serial monitor to help debug (Tools→Serial monitor). This will display the measured distance in centimeters. If this value does not seem reasonable (for example, it is always zero, or it is 100 cm and you know your drone is definitely not that far away), then you are probably not getting good readings from the sensor.
   5. If your drone drifts up or down slightly instead of hovering, try changing the value of the PWM_offset variable in your code. This variable is a number between 0–255. By default, it is set to 150. If your drone drifts downward, try increasing the number. If your drone drifts upward, try decreasing the number.

Cleanup