The Arduino Drone: Sean Eaton
This Arduino drone is based on Nikodem Bartnik's instructables tutorial which can be found here. Many thanks to Nikodem for creating his schematics and writing the Arduino code.



Introduction:
This Arduino Drone was done for the 1st Fort Lewis College Digital Design contest. Two different Arduino's are used for the Drone Flight Controller and for the Drone Pilot Remote. The Arduino Nano was used for the flight controller because of its small form factor and because it was easily integrated into my initial design. The Arduino Uno was mainly used because it was what I had available at the time. The main difference between the Arduino Nano and Uno is form factor, other than that, they are identical for the purposes of this project.

Standard drone parts such as the frame, electronic speed controllers and motors, and propellers were used in addition to a custom Arduino powered Flight Controller and Pilot Remote. The standard drone parts cost less than $120 while the Arduino components and electrical parts together can cost around $85, less if certain tools and materials are already available. Expenses for this drone could be as little as $150 if a soldering iron, wires, PCB boards, and cheap Arduino components are readily available.

This drone could be potentially used for many different applications. A different kind of frame and some adjustments to the hardware could allow for the drone able to carry loads, a camera could be mounted to the drone to capture footage, or sensors could be mounted to collect data such as temperature, air pressure, humidity, and so on. This drone also serves as a good learning tool for how drones work.

Materials:
There are three categories of parts used in this drone. The first is the standard drone parts that are commonly used in all DIY drone kits. The second are Arduino components that were used in the drone flight controller and pilot remote. Lastly there are the standard electrical parts like wiring and solderable PCB boards which one may have handy prior to this project.

Figure 1: Table of Drone Parts Used
Quantity Part Price
1 450 Drone Frame $18.99
1 11.1V 2200 mAh Lithium Polymer Battery $17.99
1 Lithium Polymer Battery Balance Charger $8.79
4 A2212 1000KV Brushless Motors * $65.99
4 30A Electronic Speed Controllers * $65.99
4 1045 Sized Propellers * $65.99
* These parts were sold together

The total for these parts is around $111.76 from Amazon. There may have been price changes since the parts were first ordered but it should be around that range. In addition, these parts are also available from different vendors who sell these parts for less compared to the prices found on Amazon.
Figure 2: Table of Arduino Parts Used
Quantity Part Price
1 MPU6050 Gryo & Accelerometer $5.39
3 NRF24L01+ 2.4 GHz Transceiver $13.99
3 Arduino Nano $13.86
10 Joysticks $11.99

The total for these parts is around $45.23 on Amazon. The MPU6050 Gryo and Accelerometer is a small board that is easy to wire up to an Arduino. It is necessary for the proportional-integral-derivative (PID) controller code. The NRF24L01+ transceivers are the antenna boards visible on the drone and controller. Arduino Nano's can be purchased in a pack of 3 which is very useful since two can be used for the flight controller and pilot remote. The pack of 10 joysticks is the cheapest option per joystick although only two are only needed.

Figure 3: Table of Electrical Parts
Quantity Part Price
1 Soldering Iron Kit $19.99
1 Pack of Wires $16.75
1 Stripboard $10.78
1 Set of Spacer Screws $9.99

The total for these parts is around $57.51 on Amazon once again. The stripboard isn't necessary, any type of solderable PCB board will do. Many of these components may already be available to someone too which decreases the total cost of the drone substantially.

Methods:
The Drone Frame: The drone frame is easily constructed and the kit will contain all the necessary screws. An allen wrench or hex key is needed to fasten the screws correctly or a flat head screwdriver can also work.


Figure 4: 450 Drone Frame parts laid out

Keep in mind that the electronic speed controllers (ESCs) must connect to each brushless motor and be soldered to the built in power distribution board of the frame. The power distribution board is the uppermost board in the picture above. The connections are also shown below. This process has to be repeated four times for each of the frame's four legs.


