Meet HARPY - my first quadcopter, built mostly from scratch. This was an exciting yet difficult project that spanned over three months. While undertaking this project, I found a lack of a single comprehensive guide on the basics of drone - building. Thus I decided to create this extremely simple guide to explain the fundamentals of drone building to beginners.

This is certainly an interesting project to undertake, especially if you are into robotics, physics, and computer science. You don't have to learn about flight physics to make a drone, but if you're a physics nerd (like me) then you may want to, just to understand how the parts work together successfully to create flight. This is also an impressive project you could present to school, use in a robotics competition, or just do for fun.

Here are a few videos of my Drone:

Step 1: The Materials

1) Tools

Wrench - This is used to tighten the propellers onto the motors as well as tighten any and all screws used in the body.

Screwdrivers - To tighten screws (duh)

Soldering Equipment- This is for electrical connections, such as soldering your ESC's onto your power distribution board (more on this later)
Hot Glue Gun - This is used to cover up solder joints and exposed electrical connections to prevent shorting. It can also be used to secure parts of your drone together.

2) Tape/Zipties

These are basics you'll need to secure parts of the frame and components together

3) Frame

This will be the body and arms of your quadcopter. It acts as a mount for electrical components and your FC, and also provides a place to maintain the quad's center of balance. There are plenty of good carbon fiber/metal frames out there, but I decided to build my own frame from aluminum.

4) Lithium Polymer Battery

This will be the power source of your quad. The larger the battery, the more power it will provide, but keep in mind that it will also be heavier. In the end your choice of battery will be a trade-off between flight time and weight.

5) Electrical system

Your Power Distribution Board and Electronic Speed Controllers fall under this category; think of it as the nervous system of your drone. The PDB is a small board with 2 conductive rings on its surface. The terminals of your battery will be soldered to the starting points of both rings. Your ESC's will then be soldered to the PDB, with each terminal corresponding to the correct ring. Your ESC's do exactly what the name suggests - they essentially direct the flow of current into your motors to adjust their speed.

6) Brushless Motors

Motors are what provide thrust for your quad.

7) Propellers

These go on your motors - the curvature of a propeller is such that it pushes air downwards as it spins, creating an equal and opposite force upwards on the drone. Buy plenty of these as they're the most vulnerable part of your quad (you'll break several before your quad becomes stable).

8) Flight Controller

The FC is the 'brain' of your drone. It usually internally contains a compass, accelerometer, and g-sensor. It takes inputs from your transmitter and outputs signals to your ESC's to get the desired response. Everything from hovering your quad to doing simple turns requires a lot of math specific to your drone - luckily, the FC performs all of these calculations hundreds of times a second.

The FC may or may not also require a UBEC - that is, a transformer that steps down the voltage of the battery to a level the FC can handle. Some ESC's come with UBEC's inbuilt, though, so this part depends on your ESC's.

9) TX/RX

To give your quad flight instructions, you'll need a transmitter (TX) that has at least 4 channels - for thrust, yaw, pitch, and roll. I recommend using at least six channels to enable flight modes as well. Transmitters come with specific receivers (RX) that receive analogue signals from the TX and transmit them to the FC.

10) Ground Control Software

This is the software that will run you through calibrating your FC and allows you to alter certain parameters. You will also use this to plan out autonomous missions and configure additional modules later on.

11 Optional Stuff

There are plenty of add-ons to a drone you can add once everything is up and running. This guide aims only to instruct on the most basic of components, so I wont explain how any of these things work. Add-ons may include GPS, retractable landing gear, barometers, externals compasses, airspeed sensors, sonar modules, infra-red sensors, lights, video cameras, propeller guards, and more.

Step 2: Creating the Body

As I mentioned earlier, the body is a highly personal choice that depends on your needs and tastes. A photography/casual flight drone would benefit from an X/+-shaped body, centralized FC unit, and a stable center of mass, while an FPV racing quad would be more efficient with an H-frame.

For more on choosing your frame type, go to:

http://myfirstdrone.com/tutorials/best-multirotor-...

For the frame of HARPY's body, I used two plates, each 20 by 20 cm across, made of 18-guage aluminum. I created 8 'pillars', each 4 cm high, out of aluminum tubing to act as braces to hold the two plates apart.

For the arms, I simply took two 50 cm long aluminum pipes and bent them at 90 degrees. I placed these in the middle and aligned them with the corners of the frame.