Figure 5: Motor to ESC connections


Figure 6: ESC on the frame


Figure 7: ESC connection to power distribution board on the frame

The Flight Controller: The flight controller has a somewhat easy set up. The main components to be wired up are the MPU6050, NRF24L01+, the Arduino Nano, and header pins for the ESCs. I used a strip board because it made wiring easier for me but any type of solderable PCB board can be used.


Figure 8: On board flight controller

The following schematic was used as a guide. This was the schematic Nikodem Bartnik uploaded to his instructables page.

Figure 9: Flight controller schematic by Nikodem Bartnik

Some things were omitted because I was using the Arduino Nano instead of the Atmega328 chip by itself. These were things like the linear voltage regulator, capacitors, and the 16 MHz crystal oscillator since the Arduino Nano already had those things handled. The Atmega328 pins correspond to the pins of the Arduino Nano (and Uno). With the help of this pinout diagram I was able to figure out the equivalent connections for the different components on the flight controller.


Figure 10: Atmega328 pinout and equivalent Arduino Pins

The Pilot Remote: The pilot remote is very simple compared to the flight controller. The wiring for the NRF24L01+ is identical to the flight controller and the only other components are the two joysticks. Nikodem Bartnik's schematic was again used for this with similar minor adjustments as well as aided by the previous pinout diagram.


Figure 11: Drone pilot remote schematic by Nikodem Bartnik

The pilot remote is very rough right now. It's main purpose was for testing and the green PCB board is unnecessary right now. The main challenge with the pilot remote was wiring the joysticks correctly. The pins for the joy sticks are on the left side which is why they are floating right now. They can be reworked to fit on a single board but different joysticks would be required or some easy method of detaching the joystick from the PCB.


Figure 12: Drone pilot remote

Results:
I initially built the flight controller by following Nikodem Bartnik's schematic as closely as I could. This meant I had to use the Atmega328 microcontroller by itself and order the 16 MHz crystal oscillators, capacitors, and linear voltage regulators. Unfortanely the flight controller wasn't functional. This first version of the flight controller is shown below:


Figure 13: Flight Controller 1.0

The linear voltage regulator is the black part with the silver protrusion on the left side of the board. The Atmega328 microcontroller is the large black rectangle. The blue board on the right side of the board is the MPU6050. The yellow blobs are ceramic capacitors and the silver component between them is the crystal oscillator.

The Atmega328 microcontroller is actually the  same microcontroller used on the Arduino Uno. This can be seen in Figure 14 which also shows a comparison of the sizes of these two boards. The major advantage gained from building the flight controller this way is that the size of the flight controller can be cut down signficantly. A separate Arduino Uno is not required and mounting and stabilizing the MPU6050 is taken care of easily. The major disadvantage to this is the loss of the USB port which can be used for debugging. The code for the Atmega328 is written using the Arduino IDE (Integrated Development Environment). The Arduino IDE has a useful tool called the serial monitor which can be used to debug issues by displaying messages to the user. Since Flight Controller 1.0 was not functional and I couldn't use the serial monitor to identify any issues I decided that it would be simpler to use an Arduino Nano.


Figure 14: Arduino Uno compared to Flight Controller 1.0

The Arduino Nano was chosen for its small form factor and most importantly because it is nearly identical to an Uno in functionality. The microcontroller used on the Arduino Nano is the Atmega328P which is the small black square seen on the Arduino Nano in Figure 15. There are minimal differences in the functionality of the Atmega328 and Atmega328P such as the two additional analog inputs. All that had to be done to get the code working on the Nano was changing the settings in the Arduino IDE to upload to the Nano.


Figure 15: Arduino Nano on Flight Controller 2.0

Using the pinout diagram shown in Figure 10, Flight Controller 2.0 was built. Flight Controller 2.0 is larger than the Arduino Uno and Flight Controller 1.0 but it is very simplified and functional. The sides could even be trimmed down further or a different layout could decrease the size of the board as well. Figure 16 shows a size comparison of the different boards.


Figure 16: Comparisons between Flight Controller 2.0 (top), Arduino Uno (left), and Flight Controller 1.0 (right)

The Arduino Nano gets powered by drone's 11.1V lithium polymer battery. Using the 5V pin on the Arduino Nano a 5V rail is used to supply power to the MPU6050 and NRF24L01+ in addition to the ESC pin headers. The MPU6050 has SCL and SDA pins that must connect to the designated SCL and SDA pins on the Arduino. SCL is the clock line while SDA is the data line and this connection is necessary for the MPU6050 to function correctly. The NRF24L01+ has similar requirements where the SCK (serial clock), MOSI (Master Out Slave In), and MISO (Master In Slave Out) must be correctly connected. These pins are necessary for the transceiver and Arduino to communicate. The ESC pin headers are connected to 5V and ground as well as an additional pin that connects to a digital pin on the Arduino.

The pilot remote (Figure 12) hasn't been modified yet since I first began testing. The current design is not ideal at all. The necessary pins for the joysticks are power, ground, VRX, VRY, and SW. VRX and VRY tell the Arduino how the joystick is positioned in X and Y directions while SW lets the Arduino know if the joystick has been pressed down like a button. Analog pins are used for VRX and VRY and a digital pin is used for SW. The breakout boards of the joysticks have the pins on the left side only which prevented me from soldering the joysticks to a board directly. Figure 17 shows this and the connections for the transceiver.


Figure 17: Pilot remote joysticks and transceiver

Discussion:
The drone has not flown yet due to an issue with getting the pilot remote to control the drone consistently. You may have noticed that the NRF24L01+ transceiver is set up differently on the flight controller (Figure 8 and Figure 16) compared to the pilot remote (Figure 12). I am currently experimenting with using an adapter to fix this problem which is the major challenge I am facing right now. I was able to get the pilot remote to control the drone's motors only once. This is shown below:




I researched how other people were using the NRF24L01+ tranceivers and it appears that the issue is likely power related. The transceivers are probably experiencing power fluctuations significant enough to break communication. The transceiver can only handle 3.3V as a power source and Nikodem Bartnik indicated in his pilot remote schematic that a 10uF capacitor should connect the transceiver's ground and power to prevent power fluctuations which is what others suggested too. People had success with the adapter board so I ordered those and experimented with what works best. After testing the transceivers with breakout boards and 10uF capacitors, I know that using the breakout board in addition to the capacitor works but now positioning is an issue. I was able to get the transcievers to communicate consistently for a while but after moving them I wasn't able to get the same results. During testing I used the serial monitor in the Arduino IDE and took screenshots of the results (Figure 18 and Figure 19).


Figure 18: shows consistent communication between the transceivers


Figure 19: shows inconsistent communication between the transceivers

In Figure 18 and Figure 19 the number of milliseconds since the transmitting Arduino is turned on is sent using the transceiver. The receiving Arduino then receives this payload and sends a response back. There is successful communication between them when the transmitting Arduino is able to receive the response. Figure 18 shows the results of positioning the adapters in just the right way to maintain good communications between them. In Figure 19 the positioning was changed and the transmitting Arduino isn't able to detect a response a lot of the time. The challenge is figuring out how to attach and position the transciever on the flight controller because it is not able to be soldered onto the board like the MPU6050 or Arduino Nano because of its design.

Moving forward, there is one other transceiver adapter board that is different from the one I am currently using that I may try. This other adapter doesn't have a 3.3V regulator but it can be easily soldered to a PCB board and can maintain a steady position easier than the current adapter.

I also need to update the pilot remote (Figure 12). The green PCB board is unnecessary right now and I want to use an Arduino Nano instead of the Uno. I kept this version of the remote around because of it was the only one able to communicate with the drone so far. The joysticks can also use some pin headers so I can solder the joysticks to a PCB board instead of allowing them to hang in mid air.