For the motors mounts, I cut 8 cm long strips of aluminum from square tubing. I fit these around the arms and cut holes in them to slot screws for the motors.

For a time-lapse of me creating the frame (so you understand what I'm talking about), go to:

Step 3: Electronics

PDB (Power Distribution Board) and ESC's (Electronic Speed Controllers)

The PDB is a small board with 2 conductive rings on its surface. The terminals of your battery will be soldered to the starting points of both rings. Your ESC's will then be soldered to the PDB, with each terminal corresponding to the correct ring. Your ESC's do exactly what the name suggests - they essentially direct the flow of current into your motors to adjust their speed.

Brushless Motors

The math behind a brushless motor is a bit tedious, but you should just know that it works on the principles of motor induction to cause frictionless rotation. If you look inside a motor, you will see copper coils and neodymium magnets arranged in circles. When currents passes through the coils, a magnetic field is generated, which interacts with the magnetic field of the magnets. When they interact, a magnetic force is exerted on the coils. An equal and opposite force is exerted on the magnets on the outer ring, causing the shaft and casing of the motor to spin rapidly. You can buy motors that rotate at several thousand RPM's, but once again, your motor rating depends on what strength your drone requires. Brushless motors have three connectors, or 'phase leads'; each phase lead is required to control the 3 axes of rotation of your quad: pitch, roll, and yaw. Thrust is controlled directly by the magnitude of current entering the motor.

Lithium Polymer Battery

As mentioned, your choice of battery will be a trade-off between flight time and weight. At a certain point, the increase in weight will become higher than the increase in flight time. Finding out your optimum weight takes experimentation, which we will not explore here. Go here if you want to know more about selecting your battery:

http://www.dronetrest.com/t/lipo-batteries-how-to-...

To find out how to make a mathematical model to calculate optimum weight, go here:

https://oscarliang.com/how-to-choose-battery-for-q...

Matching the Components

You cannot randomly mix motors, ESC's, and batteries as you like. Your battery will have an 'S' rating - this is the number of cells inside the battery. Your motors will have to synchronize with this; for example, '4S' motors must draw current from a '4S' battery.

Furthermore, your ESC's and motors will have to be matched. Motors are labelled with their maximum 'draw current', i.e. the current they will draw at full throttle. Your ESC's must be rated at or higher than the max draw current of your motors. I recommend using a rating a bit higher though, so as not to put strain on your ESC's. A 20A (amp) ESC will work with an 18A motor, but high throttle flying may cause it to heat up and get damaged eventually. Thus a 30A ESC would be better as would have no problem with 18A flowing through it (it can withstand much more).

Further furthermore, your battery charger also needs to be right for your battery - for a 3S battery, use only a 3S charger.

Step 4: Configuring Your Flight Controller and Rx/Tx

Ah, the dreaded FC. There is so much subject material here that it's quite necessary to just absorb as much about how they work and the different types as possible.
Most FC's are pretty good at most things, although some are particularly good at certain modes. I went with ArduPilot 2.5 as it's quite robust, and I was already familiar with it. If you've never made an RC vehicle, I would recommend using Ardupilot as it's not too expensive and pretty simple to interface with. If you've flown a bit and want a higher-performance FC for a slightly higher price, I would recommend PixHawk. nevertheless, here is something to help you with your selection:

http://myfirstdrone.com/tutorials/buying-guides/be...

Your transmitter/receiver set must have 4 channels at the bare minimum. However I highly recommend using 6 or higher, as you will want extra channels later for flight modes. I chose the FlySky i6 as it wasn't too pricey and had a nice interface with an extra flight mode channel. This will probably be the most expensive part of your quad, so choose wisely. Here's some help with that:

https://oscarliang.com/choose-rc-transmitter-quadc...

Your set will also come with a bind key to bind the Rx and Tx. Here's a video on binding the FlySky i6:

https://www.youtube.com/watch?v=BRzvMgoBHdc

Another thing to keep in mind it that your ESC connectors must be connected to your FC in a specific order, not just 1-->1, 2-->2, and so forth. The order may seem random, but please check the order I which your specific FC requires your ESC's to be placed in. Alternatively, you can test each motor independently to check if they rotate in the correct order. Most newbie drone makers think they've done some horrible mistake when they power their quad up for the first time and it flips over violently upon thrust. The reality is that they probably connected the ESC's to the FC in the wrong order. In fact, I wasted about a month with HARPY testing out other random stuff because I thought there was something fundamentally wrong with my setup. in the end, I just had to swap two ESC cables and everything was smooth after that. This is a big problem because no guides seem to address this, leading to situations like mine. Then again, maybe i'm just unobservant.

Step 5: Flight

Here comes the best part.

Once everything is together, you'll need to learn how to fly. If you've ever flown a ready-made quadcopter before, flying your own drone will be significantly less smooth. This is because it's likely that there are more imperfections in yours; however, your flying can be made smooth with a few simple fixes:

Trimming

When you first take off, you will notice your quad drifting in one direction or the other. It may also have some yaw. The trims on your transmitter are meant to cancel this out. They are the little silver buttons on your transmitter that beep when you press them. On your display you will see 4 sliders, which will move corresponding with your trims.

To view the trims on a typical transmitter, look at the image attached.

In general, you should trim to cancel out your quad's drifting - for e.g. if it drifts forwards, press the backward pitch trim button until it stops going forward. Going further will overcompensate, making it drift backwards. It might take a while to find the balance point, but when you do, your drone should hover in space.

Throttle Gain

You may find your throttle way too responsive, making your drone rush upwards to the sky while you hurriedly cut the throttle and watch it fall down and crash in a mangled heap of metal and wires (never happened to me, I swear).

Your throttle trim will adjust your throttle at max thrust. You should aim for full throttle to be a fast rise, and mid to high throttle to give you a steady rise.

Flight modes

Your FC will come with a variety of flight modes. For our drone (due to limited channels) we used two modes: AltHold and Stabilize mode. Here we will explain some, of many, flight modes.

Stabilize mode

Stabilize mode allows you to fly your vehicle manually, but self-levels the roll and pitch axis

More about Stabilize mode: http://ardupilot.org/copter/docs/stabilize-mode.ht...

AltHold (Altitude Hold) mode

In altitude hold mode, the drone maintains a consistent altitude while allowing roll, pitch, and yaw to be controlled normally.

More about AltHold mode: http://ardupilot.org/copter/docs/altholdmode.html#...

Loiter mode

Loiter Mode automatically attempts to maintain the current location, heading and altitude. The pilot may fly the copter in Loiter mode as if it were in a more manual flight mode but when the sticks are released, the vehicle will slow to a stop and hold position.

More about Loiter mode: http://ardupilot.org/copter/docs/loiter-mode.html#...

Here is a list of many flight modes you can choose from:

http://ardupilot.org/copter/docs/flight-modes.html

PID Tuning

This is where the mathematics of your FC comes into play. PID Loops are a set-point variable-based feedback system used in manufacturing industries There is a ton of math here which, unless you're learning control theory in college, you probably don't wanna know about. So let me give you the rundown in Laymen's terms:

P-Proportional

This is the main value which determines the drone's need to stabilize itself. With a low P value, it will correct sluggishly and be relatively unresponsive to controls. If P is too high, your drone will oscillate rapidly by trying to stabilize itself and overshooting repeatedly. You want to tune this first (set I and D to 0) by hovering in a windless environment and increasing P until just before your quad starts oscillating.

I-Integral

Your P value determines how much your quad will stabilize. However, this is just the amount by which your drone will correct. The timing is irrelevant to your FC as far as P is concerned; it could stabilize in 1 second or 1 minute. Your I value exists to speed things up - it dictates the force exerted to push the quad back into a stable position. This is why I is important in outdoor flying; with factors like wind, your I is what controls how quickly your drone will respond to outside factors. Use a low I, and your quad will just drift away in the wind.

D-Derivative

This one is the least important; some FC's don't even let you change this so as not to mess with the PID loops too much. Think of D like a dampener; it smoothens out the corrections made by P and I. Instead of jerking back to a hovering position, a drone with a high D value will gracefully return horizontal after getting to its new position.

Here's another super-simple guide to PID tuning:

https://oscarliang.com/quadcopter-pid-explained-tu...

Here's a slightly more hardcore version:

https://oscarliang.com/understanding-pid-for-quadc...

For an even more detailed version, go here:

http://myfirstdrone.com/tutorials/how-to-tune-a-qu...

If you're interested in the math behind PID-loop theory and have Alan Turing's brain, go here:

http://innovativecontrols.com/blog/basics-tuning-p...

http://www.expertune.com/tutor.aspx

Finally, for a cool analogy to help you understand all of this a bit better, go here:

http://diydrones.com/forum/topics/pid-explained